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

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jkwilson

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Posted: 01/04/21 07:26am Link  |  Quote  |  Print  |  Notify Moderator

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.


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SlowBro

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Posted: 01/04/21 07:34am Link  |  Quote  |  Print  |  Notify Moderator

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?

* This post was edited 01/04/21 07:41am by SlowBro *


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BFL13

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Posted: 01/04/21 07:50am Link  |  Quote  |  Print  |  Notify Moderator

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.

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SlowBro

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Posted: 01/04/21 07:51am Link  |  Quote  |  Print  |  Notify Moderator

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!

QCMan

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Posted: 01/04/21 07:53am Link  |  Quote  |  Print  |  Notify Moderator

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.


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SlowBro

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Posted: 01/04/21 07:57am Link  |  Quote  |  Print  |  Notify Moderator

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.

SlowBro

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Posted: 01/04/21 07:58am Link  |  Quote  |  Print  |  Notify Moderator

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.

YC 1

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Posted: 01/04/21 08:08am Link  |  Quote  |  Print  |  Notify Moderator

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.


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SlowBro

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Posted: 01/04/21 08:12am Link  |  Quote  |  Print  |  Notify Moderator

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...

Gdetrailer

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Posted: 01/04/21 08:54am Link  |  Quote  |  Print  |  Notify Moderator

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!


[emoticon]

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.

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