# Convert a 12v alternator to 24v

#### Autowood

Joined Nov 9, 2013
8
After searching the Internet and not finding a specific way to convert an automotive alternator from 12v to 24v output, I found "All About Circuits" and figured this would be a good place to start. Does anyone have a specific plan or set of directions?

#### wmodavis

Joined Oct 23, 2010
739
Wire two 12 v alternators in series.

#### Autowood

Joined Nov 9, 2013
8
Yes, two alternators can be wired in series, but the grounds must be kept isolated. Or a negative and positive ground alternator can be teamed up on a common chassis.

That kind of defeats my purpose. What I am building is a fairly lightweight trailer for an electric bicycle with a 79cc gas motor, an alternator and to 12v batteries. LiFePO4 batteries with enough range are VERY expensive. I figure this set up will give me ultimate range with minimal cost.

#### tcmtech

Joined Nov 4, 2013
2,868
Easy to do. It's all about the regulator and how many amps you are drawing at a specific RPM.

First off what type of alternator is it?

The Delco 10si and 12si series are by far the most common for moding to get different voltages out of. Most can be made into 24 volt units just by changing their internal regulator.

#### bountyhunter

Joined Sep 7, 2009
2,512
Yes, two alternators can be wired in series, but the grounds must be kept isolated. Or a negative and positive ground alternator can be teamed up on a common chassis.

That kind of defeats my purpose. What I am building is a fairly lightweight trailer for an electric bicycle with a 79cc gas motor, an alternator and to 12v batteries. LiFePO4 batteries with enough range are VERY expensive. I figure this set up will give me ultimate range with minimal cost.
You could wire each 12V battery out for charging independently and do them separately from a 12V alternator.

#### ronv

Joined Nov 12, 2008
3,770
I think TCMTECH is probably right. You can probably get 24 volts out by changing the field voltage. May find some circuits on the net.

#### crutschow

Joined Mar 14, 2008
23,791
I think TCMTECH is probably right. You can probably get 24 volts out by changing the field voltage. May find some circuits on the net.
Running the field at a higher voltage could overheat the field windings.

#### wmodavis

Joined Oct 23, 2010
739
Yes, two alternators can be wired in series, but the grounds must be kept isolated. Or a negative and positive ground alternator can be teamed up on a common chassis.

That kind of defeats my purpose. What I am building is a fairly lightweight trailer for an electric bicycle with a 79cc gas motor, an alternator and to 12v batteries. LiFePO4 batteries with enough range are VERY expensive. I figure this set up will give me ultimate range with minimal cost.
Well you didn't mention any of that in OP did you? I'm
Not a mind reader. Answered based on the slim information you gave.

Joined Jul 18, 2013
19,442
After searching the Internet and not finding a specific way to convert an automotive alternator from 12v to 24v output, I found "All About Circuits" and figured this would be a good place to start. Does anyone have a specific plan or set of directions?
The automotive alternator uses a PWM regulator using the slip ring fed rotor to control the output to 14.5v.
When the original electronic version regulator was designed to replace the old relay/mechanical regulator (anyone remember them?) it caused interference on the car radio, so PWM version was developed.
The old electronic method could be used or a PWM version to set the output to something over 24v.
Max.

#### inwo

Joined Nov 7, 2013
2,419
After searching the Internet and not finding a specific way to convert an automotive alternator from 12v to 24v output, I found "All About Circuits" and figured this would be a good place to start. Does anyone have a specific plan or set of directions?
Specific plans would require specific information not given.

In general a 12 volt alternator will easily output over 100 volts by full fielding with 12 volts.

I've done it to run power tools in a pinch.

Regulating to 24 volts should be simple. Alternator will have to run at higher rpm however.

Find one with external alternator and use a 24v regulator.

If you can find a way to isolate the regulator, raise ground reference 12volts. Zener to ground?

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.

#### bwilliams60

Joined Nov 18, 2012
1,233
What you want to do is fairly easy but you need to find a local rebuilder. I was a rebuilder so the information I am going to give you is from first hand experience, no guessing.
The rotor in a 24 Volt alternator will be wound differently than a 12 V rotor and therefore needs to be done properly. It will have a different amperage draw. To go with that, you need a 24 V voltage regulator. There are many different regulators available through a rebuilder depending on the type of alternator you use. As one person said, a Delco 10SI or 12 SI alternator are a couple of the most versatile alternators available and parts are fairly cheap for these. As for the stator and rectifier, you have to choose the output you want(amps) and buy those parts accordingly. This is a fairly simple procedure and you only need to use one alternator. If you need more information, send me an email and I will try to help you out the best I can.
Cheers

#### Autowood

Joined Nov 9, 2013
8
I have to say Ronv, that this tutorial was well written and easy to understand by a novice like me. My dad, who is a EEE also found it interesting and informative. Thank you very much. Since I first submitted this post, I have learned a lot. No longer do I have any aspirations to use a PM brushed motor as a generator. I also learned from tcmtech and bwilliams60 a good lead on Delco Alternators. Turns out Delco makes a 10si and 12si in 24v already. Thanks all for your help. My problem has been solved.

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#### tcmtech

Joined Nov 4, 2013
2,868
I also learned from tcmtech and bwilliams60 a good lead on Delco Alternators. Turns out Delco makes a 10si and 12si in 24v already.
Yep they come in 24 volt types. I put a Delco 12si 24 volt 70 amp one wire on our old dozer last summer. Total cost was about $75 and it was a considerable step up over the old 24V 30 amp stock replacement units that sold for ~$230!

#### doug08

Joined Jan 30, 2011
153
You do have to limit the current into the rotor. Normally the rotor draws around 4A at 14V if the battery being charged is low. In the schematic at the link below, you will need to replace the zener with a 27V to charge a 24V battery.