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Discussion Starter · #1 ·
I am running dual alternators on my 40. It has a '92 Chevy TBI, both are stock alternators, 105 amps each. I have them both running back to the same place, a hot juction block that all engine/accersories take power from. From there the red top Optima is wired in, then I have a yellow top Optima for winching wired in with a dual battery management switch from NW Power. Is there any concern with running dual alternators in this setup? I heard through the grapevine that I would need some sort of ??? between the 2 alternators, anyone know if this is true or not. Both alternators are engaged at the same time, from the same excitor wire. Someone help! Please
 

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Electrical stuff like that can be a real challenge. I barely know enough about how the charging system needs to work, let alone talking about it. But I think you need something to balance the load. NOTHING is the same, because of the laws of electricty and physics.
If you don't get your answers here, TRY CCOT's bulletinboard. They aren't as "extreme" over there but have very good/knowledgeable people hanging out and helping. Best of luck.
 

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Why are you running dual alternators? Wouldn't it be easier to run 1 high output unit with dual batteries and a isolator. The only reason I can see running dual alternators is using one as a welder. With the welder alternator you would have to isolate 1 alternator from your normal charging system.
I guess if you really wanted to you could use 1 alternator just to run accessories, stereo, fog lights, winch.....But you would isolate this from the sytem also.
 

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Discussion Starter · #5 ·
There was an AC compressor on it, it burnt up, so I needed to put something there. I also needed more juice, so instead of buying a high output alternator at $2-300, I simply went to PNP and got a stock 105 amp and slapped it on there for $35 bucks. My plan is to convert that side to a welder, once I ugrade the stock alternator, but why would I need to isolate the 2, what type/kind of damage can occur? More importantly how do I isolate the 2, and then for the second one, how would I tell when to kick on and off? Thanks
 

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I'd really like to know what bracket you used in order to connect up the 2nd alternator to the AC compressor area. Did you have to change the belt? Also were you able to keep the stock pulley on the alternator or did you switch it with the AC pulley for belt purposes. I've very, very interested in talking with you about this setup, because I'd like to run this exact setup on a TBI 350 swap in an 80 series land cruiser.

Thanks.
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Red FJ said:
but why would I need to isolate the 2, what type/kind of damage can occur? More importantly how do I isolate the 2, and then for the second one, how would I tell when to kick on and off? Thanks
There really isn't any need to isolate the two alternators unless you want to run two separate electrical circuits. You don't need to tell when one "kicks on and off" either. They may have slightly different regulated voltages, so that one will be loafing until the voltages drops low enough for it to start puting out. Under full current load, they will both be putting out.
 

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What in the world draws 105+ amps all the time??? Holy crap, that would be about 2 ga wire at the min!!! to the isolator. I have one 105 amp on my TPI setup and I upgraded to the Iceberg 140 amp... and it is more than I need.
Also if you go the the chevy dealer you can get the non A/C idler for theA/C compressor space for about $70...
 

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Still the ability to have two seperate (being redundent) power systems is great for those of us who enjoy accessories (Lights, winch, sound system) while camping and such in the great outdoors. I've looked into getting an alternator in place of the AC compressor and everyone has said that it can't be done. While I'm not trying to do what Red FJ was and combine the circuits, I would like to remove my non-used AC compressor and install another charging circuit there to run a second and possibly third battery.
 

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Just to throw my 2 cents in, the current output of an alternator increases as the amarature voltage increases (exciter voltage), and also increases as the speed of the alternator increases. With the idea of using 2 alternators you will be able to put out more current at lower RPM's of the engine (less heat build up and less fuel).
 

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most alternators don't put out anything until they reach at least 2000 RPMs. i see no good reason whatsoever to run 2 of them. running one high output alternator will supply more juice than you will need.

and i'd sure like to see a pic of both of them mounted on the TBI engine with the stock ac brackett.
 

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Man you dug this up. I just put an alternator in place of the ac pump. The upper hole lined up, then took a piece of steel and made a plate to catch the lower hole. Nothing fancy at all. sorry no pic. Even used the same belt, been that way for about 3-4 years. I will get a pic tomorrow.
Jim
 

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How to plug Dual Alternator

Dig it up again... Hey hey,

Hello RedFJ, I just found this post and I have a hard time to find information about how to plug the two alternators in my truck.

I will like to see you pics.

I will like to know how did you finally plug the two alternator and if you used some kind of relay or basically plug them both into the positive circuit of the battery.

(For all the reader who will want to know why: My project is to add an alternator and a battery. I want to add an alternator instead that using a high amp one because the normal alternators are hundred dollars (cheap) and life time guaranty. Instead that two hundred seventy for a high amp with one year guaranty.)

I have a 1990 S10 4.3L in a ElCamino 1984.
 

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I used the AC compressor location to mount a York compressor for on board air.
I don't see a reason to run dual alternators. If you want a welder, buy a Premier power welder and be done with it.
 

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My problem is how to wire. Not how to install it.

Here is another reason to use two alternator: If one stop working, the other keep serving...
 

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Dual Alternators

Alternators are current sources, just like batteries. Batteries are different, no 2 are exaclty alike. Batteries hooked up in parallel have the potential to distroy one another. Most don't if they are the same MFR and Model, because they are close to the same. The trouble is when one is different, either different sizes, ages or one is failing. The good/more powerful one starts charging to less good/less powerful one and they start this viscous circle that ultimately destroys both batteries. This has to do with their internal resistance changing. A topic for engineers. Alternators can do the same thing. One will cook the other or their outputs will start oscillating because they each take turn providing charging.
Put a switch in to be able to turn off one of them or have each perform seperate functions and don't cross connect them. One for engine and one for accessories.
Quick Test: Put a clamp on current meter on one, vary its load, then place it on the other and do the same. It's doubtful they will perform the same under the same loads.
 
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