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

[markcouz]

Before deciding that all advice in the thread is nonsense it is worthwhile looking at how the alternator works and if it can be manipulated.

The alternator has a field winding producing a magnetic field of varying strength, controlled by the regulator. The regulator uses the information available on the sense wire connected to the alternator output to decide whether to increase the field/output voltage or decrease the field/output voltage.

If you are able to access the sense wire then you can quite easily manipulate the voltage that the regulator sees using simple electronics.

In my previous experience I wanted to raise the bulk stage output on a Mitsu Pajero from 14.1v to 14.5v (for dual battery charging when camping) - I did this by inserting a germanium diode into the sense wire which introduced a volt drop so that when the output was 14.5v the regulator saw 14.1v and it was happy.

If the OP is in dire straits and requires a 24v alternator that is not available via any other means then this would be worth trying and certainly better than a DIY rewire which appeared to be the direction he was moving.

A 24v alternator has voltages exactly double those of a 12v alternator, so this could be accomplished by using a voltage divider - with 50% of the output voltage being fed to the regulator sense terminal.

The biggest obstacle for the OP would be ensuring that the output power (volts x amps) never exceeds the original design, if he is able to control this aspect then there is no reason that this hack can't be carried out in an emergency.

[a64pilot]

Originally Posted by billgewater

Just don't apply 24 V DC to a 12 V DC starter motor. That's a recipe for disaster.

Surprisingly possibly due how short of time they are used most handle it just fine, many, many pretty much all of the old Ford 8 and 9N, Jubilee tractors have been converted from 6V to 12V by changing the generator to an alternator, the original 6V starter has handled this for decades.

There are even “fast start” kits for turbine engines that during starting it takes two 24V batteries and connects them in series for 48V, it then applies this 48V to the 24V starter generator to get the engine started faster
https://turbineconversions.com/produ...-start-system/

[witzgall]

Hi, Chris from Balmar here. I am not an engineer, but we have some pretty talented ones, and others that have been designing and building alternators for decades.

I will paraphrase some of what I have been told. Designing and producing an alternator that meets the target goals of output, heat management and reliability is based on solid engineering, but it also includes a fair amount of undefinable art.


We are just now introducing the 96 series 48v alternators. They are not on the chart yet, but I will share that the cut in speed for the 60a is 1200 and 2200 for the 100a.

What does this have to do with this tread? Getting good low-end performance is harder the higher the voltage goes. You would most likely be very disappointed with all put the top end performance of any one-off hand wound stator, and the chances of it matching the rotor well and working well as a package are very small. When designing the XT for instance, it was not a simple matter of specifying the windings, and the rotor ohms. it took many iterations before we had the right combination and design.

Chris

[The Sun King]

If you get a cheap Delco alternator, SI type, I think, with internal regulator, you can buy a 24v regulator module to swap the original. They are a few bucks on ebay. If you have an external relay, then an external 24v regulator will work.


Worried about the effect on the windings? I've had a couple of cars kitted with an extra alternator with 12v to field and no regulator. With a stick on the gas pedal the engine would buzz up and I'd have 120vdc to run power tools or lights. Never harmed the alternators.

[betwys1]

Originally Posted by SVSAVANNAH

it is my only choice, I'm in the boonies..... so I need to rewind the armature?


How do I calculate length and size of winding? what else do I need to do?

This was your response to the advice that you should rewind the field with twice the winding turns. A person that does not know a stator from a rotor, or armature from slip rings, would be well-advised to talk to a bus mechanic. Anywhere.

[skenn_ie]

1) Fit a 24V regulator. Run it at twice the speed (assuming it doesn't exceed the rev limit and disintegrate).

2) Fit a 24V regulator and run at the same speed, will work, but not efficiently. You might find that more current is going into the rotor than you are getting out of the stator.
3) Rewind the stator (rather than the rotor), with twice the number of turns (half the cross sectional area in the wire).

