12v to 24v alternator conversion

Thread Starter

Thick8

Joined Sep 16, 2017
10
Or if you can find the sensing input lead to regulator, a voltage divider (1/2) would let the regulator only see 12 volts @ a 24 volt output.
Would this work? I have a solar/battery backup system that I just converted from 12v to 24v. I made a 12v backup generator for it and want to convert the alternator to 24v. It's a Delco Remy 35SI HD 140a alternator with a remote sense wire. Can I just make a voltage divider out of a couple of 1w resistors?
 

Thread Starter

Thick8

Joined Sep 16, 2017
10
I posted this in the projects forum but didn't get any answers so I thought I'd try here.
I built a solar/battery backup system that I just converted from 12v to 24v. I made a 12v backup generator for it and want to convert the alternator to 24v as well. It's a Delco Remy 35SI HD 140a alternator with a remote sense wire. Can I just make a voltage divider out of a couple of 1w resistors and wire it to the remote sense? I've been told that internally the 12 and 24 volt HD truck alternators are the same internally. That could be miss-information though.
I found a 24v regulator for this alternator on eBay
https://www.ebay.com/itm/VOLTAGE-REGULATOR-24-Volt-Self-Exciting-1-Wire-Delco-Alternator-33SI-34SI-35SI-/263023507681Any thought on if it will work as I intend?



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shortbus

Joined Sep 30, 2009
7,078
Is the part number stamped on your existing alternator one of the ones in the Ebay listing? If so it should work. Don't think you could make something as inexpensive as that new regulator is and have it work.
 

bwilliams60

Joined Nov 18, 2012
1,199
Typically an alternator is either 12v or 24 volt but not both. The rotor and the fegulator are typically the two components that will be replaced going from one voltage to the other. A 12v rotor will have a draw in the area of 5-7 amps where the 24v rotor will be about half of that. Hence the change in regulator.
As for the self exciting part, that is done by the voltage regulator itself and relies on residual magnetism in the rotor.
Not all Gm or any OEM alternators ate 1 wire. They are generally used in the Heavy Truck and Coach industry and sometimes you will see them on farm machinery.
The remote sense circuit is used to monitor battery voltage. If a resistance is placed in series with this, the alternator will attempt to put out more amperage to comlensate for a low battery.
 

MaxHeadRoom

Joined Jul 18, 2013
19,165
The alternator has the battery to provide initial power to the field, the experiments I have done to see if a AC-Delco alternator will self excite has failed.
Seems to indicate that there is no field residual.
Max.
 

shortbus

Joined Sep 30, 2009
7,078
The alternator has the battery to provide initial power to the field, the experiments I have done to see if a AC-Delco alternator will self excite has failed.
Seems to indicate that there is no field residual.
Max.
I think we're talking two kinds of "self exciting"? I'm meaning that it doesn't need the old incandescent idiot light bulb on the dash to excite it, only the battery at a voltage(not necessarily full voltage) to self excite.
 

MaxHeadRoom

Joined Jul 18, 2013
19,165
Self excitation to me is just as the old original Edison DC generator was and how many modern DC generators achieve a non-powered start up.
IOW, they use residual field to provide the initial excitation.
e.g. scrap yard magnet cranes with 240vdc generators.
If you provide any external power to the field, then it is not really self-exciting as I see it!;)
Max.
 

bwilliams60

Joined Nov 18, 2012
1,199
Some self excited alternators need to be "flashed" to restore residual magnetism if they hav ebeen sitting dormant for a period of time. Brushless alternators are all self exciting and only run a single wire for battery input/output. That is why we have been using them on trucks for years. Most alternators have rotors that will always retain some magnetism. Used with the proper regulator, it can be turned on at a fairly reasonable RPM without problem. If you are building your own and you cant get it to turn on, I would suspect the rotor isnt correct for the application or the circuitry for the regulator is not proper.
 

bwilliams60

Joined Nov 18, 2012
1,199
Where are you looking for magnetism. I can take pictures for you tomorrow at work of rotors which have retained magnetism and come from self excited alternators. The description in this article is correct and somewhat as I would describe it. The term generator is dually used in our industry. In early terms, generators were commonly used on all vehicles until the advent of externally regulated alternators and then internally regulated alternators. GM on the other hand, still calls their alternators, "generators". It can be confusing. I was a rebuilder and have built hundreds of self excited alternators. There are several reasons why they won't turn on. I would have to see what you are working with. Not all regulators will self excite.
 

shortbus

Joined Sep 30, 2009
7,078
The self energizing like I was talking about was made necessary when they went to LED dash indicators. The LED's wouldn't pass the voltage to excite the old style alternators.
 

MaxHeadRoom

Joined Jul 18, 2013
19,165
The conditions I specified was to me a self exciting generator requires no outside source to start the generating process, initially using a outside source is not self exiting in my definition.
As per the article link.
Max.
 
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