Car power inverters damaging the car?


i wanted to ask if using a 1200 watt inverter on a car could damage a alternator? 1200 watt inverter requires on a full load 120 amps on the 12 volt battery of the car, and gives out 10.2 amps in the 120 volts power outlets it gives out.


You’ll probably need a bigger alternator. Most cars do not come with 120amp ones, but I don’t know what you drive, so I can’t tell you what you have.


1200 watts is way too big. I’d keep it 300w or less.


A 1,200 watt power inverter would have to be directly wired to the battery, which should be done by a professional. That professional will be able to ensure that you use the proper gauge wire and that the car’s electrical system can handle it.

Something like this could make your car go up in flames if it’s done wrong, so it shouldn’t be a do-it-yourself job.

I’ve seen this done in a tractor-trailer. If you’re a professional truck driver, you should still have this professionally installed. I’ve seen pictures of semis that went up in flames due to improper installation of an inverter.


What are you operating with this inverter?
How long will it be running near full capacity?

I would get a separate deep-cycle battery to feed the inverter and set it up to charge from the main system at a lower rate (like 20 amps) when the vehicle is running.

A 120 amp alternator won’t put out 120 amps at idle.
Even a heavy duty alternator might overheat running near its full rating for a long time.

More info about the vehicle and load would help our answers.


I assume you’re buying a 1200 watt inverter because your load is close to 1200 watts.
I’d be nervous, for several reasons.

1: As has been stated, you’ll need an alternator in the 120 amp range to supply that power output. There are many discussions on this board about how alternators are not designed to produce full power output for continuous operation. While I’m still on the fence as to how serious the concern is, others definitely are - why do you want to risk that?

2: If your vehicle was built with a 120 amp alternator, that means the accessories on it are capable of drawing close to 120 amp. You could find yourself driving down the road and with the combined draw from the inverter and the accessories, you could end up with a dead battery - as you drive.

When you begin to get into inverter loads like this, you need to make sure your charging system has the extra capacity, and that you’re not drawing off your main battery (but a separate deep-cycle battery as Circuitsmith noted), and that it’s properly wired to avoid a fire (as Whitey noted).


I have a 2001 International 3000 School Bus I’m putting a thousand watt inverter to directly to the battery but I am worried about the long-term effect on the alternator but this will be the power source until I can get a generator I was going to add a battery or 2 but I only plan to use it while running


I hope you’re not doing this installation yourself. Please tell me you’re hiring a certified automotive electrician.

Small free standing lawnmower size generators aren’t expensive. Maybe you’d be better off getting one or two of those?


when i had my caddy i found out some limo models had provisions for 2 alternators. there you go. add a 2nd alternator


you can get several amp ratings for alt’s for Internationals. The DT466E and 444E have 275amp alts available, but you’re going to pay a lot for them. (not sure what engine you have @Chris_Highsmith)

What are you planning to run off the 1000w inverter? Perhaps Whitey suggestion of a cheaper external generator would be a better idea.


yeah, I hope so, too. :slight_smile:


Did you just reply to the wrong thread ?