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Portable 400watt Solar Box


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So I FINALLY had time to finish my little solar project. Should have been done weeks ago, but I didn't have time to get to it, space or the tools needed. Had a friend help me build it in his shop after I bought all the parts. He basically took everything I bought and ideas I had, and then implemented the build for me so all credit to him for the labor..lol (Thanks Phil!). Plus, I don't have a shop or tools, so there is also that but it's finished and working!




Basically, it's a deep cycle battery in an ammo can hooked to a solar panel on a home made stand with feet that fold up and the ammo can fits in the center of the panel frame for storage under a seat or wherever you can fit it when transporting. Not heavy and small form factor overall.


1 large 50 Cal Ammo can (Plastic) - http://www.mtmcase-gard.com/products/shooting/50-cal-ammo-can.php (Purchased for $15 from friends Army Navy store - http://www.racersarmynavy.com/ )

1 12-18v AGM Deep-cycle battery - http://bit.ly/1CM1XzF (Think I paid less than $40, not including shipping)

1 2watt solar panel - http://bit.ly/1DGgBhd (amorphous so gathers power from facing pretty much any direction even on cloudy days)

1 8amp charge controller - http://bit.ly/1JJwR1J

1 400watt 12v DC to 120v/60hz AC Converter with 2 full size 120v wall outlets and one 5v USB outlet, On/Off switch. - http://bit.ly/1IbR8fe (about $30 depending on store)

1 KJV Bible ($9.00, walmart)

1 Rechargable LED Night light/detachable flashlight (> $9 Walmart)

misc nuts, bolts, washers, velcro, and some packing foam to secure contents while traveling, everything sites nice and snug.

All said and done, spent right around $160~ or so, and that includes a $20 rice cooker/veggie steamer I bought to go along with the setup. My friend had the wood and other stuff to help with the build so lumber was free, screws, misc stuff.

Build time probably could of taken about an hour, but my friend went overkill on how he put it all together which is uber clean and solid, counter sunk screws and angled joints on solar frame. Wish I had video taped and time lapsed it for documentation. Not a lot to all of it, but super cool to see it all come together now that it is finished. Completely water tight, power outlet on outside detaches from industrial strength velcro strips and can be moved inside, while charge controller is velcro'd to the inside to keep dry. Solar panel feeds into the box to charge controller, which goes to the battery to maintain charge; leads come out to the power converter which can be easily removed and stored inside when needed(Just remember to unhook power properly and discharge converter and not short anything since this is an always hot box once finished and the converter holds a small charge even after unhooked from the battery).

Simple stuff but really portable and for low power needs, should be plenty for what it is going to be used for. Not something you would run a gaming rig more than 5 minutes on, but charging cell phones during power outages, radios, small led lights, small cooker and few small chargeable items, it will serve it's purpose which is to go to a homeless vet near where I work who lives in the woods behind a bank.

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Your battery isn't "12-18v" but "12v 18Ah" so 216Wh total.
That means the 2W panel is able to charge the battery from nothing to full charge in a bit over 4.5 days of non-stop sun. At optimal 16 hour suntime days that means about 1 full week to get there.
At full blast the converter can suck the battery dry again in about 30 minutes.

On a 16-hour optimal sun conditions day that panel will produce 32Wh of power.
Assuming that rice & veg cooker is this one, it chugs down 300W of power (rated at 350, but the comments say 300 as verified by a Kill-a-watt) and another comment says it takes 30 minutes to cook 1.5 cups of rice. That amounts to about 150 Wh of power but it should be noted that 1.5 cups of rice is substantially more than 1 typical portion for an adult so he might get away with using a bit less power (might be less rice, but even 1 grain of rice still take 25 minutes to cook).

Generally speaking though, I think this is a really cool and honorable thing you're doing, but you should make sure the homeless guy is aware that cooker can provide him with a hot meal only once every 5-6 days and going beyond that might fully drain the battery during cooking which could result in uncooked food and potentially some aggression against the device since he might think it's "broken". Also advise the guy that if the device runs out of juice during cooking, he should keep the lid on for at least another 15 minutes - it might not be able to create additional steam, but the steam and heat that's in there will continue to cook the food, just at a slower pace, allowing him to still end up with something edible.

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Yes you are correct, 12 volt, 18amp hour battery. Was late last night in posting it and just reading off the side not thinking. Links to the battery have all the info though. I probably do need to go with a larger panel, but I think short term this is going to work for what he'll need.

