very simple question about car inverter

Thread Starter


Joined Jan 20, 2013
I work out of my vehicle and as such I've replace the battery with a deep cycle battery. I've wired a power inverter directly to the battery so that it runs even when the car is off. My problem however is that sometimes when I start the car, the inverter goes from having a green light to a red one and will not power my stuff. I have to turn off the inverter and then turn it on again to get it working. I assume the engine is drawing a huge amount of power and causing the inverter to fail. Is there a solution to this? Would a capacitor work? Thanks for your help.



Joined Feb 19, 2009
The starter motor of a vehicle draws pretty much all a battery can supply.

A solution would be a standard starter battery, as deep cycle batteries aren't built for the amount of current starting batteries are. Then add a battery isolator to separate the two batteries, making the deep cycle only charge from the alternator, rather than help start the car.

As far as a capacitor, it would depend on how much current the inverter requires. I'd guess a 1 Farad cap (size of a 2 pop cans on top of each other, for a 15V one) for a small inverter would keep it going for maybe a second or so, but it would also need to be isolated with a diode or similar so that it didn't drain helping the car start.

A car audio shop may be able to point you to a solution designed for exactly this problem.


Joined Nov 24, 2012
Yep, dual batteries is the right answer. With dual batteries you don't have to worry about running the battery down and not being able to start the vehicle. If you want plug and play, you can buy a batery isolator at most RV dealers.

Things are different today but back in the 70's I set up a Ford pickup with dual batteries for a camper. Went to a wrecking yard and bought a battery holder which I mounted under the hood for the second battery. If it's a car you probably don't have room under the hood. Put the second battery it in the trunk and run at least #10 wire.