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Dual alternator wiring??

Calicak89

SM 2018
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PM 2016
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Mar 12, 2012
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State College, PA
I'm currently running my second alt. using a Beuler BU-5088 relay tied into the rear HVAC controls and the appropriate 5 A fuse. for some reason, unknown to me, I keep toasting relays. the first one made it about 2 months, then about 2 more. then I switched the fuse tap to the airbag and the third relay lasted about 2 weeks. switched back to the rear HVAC controls and just lost the 4th relay after about 3 months again.
Can I simply wire the second alt using a factory harness and wire it in in parallel to my first alt??
Since they are internally regulated, I'm thinking that this is possible without any detriment.  I can't think of any reason why it wouldn't work just fine, but wanted to see if any of you our there have any experience with wiring multiple alternators in parallel.
 
When you add a second alternator you are really adding a secondary electrical system and you should keep it separate from your main one.

Share the same ground but you will want to keep the rest separate.

You need a second battery for your second alternator. The battery is essential for smoothing out the spikes and noise from the alternator. Without a battery on your alternator you can blow the diodes out on the alternator or blow up any electrical components hooked to it. More of a matter of when than if.

I would STRONGLY suggest against combining the alternators together or trying to have them charge the same battery. You REALLY need to keep everything that the second alternator is connected to separate from the main one or you can cause issues. If you are running your sound system off the second alternator then I would suggest running the whole thing off the second system or you will want to use something to isolate the two systems. You MAY be ok for a while but you will likely have "gremlins" in your system you will find hard to find.

One example is that you are more likely to have ground loop issues if your amplifiers are running off a different power source than the radio but if you use fiber optics from your radio to a processor that is on the same circuit as the amplifiers then you shouldn't have an issue.

Rodney
 
I do have the two systems completely isolated.
more info here http://chevyavalanchefanclub.com/cafcna/index.php/topic,145377.0.html
The stock electrical system is as it came from the factory except for the alternator being upgraded to a Delco 200A (swappped in 2011) as I used to run the sound system off of the stock charging system.
I initially switched the head and fog lights over to the new system, but after the second relay went, switched them back, as I thought that maybe somehow, somewhere there was still something connected to the stock system that was causing the issues. but two more relays have failed since returning the whole stock system to its original orientation.
I can't figure out why these relays would be failing and would like to eliminate the use of the relay to activate the second alternator.

My question is can I simply splice a second harness into the two wire lead connected to the alt that is powering the stock electrical system.  I may have been a bit confusing with my OP. I want to turn both alternators on using the same wire, not actually run their outputs together.
I would just be splitting the wires above the factory harness on the stock system's alt and tying the harness for the second alt in, using the lead to activate both alternators, essentially turning both on with the ignition, as opposed to the current orientation of the the stock system turning on with the ignition lead and the second system turning on using the relay that is tapped into an ignition activated  circuit.
 
It is helpful to have all of the information...

Are your relays fused? Would be hard to believe they would be blowing if you have a fuse protecting them as you should be...

As to the turn on lead... The ONLY issue about running them off the same ignition wire is if whatever is driving the alternator is big enough for both alternators. If it is a simple relay then you are likely OK as long as it is driven off a relay and not directly off the BCM.

You should only be blowing relays if you are overloading them or the voltage is way too high. Is the coil side blowing or are the contacts inside welding closed so it can't move? You need to make sure your relays are big enough for the load. If you are using a standard automotive relay they are rated for 30/40 amps. Without looking I am guessing it is 40 amps on the normally closed leg and 30 amps on the normally open leg. But you need to look at the relay specs to be sure.

A 30 amp relay can handle 30(amps)x12(volts) = 360 watts. If you are trying to run a load higher then you can double up the relays but your better off getting bigger relays...  At higher amperage you may get arcing across the leads which pretty much welds them together and they won't move. Or they can just get so hot they melt apart inside.

Rodney
 
Have you placed a diode in parallel with the relay's coil to allow the coil's current to loop around when the signal to it is shut off?  (Relay coils are inductors which cannot handle instantaneous current transitions.)
 
enoniam said:
Have you placed a diode in parallel with the relay's coil to allow the coil's current to loop around when the signal to it is shut off?  (Relay coils are inductors which cannot handle instantaneous current transitions.)
I forget this part... Never used them myself but I probably should.
 
redheadedrod said:
I forget this part... Never used them myself but I probably should.
Some, but not all, relays have them built in.
 
redheadedrod said:
It is helpful to have all of the information...

Are your relays fused? Would be hard to believe they would be blowing if you have a fuse protecting them as you should be...

As to the turn on lead... The ONLY issue about running them off the same ignition wire is if whatever is driving the alternator is big enough for both alternators. If it is a simple relay then you are likely OK as long as it is driven off a relay and not directly off the BCM.

