Battery Isolator

[James R Williams]

Hi! Have A 13ft Scamp w/ a Refrigerator, I all ready know how to do the wiring (wire size, Fuses, ect) but I do not know the size of the Battery Isolator I need. Jim W

[Byron Kinnaman]

The best battery isolator I know of is your hands. I use them to disconnect the trailer when I'm concerned about trailer battery usage running down my tow vehicle battery. Therefore a battery isolator isn't needed.

[David Tilston]

If you are referring to the type of isolator that allows you to charge two battery banks, one for accessories, (the trailer) and one for the starting battery, but the accessory battery can't drain the starting battery.
This type of isolator is basically two big diodes, one for each bank. Sizing this is more a function of the size of your alternator. If your alternator is a 120A unit, size the isolator accordingly.

[Raz]

Hello Jim. Be aware that charging a battery and running a fridge on DC is an iffy situation to begin with because of all the demands on the alternator. If you add a diode ( isolator) you will add about a 1volt drop from the tow vehicle battery to the trailer battery across the diode as well as any voltage drop in the charging wires due to wire resistance. Things probably won't live up to your expectations in terms of cooling or charging. Hence Byrons recommendation to skip the diode and just remember to unplug. Some folks add a relay that opens when the ignition is turned off. I think this is a better way to do it for those of us who can't remember to unplug. Raz

[James R Williams]

What size or type of relay?

[RogerDat]

According to the power your alternator might throw at it as Dave W said. The things are all about the same design, years ago I used the "go" relay for a golf cart purchased at the local auto parts store, used it for several years, worked fine.

Here are some options from Amazon to look at.
Amazon.com: Battery isolator relay

[Bob Miller]

RE: Isolator
There is a standard solenoid type "Battery Isolator" available from any RV supply house for less than $30. They come in 3 or 4 wire types and either one will work for you. It will handle more than your alternator can supply to the trailer battery and are easy to wire in. CAUTION: These may "Look" like a starter solenoid, but are very different inside. Substitution with a starter solenoid from your local auto supply store will assure you of an early failure.
Here is a link to a typical isolator and it contains a link to a wiring diagram for same,.
Dual Battery Switch for your Power Needs - PPL Motor Homes

[RogerDat]

Originally Posted by RogerDat

... years ago I used the "go" relay for a golf cart purchased at the local auto parts store, used it for several years, worked fine.

I should have said "Electric golf cart", to clarify relay was for heavy duty
continuous 12 volt supply to electric motor. Not the starter relay for a gas powered cart.

[Raz]

Same one Bob recommends. These folks have a picture.

Tekonsha 3-Terminal Battery Switch - Battery Isolators - Battery Supplies - Electrical