# Question For Electrical Expert

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I need a 110V AC to 18V DC adapter that can power an 18V DC battery powered drill. My problem is, I don't know all of the specs that I need to know in order to get the right 110 Volt AC to 18 Volt DC wall wart/power brick. I connected my meter inline with the drills main power circuit and put the drill under working load, using its battery as the power source, and I got a reading of about +20.23V DC and about 0.123 amps (And I don't know how to check for the wattage that the drill is using while it is operating). I then used an old 18V (1 AMP) AC to DC wall wart to power the drill, and the motor would barely turn, at about 3 RPM, but I got similar readings on my meter as I got when I used the drills battery to power it. I'm obviously missing some fundamental principle of electricity that is keeping the drill from running. Is the wall wart incapable of supplying enough wattage or what? Basically I just need a good estimate of the specs that a wall wart would need to have in order to power the drill reliably. If it helps, the drill has only two contact points that connect it to the battery.

Edited by NegativeSpace
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I'm not an elecrtical expert but wattage is voltage multiplied by current thus 2.49W (20.23*0.123) however I think your readings are wrong , the voltage could be on the money but I doubt your current is. How exactly are you taking your readings? i.e with the meter in series and what meter is it , i.e are you using it on a high current setting?

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I'm not an elecrtical expert but wattage is voltage multiplied by current thus 2.49W (20.23*0.123) however I think your readings are wrong , the voltage could be on the money but I doubt your current is. How exactly are you taking your readings? i.e with the meter in series and what meter is it , i.e are you using it on a high current setting?

I had my meter set to read amps, with one lead connected to the +V battery terminal, and the other lead connected to the -V battery terminal. Is that the wrong way to test for current?

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IIRC current must be read inline with a meter.

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IIRC current must be read inline with a meter.

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One lead on battery v+, then other lead on wire that should connect to v+ on battery. You do have to be careful and select the current amperage rating or you can blow the fuse (unit if cheap) checking current.

battery positive terminal ----wire--- probe (red) probe (black) ----wire---- drill positive terminal

You need to make the current flow through the meter.

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One lead on battery v+, then other lead on wire that should connect to v+ on battery. You do have to be careful and select the current amperage rating or you can blow the fuse (unit if cheap) checking current.

battery positive terminal ----wire--- probe (red) probe (black) ----wire---- drill positive terminal

You need to make the current flow through the meter.

Ohhh OK I think I got ya. My meter has a special lead terminal that says "Fused 20A MAX". I assume I need to use this terminal to check current? Will this tell me what kind of wall wart or power brick I need to run the drill?

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One lead on battery v+, then other lead on wire that should connect to v+ on battery. You do have to be careful and select the current amperage rating or you can blow the fuse (unit if cheap) checking current.

battery positive terminal ----wire--- probe (red) probe (black) ----wire---- drill positive terminal

You need to make the current flow through the meter.

I tried this out, and I must be misunderstanding because the drill wouldn't work. The configuration was; Meters leads used to connect the battery's +V terminal to the drills +V terminal, so in other words, I used the meter as the wire between the battery and drill +V. I had a jumper cable connecting the battery's -V terminal and the drills -V terminal. The drill would not run. I switched the meters red lead from the meters "V/F/C/Ohm/mA/uA" terminal to the "Fused 20A MAX" terminal. I checked the meters fuse, which is good. I tried milliamps, as well as whole Amps settings on the meter. Drill still doesn't run. I plugged the battery in to the drill directly and the drill works. I tested a wall outlet with my meter, it reads AC voltage correctly........ What next?

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You will need to use the fused lead and select mA (milli-amp) as the measurement. On a side note, it would probably be far more trouble/expense in doing all of this work (it is not a common power supply to convert 110v to 18v at sufficient amperage (6-10A at least under load) to make this a practical solution. Even a cheap corded drill is likely cheaper and possibly more effective than this solution.

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You will need to use the fused lead and select mA (milli-amp) as the measurement. On a side note, it would probably be far more trouble/expense in doing all of this work (it is not a common power supply to convert 110v to 18v at sufficient amperage (6-10A at least under load) to make this a practical solution. Even a cheap corded drill is likely cheaper and possibly more effective than this solution.

Ok I'm going to try fused terminal, set to milliamps next. The drill should run if I'm doing it right, shouldn't it?

For 18V DC power bricks or wall warts, what is the highest current that I am likely to find available? It seems like there would have to be some available. if they aren't readily available, could I possibly use two 18V wall warts, with each of them having half of the current I need to run the drill, and combine them to still have 18V and sufficient current?

I have probably a dozen 110V AC drills, and probably even more 110V AC screw guns, this is just something I want to do so I hope I can figure it out!

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Just ease into the trigger on it and measure under load slowly as well. A quick pull or heavy load may pop the fuse.

I am not sure about combining the two 18v wall warts, but most will not operate at higher currents, but I would expect you to have difficulty finding an appropriate adapter. Under load I would see your drill could easily pull >10 amps.

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Just ease into the trigger on it and measure under load slowly as well. A quick pull or heavy load may pop the fuse.

I am not sure about combining the two 18v wall warts, but most will not operate at higher currents, but I would expect you to have difficulty finding an appropriate adapter. Under load I would see your drill could easily pull >10 amps.

Bummer!

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If there is a way to set the drill up using a pig tail lead with aligator clips. Go to a high current then move it back till it is in range. Or use an auto ranging meter. I dont know if voltage drop means anything.

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If there is a way to set the drill up using a pig tail lead with aligator clips. Go to a high current then move it back till it is in range. Or use an auto ranging meter. I dont know if voltage drop means anything.

I don't quite understand what you mean...

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Depending on the power drill you are using, it could be outputting over 500watts or even more when under load, to be certain of its actual figures, I would recommend you to purchase a proper watt meter, that does amps, volts and watts measurements to get an accurate reading.

You could also use a 24volts battery, connected to an 3000 watts inverter to power up the drill.

rtm?

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