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Unread 05-28-2017, 08:40 AM   #1
Jeffy
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Default Alternator whine with dual batteries

So I just recently installed a dual battery system, complete with isolator to keep the batteries separated when the car is off. I've noticed that when the aux battery gets run down by my fridge or other accessories with the engine off, once I turn the engine on I have an alternator whine for a few minutes until both batteries are fully charged again. If I start the car with the aux battery fully charged, there's no whine.

Is this normal/ ok? Or is it a sign that my alternator is starting to go out? I had zero issues with it before the install, I'm wondering if the added stress of charging a depleted second battery is just making it complain a little.

I also upgraded the cables for the following to 1/0, and used the same cable for the dual battery system:
-alternator B terminal to battery +
-engine to ground
-battery negative to ground.

Edit: Forgot to mention that the charging voltage while the engine is running is between 13.5-13.9, measured between the main battery's terminals. Once the batteries are fully charged it drops down to 13.0-13.5 while driving, which is consistent with how it has been ever since I've owned the vehicle. My head unit has an OBDII connection so I can check it through there, and I've verified it's accuracy with a multimeter and voltmeter installed in the engine bay, they all read the same voltage.

Any thoughts?
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Last edited by Jeffy; 05-28-2017 at 11:05 AM.
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Unread 05-28-2017, 11:56 AM   #2
bulldog
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What are the ratings on the alternator?

I haven't noticed that on my 4Runner. Need to dig to see if I can find the specs, but IIRC the 03 V8 was 130A.

May just be that the extra stress is causing additional noise form the regulator on the alternator.
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Unread 05-28-2017, 12:01 PM   #3
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Quote:
Originally Posted by bulldog View Post
What are the ratings on the alternator?

I haven't noticed that on my 4Runner. Need to dig to see if I can find the specs, but IIRC the 03 V8 was 130A.

May just be that the extra stress is causing additional noise form the regulator on the alternator.
From what I've seen it's the same specs. About 130 amps max output, 90 amps at idle.

The noise gets louder with RPMs, not sure if that helps to diagnose.

I'm leaning towards (and hoping) it's just a little extra stress causing the noise. It works perfectly otherwise, and once the aux is recharged there's no more noise.
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Last edited by Jeffy; 05-28-2017 at 01:56 PM.
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Unread 06-30-2017, 12:42 AM   #4
Blowout
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I can't say I notice much more noise when the aux battery is charging. I can hear it kick it, but not too loud. The primary batt is suppose to charge first, then switch over to the Aux on my setup.

You could try disconnecting the aux and reconnecting to confirm it is the cause of the issue.

I thought about upping the alternator to a higher amp unit, but now thinking of a solar panel on the roof rack first might help enough to charge the aux batt while the truck is off. We do a lot of hunting and short trips from camp, so the battery doesn't get much time to charge.
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Unread 06-30-2017, 02:12 PM   #5
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Quote:
Originally Posted by Blowout View Post
I can't say I notice much more noise when the aux battery is charging. I can hear it kick it, but not too loud. The primary batt is suppose to charge first, then switch over to the Aux on my setup.

You could try disconnecting the aux and reconnecting to confirm it is the cause of the issue.

I thought about upping the alternator to a higher amp unit, but now thinking of a solar panel on the roof rack first might help enough to charge the aux batt while the truck is off. We do a lot of hunting and short trips from camp, so the battery doesn't get much time to charge.
It's definitely due to the drain from all my aftermarket items. Once the aux and main both reach a full charge after driving for a long time, the alternator is quiet again. I ordered a HO alternator and that should fix it.

I do the same, usually set up camp and leave the fridge running while I hike and fish, there's not much time spent with the engine running.
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Unread 07-02-2017, 11:43 AM   #6
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Now I have voltage gauges for both batteries so they can be monitored from the cab it's easy to see at a glance when the alternator is kicking in. Yesterday during a 15 mile drive each way the alternator was always running and I didn't notice a whine.

Driving - voltage on both batteries was 14.1
Idle - 13.6
Engine off - 12.6 (up from 12.4 before the drive)

I haven't confirmed these voltages with an alternate gauge yet. On my list of things to do now...

I don't drive this much truck much so the batteries drop voltage. Just replaced the primary battery 4 weeks ago. The Aux battery is probably 7 years old and should be replaced.

Not sure if this helps any with your original concern.
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