The solar panel is only 2watt but is rated to maintain (not charge) a full size car and RV battery at 6 watts trickle charge, 400mA (I don't even fully understand the math to be honest, still learning how all this works) although they do say on the paperwork - for offsetting power use only to a 12volt car/RV battery(I guess because later you'll use your alternator to recycle the battery when back on the road). They recommend using an 18v solar panel for charging full size RV and car batteries alone when not hooked to anything else, so this again isn't going to be a constant wall outlet you'll use 24/7 like a home solar farm and battery bank setup. I think for the small battery I have though since almost all the time it's going to be charging other than at night, it's working well enough to keep it charged at this time and shouldn't be much of an issue for what it will be used for. I will have to test it out today and cook something on it to see what happens and see if I need to upgrade the panel to the 18watt one which uses the same J-Plug connectors, but I need to go buy my own volt meter first to be able to check everything since I have it home now and don't have a way to keep a check on it and when it's getting low on charge. Once I give it to the guy, it's his so I want to play with it a a few days to see if it stays working outside where it is now. I should probably get a killowatt meter to use inline with the cooker as well to calculate what killowatt hours it gets since I don't know how fast it's going to kill the battery, but I don't want to test it to completely dead either until I get a stand alone charger, which I'll probably purchase as well and will come in handy in the future. Will give me something to do today I guess, so probably need to pull out the cooker (I think it is the same one you linked to) but only after I go get a higher rated volt meter so I can check not just the battery but also what's coming out of the sockets since we cut the wires shorter, the amperage and such may have changed the voltage and I don't know how that will affect power from the socket which we couldn't test last night(although the LED light didn't seem to mind). My friends tester wasn't rated for wall sockets to begin with he said, so I'll take his word on it not to stick it in the socket and not kill myself, but it was able to check small electronics and batteries so it worked for what we were doing initially and could read up to what we were doing with a digital output that told us 13v total when finished.

At full blast the converter can suck the battery dry again in about 30 minutes.

Maybe sooner, since it can do up to 800w max, not just the 400w advertised. Considering my wife and I ran our 1000w AC unit for roughly 15 minutes without it stopping, I'm not sure on how the math works, but the battery never died on us. Based on what you're telling me, that shouldn't be possible so I'm going to have to play with it a bit before giving it to him to be sure what I can get away with. This is still a learning process though as much as it is just a fun project.

We used the air conditioner few weeks ago before the final build last night as a test and it worked without killing it or catching fire..lol. Probably not the best stress test(or safest after reading up more on electrical fires and amperage with small gauge wires), but I don't see it hurting my air conditioner, and the converter will only allow a max 800w draw and never got hot enough to make me worry about a fire(although it does have a capacitor that may pop if overloaded, I doubt this setup is going to cause that). The battery doesn't have enough cranking amps as a car or RV battery, so it shouldn't be much of an issue with the wires but the converter was meant for running off full sized batteries anyway so even in cutting them a bit shorter to remove the alligator clips, I'm hoping that won't make any difference in heat dissipation or power issues from both the controller and converter and amperage should be more or less the same since we didn't increase the gauge of the wire. I would think if anything, it would drain so fast most it would do is just a constant discharge before really hurting anything with such a small battery though, but the converter does have some sort of capacitor that I don't know how much it is meant to handle or if it will pop. I was trying to see how much load I could get it to do using just the air conditioner since it was the largest thing I had nearby to put a big draw on it, but just out of the box, it ran without issue or dying with more than what the entire setup was intended for doing. All parts are still working and seem to be fine. I'm not 100% sure that a small steamer won't cause it to catch fire but will know more later today what kind of draw it is giving after I go get some stuff to cook in it and all the other supplies like a full size battery charger, volt meter and maybe a killowatt meter. if the AC didn't kill it though, not sure the steamer will be much of an issue for this, just not sure how long the life will last, and how long it will take to recharge off just the one panel since I'd have to discharge it and then recycle it completely on the panel alone outside, which I don't think going fully dead is a good for the battery or if it will come back afterwards. From what I have read and watched in videos, 30-50% range is as low as you want to really go on them under load.

Our air conditioner did sound like it was struggling compared to straight wall power (I imagine because it couldn't get the full draw it needed), but the compressor turned on and cooled the room down. I don't know how low the battery ever ended up going during all of this process, so I may have already smashed the thing close to dead. I just know it has been working and didn't die during the past few weeks and is still giving power and geting the charge controller to go green on fully charged. Most I've put on it other than the air conditioner test was just my phone to check the USB port, so the cooker will be the real test.

It's on my porch at the moment since the fully charged light is not on but that goes on and off at times anyway so I'm not going to go by the controller since it's just an LED light and not actually a digital read out where the battery actually is. It is giving me power with no issues though, just not sure for how long that will last and how full the battery is.

All the wires are shorter than what they came with now since it's shoved partly in the box and we only needed it to reach from the battery to the controller and converter. The longest wires are the solar panel wires, which we didn't have to cut since they have the mated jplug on the one end that hooks to the one coming out of the ammo can which is sealed with a metal connector, rubber gromet and some liquid nail silicone stuff to keeop the inside dry. We can pull off the wires and converter off the velcro and tuck it inside the can if needed too, so only external parts really are the panel, stand and cord.

Realisticly this will be used in small spurts while charging every day. This will be used mostly for small meals(need to research online RV sites for lower watt cooking devices since this steamer may be too much as you mentioned, so my wife may be getting the rice cooker she wanted anyway) and for the light and radio, which I don't think are going to kill it over night. If he left the cooker on more than an hour, probably will kill the battery, but after the AC test, not sure on that yet so I'll need to actually test more this week.

I also bought him a heated vest back in January and he's kept it charged at a local Wendy's with extra battery packs I had donated from the place I purchased it from local to me (http://www.nevertoowarm.com/) - he said it has kept him more than warm enough in his little make shift duck blind home even when there was snow on the ground.

