Wiring for on-board battery isolator - Fiberglass RV


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Old 04-13-2017, 10:40 AM   #1
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Name: BARNEY
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Wiring for on-board battery isolator

Ideas, experence, diagrams welcomed!!!
Thanks
barney cone ii
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Old 04-13-2017, 10:56 AM   #2
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Originally Posted by BARNEYCONE View Post
Ideas, experence, diagrams welcomed!!!
Thanks
barney cone ii
What are you trying to isolate from. Usually an isolator is used in Motor homes to keep from running down the cranking battery. In trailers there's several methods of isolating the tow vehicle's battery from the trailer. The easiest and most common (my opinion) is to simply unplug the cord going from the tow to the trailer. A soliniod (relay) that only connects the trailer power to the tow power when the tow engine is running. In any case Isolation is usually done in the tow vehicle.

I've had the relay type and relay failed to close so the battery didn't get charged. Now I have the manual unplug type. One of problems with unplug type is forgetting to plug it back in. However if do as you should and every time you get ready to leave someplace check all the lights it no longer a problem. The worst you could do is stay connected for several days and maybe, that's maybe, you could run the tow vehicle's battery down. If you're mostly a week end camper I wouldn't worry about it, unless you're trying to run a whole lot of stuff.
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Old 04-13-2017, 07:57 PM   #3
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There are automatic "solenoids", simple solenoids, and then there are diodes.

Diodes come with a cost, they have a small voltage drop and that small drop means that your camper battery will never reach a full State of Charge (SoC). Neither will your starting battery unless the regulator is set for a different charge voltage - which is something few can do.

Simple solenoids use an ignition position source to turn on. The downside to this is that if you've just started the engine it's alternator will need to not only immediately recharge the starting battery, it will also need to immediately recharge the camper battery. Few automotive alternators are made to work that hard for that long, so alternator life-span can be shortened.

There are basically two kinds of automatic relays or solenoids. They come with the names of "Automatic Charge Relay" (ACR) or "Voltage Sensing Relay" (VSR). Some of these wait a predetermined amount of time before connecting the camper battery to the TR's charging system. Others wait until the starting battery SoC is high enough that it is nearly fully recharged before connecting the camper. This way the alternator isn't working at full capacity for a long time. Be careful though, some of these units will not connect if the camper battery voltage is too low.
Some of these units are also "dual sensing" meaning that if either battery is getting a charging voltage (say in the case of solar on the trailer) and is nearly 100% SoC the unit will close and allow charging of the other battery!
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Old 04-14-2017, 11:37 AM   #4
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Then, there's also the simple make & break switch. It doesn't need to be complicated or expensive to have a battery cut-off switch. It just cuts into the POS (+) line between the battery's anode terminal to the rest of the same wire that runs to the converter. Very simple. It's either ON or it's OFF. No extra wiring and other expensive components needed.
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Old 04-14-2017, 12:29 PM   #5
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Just make sure that the switch chosen can make or break at maximum alternator output, at the minimum. Making/breaking at those amperages is a lot different than being able to carry that current. If the trailer battery's SoC is really low the amperage could be significantly higher.
As an example, have a look at this switch's specs as it can make/break at rated ampacity but not all high current switches can: http://www.gigavac.com/sites/default...heet/HBD21.pdf
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