Dual Alternator

Black LT

Original poster
Member
Dec 4, 2011
211
So, I had the lights dimming thing going on when the bass would hit and it was driving me nuts.
Because of how the PCM controls the charging .... long story.
So I decided to put in a second alternator - not tied into the vehicle charging system.
I have a battery in the back being charged by the second alternator powering my sub amp. The grounds are together - actually have them grounded to each other. But the positives are completely separate.
Ahh, but this is about the alternator.
Pics;
 

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RayVoy

Member
Nov 20, 2011
939
I don't want to be a party poop, but I can see a couple of problems with your idea.

- you need a switch to disconnect the rear battery from the field coil. The ignition switch handles this on the factory set up.

- suspect the reversed rotation of the alternator will cause heating problems, the cooling fan will be turning the wrong way.
 

Black LT

Original poster
Member
Dec 4, 2011
211
I cleared the poop before the party! All is on and working well.
It's a one wire alternator. I don't know all the technical off hand, but they are self exciting.
I looked around until I found an alternator that operates counter clockwise.
 

RayVoy

Member
Nov 20, 2011
939
Sounds good, but with out a switch, the field coil, in a stopped alt, becomes a load for the battery being charged, discharging the battery. Your not using it for a starting battery, so no big deal, except, the non rotating alt is getting hot and no spin, no cooling fan. Too much heat, no alt.
 

Black LT

Original poster
Member
Dec 4, 2011
211
What is a Self Exciting One-wire Alternator?


A self exciting or "One wire" alternator as it some times called, has only one wire running to it., that one wire is the main large battery wire. Don't confuse one wire because the plug going to the alternator only has one wire to it, this is a two wire system. The one wire, self exciting alternator uses a special voltage regulator that doesn't need an ignition wire to activate it.

This type alternator only requires a battery wire hooked to it. The voltage regulator contains circuitry that uses the residual magnetism in the alternators fields to determine when to turn the alternator on, the regulator does this by sensing the RPM the alternator is turning. When the alternator gets to a certain rpm the voltage regulator "turns on". Typically you start the vehicle, rev the motor slightly then the alternator starts charging. This type alternator is commonly used on custom cars, trucks, tractors and other non standard applications when wiring is a factor. In choosing this type alternator you must consider, do you want to rev your motor slightly to get the alternator to turn on. Also, when using the self-exciting alternator on tractors or other slow turning motors does the engine have enough RPM's to start the alternator charging. This can be overcome by using a smaller pulley or by adding an ignition wire. Is another name for the Self-Exciting Alternator mentioned above. You only need connect the battery wire (one-wire).
 

MAY03LT

Member
Nov 18, 2011
3,422
Delmarva
People Order Our Patties

I saw it get loaded down pretty darn good and it didn't break a sweat.

For all the threads that I've seen about dual alts, I never thought about the second alt facing inwards.

Props, respect, and cake too for sharing this.:thumbsup:
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,160
Brighton, CO
Love those GM 1 wire alternators. I used to run 6 of them on a Suburban I had to run a 10000 watt linear. They never broke a sweat.
 

meerschm

Member
Aug 26, 2012
1,079
two questions. how do you route the belt, and how did you figure out how long to make it?

ok, one more.. did you need to add another idler pulley?

nice job.
 

Black LT

Original poster
Member
Dec 4, 2011
211
Steve A said:
So in theory you can use this to power say a trailer that is hooked to the truck?

I'm not talking through the plug, I'm saying say in a remote location or what ever..
Yeah, but it'd probably be easier to just use a relay and two batteries for that. Unless I ain't see'n what you're see'n!
meerschm said:
two questions. how do you route the belt, and how did you figure out how long to make it?

ok, one more.. did you need to add another idler pulley?

nice job.

I tried to keep the factory routing and go up to the new alternator - went to the parts store and ask to try 119" belt (I used string around the pulleys and guessed from there!). Ends up it would have to be about 123". So after some creative thinking and making sure all the pulleys' turn the right way I rerouted and a 90.5" belt works. (thanks for the spare I got from you!)
No new idler. The least contact is the water pump - but it's not as bad as it looks - I'm not worried at all.

 

RayVoy

Member
Nov 20, 2011
939
Black LT said:
So after some creative thinking and making sure all the pulleys' turn the right way I rerouted and a 90.5" belt works.

Very creative :thumbsup:, and thanks for the education. I have discovered, the key is in the rectifier used in the one wire alt. I haven't figured out how the rpms trip the circuit into charging (I need a schematic of the rectifier assembly), but you, and the internet, have convinced me that it will be fine. Good job.
 

gmcman

Member
Dec 12, 2011
4,656
Very slick setup..nice work! Just keep an eye on the water pump pulley and monitor it's temp initially...make sure the belt doesn't slip and cook the seal.
 

gmcman

Member
Dec 12, 2011
4,656
Black LT said:
No new idler. The least contact is the water pump - but it's not as bad as it looks - I'm not worried at all.


Well, after looking at the drawing for the new routing, I'm a little concerned about the water pump pulley. Circulating coolant may not be the issue and I hope I'm wrong but I don't see how that small amount of contact is going to run the fan when it's fully engaged, or even halfway.
 

Black LT

Original poster
Member
Dec 4, 2011
211
gmcman said:
Well, after looking at the drawing for the new routing, I'm a little concerned about the water pump pulley. Circulating coolant may not be the issue and I hope I'm wrong but I don't see how that small amount of contact is going to run the fan when it's fully engaged, or even halfway.

Agree with the concern. If it does pose a problem I can add an idler between it and the power steering to lift the belt a little. What'd be the best way to put the ultimate test to it?
It's fine with the AC kicking in and out - how can I stress it more?


EDIT; Maybe I'll look into adding the idler just because I don't like iffy.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,160
Brighton, CO
or go back to the 123 inch belt.. Its what I would do. A 123 inch belt is cheaper (I think) and easier to install than another idler pulley.
 

jimmyjam

Member
Nov 18, 2011
1,634
or just swap in efans, would give you some much needed room in there..
 

meerschm

Member
Aug 26, 2012
1,079
since the water pump is built with the smooth pulley, I do not think the load is that great, and is not that variable.

ribbed side of belt against ribbed pulley has much more surface area and grip. needed for generator, power steering and A/C compressor.

perhaps Roadie has some info on HP use by the water pump.

can you move the water pump pulley when the belt is not moving?
 

gmcman

Member
Dec 12, 2011
4,656
meerschm said:
since the water pump is built with the smooth pulley, I do not think the load is that great, and is not that variable.

ribbed side of belt against ribbed pulley has much more surface area and grip.

In stock setup though the smooth side of belt wraps a good bit around the water pump.
 

Grimor

Member
Mar 28, 2013
954
I've used ford 3G 200A alts a lot for seconds. Been almost a year, how'd your setup work for you?
 

Black LT

Original poster
Member
Dec 4, 2011
211
It's still running fine with no issues.
I did go with the longer belt to alleviate some periodic belt squeal. Other than that all's working as posted.
No headlight dimming or voltage drops when the subs thump'n.
 

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