Continuous Duty Solenoid for Dual Battery Question

Hey guys,

I have one of these lying around, and I am hoping that it will work for adding an additional battery for accessories. I will be powering two small LED exterior lights, as well as a few small appliances (phone chargers, laptops, electric griddle :chowtime: etc.). The goal is to use the second battery for some extra oomph while cranking, and to use electronics without running down the primary battery. I realize that a battery isolator would be ideal, but I don't think it's necessary for what I am trying to accomplish.

I found some good information regarding dual battery wiring with similar solenoids here.

Will this solenoid be up to the task?
 

Patman

Explorer
Should work fine for everything but the self jump. May not be up to the high draw of the starter. Although the proper way to self jump is to connect the batteries with the solenoid and wait for the amperage to balance between the two batteries and then cranking off of the main starting battery, that way you're not pulling the amperage through the battery solenoid, only from the main starter battery.
 

dwh

Tail-End Charlie
If you are going to use it to tie the two batteries together while the engine is running, and separate them when the engine isn't running, the it -is- an isolator. It's just a different type of isolator.

What is being done on that page you linked is a pretty common setup called a "split-charge relay". That setup is preferred over diode-type isolators (the ones with the heat sink that you see at auto parts stores) because they don't drop the voltage passing through them like a diode does.

The solenoid you linked to has a continuous duty rating of 80 amps. As long as you stay below that, then it will work fine. Just charging up the second battery - no problem.

If you had some load connected to the second battery which could draw over 80a while the engine is running, AND had an alternator that is capable of putting out more than 80a, then you could overload that solenoid.

A 1000w inverter could draw over 80a, so you'd want to try not to run any loads greater than that from an inverter while the engine is running.
 

Antichrist

Expedition Leader
As others have said, fine as long as you don't use it for powering anything drawing more than 80a.

But I'll diverge and say that even for self jumping it would probably be ok, depending on your starter draw. The inrush capacity is 400a, so it could probably handle 200 without a problem for the 30 seconds of cranking to start your vehicle.
 

rusty_tlc

Explorer
I've been using that type of relay for trailer charging circuits for over 20 years and they work great, never had one fail. For safety add a 75A* thermal breaker on the supply side, that will open up and protect the solenoid from damage if there is an unexpected load or a short in the system.

MY GMC had dual under hood batteries, I just used jumper cables to hook the batteries in parallel when I needed a self jump. Worked fine and never damaged anything. I see little sense in adding a complex circuit for self jumps when a set of cables you should be carrying to help others any way works just as well. How often do you need to jump start your vehicle? If it's more than once or twice a year you need to look at system maintenance before you add even more parts that can fail.


*You could probably go with an 80A breaker but I like a margin of error.
 
Thanks for the input guys!

I did some more research after reading all of your posts, and I think I found a winner. Sierra Expeditions sells their 200A relay separate from their dual battery kit. I can't wait to get the second battery in there so that I can enjoy using my electronics without constantly worrying about a dead battery.

With this bad boy I can use my winch and not worry about damaging anything. :^)
 

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