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

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. The converter will draw in VoltAmps (VA) which is after counting the Power Factor it has of 0.7 so that 780w will be 1114 VA.

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

As mentioned earlier you can do the thing when stationary so that the inverter is clamped to the car battery with short fat wires, hanging outside the engine compartment away from the heat, with the hood up and engine idling. But you must use an inverter that can handle the charger, and a charger that only pulls what the car can supply to the inverter while maintaining its voltage.

Doing this while driving means using fatter and longer wires routed somehow to get the inverter away from the engine heat. You can get the long 120v wire back to the trailer where the charger would be close to the RV battery though, if you rig it so it stays off the road.

What happens is when the car system is overloaded, the car's voltage sags. You can find what it can do by trial and error if you had a charger with amps settings, such as a Vector with 35, 20, 10 amp settings.

I was able to run at 35 amps of charger with a 1000w MSW inverter with the 2003 Chev truck idling, but higher amps caused the truck's voltage to fall off. Don't forget to turn off the car's blower etc, which uses some that you want for the inverter.

I also can run a Vector at the 20 amp setting with a 400w MSW inverter that runs at 320w.

2112 wrote:
Can you get your vehicle close enough to the house battery to use jumper cables? That's how I do it.

Per this battery manufacturer, alternators direct connected (using battery cables or jumper cables) are not designed to charge batteries, only maintain them. Also, I recall an Interstate battery tech telling me the same.

But inverters are common, provided I get the sizing right, engine RPMs, all that.

Idling cars are also common, and running the headlights, A/C, and radio uses about the same amount of current as the inverter would.

I feel pretty safe doing this occasionally. Six hours of idling every six months or year.

2112 wrote:
Most newer model vehicles are smart enough to not over-tax the alternator.

That's good to know. Do they have temperature sensors to detect overheating?

You have around 10% inefficiency on the inverter and 15-20% on the converter. So around 25% of the power generated by the vehicle is wasted doing this.

As mentioned above, an alternator at idle generates very little power beyond what it takes to operate the vehicle.

It would be much faster and cheaper to get a 2000W inverter generator to do the job. The expense of a $500 Predator is a drop in the bucket compared to the wear and tear on your car.

SpeakEasy wrote:
Do NOT under any circumstances, connect the inverter through your cigarette lighter port.

Yes indeedie. The inverter has ring terminals for the battery.

valhalla360 wrote:
Is this a high output 150amp alternator or the stock alternator?

Sienna stock alternator is rated at 150A.

valhalla360 wrote:
Also, were is the inverter? You mention in the "cabin" but does that mean in the vehicle or in the trailer cabin?

Vehicle cabin.

valhalla360 wrote:
Be prepared with a jump pack if you try this (or at a site with shorepower) as you could find your starter battery dead as the inverter drags it down.

Good to know. I was told above to watch that voltage stays above 12.7.

valhalla360 wrote:
Once you get past the inverter of appropriate size, no issues charging...at that point it's no different than being plugged into shore power.

Yeah, that's what I thought. Was criticized above for "reinventing the wheel" when I thought, surely someone somewhere has done this already and I just missed it in my search.

It's been mentioned, once, in this discussion, but it bears repeating: you have to connect your inverter directly to your car battery. Do NOT under any circumstances, connect the inverter through your cigarette lighter port.

You probably already know this, but it is important enough to repeat.


-Speak

pianotuna wrote:
The inverter is too small IF the converter will go to bulk charging mode.

The WF-8945 draws 780 watts or 11.6 amps @ 120 volts, when running flat out.

780 watts at 80% efficiency and 14.4V = 43.3A which is in line with the rating on the plate.

Wouldn't that be for everything though? Lights, accessories, and battery? The branch for the battery is 30A so I can't see how it'd be more than that. Unless the branch circuit isn't where the battery is plugged in... I'm not near the RV at the moment to check.

pianotuna wrote:
Do a short time test, preferably with the house batteries cycled to 50%.

If the voltage drops to 12.7 on the engine battery STOP the test.

Good to know.

Gdetrailer wrote:
I know that this is/has been done by quite a few "members" of this forum

Oh sorry, I searched before asking and couldn't find others doing it. Maybe my search skills are off.

Gdetrailer wrote:
Your gonna "idle" a large vehicle engine for hrs on end to do something that can be done with a very small portable gen..

I do have one of 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.

here we go. Reinventing the wheel again!!

SlowBro wrote:
Inverter is a WF-8945. Charge profile is on page 7 of this PDF. Charge current isn’t listed, but the circuit branch is I believe only 30A, which the inverter can handle just fine.
The PDF references another document for more details on the charge profile, that I’ll have to check out tomorrow.

https://wfcoelectronics.com/wp-content/uploads/2020/11/8900-Series-Manual-Updated.pdf

Sitting in a car idling with the A/C on, radio going, lights on, uses about the same amount of current the inverter would use, and those kinds of conditions are seen regularly. I believe I should be fine.

https://www.aa1car.com/library/electrical_amp_loads.htm

:R

I know that this is/has been done by quite a few "members" of this forum, BUT, do you realize that this is the same thing as using a "cannon" to swat a fly?

745W = 1 HP..

Your gonna "idle" a large vehicle engine for hrs on end to do something that can be done with a very small portable gen..

One should also realize that the alternator on said vehicle is at MINIMAL charging when engine is at idle.. The alternator should be operated ABOVE idle speeds when drawing a lot of current (as in attempting to charge via a inverter), otherwise you do risk running your starting battery down in the process.

Most car alternators are designed for INTERMITTENT heavy charging, they are compact, have the voltage regulator and the diodes built in, that package gets pretty darn hot under normal use, heat buildup is the enemy..

Getting back to the 1 HP.. depending on size of your engine, you are most likely going to use more fuel than you would with a small purpose built inverter gen. Small gens sip fuel, less than a PINT per hr, larger vehicle engines can consume GALLONS per hr at idle

Your gonna put a lot of idle time on a very expensive vehicle engine and transmission which if it breaks down is going to leave you somewhere that you don't want to be and it will cost you many times more to repair than throwing away a small gen.. Excessive idling also can be very hard on the emissions systems and if a Diesel, something called "wet stacking" can happen and be harmful and shorten the life of the engine.

I personally would never intentionally do this to any of my $50K trucks, too expensive to replace a truck, too expensive to replace/repair engine and transmission (a short block can cost as much as $10K just for the block and transmissions can cost $5K not including labor).. Too expensive and difficult to troubleshoot modern vehicle computerized systems (most mechanics charge at a min of $150 per hr now days)..

Just because it has been or is being done, doesn't mean that it is a good idea to do it.

Buy a small gen and or solar, instead of cobbling up some half baked idea.