I'm also looking into more camping gear/cooking stuff that requires low watt and cook times, but most things I've seen, like single burners, draw 900-1000 watts alone for boiling water or small electric griddles that are 600watts and up so I probably need to shop online RV places vs department stores for this kind of specialized cooking gear. Getting him a larger panel if needed, won't be an issue though and you can get a few of these tied in parallel to charge the battery as well for a small solar farm that he can push around in his Sam's club shopping cart he uses for scavanging, although I'd probably need to go to a larger charge controller depending on what I go with, this was meant for fitting in a small form factor and just a "what can I do with this shit" kind of project to help someone out. He was largely in part what inspired me to try this, since his last job was for a contractor doing solar installations. It's a long story on why he is where he is and what not, and mostly his choice, but I felt inspired to help him out and check on him during work hours since I deliver parts and see him in my travels at work.

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To be honest, I don't think that panel, or even a larger one, will be a viable long-term solution for cooking stuff - cooking electric just takes a lot of energy. It takes 30Wh to boil a cup (250 ml) of water at 70% efficiency (quoted from the "What of it?", a quarter down on this loooong page). The math says that's what this solar panel is capable of when charging at full efficiency for a full day. It can probably work miracles on that heated vest (*WAY* cool!) and should have no issues keeping a mobile charged.

For the actual cooking though, while it isn't as high-tech as this solar thing I first noticed this hexamine stove which is highly portable and efficient, but the fuel blocks are probably too expensive for use as an every-day solution. Instead, something like

would seem quite capable. It's cheap to make, pretty sturdy, easy to repair if need be and since it's very efficient with its fuel the guy can probably get it to work with twigs and shit he can collect from some nearby forest/park/woodland. All you need to do is start a flame then orient the fuel intake such that it faces the direction from where the wind is blowing so that can help fan the flame. Also note that the design requires some air gap between the top of the stove and the pan.

Changes relative to that video is that some people filled the bucket with concrete to make it stronger and allowing him to even hold it upside down without issue. Only drawback here is that the concrete takes upwards of a month to cure sufficiently to be used for this purpose.

Some videos talk about using 'perlite' or 'vericulite' (or whatever) with the concrete. That's to save on weight, at the expense of insulation. The guy in the clip I linked can touch the outer shell of his over after a good amount of burn time whereas with another video where only 'vericulite' was used the outside of the can was noticeably hot. I would argue that the safety incurred by not burning yourself on the outer shell easily combined with the ability to just pick it up and move instantly after having cooked something outweighs the drawback of it being a bit heavier.

Supposedly the funnel up should be 3x the width of the pipe. I don't think the video I linked adheres to those measurements, but it might be something to consider.

Finally, things that consume a considerable amount of power relatively constantly, aside from that AC which I never would've thought of since they're not particularly prevalent here in .nl, are electric kettles, irons (the things for ironing clothes) and vacuum cleaners. Although when a device is rated at 400W and you're drawing 1KW chances are you're indeed going to pop something on that inverter. I'm quite sure if you put your hand on it after 15 minutes you stand a fair chance of burning yourself. Better go with a more moderate load (say, a monintor) for a prolonged period of time if it's the battery you want to test (I'd say the inverter itself has by now been adequately tested and passed with flying colours).

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Well, we just tested it out. We cooked 2 cups of rice and 3 steamed rice buns(from frozen) and set the microwave timer for 25 minutes while the setup was outside on the back deck. We wanted to see what would happen so just let it go for the 25 minutes. About 6 minutes before the microwave dinged, the converter started to whistle, which is a sign of discharge and low voltage/not enough current (basically battery not giving enough steady juice to maintain full 120v conversion but it was turning the cooker on and off still, and into warm mode, which means nearly done cooking once the warm light comes on).

I believe it is the same rice cooker too @cooper:


After about an hour now, the food is still warm, just now cleaning it out. Water, rice, and steamed buns, easy clean up with the included spoon, and should need minimal washing of the inner removable tin bowl, non stick, no oil or butter needed to cook it. He will need water to cook the rice in, which he has some plastic drip things he's using tied between trees that look almost like bird feeders, but not sure how clean rain water is off that stuff and I would open a sterile beer before I drank from run off water, yet he does it all the time. It might work for cooking, but I don't think this gets hot enough to boil and sterilize water from the rain collectors he made, even if it is too hot to touch after opening the lid. That's an issue for him to work out though since he's already been doing this for a while now, he must have a stomach for the water.