You should only be blowing relays if you are overloading them or the voltage is way too high. Is the coil side blowing or are the contacts inside welding closed so it can't move?
Yes, it is fused, a 5A as is recommended by Bueler ( the manufacturer)
I can't imagine that it's being overloaded, as it's sole and only purpose is exciting the alternator
I'm not sure where the failure is occurring as I have not taken any of them apart

enoniam said:
Have you placed a diode in parallel with the relay's coil to allow the coil's current to loop around when the signal to it is shut off?  (Relay coils are inductors which cannot handle instantaneous current transitions.)

I did not, didn't even think of that.
I was looking for a way to excite the alternator without using the relay at all, but maybe ill try that and see what happens.
 
Reviving an old thread... Did you have problems getting your secondary Alternator to come on?

I have mine setup similar to what you have and I can't get the alternator to actually do anything. I have swapped the alternator back and forth to no avail.

Currently wanting to use the Factory alternator for the truck and the Secondary 250 amp Alternator to run the audio system but can't seem to get the second alternator to actually turn on.

The brackets were all powder coated so I wonder if maybe I have no grounding. My wire has the relay going to a spot and a blue wire going to another spot. One is supposed to turn on the alternator and the other is supposed to feed back to the alternator I think but not sure.

Rodney
 
redheadedrod said:
Reviving an old thread... Did you have problems getting your secondary Alternator to come on?
2 pin or 4 pin alt?
Did you ground the case independently or are you relying on the bracket and through bolts for grounding?


 
Ended up being the Bracket wasn't grounding enough. I grounded the case separately and it started working great.

Had the factory alternator in the "supplimental" location. I need to do some more testing because the new alternator isn't working. Need to insure I didn't damage the stock wiring and assuming I didn't then this 250 amp alternator goes back.  The positive bolt was very warm when I originally installed it as a factory replacement before upgrading anything else.

Currently the factory alternator is working great in the second location.

Would like to hear from MS03 2500 if he had any issues with his alternator since I bought this from the link he posted a while ago. Hopefully it was just a bad unit. I have under 500 miles on this 250 amp alternator. It was fluttering around a little bit from 12-14.5 on the gauge and verified via VOM. It now solidly is not working. Going to try the "exciter" wiring on this alternator and unplug the factory wire and see if the alternator works.

I think I can go back to 1 alternator with this setup by removing the extra idler and putting the old belt on until I get a replacement alternator assuming the alternator is bad. Hoping I just pulled a wire loose in the connector when I was trying to sort it all out.

Now I have 1/0 gauge wiring from the positive of each battery to the terminal on the alternators, 1/0 gauge wire going to the side of the alternator bracket where the red box used to be... I ran another 1/0 gauge wire from the same location on the bracket to one of the bolts on the secondary alternator and one to the firewall where the engine ground is located. Should have a better power path now. Not showing ANY drop from the alternator to the batteries where I was showing about a half volt drop before upgrading the wiring.

Right after I posted this message I started to consider what was grounding the alternator since it is 3/8" plate steel that is powder coated. Grounded it and now its all good. Don't think I toasted the alternator without the ground because the new alternator was working great in the factory location where it currently is. The original alternator is in the secondary location and running great now.

Planned to switch them back around after I verified the secondary location didn't blow up the original alternator. Didn't expect the new alternator to crap out.

Rodney
 
redheadedrod said:
Would like to hear from MS03 2500 if he had any issues with his alternator since I bought this from the link he posted a while ago. Hopefully it was just a bad unit. I have under 500 miles on this 250 amp alternator.


Rodney

Of course I didn't have any issues, I know what a big 3 upgrade is.

1. Positive Wire
2. Ground Wire
3. Ground wire from the Alternator bracket to the frame.

You can't just add a 250 amp Alternator and not have the problems you have.

PS the motor is not a good ground the frame is.

 
All I wanted to know Byron was if you had any issues with yours for quality control purposes. I questioned mine from day one because the stud was very warm after running for a couple minutes. Factory Alternator never did and currently isn't doing that.

Will verify that the unit is bad tomorrow and get it replaced.
 
Ended up sending Alternator back. Was getting WAY too hot and burned my connectors to the point the Brass plating melted off. The case and the stud were too hot to the touch within seconds of starting my truck.

Factory alternator in same only warmed up with the engine.

The thread on the new alternator got so hot the threads on the stud and nut were not matching up well anymore as well.

Hopefully will get a new one instead of just a refund. And I probably already mentioned this but the Powder coat makes a great insulator... Needed to install a ground wire to the second alternator and all was working other that the new alternator being WAY too hot.

 
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