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Battery isolator giving me fits.....(long)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by danielzink, Aug 19, 2003.

  1. danielzink

    danielzink Registered Member

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    Okay - got every thing I need to install 2nd battery in an 87 4x4 Suburban. Battery - tray - isolator and plug for alternator.

    Looking at the plug that was originally on my alternator - the Thick red wire and the brown wire are connected together and the black wire in the center isn't doing anything - it's taped off.
    The combined red and brown wire are connected to the pink/black stripe wire coming out of the loom and the brown wire from the loom is also taped off (not connected to anything)

    The new plug for the alternator has a long red wire that goes to the same post on the isolator as the aux. battery. and also a pink/black wire and a brown wire.

    If I hook up the pink wire to the pink wire from the loom and re-connect the brown wires and run the red to the isolator (both batteries are hooked to the isolator as well as the alternator ) I get no output from the alternator.

    On the plug itself - if I strip a little of the red wire away and connect the brown wire (from the plug) to it and then connect those to the pink wire from the loom - the alt. puts out 14+ volts (to both batteries it seems) I thought the isolator would only send voltage to one battery at a time ( the idle goes way low - like the alt. is working overtime to charge both batteries).
    At this point the pink wire from the plug isn't connected to anything and the brown and red wire are connected together and connected to the pink wire from the loom (just to reiterate...)

    I can also not even connect any wires from the plug to the brown or pink wires on the loom and the alternator will make voltage (as long as the brown wire on the plug is connected to the red wire on the plug)

    oh - and the isolator has a spot for "excitation" (key on) and yes that's hooked up and verified.

    You think this is confusing for you ?....

    Any help would be appreciated....

    Dan

    87 burban
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Not sure about the wiring colors, etc. However, I can shed some light on this one for ya:
    [ QUOTE ]
    I thought the isolator would only send voltage to one battery at a time

    [/ QUOTE ]
    The isolator will charge both batteries at the same time. What it "isolates" is the batteries from each other. It will allow either battery to go completely dead, without taking any power from the other battery. It's just a big, honkin' pair of diodes that will let current flow from the alternator to both batteries, but it won't let current flow from either battery back to the alternator or to the other battery. /forums/images/graemlins/cool.gif
     
  3. wrathORC

    wrathORC 1/2 ton status

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    For the most part, you're right. Oldschool ones are merely a relay with a self-resetting circuit breaker in them. No diodes.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Actually, I'm 100% right. /forums/images/graemlins/grin.gif I don't consider what you're describing to be a battery isolator. It's just a relay. /forums/images/graemlins/eek.gif Once the relay is closed, then the 2 batteries are no longer isolated from each other at all. So if one battery is fully charged and the other is totally dead, then there will be a huge current drawn from the charged battery to the dead one since the relay contacts have connected them together in parallel. /forums/images/graemlins/frown.gif A true battery isolator will never allow that scenario to happen. /forums/images/graemlins/cool.gif
     
  5. wrathORC

    wrathORC 1/2 ton status

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    [ QUOTE ]
    Actually, I'm 100% right. /forums/images/graemlins/grin.gif I don't consider what you're describing to be a battery isolator. It's just a relay. /forums/images/graemlins/eek.gif Once the relay is closed, then the 2 batteries are no longer isolated from each other at all. So if one battery is fully charged and the other is totally dead, then there will be a huge current drawn from the charged battery to the dead one since the relay contacts have connected them together in parallel. /forums/images/graemlins/frown.gif A true battery isolator will never allow that scenario to happen. /forums/images/graemlins/cool.gif

    [/ QUOTE ]

    Modern ones use diodes. In fact, most of them use generic bridge rectifiers (full wave rectifier) to do it because they come in high-amperage forms with heat sinks already on them. It's more cost effective believe it or not to buy a bridge rectifier with four diodes in it than it is to buy a single high-amperage diode. You can purchase a 25amp bridge rectifier from Radio Shack for $2.50.

    Not so modern ones use power transistors. They sense which side has the higher voltage and will only open one way. IE: it won't open unless the correct side has more voltage (which is coming from the alternator). Pretty simple to do with transistors but power transistors generate a lot of heat.

    Even older ones were like I described above only they used a relay. It sensed voltage in a redneck way but same design as the power transistor one above.

    30amps and the self-resetting circuit breaker will trip. It's not like it matters anyway since if it is the auxilary battery that took a dump the circuit breaker will just stay tripped. If the main battery is dead the truck won't start. Besides, all battery isolators have a switch on them so it can't let current flow unless the ignition is on. There's nothing wrong with any of these setups, it's just that diodes are more reliable and are now cheaper.
     
  6. danielzink

    danielzink Registered Member

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    Okay - I got my alternator making voltage again whoopee....Now......when I key off at the ignition...It's all off - as in - radio resets - no interior lights work...I'm about to give up..

    There's only 4 dang posts on this thing how hard can it be?

    Post #1 main battery
    Post #2 from Alternator
    Post #3 aux. battery
    Post #4 "excitation" (from fuse panel - labeled ign - key on)

    Dan
     

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