can you make a 12v alternator into a 24v alternator

[14p]

Ok so the rotor is the same for 12 and 24 volt? I thought the windings were finer and twice as much on rotor as well as the stator. I will put the 12 volt rotor back in it.

[skenn_ie]

Originally Posted by 14p

Ok so the rotor is the same for 12 and 24 volt? I thought the windings were finer and twice as much on rotor as well as the stator. I will put the 12 volt rotor back in it.

Same for 12 as 24 ? Possible, but unlikely. I THINK, field strength is current x number of turns. Inductance is proportional to turns squared, but inductance isn't relevant with DC.
Rotor resistance is probably 4 x on 24V (CSA halved, turns doubled) what it is on 12V, so current is half. Still A x t is the same.

Stator windings will be 1/2 CSA, twice as many turns too. If you run a 12V stator with a 24V regulator, and with same pulleys, rotor current will be increased considerably by the regulator, making the thing less efficient. If you double the speed, rotor current will be less, but bearing and brush wear will increase, and possibly over-rev the assembly.

[14p]

Thanks, I will take resistance reading on the rotors today, I believe the 24 volt is about 8 ohms, not sure the 12 volt.

[14p]

Why the finer wire of windings on 24v?

[Westcliffe01]

OK, for a different angle on this problem: Leave the basic alternator alone.


Change the rectifying section so that it is a voltage doubler. An alternator is basically just a 3 phase high frequency device. Here is a schematic for a single phase voltage doubler.



Forget about the transformer and just focus on the output of the transformer onward.


You basically need 3 sets of the voltage doubling circuit for the 3 phases of the alternator. You probably have enough diodes to work with but they may have to be re-packaged because they are more or less wired in place on the alternator to output regular voltage.


To provide sense voltage to the field winding you will need a source of 12V, so would probably have to add another rectifier to the second leg of the ac output on 1 winding so that you got a source of 12V to feed into the regulator.


This way, both field and stator windings stay as designed, the currents internal to both stay as they are and all you are doing is stacking the 2 out of phase voltage components on top of each other to double the voltage.


Disclaimer, Im not an electrical engineer, nor a marine electrician. Im sure there are more qualified people on this forum who could draw you a full circuit diagram to make this change. But I am putting this out there because it doesnt require your hardware to be changed or operating the windings in a manner that they were designed for.
I cant tell you what will happen to the current capability of this setup, but based on the laws of physice I have to imagine that double the voltage = half the current for equivalent power ?


Good luck, you should be able to do this without much additional hardware. Experts chime in please.

[Bycrick]

Voltage multiplier circuits are very common. But they’re normally used where you need high voltage, not high current. They work because the capacitor is able to store sufficient energy on one half-cycle to add to the voltage on the other half-cycle. I’m not going to look up the math, but I suspect that a capacitor that can store the energy of a big alternator would be quite large.

[Westcliffe01]

I think what you say is correct, but given that the alternator output is not at 60hz but a substantially higher frequency, I believe that factors back into not needing as large of a capacitor size as you might expect. But we would need to know approximately the frequency range from idle to 3000 engine rpm to be able to select the cap values.


Sounds like 300-900hz based on some Bosch data

[14p]

I guess I will take it to an alternator shop and have them put it on a tester and spin it up to a certain rpm and see what it does.

Thanks all

[betwys1]

Half the rotor drive current for 24V stator with 12 v stator so stator may put out ~ 8 volts.

[14p]

Can someone explain exactly what takes place from the moment I hit the starter and the engine turns the alternator? I am having a hard time visualizing something, I am sitting in the tractor its idling and air condition is off, I turn the air condition on and it works, the amp gage indicates a 5 amp or so draw, everything is good. But how is the alternator boosting power to run the A/C if the engine rpm did not increase to speed up the alternator rotor, its a direct conection from the crank to the alternator pulley I think?

