Possible APU alternative

truckdriver31 · Sep 24, 2022

Me Too said: ↑

An electrical engineer here that is changing careers (that's a story for another day) but I do know of what I speak here.

Power is Amps (current) times Volts, so your 200 Amp/Hr battery stores 12V times 200 Amp/hrs of power i.e. 2400 Watt/hrs. If you use the three batteries in parallel, this gives you 7200 Watt/Hrs. So what is a Watt/Hr? It's how much power the batter can store. You could run a 7200 Watt heater for 1 hr, or a 100 watt lightbulb 720.

I think the first question that you need to ask yourself is what do you want to power and for how long? Your setup would ideally (we are going to circle back to this later) 720 Watts for 10 hrs. My TV in the bedroom draws 144 watts, my wife's hairdryer draws over 1000. A SMALL room air conditioner draws 6000. You need to add up all the things that you are going to run, for how long, hang 10% extra onto that minimum and see if this will do what you want.

You said that the inverter draws 8 amps. 8 times 12 is 96 Watts. Notice that we are not in Watt/Hrs. here. Watts are an instantaneous value. Think of Watt/hrs as the odometer on your truck, Watts as the speedometer. You can only get the same amount of power out of an inverter that you put in (it is just converted to 120 Volts AC) so that little inverter can't power ANYTHING that I listed above.

And all these numbers are ideal. Nothing in the world is Ideal. The inverter is going to lose some power in converting the power, the batteries are slowly going to fade, etc.

I'm also assuming that the battery can provide that Watts that you need (the instantaneous value.) I'm not sure if this is the case with deep cycle batteries, you need to look.

Then how are you going charge them? If you hang it of the truck's batteries, your batteries will back-feed into the truck batteries. When the truck starts, its going to be using your batteries too. If the truck batteries are dying, it will drag your batteries down too. You could put a big diode in, but that's another thing you are going to need to size.

I hope this helps, good luck.
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Its amps x 117volts gives you the watts. Plus you got discharge rates. You will burn the whole truck down if you discharge to fast

Kowclub173 · Mar 24, 2023

I know this is an old post but I just skimmed it and I didn’t see anybody mention that 8amp is what the ac pull on 110v. That would be more like 80 amps on 12v. So you’d need 800 amp hours of capacity to run 10 hours. A traditional deep cycle should only be discharged to 50% so that would mean you need 1600AH of total capacity. That’s a lot of juice.

truckdriver31 · Mar 24, 2023

Kowclub173 said: ↑

I know this is an old post but I just skimmed it and I didn’t see anybody mention that 8amp is what the ac pull on 110v. That would be more like 80 amps on 12v. So you’d need 800 amp hours of capacity to run 10 hours. A traditional deep cycle should only be discharged to 50% so that would mean you need 1600AH of total capacity. That’s a lot of juice.
Click to expand...

You forgot start up amps

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