Yeah, I know those yellow tops are good, and they have a good price, haha.
I got two mega batteries, so I don't have a problem with my equipment drawing them down.
Here's whats going on in more detail.. for those that are experiencing similar problems. And hey its just good to figure this stuff out so you can trouble shoot....
A charged battery shows a potential of around 12.6 volts. When your car is running your alternator is kicking out over 13 volts, sometimes more. An inverter likes voltage that is greater than 12 volts. When a battery is becoming depleted it starts showing a voltage of less than 12 volts... down to 11 then 10 and I guess it would keep dropping. An inverter (at least mine is according to the specs) is designed to turn itself off when the voltage gets down below 11 volts, in the event you forget and leave it on, so hopefully you still have enough juice to start your car.
Another way a battery will show less voltage is when there is a large load on it... as when your starter is trying to start your car. My truck has a huge starter to turn over the diesel engine, and it draws a lot of amps, especially after it has set without running for an hour or so. When the starter is trying to turn over the engine, the voltage that the inverter sees starts dropping. So when the starter starts stealing all the juice, and the voltage the inverter sees starts going down, the inverter thinks "Oh no, the battery is going dead I better shut down"... so it does. But the battery is not going dead, the starter is just stealing all the juice for a very short time, everything is fine as soon as the truck starts up.... but.... the inverter has already shut down.... That then makes me beat my head against the steering wheel because it has interrupted everything I had hooked to the inverter, namely my laptop, with all my stuff running on it. Those of you with a good battery and smaller cars with smaller engines and smaller starters probably don't have this same problem as your starter doesn't steal near as much juice...
There is some additional voltage loss that comes with using small wire, as in what is used with a standard cigarette plug connector, which is what I'm using now to run my inverter. If I run some large wire from the battery directly to the inverter, it will help... but I'm not sure it will be a big enough help to keep it from shutting down. After reading what others have said (thanks for the suggestions) I have figured out the sure way to fix the problem is to install a small battery that is charged off the vehicle charging system, hook my inverter to it, and put an isolator on it so the starter can not steal any of its juice. Therefor the inverter will always see the full 12.6 volts and be able to draw power from the whole system when I'm sitting with out the truck running. Of course there could still be something I'm missing, but I think that will fix it.