Battery still reads about +12v (Bought a cheap multimeter) at the terminals on the battery after using the cooker, and nothing seemed like it was getting hot or damaged, and same readings at the connection to the converter so doesn't look like any resistance from the battery to the converter or too drained(yet). Battery just needs a recharge now since it's probably lower than what the cooker needed to begin with. Converter still has enough juice to charge my phone with no issue, along with the bedroom lamp and the LED flashlight. Before I do the overnight charge and start over(Bedroom light, 60watt bulb is working fine at the moment, so lights and simple things with low draw, like a radio work great great, but as cooper mentioned, cooking, probably need super efficient low watt with high heat cooking, like RV Microwave that only takes 3-5 minutes to cook something or work out second bank for optimal cook time). http://i.imgur.com/oJiTxJN.jpg

It's almost dark soon, so not going to have enough sunlight to play with it via the solar panel and see how far up it charges with the volt meter in the sunlight each hour, so will use the indoor ac power charger I just bought to start over. Ideally I need a full day to check hour per hour, before cooking, after cooking, and at the end of the day when the sun goes down, what it goes back up to. The little LED light is not making it whistle, nor is the bedroom light, and cell phone on at same time, and at the moment have my stereo plugged in playing a CD, so it doesn't care that it's less than 120v for things that don't have high watt needs, just the cooker probably needs higher constant wattage and kills the batter quicker. Probably not realistic long term use on the cooking side unless I find a better appliance solution or build a second unit to bank them together for the longer cook time. Live and learn I guess, but still kind of cool that we cooked this without a fully charged battery and still have juice in reserve with no issues on the other things plugged into it.

When I checked AC power from the outlets, initially I was getting a bouncing 100-120+v on the multimeter pretty good so that probably was fine for initial output, but it now reads at a bouncing 50 ~ 105v AC up and down with the stereo on, so after 20 minutes, the rice cooker def put enough drain to make it whistle on the converter and drop its output which if left unattended, will damage the converter and discharge the battery below 12 volts. It would eventually kill it, so that isn't what I want ultimately, so maybe an inline wall timer that you can set to the cooker to turn off at like 18 minutes, would save the battery after cooking and just standing for 5-10 minutes, it can then take the day to charge and by night, maybe cooke another meal at bed time and run the radio and light off the rest of the night. Longer devices are on, less life and longer charge time obviously, so I need to figure out total charge time and drain time stuff for general every day use.

I also want to test what is coming out of the USB side(I imagine still +-5v as usual since it's low power USB anyway) but I've yet to try this -

Also don't like the idea of live wires plugged into the outlet to fart with since I may damage the converter in the process, this seemds not worth the effort to take that risk of shorting something out so I'm going to assume it's working fine still since the phone came up a few percent in the time I left it in and didn't make the unit whistle.

Ultimately, I may have to do something like using two batteries in parallel (doubling the capacity, same voltage needs), but will need larger panels and charge controller, which means larger storage rig(or second ammo can and more holes, wires between them, etc, which to move it would be a pain in the ass). If I can find small watt cookers or a low watt microwave like sandwhich size, this may be a viable use as is. My wife even mentioned using coffe pot to cook rice quicker and boil water, but most draw 600+ watt at once, but only need to run like 5 minutes at a time. That might be easier to recover from just to use a coffee pot for heating water and rice or condensed can of soup while water dripping fills the remaining dilution. She may have solved the cooking issue if I can find the right watt coffe pot and size for easy clean up and tre a few dry runs of cooking various things in it. She said she saw people using them to cook rice, only after we cooked it tonight. Thanks for the late info hun. Some of these probably aren't doable since they say an hour, but most hot dogs are precooked, so a coffe drip and sit should cook them way faster than an hour -

Things to note, I do not know how fully charged the battery actually is still. I have no way of knowing other than it was throwing 13v and now reading 12-12.2v. I never did the full charge up, but I did buy a battery charger today, so I'm going to do that tonight, break it down, unhook the panel, controller and converter, and fully charge it up till I get green on the wall unit battery charger, then before I leave for work tomorrow, I'll take it all outside and hook it up in the yard somewhere that has all day sun, and have the wife try cooking another pot of rice and see what happens. If after tomorrow it cooks 25 minutes without the whistling, then I'll have her turn off the converter, and let it sit outside to see if it comes back to full charge on the controller and when I get home, check the voltage on the DC and AC side of things from just a day of sitting out side.

Thing to note, it was already done when it was whistling and the unit went into warm mode, for which we just unplugged it and let it sit the last six minutes, so overall, better than expected but ultimately, not ideal with the amount of juice it used. I'm wondering now if I should of shelled out the money for the extra battery tester, which in itself was like 3 times the multimeter cost, but I don't know if it would show me anything more than what the multimeter will. Someone chime in on that and if it's worth the cost. I think a multimeter will be more useful for me in the long run, so I bought it instead since the other, is only for testing batteries.

Dinner is served:


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I grabbed myself a cheap-ass multimeter from China which has already proved its worth with my fileserver project and which I've also since used to determine the death of 2 AAA batteries. By my reckoning, a battery tester is just a restricted multimeter so by all means, stick with the multimeter.

In this video some guy checks his car battery with a multimeter and all he does is see if the voltage drops too low when he's cranking the car. In your case I'd consider simly checking the voltage while you're using it to cook stuff to see if it remains within range of what the converter can handle. Another thing to check would be to get within the circuit as the battery is powering something and measure the amps. I'd expect that to drop off when the battery is losing its charge and if you're powering a 300W cooker off of a 12V power source it should be pulling over 25 amps into the converter.