[Cadence]

Originally Posted by betwys1

This was your response to the advice that you should rewind the field with twice the winding turns. A person that does not know a stator from a rotor, or armature from slip rings, would be well-advised to talk to a bus mechanic. Anywhere.

Everyone's an expert! Whether they are or haven't got a clue.

[skenn_ie]

Not halve the diameter, halve the cross-sectional-area (divide the diameter by 1.4 i.e. root2)

[Axel Rappe]

Or you can just hook it up to a boost converter. Not as fancy or efficient as rewinding, but much easier. And cheap.

[skenn_ie]

Originally Posted by billgewater

Forgot to mention ..... what voltage are the engine instruments? But more importantly, what is the voltage requirements of the starter motor? Just don't apply 24 V DC to a 12 V DC starter motor. That's a recipe for disaster.

Starter motor won't be much of a problem, it will just spin faster and substantially self regulate. Solenoids, and especially heater plugs, won't last long though. Heater plugs, just a very few seconds.


As for a DC-DC converter, that would work if you put a gang of capacitors on the input side. The ripple on the alternator output could upset the converter otherwise.

[Cadence]

I went back to his OP. The best and cheapest solution might be to sell his current unit and buy a 24v alternator and not have a bastard.

[RaymondR]

Originally Posted by Cadence

I went back to his OP. The best and cheapest solution might be to sell his current unit and buy a 24v alternator and not have a bastard.

I read it that he's in a place which is not particularly over endowed with auto electrical service or parts suppliers and he needed a way to get by.

Whilst the 12V alternator he may be contemplating attempting to get to output 24V may not end up the most efficient of gadgets it could provide a contingency solution until he is at a place without the subject deficiency.

The easiest way to get the 12V alternator to produce 24V is to fool the regulator into believing it is only seeing 12V whilst the alternator output voltage is 24V. If the regulator has a voltage input terminal the fooling can be done with a zener diode.

The voltage sensing terminal is normally used to detect the actual voltage at the battery terminal. Any current through the conductor between battery terminal and regulator terminal will create a voltage drop and consequently the regulator is designed so that the voltage terminal only needs to see voltage with maybe an extremely small current. For this reason a zener diode is adequete to provide the needed voltage reduction at the terminal.

A 12V zener will block any alternator output voltage until at least the zener voltage is reached. After 12V is achieved the zener will reverse breakdown and the regulator will see only the output voltage which is above the breakdown voltage ie. output voltage minus zener voltage.

If excessive output current occurs and the alternator overheats this can be cured by placing a series resistance in the alternator. For the current and consequent high heat production a very high wattage resister is required. My normal solution to this problem is an air cooled resister made from a SS bike spoke.

Fix wire to one using a crimp lug and make a sliding connection to the other so that you can adjust the resistance by sliding the wire backwards and forwards. MOST IMPORTANTLY HAND HORIZONTAL IN A PLACE WHERE HUMAN CONTACT IS UNLIKELY AND WHERE YOU ARE NOT GOING TO SET THE BOAT ON FIRE, that bike spoke is going to get damned hot.

Some times you just gotta innovate like hell.

[GrowleyMonster]

Originally Posted by Lepke

I've made 48v alts out of 12v alts by changing the zener diode in the voltage regulator. But you only get 1/4 of the original amps (1/2 at 24v).

Before all the modern regulators, fishermen use to disconnect the regulator and control the brush voltage with a rheostat, but you have to change the setting as the battery is charged or the engine rpm changes. Any alternator or generator will make any voltage. But with a rheostat, it's easy to make a flash bulb out of your alternator.

I worked on boats with that setup, 32VDC and when you would set over you began at low engine RPM for the Rigman on the winch to engage and undog. Then he would lower doors to the water and the Captain or sometimes the RigMan if the Captain preferred to set his own rigs, would shove the throttle in the corner. If you forgot to turn around and adjust the sense rheostat you would soon be trying to stuff about 44 volts into the batteries. Once the rigs were on the bottom and the winches dogged off, the throttle would be pulled back to dragging speed, sometimes before then if the man on the winch couldn't stop the winch paying out with the brakes. So then you settled into the drag, working the try net, trying to find shrimp and turn on them, and if you forgot to adjust the voltage again it would drop because the galley fridge as well as bunk fans would be running, Radar and radios, and all nav lights and deck lights. New guys who didn't grow up with the old flat toppers caused a lot of problems cause they wouldn't remember to keep checking system voltage.


