# Thread: how long will yellow top last with 400watt inverter

1. ## how long will yellow top last with 400watt inverter

not really carPC per se, but I bet you guys can answer my question.

I am going to be using the yellow top out of my camaro (the yellow top is the big GM one that has both side and top terminals) to power an inverter at a camp site to run a small TV and some small spot lights. Can anyone give me an estimate on how long the battery will last? I don't care if I kill it, but would like to know how often I will have to plug it into some vehicle to recharge it.

2. I think that'll depend largely on the draw you're pulling from it. Can you provide some more specifics such as battery capacity/draw?

3. according to the specs, the battery is 55A, and I won't be maxing out the inverter. So probably a draw of around 350 watts.

Is my math of 55a * 12v = 660 watts correct? if so that sucks, (around 2 hours)

4. the yellow top is great as long as you don't get it down to 8-9 volts from my experience... (Many times letting the car sit w/ no trickle charge) After that its bad cells and wont hold a charge, I'm on my 3rd one in my current car for that reason (all under warranty though).

5. I was under the impression you could kill an optima without any damage to the battery?

6. The math is correct, but you went about it in a weird way. You have an idea of what you're doing, but I'll explain it just so you're positive next time you need to do the calculations.

So heres the way I usually see it done:

The battery has 55AH which stands for amp-hours, not amps.

Dividing the AH of the battery by the number of hours you are drawing a certain number of amps for tells you how long it will last.

So 350 watts divided by 12 volts is 29.2 amps. Meaning the inverter is drawing about 29 amps.

So now you take the 55 AH and divide it by a 29 amp draw and get 1.9 hours.

When you did your math, you actually used watt-hours instead of amp-hours. Which works too but I never see anyone use that method. To do it that way, you would take the amp-hours of the battery and multiply it by the number of volts of the battery to get the watt hours of the battery.

So 55 AH x 12 volts = 660 watt-hours. 660 watt hours divided by 350 watts is also 1.9.

Two ways to tackle the same problem.

The issue with inverters now is they are inefficient. Meaning that, if you draw 350 watts from the AC side of the inverter, it my actually be pulling 397.7 watts if its efficiency is 88%. Check the ratings on the inverter to find the exact number.

7. Don't forget that the relationship between current draw and time is not linear in Ah rating. Battery may give you 55h @ 1A, but less than 1h @ 55A. All depends on a battery type, battery temperature and how it was maintained.

Use 80% of provided Ah rating for calculations.

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