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Old 04-01-2016, 05:22 PM   #1
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Battery Disconnect Switch

I want to add a battery discount switch. Is it best to put the switch in the positive line or the negative line? What is the reason one is better than the other?

Also, if you charge your battery with an external battery charge, (in other words a battery charger other than your on board converter), do you have to completely disconnect the battery during the charging process?

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Old 04-01-2016, 05:30 PM   #2
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Doesn't matter which lead you insert the switch in, pos or neg. I think it is generally accepted that the pos lead is the norm. I would think there is no need to disconnect the battery with an external charger WHEN no devices are on in the rv, but if you have the disconnect I would switch it off anyway.

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Old 04-01-2016, 05:54 PM   #3
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I would cut off the positive side with the switch, but technically either side will work.

It is my practice to only have one charging source at a time. The chargers (if relatively smart) will see each other then "think" the voltage is the battery(ies) without "knowing' the higher voltage is being produced by another charger. You may or may not get a good charge by using more than one at a time and if you do it could take a long time.

Make sure the converter/ charger you have charges correctly, most do not; causing premature battery failure or starting the evening with 80% or less of its (their) potential.

Also, don't expect the +B from the tow vehicle to charge the battery while traveling.
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Old 04-01-2016, 06:13 PM   #4
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X2 with WolfWhistle on the positive side for the switch.
Also, on the trailer plug connection, just because you have an alternator that is rated at 150 amps [hypothetical], doesn't mean you will be charging the batteries at anywhere near that amperage. Not even close. I would venture a guess at 10-15 amps tops. I may be wrong and I've never checked it, but the wiring would be much larger if it was more than that.
If you run two chargers [converter and external charger] at the same time, they are "reading each other". One at a time as WolfWhistle said. You can just hit your breaker for the converter when using an external charger or your disconnect switch.
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Old 04-01-2016, 06:38 PM   #5
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The reason I am charging with an external is to see if I can get the battery fully charged. As I understand fully charged, I should be 13 volts plus. I am only reading 12.6 after being plugged in all weekend, (and I have checked it a few times). So currently I am not on shore power at all. I have the battery totally disconnected and have a battery charger on it set to charge at 2 amps. I want to take a reading in the morning and see if I have more than 12.6 amps showing on the battery.

Also, I will add the discount switch to the positive side. Thank you for the input. Anyone with any input on the battery voltage, I would be happy to read.
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Old 04-01-2016, 06:46 PM   #6
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The standard car battery voltage in today's vehicles is 12 volts. Each battery has six cells with 2.1V. ... A fully charged car battery has 12.6 volts.
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Old 04-01-2016, 06:59 PM   #7
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Here is a handy chart.
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Old 04-01-2016, 07:31 PM   #8
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Well I guess my battery was fully charged. For some reason I had in my mind that normally a battery will read over 13 volts. Learn something new every day.
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Old 04-01-2016, 07:53 PM   #9
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Originally Posted by Asrabbit View Post
Well I guess my battery was fully charged. For some reason I had in my mind that normally a battery will read over 13 volts. Learn something new every day.
That is the typical charging voltage. Easy to misinterpret.

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Old 04-01-2016, 08:25 PM   #10
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In many forums. one has to get to the fact vs opinion. A review of the previous post have some validity, but ... I'll try to help.

The switch MUST be on the Positive lead and as close as possible to the battery. If not, you still have a HOT battery that can cause a short, .... Granted the circuit would be open, but if you touch ANY positive wire inside to ground, you WILL have a complete circuit and KABOOM!

I would disconnect the battery whenever doing external charging so that the charger can get proper load measurements it needs from just the battery alone.

Battery Charging is a long story - You can read the following FAQ from a website that explains it in detail, but it has a lot of extras too. ZRD FAQ - Charging, Remote Charging, Battery Requirements Personally, I ensure charge is initiated when the battery bank gets near 12.5volts and certainly by the 12.3-12.0 volt range to ensure long life.

Most standard cells are 2.2Volts when they are fully charged (times 6 = 13.2Vdc). Charging Voltage has to be 1.0 Volt above battery voltage to work. This is why the typical single stage automotive type alternator is set to output at 14.2-14.4 Vdc. This will enable the battery to reach the 13.2Vdc to complete a charge. Read the FAQ above for additional info on 3stage charging. For a single automotive type battery, it is not necessary, but if you have a large expensive battery bank it is imperative.

Multiple charging sources are great, but only use 1 at a time to charge a battery/ bank. Ensure your solar is turned off/disconnected or it will confuse everything if you are not using the solar exclusively.

BTW, one of the biggest killers of batteries is leaving them almost permanently on a charger. Consider it eating one teaspoon at a time, but never stopping.

I hope this helps/clears some thing up. Ask away if you need additional info.

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