Given that expected power draw, this page I think says you should use 15 gauge wires or thicker between the battery and the converter. It also has a helpful form at the bottom of the page that says a total of 2 feet or 16 gauge wire between the battery and the converter (combination of back and forth, probably much more than it really is) at 25A would drop a 12V power source by over 0.4V. If you change it to a 10 gauge wire, the voltage drop is reduced to just 0.1V.
If you consider the resistance of various wire gauges at 1000ft length and the fact that heat generated in the wire itself is computed by multiplying the resistance of the wire in Ohms times the amps on the wire squared. So 1000ft of 16 gauge wire is 4 Ohm and at 25 amps that's 2500W over 1000ft or 2.5W for 1ft which is converted to heat within the wire itself and that might be sufficient to burn through it (eventually). If you were to instead use 10 gauge wire the resistance drops to 1 Ohm, the power loss over 1000ft becomes 625W which means 0.625W for 1ft. I have no idea at what wattage a wire is likely to die, but since you preferably don't want to waste any of the precious power generated by the solar panel it might be worth it to ensure the wires between the battery and the converter are both quite thick and quite short.

I think your battery at its current capacity of 216Wh is proper for the usage scenario including the use with that cooker. When the battery is at full charge it can power that cooker for 45 minutes and the cooker shouldn't need more than 25 to do its thing. That should leave more than enough juice to keep everything happy. No, I believe the only issue here is the slow recharge due to the small panel. Adding more batteries doesn't help in any way. The problem is that if you want to be able to fully charge that battery daily, it means you need panels that generate 216Wh during the 12 or so hours of adequate sunlight you have in a day. That means you'd need something like a 20W panel, which needs to be actively charging the battery all day. I don't know if the guy can manage that since your description seems to suggest he's on the move quite a bit. Not sure if you or him are comfortable leaving the device unattended somewhere as he's roaming around, and it might look weird to have him trotting around with his cart with a solar panel exposed over it to charge the battery for his evening meal as he goes.

Cooking in a coffee pot is a nice idea, but I think a coffee pot is too fragile. Also note that you can eat hotdogs raw (done it myself many times for a quick on the road lunch - a bun, some mustard and a dog or 2 is all you need). Most people just prefer them warm/hot.

No, what I think the real goal here is is to put more difficult to prepare foodstuffs within easy reach regardless of the climate/weather. You can't really (really can't) eat rice raw. Or a potato. Or pasta. These are really cheap foodstuffs but require some amount of hot water for a considerable amount of time. I'm guessing he's currently preparing this (assuming he's actually cooking food, but I'd be surprised if he wasn't) over some open flame which is why I mentioned the rocket oven - it's popular in developing countries because it's an efficient design that requires very little fuel, can operate in pouring rain so long as your fuel stays dry-ish, it's cheap to make one from junk and it's quite sturdy.

If this solar project works out he could instead reliably get a coocked meal on a daily basis without needing to burn anything, which would be a tricky thing to do when you're surrounded by snow.

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thanks for the feedback. the thicker shorter wire idea and a larger panel may be in order. we ended up in hotel last night so I haven't even unboxed the charger but I think at this point its a matter of timing, good wire, and a larger panel(s) or such and it may be sufficient. key goal, no need for replenishable fuels. he had a propane tank that he riggged the top open to light and give heat but that was both dangerous and short lived since he doesn't have the money to exchange them. I think he swiped it from someone's BBQ nearby.. lol

edit: charging it up now, but pulled off the converter to look at it, it is rated already(with wires it came with) up to 40amps so the wires on it are probably the right gauge for it, even though they aren't hugely thick(I don't own a wire gauge so not sure what the existing ones are) I'm going to leave them alone for now since it came with them and I don't more power than needed coming out of the AC outlets than 125 or so volts.

For the charging though, the controller will only handles 8 amps in and up to 130 watts(which that little panel is probably only doing 20-30 watts) so I can def increase gauge there from the panels and also go larger panel but have to be sure not to send more than 8 amps to the controller and no more than 130 watts.

The battery charger I bought sends 6 amps for the 12 volt charging and 3 while maintaining(auto adjusts and says blocks reversed connections so shouldn't arc if touched together but not going to test that out). I may need to step up the controller if I go larger panel and wires though if it goes over 8amps since the controller doesn't handle more than this. 8 amps will charge this small battery nicely then if I can get the panel to produce it but I think it is probably just too small. It's probably not getting even close to that with the small panel and long thin wires so this will need some more research on changing the wire on the panel that exists now and then seeing what amps it puts out before going back into the controller. If it is too high after changing the wires on the panel, then I'll need a larger controller which is probably going to be more expensive than just some thicker wire and too large for the ammo can setup. Length and gauge being key here I guess for upping charge power without blowing the controller, I'm going to need more help on the math side. Is there an easy web app or phone app for calculating this sort of stuff?(I'll google that later though, cause there probably is an easier way to check this).

Edited by digip
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Ok, so with the home electric AC charger, I plugged it in around 5:30pm and at 9pm, green fully charged light came on the home charger, so battery must not have been as dead as I thought, which is a good sign I guess. However, we may have managed to break the controller during the build when we had the little arc fest in hooking it up permanently to the terminals since it doesn't say fully charged any more but I trust the home charger a bit more. 14+ volts is pretty good and under load it stayed in the 13+ volt range. How long it will stay there when cooking, don't know.