[14p]

Back to what happens from the moment I turn the key and start the alternator turning, the rotor and stator make something happen... so the resistance is less on a 24v rotor than a 12v rotor, from what I gathered the 24v rotor has fine wire winding compared to the 12v rotors coarser winding and the 24v winding is two times as much as the 12v rotor winding? And correct me please if wrong, that the same goes for the windings in the stator, finer wire and twice the windings in the 24 volt stator compared to the 12 volt stator?

Trying to understand in SIMPLE language what the affect on the output to the battery is? Visualizing two tractors running same idle speed, rotors spinning same speed one has a 12v rotor and one 24v rotor, both are inside the same type of 12v alternator with its 12v stator, and being regulated by a 24v regulator.

From what I read here the tractor with the strait 12v alternator and 12v rotor will produce 24 volts because the 24v regulator is making the rotor spin twice as fast as it would with a 12v regulator, this makes the 24 volts.. but will heat up and blow the alternator up.

So now I am trying to understand what the difference is in the other tractor sitting next to it with the same 12v alternator but it has the 24v rotor installed in it, the only difference. That was my initial question, and a few have jumped in and answered that it wont make the 24 volts.

But the 24v regulator will try to get it to.. so I am wondering if the strait 12v alternator is going to be turning slower than the tractor with the the modified 12v alternator that has the 24v rotor in it?

So let me add a third tractor, it is normal and has a the correct 24v alternator and regulator. So its rotor will be spinning say 1000 rpm to keep it simple, calling this normal setup Tractor #1

The second tractor #2 has the strait unmodified 12v alternator, it is sitting there next to #1 and after a few minutes it goes kapoo because the 12v alternator got hot running at 2000rpm exactly double what it was meant to in order to output 24 volts. (I know 2000rpm is fine but just to keep simple)

Now the third tractor #3 has the modified 12v alternator with the 24v rotor the only thing changed, what the heck is that going to be doing? The last post says it may put out 8 volts.. just wondered if anyone knows for sure, I will try to find a shop to test this monday and see what it actually does.

Thanks for the help.

[14p]

Tried to edit last post and said cant after 30 minutes, so here is the edit I tried to post

So let me add a third tractor, it is normal and has a the correct 24v alternator and regulator. So its rotor will be spinning say 1000 rpm to keep it simple, calling this normal setup Tractor #1

The second tractor #2 has the strait unmodified 12v alternator, it is sitting there next to #1 and after a few minutes it goes kapoo because the 12v alternator got hot running at 2000rpm exactly double what it was meant to in order to output 24 volts. (I know 2000rpm is fine but just to keep simple)

Now the third tractor #3 has the modified 12v alternator with the 24v rotor the only thing changed, what the heck is that going to be doing? It has the 24v rotor with finer winding and twice as much winding as the 12v rotor that blew up, and its spinning up next to the course wound 12v stator with only half of the winding it normally sees in its 24v stator.

The last post says it may put out 8 volts.. just wondered if anyone knows for sure, I will try to find a shop to test this monday and see what it actually does.

Thanks for the help.

[14p]

Disregard the how it works part... found a good video, but still dont undrrstand the effects of fine wire vs coarse wire and how that 3rd tractor is going to turn out

https://youtu.be/olA3xTzQBkk

[Cadence]

JMHO, it is pissing up wind.

[Westcliffe01]

You turn on the ac, the demand (current) increases so the voltage drops. The regulator senses the voltage drop and increases the current to the field winding, making the magnetic field stronger, which then induces a higher current in the stator, the voltage rises. At some point it will exceed the regulator setpoint, then the regulator will decrease the field current and so it goes with the regulator trying to hold the output voltage constant.

Originally Posted by 14p

Can someone explain exactly what takes place from the moment I hit the starter and the engine turns the alternator? I am having a hard time visualizing something, I am sitting in the tractor its idling and air condition is off, I turn the air condition on and it works, the amp gage indicates a 5 amp or so draw, everything is good. But how is the alternator boosting power to run the A/C if the engine rpm did not increase to speed up the alternator rotor, its a direct conection from the crank to the alternator pulley I think?