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Old 07-31-2014, 12:54 PM   #1
Join Date: May 2014
Location: Elgin, Oklahoma
Posts: 37
How big of a battery disconnect do I need?

I keep having the problem of my house batteries draining. I have a 2000 40' Safari Serengeti 330hp cat. I have 4 new trojan 105 batteries, and a new xantrex freedom 3000 watt inverter charger. The batteries will drain completely overnight, down to 1-2 volts each. So then I have to charge them individually with a sears battery charger that I don't think it even works right. I do make sure I shut off the dc power at the switch on my way out the door and everything seems to go off. I have traced wires, cleaned connections and i can't find what is draining it. I want to put a battery disconnect on the battery bank but there are different kinds and different sizes, as in how many amps. If my bank is a total of 900amps what disconnect should I use? and I should install it on the negative terminal, correct?

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Old 07-31-2014, 01:17 PM   #2
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how big of a battery disconnect do I need?

Using a voltmeter to find out why your inverter/charger is not working should be first priority.

Well if you loaded your 3000 watt inverter to the max it would draw 250+ amps

(250 amps x 12 volts = 3000 watts)

Get a disconnect that can handle above 300 amps ( for fudge factor) and should be good.


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Old 07-31-2014, 01:30 PM   #3
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I think I would at least unhook the batteries until you fix the problem and get a disconnect before it's to late to save the batteries running them down to 1 volt.
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Old 07-31-2014, 01:33 PM   #4
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I have started disconnecting the neg side of the batt bank. I haven't checked it sence then though.
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Old 07-31-2014, 03:24 PM   #5
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I have been looking at battery disconnect switches online and some of them say 'for up to 2 batteries' Is my 4 battery battery bank considered 1 or 4?
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Old 07-31-2014, 03:55 PM   #6
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If they are going to 1 volt overnight there is a serious problem somewhere.

I'd get a hydrometer and check every cell on all four batteries.

Why did you replace the existing batteries? Were they doing the same thing?
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Old 07-31-2014, 04:02 PM   #7
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the old batteries were about 4 yrs old and bulging at the sides and the inverter/charger fried a circuit board the first time I drove it. So I replaced it all.
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Old 07-31-2014, 04:36 PM   #8
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You need to find what is drawing your batteries down so quickly. Turn off, or better yet, disconnect the + side of the battery bank, pull out each 12 volt fuse and reconnect your + feed from the batteries. Take your VOM and set it to 10 DC amps and make sure your leads are connected in the right inputs in your VOM. Be certain everything in the rig is off. Now connect leads across both sides of each spade connector in the fuse block. Write down what each circuit is drawing. Remember the current draw is measured in series with each circuit. That is why we are reading across each fuse without the fuse in place. This test will tell you in amps what each circuit is drawing with all 12 volt lamps, fans, etc, turned off. Now disconnect, with all fuses still out, the + battery cable again. Measure between the battery stud and the + cable. This tells you if there is current draw with no circuits connected.There should be little or no current draw. If there is draw, you need to look between the battery and the fuses. I know some 5th wheels grab power for certain circuits like brakes and smoke detectors and propane detectors (usually emergency or safety items) there through circuit breakers before power ever gets to the fuses.
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Old 07-31-2014, 05:14 PM   #9
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Paul has good instructions.

One suggestion...

As doon as you are finished REMOVE THE LEADS FROM YOUR METER!

Lots of folks leave the leads in and wind them around the meter then just unwind them and use it next time.

Problem is while in amps mode the meter is a piece of wire...will cause damage to something...
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Old 07-31-2014, 07:32 PM   #10
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Your bank is not 900 amps, it is 450 I will explain

In the following Each battery is 6 volt 225 amp hours (for rounding ease, actually I think a T-105 is 220)

.Battery--Battery = 12 volt at 225 amp hours
+Battery--Battery = 12 volt at 225 amp hours
12 volts at 450 amp hours

That is the math involved Batteries in series add voltage
Batteries in parallel add amp hours (Capacity)

now what 120 volt things is that 3KW inverter running, the fridge (For example) if RV type is about 350 watts or 175 watts per hour, at 12 volts (use 10 for ease) that is 17.5 amp hours per hour

Residential types run 100-300 watts

And this assumes no ice maker (that adds watts)

Televisions: Tube type or LED/LCD

Other stuff.

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