Dual Batteries

[Todd]

I have a question regarding dual batteries for any electrical gurus out there...
1. Do the dual batteries have to be the same size?
2. I am going to wire the batteries in parallel. One for the stock vehicle components and one for added components. I am wanting to put a relay between the positive posts of the batteries that is connected to the ignition wire. That way, the batteries will charge while the vehicle is running and be independent when the vehicle is off. The question is, will I have to purchase a special isolator relay or could I use a Ford Starter relay. I know that high surge currents can flow through the starter relay. However, can the starter relay take the constant flow of up to 130 amps while the alternator is charging?
Anyone have any ideas. I want to go with this setup so that I do not have to worry about flipping switches, etc.

Thanks in advance!


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Todd Metzger
tmetz@umr.edu
'Off-Road and More!'
93 "Ford X 4" XLT

 

[Todd]

Well, I found the answer to one of the questions last night. Starter selonoids are not rated for continuous duty. So, that answers my second question.
As for the first question, if anyone has any input, I would be more than happy to take it.
Thanks again everyone!
Take care and happy exploring!


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Todd Metzger
tmetz@umr.edu
'Off-Road and More!'
93 "Ford X 4" XLT

 

[Maniak]

Answer 1: You don't need the same size batteries. I had a 550cca battery for my starter and a 1000cca for my stereo in my old honda (in my young and stupid days)..

Answer 2: You are describing an isolator. There are even a few isolators that will not only just isolate the batteries (so they don't drain each other) but they will also combine the batteries for the starter at the push of a button (kinda like jump starting yourself)

Mark

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Mark
mark@legendz.com
http://mark.legendz.com
Off-Road and Motorcycle Information, Pictures and Movies

 

[Kampy]

You're going in the right direction,

1. No, the batteries don't have to be, but it's best to keep the batteries the same size, they will charge more evenly. Especially if you dont use a charging isolator. Rotate the battery position every six months or so. And I would suggest a manual overide switch for the solenoid in case your primary battery ever goes dead. Self jumping capability.

You found your answer for the solenoid question so, FWIW, starter relays can take the current, the internal current carrying contacts are the same. The reason they aren't rated for C/D is they will burn themselves up. The holding coils inside them are designed for intermittent duty and if continuously energized will basically melt.

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Kampy

kampy@internetni.com