Battery is giving 14+v at terminals and at connector to converter DC, and when I plug in the rice cooker(nothing in it, just checking draw) I get a bouncing 100-120v out of the second outlet on the AC side, so that looks to be good enough to but until I cook a full meal won't know if it will work before making the converter scream. I think the 14 volts it's putting down to the converter isn't going to hurt it(I hope) but will have to do a run tomorrow and check a full cook from charged, make some rice, turn off the converter and then let it sit in the sun till I get home. Then I can check what voltage I get DC and AC and if good, try cooking another one at night, see how things go from there. We may only get one meal a day out of it since after the second use, it may be too low to recover before morning cook time depending on time of day he makes a second meal and he probably won't want rice every time, so cook times may vary. I think little water and hotdogs in it would work fine, fleshy veggies steamed and possibly small thin meats if he catches any rabbit, birds or squirells. Hell, he may be able to make soft boiled eggs although not sure I'd want to put too messy of stuff in it, sure he can figure out some sort of stuff to work with since it's just an induction pot for water and whatever you want to steam, even canned soups would cook in this which he can get at the local food pantry I'm sure.

Either way, he'll have a morning or mid day cooker, and rest of the day radio and at night some light to read by, then by next day should be ok to start over(I'm hoping) although I do think I need a larger panel and probably change the default wire gauge setup from panel to controller to get a quicker charge/larger amperage to the battery during the day time recycle.

Any suggestions for more things to try with it I'm open. There is a local RV store near us so I may swing by there and see what they have for low watt cooking, coffee tin peculator or skillet type things. I think even a regular coffe pot is doable since it's pretty much instant hot drip, he can maybe get dehydrated foods at the pantry to make quickly(if they keep that sort of thing).

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One of the reviews for the 2W (not 20-30 as you seem to think. 2W) panel you're currently using says:

On a bright and sunny day it put out 20 volts at 140 ma.
When it was very cloudy the voltage dropped to 18 volts and it still charged at 7 ma.

I believe those voltages are fairly standard for solar panels - high in voltage, low in amps. Because loss in the wire comes from the wire resistance(constant) and the amperage squared, you lose less when you provide higher volts and lower amps while providing the same wattage (Example: 10W source, 4 Ohm wire resistance over 1000ft. 1V 10A source = 4 * 10^2 = 400W wire loss (so reduce wire length and/or use thicker wire else nothing goes through) whereas 20V 0.5A source = 4 * 0.5^2 = 1W).

If you were to upgrade to 20W panels, you'd still only be providing, at best, 1A in full sunlight. So your charge controller is still utter overkill, even after such a substantial upgrade of the panels. And because all panels provide current at such high voltage even with shitty 4 Ohm wires those upgraded panels would lose just 2W over 1000ft which would be considerable (10% of total) were it not for the simple fact that cable length for the full circuit between the panel and the charge controller is more like 4ft meaning the wire loss even with such thin cables is something like 0.008W. So here aswell, nothing to worry about.

So at least from where I'm sitting, the only thing that might warrant an upgrade is the panel itself to improve recharge rate.

The battery charger provides the battery with 12V 6A which is 72W. That would charge the battery from nothing to full capacity in exactly 3 hours. If you checked in a few times between 5:30 and 9 and each time the light remained off it means your battery was pretty much completely drained when you began charging it.

With any foodstuff, there are 2 factors that influence price: availability/shelf life and amount of processing before it gets sold.

- When food is in season (veg) or has a shelf life measured in years (dried pasta, rice, frozen things) it's abundantly available which makes it (relatively) cheap.

- When you compare buying a head of lettuce vs a package of pre-cut lettuce, someone had to go to the effort of cutting that lettuce and wants to get paid for that, driving up price.

Since dehydrated foodstuffs got that way through some sort of processing, even though the shelf-life improved because of it chances are it's still more expensive than buying fresh. Plus I'd be kinda surprised if this guy manages to retain something of a storage for foodstuffs. If you're not going to consume it anytime soon, it's going to be that much more stuff he's either going to be lugging around or have to worry about getting nicked from his 'home' while he's out and about. And it's good to remember that just 1 pound of rice provides an adult a daily portion for a full week. Naturally you'd prefer something more than that (veg, fruit, perhaps some meat now and then), but when push comes to shove these can be the carbs that keep you going.

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Yeah, he has squatters in the woods near him who steal from one another but he also has a sign on his entrance "I've got big balls, don't fuck with me" and has been in a few fights with locals..lol. Most of the others, he has welcomed in and shared his space with a few times when their stuff had blown away. He had a nice black eye when I met him and some banged up knuckles from someone who tried robbing him when he has no money other than handouts and he has been arrested a few times, one time just for squatting behind a local bar in the woods not far from where he is now. I wouldn't call him a bad ass, but he does seem to know how to take care of himself considering he made it through the winter out there with minimal supplies, he has a bow, ax, a knife and some other small camping stuff, but the propane take I think was nabbed from someones BBQ in the neighborhood, since it now sits empty outside with the broken top he rigged to light directly. This is why I tried to help with the vest and a few food drops between January and now, getting him hand and foot warmers from sports authority and hiking socks which are pretty thick and warm. He had gloves but they are more like giant cotton mitts that are more than likely useless when wet and his hands show signs of frostbite. Lot of black on the tips and palms, but he still kicks around.

