Toyota FJ Cruiser Forum - View Single Post - Dual battery -- why bother?
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post #42 of (permalink) Old 08-17-2013, 09:34 PM
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Re: Dual battery -- why bother?

maxtor previously said: View Post
As far as I know, the battery in a car is only needed to start the engine. Once the engine starts, the power needed to run the radio, speakers, and all fancy electrical components, are all powered by the alternator.

To me it seems if one needs more power (due to added equipments that need more power), one needs a better alternator.

Could someone tell me what's going on?
Unless you want to apply your electrical loads with the off, then battery storage is what you want. If that's the way the loads are applied then you should use a disconnect in the circuit so you still have a battery to start the engine. Resistance type battery isolators are really a waste of time, they turn a lot of amperage into heat and the charge rates in vehicles nowadays are a little much for them. Diode type are OK but still kind of funny. The relay type or "smart" voltage sensing type are what you want. You will get full amperage through them and when your voltage drops too far they will open the circuit.
If you can run the engine that is the way to go. Your battery/batteries is just a reference point so your alternator knows what to do.

If you have...
150 amps charging,
A 500 amp load,
6 batteries,
You are still discharging.

For a small or normal case alternator dcpowerinc makes some nice alternators that I have used and have tested before. Premier power (the onboard welder guys) makes some tough ones, again that I have used and have tested under load.
For the larger size cases either leece-neville or neihoff is what you want.

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