dual alternators stay on w dual batteries

Hello All and good afternoon. I have a 2001 Tahoe with dual 220Amp Stinger Alternators, 2 Optima Yellowtops, and one BatCap 3000. When I hook both batteries up to each alternator separately both alternators stay on when the ignition is off. I can hear a 'humm' when i put my ear next to the alternators; also, about a 6-7 Amp draw when car is off and no draw when second battery is disconnected. I can hook up one alternator to one battery at a time with either alternator or battery, so each pair turns on and off correctly individually, but not when both are connected simultaneously. Also, Output is good with both alternators. I have a true ignition source to power the alternators on/off with the key so the turn-on wire is correct. when both are simultaneously connected when the key is off the ignition source is off, so power doesn't back-feed through the ignition line when the alternators stay on. I thought about Diode-Isolating them but the inside of the alternators has diodes preventing the possibility from back-feeding through to power each other, right?? I have tried isolators also, but isolators only work when both positive and negative are isolated, and this doesn't seem like a correct configuration (normally just the positive is isolated). Is it possible one of my alternators could be bad? or at least one diode in at least one alternator is bad allowing back-feeding current? This is what I've tried so far and sorry for the lengthy post, but more info is better than not enough! Any help would be greatly appreciated. Stuart

You have a wiring issue.  Sounds like your alts are actually shorting out the batteries.  DISCONNECT THEM IMMEDIATELY.  Get the vehicle towed to an auto electrical shop before you burn it to the ground.Support the12volt.com

I don't think the alternators are shorting the batteries. Even when both are hooked up yes, they stay on after car is off, but function properly as far as charging is concerned. they are still pumping 14.3+ volts and only one battery and one alternator is hooked up right now. Additionally, there is no spark or arc of current when connecting either ground or power (not shorting).Stuart

If you are seeing 6-7 amps with the car off, there is something wired dreadfully wrong.  The only place that current could be coming from is your battery.  Go get the system checked.  Please!Support the12volt.com

Anyone else have any ideas? The configuration of alternator to battery is fairly simple: ignition lead to turn alternator output on, positive output from alternator to positive on battery, and ground to chassis, link the different battery positive terminals together via Isolator. If this is dreadfully wrong then someone please provide me an anecdote.Stuart

Really Man, With a problem as potentially dangerous as this, A few bucks to have someone check it out is MUCH cheaper than another Tahoe is gonna be when this one burns down to the chassis.UNLABELED Custom Car Club President

Does anyone actually have any technical advice for this configuration aside from taking it to a shop?Stuart

tommy... wrote: DYohn wrote: If you are seeing 6-7 amps with the car off, there is something wired dreadfully wrong.  The only place that current could be coming from is your battery.  Go get the system checked.  Please!

PLEASE!!!! Now, to the technical advice... 1: Call your insurance company, and get your agent's email address. 2: Forward this link to your agent: https://www.the12volt.com/installbay/forum_posts.asp~TID~117094~PN~1 3: Prepare to buy your new Tahoe out of your own pocket, because you are too stubborn to accept the HEARTFELT advice requested and given you. That's all I've got...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Does anyone that's not a laymen read this forum? How disappointing...Stuart