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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Archive for the ‘Car/Truck battery’ Category


Car/Truck Battery power for existing well pump

Sunday, December 7th, 2008

How would you convert a well pump to run off of a truck battery? This well pump takes care of my house and spout near my horse barn.


Most likely you would not unless the engine was running at fast idle and a high capacity alternator was charging the battery. I have an 1800 watt sinewave inverter in my dual battery F-250 diesel truck and it may be able to start and run a small 120 VAC well pump in the 1/3 to 1/2 HP range if it is not too deep, but remember most well pumps are 240 VAC. This would require using two large inverters designed to work together to provide 240 VAC output since most residential inverters are 120 VAC output.

Also keep in mind that the current draw on a 12 volt battery from an inverter will be 10 times the current of any 120 VAC load due to the voltage difference. A 1/2 HP deep-well 120 VAC pump can draw over 20 amps at start-up surge with a run-time load of around 12 amps. This is over 200 amps draw on the battery and DC side of the inverter. Most vehicle batteries cannot take this high current for more than a few seconds, and your battery cables would need to be the size of welding cables, and most inverters this large are 24 volt.

If I were you, a much less costly way to do this is a transfer switch and a plug to connect to a generator.

Good luck,

Jeff Yago


Air conditioning for a pickup camper

Thursday, November 27th, 2008

Hi Jeff.

I would like to put Air conditioning in my pickup truck camper shell to keep my dogs cool in the summer. It would only be in use when I was traveling down the road, not while the truck was turned off. Here was what I was thinking – could you offer an opinion on whether it would work or how to to do it, if it is even possible.

[I want to] put an RV air conditioning unit on the top of my camper shell and run that off an inverter connected to my pickups battery.

I do have a 2500/5000 watt inverter but I wonder if the air conditioning unit would suck so much energy that the alternator could not keep the truck battery charged up going down the road.. My truck has two batteries up front


Hello, MIke.

The problem is not battery size, it’s your alternator capacity. There is no way an RV air conditioner can run off one or two truck batteries for more than a few minutes without draining them. For example, the smallest, newest, and most efficient truck camper AC unit draws 8 amps at 120 VAC. Assuming a 90% system efficiency, this would be a 1,100 watt “run” load on your inverter, and require an inverter that can handle at least 2 kW “start” load since any compressor load is a dead short on the power source for the first few seconds it is trying to rotate.

You said you had a 2,500 watt inverter which should be able to handle a small RV air conditioner, but that is not your main problem. Your inverter will have a constant draw of 88 amps at 12 volts DC while an 8 amp load air conditioner is running, and could draw up to 150 amps for a few seconds every time the compressor kicks in. This means your truck alternator and all related cables need to be large enough to handle these larger current flows and still have enough excess power to operate your lights and other electrical loads in the truck. Each time you stop at a light, there will not be enough amps coming from your alternator even if it is a larger 150 to 170 amp heavy duty model.

This is why the air conditioning unit in an RV is always wired into the exterior shore power or generator panel, and not powered from the batteries. Any 120 VAC electrical load on an inverter will draw 11 times the AC amps from a 12 volt DC battery.

I suggest letting the dogs ride in the back seat!

Jeff Yago



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