Can someone explain to me why a standard Battery Isolator won't work with A GM?

I purchased a battery isolator from Summit Racing last winter. I mounted it to my 99 Tahoe, but never got a chance to hook it up. I finally hooked it up and it doesn't work.

I researched it and it's a standard battery isolator. Apparently, I need a CS battery isolator designed for a GM. The CS type battery isolator has an extra input for the ignition. ???

When I apply 12-14VDC to the center, I get 12-14VDC -0.7VDC at each terminal. When I hook the isolator up to the alternator, it sees ZERO voltage at the center terminal.

Can someone explain why the 4th terminal for the ignition is on the CS battery isolator. Can someone help me hook this standard battery isolator up so it'll work or am I screwed and have to sell it and buy a CS type battery isolator?
Thanks

Hardwarz

I am not sure but I thought it want by your alternator. As far as I know the extra terminal is for powering the alternator in start and run positions. if you don't have power going in to the alternator to initially charge the field coil, you won't get any power out of your alternator.
But like I said I am not sure on that. anyone else??

So, could i hook a relay to the crank position of the ignition and supply the alternator with +12VDC at crank to get the alternator to start up?

Hardwarz

it has to be a wire that is hot with key on position, but not hot in ket start position. But yes you can run a wire. I would look up what the stock current of that wire is and find a wire that has simular specs, but any key on wire will work.

First, tell me the model number of your isolator so I can tell you properly. I wouldn't like to give bad direction.

Just to add, I have no experience with the alternator on your truck, I was hoping to have someone else chime in but noone did. do some research before just hooking up wires and relays. Fires start if you don't. I will look at some stuff on my free time today and tomarrow, anything I find out I will post.

My isolator is a Transpo 130A 3 post. I bought it from Summit Racing, they don't carry it anymore. I'll try to post a wiring diagram soon of what I'm thinking of doing, maybe that'll help too.

BTW, thanks for all the help.

Hardwarz

Ok what I found out. basicly the battery wire on the alternator excites the coil in a cs alternator. The isolator you have has restricts flow of current backwards thru the circuit. Without this current the alternator won't work. I am still researching on how a cs isolator works with key on power on the extra terminal(if it is a constant or turns on till the alternator outputs increases then turns off). Mattering on that is how you would fix the problem.

Am I helping at all btw or just making things worst....lol

BTW did you connect a sensing wire to the s terminal on the alternator?

marinekilz said:

BTW did you connect a sensing wire to the s terminal on the alternator?

Click to expand...

No, not 100% sure what that was. I see I have a harness on the top of my alternator. I was thinking about trying to provide it +12vdc directly from the battery with a relay (and fuse protection).

Here's what I've been thinking about.



I forgot about the sensing wire in that diagram.

Again, thanks for all the help.

Hardwarz

Hummm, been thinking about it, i wonder if I can connect a 1A diode between the post on the isolator where Battery 1 connect to and the center terminal where the alternator hooks up to.

That would provide + flow from the batter to the alternator, but will it cause any other problems?

Hardwarz