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Old 04-08-2016, 06:24 PM   #1
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Default dual battery switch

hi guys i recently put in a new stereo with an amp and all as well as a lot of lighting.. i have a deep cycle battery for all the house equipment and a starting battery for starting. i just purchased a perko battery switch, but im wondering what size cable i should be running. ive understand to an extent how electricity works and realize that in this case bigger is essentially better. but 2/0 is very expensive. whats the minimum i can get away with without a huge loss in performance.
also any other tips with these things would be welcomed this is my first attempt at one.
thanks!
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Old 04-08-2016, 06:43 PM   #2
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You can calculate that yourself. First determine the wire resistance that you think you want to use from wire charts and remember, the length consists of both to and from. The wire resistances will probably be in 1000 foot lengths but you need resistance/foot. Next determine how much current you need......... a 100 watt load will need

I = watts/ volts; I = 100/12 or 8.3 amperes. Note if the battery is fully charged for the same load the current will be a little less 100/12.8 = 7.8 amperes


Next for the wire size you most likely will want to keep the voltage drop in the wire limited to about 0.1 volts and this is arbitrary. The voltage drop in the wiring means the load will see the battery's voltage minus the wire drop.

Most likely you will have a bunch of circuit breakers located in a panel that is connected to your battery. So just add up the number of ampere the switches/circuit breakers are rated for, use a utilization factor ... maybe 25% because not all your breakers will have loads simultaneously and use that amperage to calculate just how much voltage drop your loads can sustain. A bulb will not be as sensitive as a VHF radio AND a VHF radio will state what minimum voltage it requires.

OK... this is kind of long but anybody can make a guess at wire sizes. You really want to be on teh safe side? Use #1 or #00................or do the calculations
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Old 04-09-2016, 07:51 AM   #3
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A modern good quality amplifier should have a built in, regulated, low impedance power supply that will work from less stable sources and should not need the over sized power cables that were common in the past.

You cannot do power supply requirement calculations based on WATTS of audio output, they use all sorts of fancy calculations to make that number as high as they can. The is no way a 500 watt amplifier can put out 500 watts of "real" electrical energy.

Try and get the amplifier manufacturer's specification on power required and size the wire to a gauge they recommend.
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Old 04-09-2016, 07:22 PM   #4
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2/0 Battery cable is probably not expensive at all if you compare it to the other goodies you just mentioned, and I wouldn't be surprised if you didn't have some that you didn't mention. Do it right the first time, and remember that it might be possible that you would need to use that battery switch to start your engine at some point in time and having the right size cable might help get you home.
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Old 04-10-2016, 06:11 PM   #5
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Quote:
Originally Posted by yandina View Post

You cannot do power supply requirement calculations based on WATTS of audio output, they use all sorts of fancy calculations to make that number as high as they can. The is no way a 500 watt amplifier can put out 500 watts of "real" electrical energy.

Of course! If you're referring to my above post I thought it was elementary and clear that the watts needed to calculate input wiring sizes related to the manufacturer's label that describes the input power for proper operation.
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Old 04-11-2016, 01:55 PM   #6
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so the general consensus would be to pony up for 15' or so of 2/0 cable?
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Old 04-12-2016, 10:11 AM   #7
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wow.... 2/O really?

#2 cable should be more than enough for house voltage.... what, maybe 60-70 amps max?

#2 is larger than most starter cables on a truck
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