Last time I saw him was about 2 weeks ago, and he has lost weight so it is taking a toll on him, which is why I want to get him something simple to have on hand that doesn't require fuel. He usually panhandles near the 7-11 which is now closed and at the bank which is right near the Wendy's fast food that gives him coffee for free and if he has change something to eat now and then. They've been pretty nice in not throwing him out and allowing him to sit inside to stay warm over the winter at times but I'm sure they'd rather not have a beer smelling man who rarely baths or changes his clothes in there all the time(another reason I sent him some new underwear,socks and tshirt packs). I'd say he's about mid to high 50's and maybe just under 6ft, about my height and when we first met, maybe 200+ pounds. He now looks well under 200 pounds and his pants ride low, so he def isn't eating as much. We have some local food pantries that give out canned goods and such nearby so he can get some food from the churches on different days, it's just a matter of whatever he opens, there is no refrigerator so leftovers is not really going to be viable. He has a cooler, but I think that is where he stores his dry stuff and most likely his beer which he always seems to have on hand.

As for the panel, yeah, I think I may need to increase the panels wire gauge and figure out a way to mate it to the jplug since its thin wire and a sealed connector at the moment, but I can snip them off both connectors and just make some kind of new plugs I'm sure with something from radio shack or such. My friend probably will have a better idea of what to do with that and may have things in his tool shed to make it work if I get the larger wires. The 18w panel or two 18w panels may be easier with the inline parallel jplugs, but wire is much cheaper than more panels if I can get away with it. Not just for budget but to see how cheap this can all be done is also the goal for me, even if I have the money to splurge on a huge rig, I want this to be kind of an affordable kit idea that can be rapidly deployed and stored for others who want to do something similar for themselves, like trips to the beach for radio and food cooking or camping out.

edit: and, it's raining, so not going to be able to test this out today. his shack has a clear roof so he would probably be able to get away with it but I don't have any kind of shelter to put it under so will have to wait for a dry day.

Edited by digip
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I would try a small 12v cooking pot and griddle. They sell them for truckers, they might draw less power than having to convert to 120v for the same type of appliance and you could eliminate the converter.

I found some that only use 150 watts. http://www.globaltrucker.com/12-volt-cookers-12-volt-stoves/

Edited by khaotic57
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I think I may need to increase the panels wire

Please reread what I wrote. Due to the low amps coming from the panel the wires can be rediculously thin. Even more so because of the short length of wire you need to make the circuit between it and the battery charger.

The main issue w.r.t. wires is between the battery and the converter, as that circuit is pushing 25 amps and over at full crank. Which is a LOT of amps and in the formula to compute the wire loss that number gets squared so it's a major contributor. On the wikipedia page for American Wire Gauge you get a nice table that includes the core diameter. That might allow you to measure the diameter of the insulated wire, subtract a bit for the isolation and you can make an educated guess on the wire's core thickness and, thus, gauge.

Assuming the circuit betwen the battery and the converter is 1ft long the wire loss during 30 minutes of cooking is approximately 0.313 * O where O is the value from the table for resistance in Ω/kft. The number you get is the loss in Watt. Divide the number by 2 to get the amount of hours the current panel needs to receive ideal sun conditions to make up for it.

Quick reference:

WG | R | W/ft | T

16 | 4.0 | 1.25 | 37m

14 | 2.5 | 0.78 | 24m

12 | 1.6 | 0.50 | 15m

10 | 1.0 | 0.31 | 9m

8 | 0.6 | 0.19 | 6m

WG: Wire Gauge

R: Resistance in Ω/kft (see wikipedia table)

W/ft: Wire loss per foot of circuit. Multiply/divide as required.

T: Time the current panel needs to operate in optimal conditions to make up for the loss.

I don't think 8 gauge is realistic. The diameter of the copper core of those wires would be over 3mm which is HUUUGE. 12 gauge with a core thickness of 2mm is already quite substantial. Looking at the pic and not really having anything on image for scale I'm guessing it's currently using 14 gauge.

It might be an idea to put that converter inside the case, hugging the battery to allow you to make the wire lengths much shorter. If you halve the wire length for the circuit, you halve the wire loss. You can then have an outdoor power socket connect to it (think: extension cable) which gets mounted on the outside of the ammo case for safe, practical use. You could even run a USB extension cable from the inside out to allow him to connect a USB device without needing to open the case if you really must, but I'm thinking that's mostly luxury. He probably doesn't have a lot of USB-powered devices and those he has he can probably connect on the inside for charging, close the lid and forget about until he needs the device again or alternatively simply keep the ammo case's lid open.

If you choose to spend some more money to upgrade the panel, for $50 you can get a 20W panel from china but the main drawback for these beefier panels is that they're somewhat large at 41x38cm. I can't tell if that would fit on the current frame. It might be more practical to go with 2 separate 10W panels at 41x21cm for $40. As with all things from China, if you want it cheap you're going to have to wait about 3 weeks for the thing to arrive on your doorstep...

