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My issue lies with my new lighting system. I am installing lights on my 1500 91' Sil Pick- up on a custom made roll bar. I am putting 4 100 watt lights in the rear, 2 100 watt lights in the front and 2 - 55 watt lights on the side. Do I have to get a new bigger alternaterfor the extra load or can I put a double battery system under the hood , connect them together and run off of it? Any suggestions would be nice.

'Stock' is just wrong!
46 Posts
Light em up!

I'm an electrical engineer by day, kustomizer by night. Got a cape and everything.

Anyway, a Watt is simply a measurement of power, defined as Voltage x Current. Adding up your expected lighting, you'll be using 710Watts of power if you leave all the lights on at once.

710Watts on a 12V battery would be roughly 60Amps (impressive!). I wouldn't want to be running 60A off strictly battery, even the best deep-cycle marine batteries are good for only around 100AH (see ). Deep-cycle batteries are capable of discharging to almost zero without being destroyed, but not typical autmotive batteries.

100AH means 100 Amp-Hours. So, if you're drawing 60Amps, expect your battery to be completely dead in around 1.5hours.

Typical low-end altenators put-out 130Amps, and you're actually doing the altenator a favor by using up the current it's producing in your lights (or else the altenator has to dissipate the current internally in the form of heat, to protect the battery from overcharging). So basically, even a low-end altenator will sustain your lights without any trouble. Cadillacs and Police cruisers typically have altenators capable of 200+Amps.

So, to answer your question more simply... yes, you can do it, provided you take some precautions:
1) 60A is about 6X-too-much current to switch-in using a standard toggle-switch. So, you'll either need 6-switches, or you'll need to switch-in two automotive relays (usually good for under 30A each).
2) You'll need to run 6ga wire to handle that current in one-line. That's not really practical. I'd recommend you run at-least two lengths of 10ga wire, fuse-protected for 30A each, into an automotive cube relay. Check out Data/CB Relays.pdf
to see what I'm talking about. These relays are probably carried by your local autoparts store as a brake-light relay or a air-conditioning relay.

Basically, you can deilver (at-least 20-feet):
30A into 10ga wire
20A into 12ga wire
15A into 14ga wire
12A into 18ga wire
10A into 20ga wire

You WON'T want to run that much current through your truck's power harness.

Hope it helps!

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