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

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

Most stock OEM alternators are designed to put out big amperage for a few minutes right after start up then drop back to a much lower output.

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

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.

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.

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

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

SlowBro,

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.

11.6 amps @ 120 volts = 116 amps @ 12 volts.

Sizing the inverter suggests that 1000 watts might be a better fit.

C/8 is the acceptance rate of a lead acid battery at 85% state of charge. If it is at 50% that may be a LOT higher.

Most alternators have a duty cycle of 2/3, so if the battery bank is "hungry" the alternator may let out the magic blue smoke, with the caveat that the cables to the inverter are thick enough to handle that much current.

On the other hand, WF converters are FAMOUS for not going into bulk charging mode. In that case the 800 watt inverter would not over load, nor would the alternator fail.

It is far better and probably cheaper to use a dc to DC converter between the alternator and the battery bank. That way charge current may be set where you want it.

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.

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

time2roll wrote:
A 45 amp converter is fully capable of putting 45 amps into the G24 battery. Although depending
on the converter brand and charging profile and the 12v wiring you may not get 45 amps for long or only half that amount. A good converter could put a solid 45 amps in for maybe 30 minutes before the battery acceptance rate causes the amps to begin tapering off.

If you were buying a separate charger a 10 amp rated unit would work perfectly good.

That’s good to know. The inverter does 800W continuous, so 45A at the converter x 14V and at 80% efficiency, that comes to 787W at the inverter. Mighty close.

If I do use the 6A car charger I have now it’d be a lot more polite.

A 45 amp converter is fully capable of putting 45 amps into the G24 battery. Although depending
on the converter brand and charging profile and the 12v wiring you may not get 45 amps for long or only half that amount. A good converter could put a solid 45 amps in for maybe 30 minutes before the battery acceptance rate causes the amps to begin tapering off.

If you were buying a separate charger a 10 amp rated unit would work perfectly good.

time2roll wrote:
If the converter actually puts 45 amps into the battery you might overload the inverter. A single test will confirm with no harm. Of course the inverter would need to be hardwired to the vehicle start battery. And inverters don't really like heat under the hood. If you plan to do this while idling stationary the alternator may not keep up. Otherwise you are good to go. No harm to the alternator.

I am fairly certain it doesn't put all 45 amps into the battery. It's a three-stage converter so it has some smarts about sending the right amount of current into the battery. Lead-acid charge rate (I read somewhere) is C/6 to C/8, and group 24 batteries are 80AH, for a charge rate of between 10-13A on DC, to about 1-1.5A on AC, back to about 14-21A on the alternator.

Couldn't find solid numbers on what the alternator is capable of when idling but I think I saw it's 10% of full rated output, so I may have to jam a stick against the gas pedal to rev it up a little while charging.

Inverter runs from inside the cabin, no overheating.

I'm hoping to try it this week to be sure it doesn't scream.

Further reading, I think I'll be okay. Battery charge rate for lead acid is about C/8, a group 24 is about 80AH, and charge rate is I think C/8, so charge current I believe will be 10A. That's approximately 1A at the 120V inverter outlet, and this forum discussion says, "It takes approximately 12 to 14 amps of DC power to produce 1 amp of AC power from an inverter." 14 amps on an alternator shouldn't be TOO bad--I think.

If the converter actually puts 45 amps into the battery you might overload the inverter. A single test will confirm with no harm. Of course the inverter would need to be hardwired to the vehicle start battery. And inverters don't really like heat under the hood. If you plan to do this while idling stationary the alternator may not keep up. Otherwise you are good to go. No harm to the alternator.

Deleted my comments about alternators charging batteries. Don't want to distract from the main question: Is it feasible to use a medium-sized 150A alternator, 800W inverter, 15A adapter, and a 45A converter to charge a group 24 battery? Will that burn up the alternator if only performed occasionally, not daily?