Use my running car to power inverter

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20052

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Dec 29, 2018
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Yes its me again, back from the drawing board, ha ha. Here it is, can i connect the battery in my car to the batteries on my trailer to a inverter then power my rooftop ac while the car is idling ?

I have a new vehicle with a 175 amp alternator, 2 brand new 6 volt golf cart batteries in series (225ah), brand new 13.5 brisk air ii and i plan to purchase a new 3000-4000 watt inverter.

I am trying to figure out a slick way to occasionally run my ac while boon docking and its the only 120 volt device. I do not have the space in my sienna van or 20 foot trailer to put a 3500 watt generator. From your feedback I can run the ac with the microair device using a 2500 watt generator but I just dont like the sound of generators on my neighbors when camping. if i did get a generator (and a microair kit) it would have to run on propane (-10%).

thanks
 
The A/C draws too much juice for that, even ignoring the fact that it's not good for your car to idle for that long. The car, at idle doesn't provide very many amps (that 175 amp rating is at a high RPM, not at idle), so you'd be drawing down your car's battery even IF you could get the A/C to run, and it wouldn't last long. The startup current for an A/C is huge (something over twice the running current), and I suspect even a 4000 watt inverter wouldn't stand that for long without damage -- even if it does, your batteries won't last more than a few minutes. I'm not sure that all the DC wiring would stand that load, either.

You'll really need a proper generator for air conditioning. The A/C will use around 15 amps on 120 VAC, which would be around 150 amps on 12 VDC.

That being said, perhaps someone knows of a way to do this, but it's not something I've come across -- there's just too much current draw for using batteries.
 
similar to what this chap has done except my trailer batteries will be the optional battery shown in the diagram.
 
The fundamental problem here is that those 175 amp alternators are not designed to output anywhere near that amount of power continuously, they also need to be well above idle to do so, and need ample cooling air passing by the case, all things you would not have with a car sitting in one location.  Add to this that the DC running amp draw from Brisk II 13.5 will be somewhere between 100 - 130 amps (air conditioner amp draw varies with how hot it is), this is one of those situations where the best option for fuel economy, etc is a mid sized inverter generator such as a Honda EU3000, possibly a Yamaha EF2400.
 
Thanks, i will ck that output thing on the alt, like this article bit the optional battery will be my 2 golf cart batteries, would that take up the slack?

https://www.familyhandyman.com/automotive/how-to-turn-your-truck-into-a-generator/view-all/

 
Simply not practical with anything remotely like your set-up.  The 2 batteries by themselves might run the a/c for a few minutes before the voltage dropped enough to force inverter shutdown. Under a heavy amp load, the battery voltage drops like a rock. The inverter will trip-out at about 10.5v-11.0v, but with a 100A+ load the battery voltage will probably hit 7v.  The same thing happens to the starting battery when you crank the engine - the voltage falls below 10v.

The set-up in that article will run a power drill or similar light load but is nowhere near capable of the 1800 watts it claims.  Even with the truck engine running at 1800-2000 rpms.
 
The problem here when looking at the article and comparing it to running an air conditioner is a matter of duty cycle, sure you can run a circular saw off an 1800 watt inverter (though it is marginal), the question is how much of the time will it be running.  In the case of circular saw it is rare for them to be used continuously for more than a minute, assuming worst case something like a 25% duty cycle being ran for at most 1 minute out of 4, though probably more likely 10% duty cycle with something like 10-20 seconds every minute, then with multi minute breaks allowing the alternator to catch up and recharge the battery and for the inverter to cool down. 

By comparison in a warm climate the air conditioner compressor might have a near 100% duty cycle and run for hours at a time, and never reach the cut off point until the sun goes down.
 
ok, got it, thanks, back to the drawing board, ha ha. but you have admit at least i tried.
 
20052 said:
ok, got it, thanks, back to the drawing board, ha ha. but you have admit at least i tried.
Click to expand...

By asking questions ..You saved a bunch of money.

In the other hand if it get to hot it would be a good time to drive somewhere with A/C :D
 
120 amp times 12 volt = 1440 that is a bit tight...  and the alternator is not designed to deliver full power full time so you are risking a very expensive auto component.

About the same price as a new alternator.. Installed.. You can pick up a 3,000 watt Inverter Generator. That MIGHT be enough to kick start your A/C and will be enough to run it.  NOTE you also can get buy with a much smaller (And thus cheaper) Inverter for the stuff you want to run inside the RV exclusive of hte A/C so it might actually be cheaper.. Uses less gasoline too. the Car is a very ineffiencent charger.
 
As Larry said, the A/C will draw 150 Amps per hour, not including startup draw.
The battery bank has 225 ah capacity, or about 110 ah available.  You should not draw over half of the available power or permanent battery damage will result.
Assuming no alternator, these batteries MIGHT power an A/C for half an hour, IF they could survive the startup.  As others have stated, the alternator will produce FAR less power than would be needed to extend run time more than a few minutes.

Gizmo nailed it.      By asking questions ..You saved a bunch of money.
 
>. if i did get a generator (and a microair kit) it would have to run on propane (-10%).<

Why?  I carry a small jug of gasoline with me in the back of my diesel truck. 2kw generators don't suck back a lot of fuel, and they already have their own fuel reservoir.
 
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