Edited by Cooper
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I would try a small 12v cooking pot and griddle. They sell them for truckers, they might draw less power than having to convert to 120v for the same type of appliance and you could eliminate the converter.

I found some that only use 150 watts. http://www.globaltrucker.com/12-volt-cookers-12-volt-stoves/

I think if I build another one of these(which I might just for myself), I'll probably go that route with a DC outlet on the box. I like the idea of not having more things like the converter in line since less wires and more room inside although you still need a charge controller for the panels to regulate and not over charge the battery. I'd have to make some sort of little on off switch setup so the DC outlet doesn't also put a constant draw if you leave something plugged in. This way he can leave something connected and just switch power off. Thanks for the link.
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Those appliances tend to have long, 8+ft cables (don't want to do the actual cooking in the cabin, so you need a long cable, and the full circuit is counted so that's cable length times 2) and not particularly thick ones to boot. I've got a cooler that you can plug into your car's cigarette lighter. It consumes just 50W but when you pull that plug from the socket after a few hours driving you can quite literally burn yourself on the metal pin, that's how hot it's gotten. It's got 18AWG cables (says so on the wire) and I'd be shocked if these cookers use something else. They don't give a shit about wire loss. You've got a MASSIVE diesel engine at your disposal. Who gives a shit?

This online calculator allows you to compute loss for both AC and DC circuits.

Using identical wire dimension of 1 mm² and 1 meter wire length that same 150W load results in 7.19W loss on a 12V DC circuit whereas a 120V 60Hz circuit pulling 1.25A to get 150W in results in just 0.07W loss. Yes, a factor of 100! Why do you think your house isn't wired for DC current?

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Yeah, that was one thing I was going to ask, since AC is alternating current and bounces, wouldn't DC kill a battery faster even if it used less wattage since it's a direct line of power at all times? I would think that is probably why they are lower watts since they have more constant voltage. I do like the little lunch box cooker they had on the one site though.

Reasons I like the rice cooker, it's basically a small pressure cooker and holds heat really well. It can keep food warm for a long time too and needs minimal prepping to cook things. It's versatile for multiple types of meals other than just rice even though it's the main selling point. You could cook virtually anything in it if you're savvy in the kitchen.

It does have it's drawbacks though, like getting really hot without liquid in the pot and would melt the whole thing quickly if you didn't use water in the bottom part or some sort of sauce/liquid. You have a small induction burner on the bottom, a metal pot and then a steam tray on top, inside a plastic shell with a lid that latches shut, so the potential for hurting yourself let alone burning the woods down are pretty solid if you aren't paying attention. Just plugging it in to test without water, it heated up too hot to touch the pot and the plastic inner steamer tray seems like it would only take a few minutes to melt it. Just need to make sure you keep water or liquid in it, since it releases moisture over the edge to a drip cup for overflow when it gets up to temperature and steams.

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wouldn't DC kill a battery faster even if it used less wattage since it's a direct line of power at all times?

I think I understand what you're asking: Since the alternating current is a waveform the amperage drawn from the battery by the inverter is probably a waveform too. You know what? I have NO IDEA if that's even true and also no means to test it. Sorry. But even if this is indeed how the inverter's load is placed on your DC battery, it won't result in a faster demise of the battery. One thing I do find is that as you increase the sustained load on the battery, that battery's ability to provide you with that power diminishes. Do if you have a 10Ah battery and you put at 10A load on it, it won't be able to do that for the full hour. It's not that the electricity isn't in the battery, but rather that it won't come out at that rate. So if you're demanding 30A from your battery you might be able to drain it to, so, 50% capacity before it's unable to meet your demand. If you then hook up something else that only demands 5A things will be a-okay. Also, this is where your deep-cycle feature pays off. Relative to a non-deep-cycle battery, this one will deliver more of its capacity at higher loads.

To kill your battery you're going to have to short it somehow or drain way, way, way too much. There should have been some kind of manual provided with the battery that tells you how far you can go.

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Just ordered 2 18watt charging panels since they were on sale half off all other online stores I could find. I'm going to upgrade the one box, and make a second one for myself, possibly with a larger amp hours batter as well. Will probably have to build a new stand since the other panel is probably going to not match the mounting holes from the bottom, but that isn't a huge deal.

This is the site I use to lookup the parts, but they don't sell directly from their site, so you have to search for the model or UPS, which UPC usually limits your results. Just the brand name shows more than the UPC.


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  • 2 weeks later...

Delivered last Saturday, so far still good. Today was my last day at work which was just down the road from where lives, so I won't be up that way much to check in on him, but happy it's done and at little camp site. Wife and I liked his little rice cooker so much, we bought our own. Damn handy little bugger, we've cooked curry chicken over couscous, fish, rice, some veggies and soup so far, so he should be able to make just about anything so long as he has water and a few small ingredients. Picked him up some supplies to get him started. Hopefully he uses some of his beer money on real food now, but that is up to him.

Larger panel:


His camp:




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Good stuff, man. That's a pretty decent campsite for the guy. Reminds me of when I would go to the field in the Marine Corps. It's nice that he was able to acquire that stuff so he can at least have some shelter. I really hope your project works wonders for him. I'm sure he really appreciates it.

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