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Thread: difference between battery isolator and battery relay

  1. #1
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    difference between battery isolator and battery relay

    On ebay you can find battery isolators and battery relay isolators. What is the difference?

    from what I see.. the isolator still creates a draw on the batteries but not with the relay?

    I currently have
    63a alternator - new (factory 1978 chevy)
    90a battery isolator
    2x duralast gold 1000ca batteries in parallel on A of isolator
    2 x 1300ca dump truck batteries in parallel on B of isolator

    I am going to upgrade my alternator to a pontiac transport 140a and will need a new isolator/relay

  2. #2
    Variable Bitrate eric_barcus's Avatar
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    from what i know all isolators have relays in them thats the way that they keep the "backup batterys" "away" from the main battery AFTER the car is turned off my unit simply says "battery isolator" but when you read the instructions it talks about which side of the binding posts are going to be in which position of the relay

    so i believe you are safe with either

  3. #3
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    ahh ok that makes more sense... doing some more reading... I thought I read that you also want the same batteries with a relay.....

    so do you think with a relay you can tie 2 different batteries together as I did?
    I know you have to match your current batteries if you put 2 on 1 leg of an isolator... but can you put 2 of the same on one leg and 2 of the same on another but there are 2 different types of batteries being used?

    confuse ya??? hah

  4. #4
    Variable Bitrate eric_barcus's Avatar
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    ah well the reason why they want you to use the same batteries (and new batteries) is so the draw (or usage) from the batteries is the same if you have one battery that will only take a 80% charge with a battery that is taking a 100% charge and the 80% has a much longer APM HR than the 100% the 100% battery will still drain faster than the 80%

    that jsut a few reasons, but it is the ONLY reason i havent installed my isolator yet because i purchased a new battery 3 months ago and i dont want to purchace two more QUITE yet they are not cheap

    in the interum i am using a cap so that there is less draw and more steady power being feed to my amps and computer
    il have pics up soon of my wireing and plans from the isolator

  5. #5
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    battery isolator
    Many people listen to their stereo without the engine running. This often leads to dead batteries and a vehicle that won't start. A battery isolator will let you completely discharge one battery without discharging the starting battery. The primary purpose for their use is to insure that a failure of a single battery or battery bank, will not wipe out an entire battery network. These are also used in vehicles with large car stereos which require multiple batteries.

    battery relay
    An electrically controlled mechanical device that opens and closes electrical contacts when a voltage (or current) is applied to a coil. A relay provides isolation of control signals from switched signals and is operated by a solenoid.

    for example like If u have dual battery through the relay (actually a starter solenoid) if the ignition was on, the relay was closed and both batteries got charged, with the switch off...(or even during the start cycle) the batteries were isolated.

    So u can run your stereo with the engine off, and which will not drain your battery.

    The isolator has no moving parts, and always keeps the batteries isolated, with the relay the batteries are tied together after the engine starts.

    Hopefully tht helps

  6. #6
    FLAC DodgeCummins's Avatar
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    The isolator is a giant diode with a big heatsink.

    no moving parts (like was said before) batteries are always being charged, but can't discharge each other...but if the main car battery goes dead (left lights on etc) then you have to pop the hood and manually jump start your car.

    The relay connects the two batteries together when switched on, so you always crank with both batteries (good or bad, depending).

    The relay is way cheaper than the isolator.

    Another benefit of the isolator is one battery can't overcharge the other one (like what happens when your flashlight batteries leak.)

  7. #7
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    Quote Originally Posted by DodgeCummins View Post

    Another benefit of the isolator is one battery can't overcharge the other one (like what happens when your flashlight batteries leak.)

    so in my case... having different sized batteries I do not want the relay...

    crap....

    I just bought a 200a relay from ebay...

    so with truck running I will train ALL batteries...

    my main reasoning for this was for my winch.... however that is not good then...
    if the truck is stuck and shuts off.. great.. I know now to have the key off (column unlocked) and can winch away discharging the bed batteries... once I get out fire the truck up.... but if the truck is stuck and running... I should shut it off to preserve the batts under the hood...


    now the biggie..
    with 2x1000ca under the hood and 2x1300ca in the bed.... I will not charge correctly and this will suck as I will not charge all the batteries correctly???

    ...... so the relay is not for me right? If not I will just sell it and get an isolator...

  8. #8
    FLAC DodgeCummins's Avatar
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    How big is your alternator? How much power does it produce at idle RPM?

    I think you would be happier with an isolator.

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