[SOLVED] Can an inverter on a car charge the house battery?

SlowBro wrote:
those cheap and inefficient Chinese generators and my van uses less gas per hour idling, despite having a larger engine.

Gdetrailer wrote:
Most car alternators are designed for INTERMITTENT heavy charging

Oh then that's perfect. I have in mind intermittent use, otherwise I would be buying solar.

By INTERMITTENT heavy charging, that means for a few minutes at a time. Basically when you start the motor, it's pulling hundreds of amps to turn the starter for a few seconds...so a few minutes charging at 80-100amps will replace the amp-hr that were pulled. After that it just puts out a few amps to run the lights, radio and other light loads. Nothing close to 150amps.

You can buy specialty after market alternators designed to put out high amperage for a longer period of time. Most are geared toward full size pickups with big V8 engines that won't notice the power needed to run them. They are also frequently optimized to put out significant amperage at lower engine RPM.

As you indicated it's the stock alternator, I would be very surprised if it can withstand anything close to 150amps output for more than a few minutes. If you are lucky, there will be a cut out that stops the output. Otherwise, very good chance of burning out the alternator. (This is made even worse by the idea of doing it with the vehicle parked and no airflow flushing the heat out of the engine bay)

From the battery to the inverter, you will need some pretty heavy cables as you are going to be pulling upwards of 80-100amps off the truck battery.

You will need to look at the continuous output of the inverter. Usually, they give a peak load rating as the main number. That peak load is usually only good for seconds or minutes. There is a continuous rating (often hard to find) that is much lower.

If you upgrade everything from the alternator thru the inverter to handle the loads, it's pretty straight forward and at 120v, the cabling to go back to the trailer converter (charger) doesn't have to be excessively large due to the higher voltage (typical extension cords is good for this size load) and as previously mentioned once you get 120v power of sufficient amperage back to the trailer, the converter won't know the difference between your system and shore power.

If you have the alternator that can provide the amps, it's actually a good solution to charging while towing (not so much while stationary). The problem with charging directly off the 12v system is the wires going to the hitch are tiny and often the connections are of poor quality with low voltage (12v) you get a lot of power lost. This results in only a few amps making it back to the trailer battery.

Probably not worth replacing the generator if it's in good running condition but watch and you can find a good quality inverter generator for $4-500 (helped a friend pick out a 3100w dual fuel Champion last summer for $500). And yes, they do save on fuel consumption compared to the old cheap fixed speed generators. Only under high loads will it be comparable fuel consumption. So an 800w load on a 3000w generator will be throttled way back with an inverter generator and do significantly better (and be much quieter).

There is no magic in inverter generators. Under the same load they use about the same amount of fuel as a non inverter generator. The only time they 'save' fuel is when the inverter generator is idling and producing little power.

In my case, that is almost never. I have remote electric start. So the generator only idles until my inverter charger "flips" to generator power.

Gdetrailer wrote:
At least you do now realize the gen you already have will use far less fuel..

No it uses far more, because it's not an inverter genny. It's a cheap inefficient Chinese genny. Uses at least 50% more gas per hour, maybe as much as 300% more. My car uses about 0.25gph idling but the rating on the genny at half load is 0.47gph, and if that's overly optimistic it would be even worse. The RV would only need half the genny load so maybe it is only 0.47gph.

However, the cost difference for such a small amount of usage is what convinced me. Not worth saving eight bucks or so.

Alrighty thanks everyone, I have the answers I need and have marked this thread solved, so I am unsubscribing from this thread. Have a great day!

SlowBro wrote:
Well, maybe nevermind. I found my cheap Chinese generator's manual, and the rated gallons per hour is 0.47 which is much lower than I thought. Even if the number is really twice that it's only about $12 to run for six hours, which isn't enough of a difference to justify using the van.

Yeah, I'll stick to the cheap genny--but feel comfortable knowing that if for some reason I can't use the genny, using it on the van once in a great while SHOULDN'T blow up the alternator.

Thanks all!

:)

Yep!

At least you do now realize the gen you already have will use far less fuel.. A very smart move for this application.

As far as "blowing up" your vehicles alternator, you most likely would not have done that, but just drives me nuts that folks think it is efficient to use the vehicle engine/alternator/drive train for a charging application like this as an inexpensive "substitute".

Break your vehicle just once and the cost to repair will be many times more than your portable gen.

Besides, using such an oversized engine in an underutilized mode like 1 HP of engine really flies in the face of being "Earth Friendly" when it comes to using considerably more carbon based fuels for no real good reason (and NO, I am not a "tree hugger").. Just pointing out an "oxymoron" which is counter culture to todays modern tree hugging society.

YC 1 wrote:
Sure seems like a long road to get there on with lots of twists and efficiencies.

A good set of battery jumper cables while parked close to the rv will do the trick.

I had that thought as well, but...

Sure seems like a long road to get there on with lots of twists and efficiencies.

A good set of battery jumper cables while parked close to the rv will do the trick.

QCMan wrote:
If you are only going to charge the battery once or twice a year why don't you just take it home and put a battery tender on it?

It's a long story and I don't want to derail the thread. Let's stick to the tech, and I believe my problem is solved.

Thank you.

BFL13 wrote:
You can't run the 45 amp converter at 45 amps from an 800w inverter. First the inverter will have a continuous rating of maybe 600w.

Its continuous rating is 800W.

BFL13 wrote:
Not clear but that "30a" could be the converter's 120v spec as opposed to 50a like in a bigger RV.

The user manual says the branch is 30A DC, but that may not be for the battery. It's unclear.

Thanks for the picture and confirmation! That's more-or-less what I had in mind.

If you are only going to charge the battery once or twice a year why don't you just take it home and put a battery tender on it? Or is that too simple and you want to throw technology at a simple problem that was solved 75+ years ago? If you just want to churn the economy, thank you.

Well, maybe nevermind. I found my cheap Chinese generator's manual, and the rated gallons per hour is 0.47 which is much lower than I thought. Even if the number is really twice that it's only about $12 to run for six hours, which isn't enough of a difference to justify using the van.

Yeah, I'll stick to the cheap genny--but feel comfortable knowing that if for some reason I can't use the genny, using it on the van once in a great while SHOULDN'T blow up the alternator.

Thanks all!