By the time freezer boats with stepped up wheelhouses were popular, we mostly had good automatic regulators on the 32VDC system and some boats had 120VAC generators for air conditioning, hold freezer, etc.



The alternators/generators that we used for the DC system would seldom give up the ghost even when abused. Mostly the batteries got cooked and occasionally 32V electronics such as fathometers (stylus on paper type) or LORAN (LORAN A back then) got fried. These were very tough, rugged, overbuilt alternators, not like what you get today that will go into meltdown as soon as you exceed ratings.



NOT a good idea to overvolt modern 12V alternators though it is simple to do so with a voltage divider on the sense wire. If you make it see 12V when the system voltage is 24V it will maintain system voltage. However I don't believe you can get away with limiting load to half the rated load at 12V. I think you need to derate a lot more than that if you want this to work for more than just a few minutes. The heat in the copper has a cumulative component to it. Remember your cooling is either a cheesy little fan in an open frame alternator, or none at all. I think expecting this to work for days instead of minutes will prove to be unrealistic wishful thinking. Can't say for sure since I have never done it.



By all means, try it. Then please please please report back with your results. I think you will set your alternator on fire but like I said I haven't tried such a thing and I could be wrong.


No, I don't think it is a good idea to connect a 1:2 transformer between windings and rectifier. Transformer design is somewhat frequency dependant. A 60hz or 50hz transformer won't work. Let's see... assume a 3 phase 4 pole anternator being turned at 2400RPM. That is what... 4800 cycles per minute? I make it to be 80Hz. MIGHT work. I wouldn't go there on a boat, maybe as a youtube experiment in the workshop LOL!



Can't find a 24V marine alternator? Okay, look for a bus or truck alternator. It will not be safe to use if you have gasoline or propane onboard! But it will charge your batteries. You may have to adjust or change your regulator if it is 32V but most truck alternators will be 24V. From bus parts it might be 12V, maybe 24V.


Many fishing boats will have 32V systems and you should be able to do something with a fishing boat alternator.


Another option would be to simply convert to 12V. Starter will cost some bucks. Make sure your wire and breakers and stuff is up to the doubled current required to do the same work formerly done at 24V. Does that sound practical? No not to me, either.



Finally there is the DC/DC converter to consider. The ones you see on amazon and fleabay are dirt cheap but mostly rated at 20 amps. Running them in parallel on different load circuits, one per circuit, is fine. Running more than one on the same circuit could have unpredictable results. You need to be able to supply high starting current to motors, and maybe high current to radio equipment when transmitting, and depending on your bank, maybe more current in bulk stage charging. Don't base your electrical system around these inexpensive and admittedly very cool and useful devices.


If you are just trying to save a few bucks I suggest you forget about it and buy a 24V marine alternator. You apparently have access to a computer. You will probably have to pay customs and stuff. Shipping will be either expensive or slow. Take your pick. Next opportunity you probably ought to have your old alternator rebuilt so you have a spare.

[14p]

Old thread but I am in the same boat. I have two tractors, both of the tractors are 24 volt systems, and use an old Delco 24 volt 50 amp 10DN style externally regulated alternator. I just bought the second tractor and it is missing an alternator, I cant find a 24 volt 10DN alternator to put on it, but I have a spare 24 volt rotor and a 12 volt 55 amp 10DN alternator in my '66 El Camino, I took the 12 volt rotor out of the el Camino alternator and put the spare 24 volt rotor in it, thats all I did was 12 volt rotor out of 12 volt alternator and stuck a 24 volt rotor in it. I wonder what it will do now when I put it on the tractor with the 24 volt external regulator, 12 volt alternator with no changes except for swapping the 12 volt rotor for a 24 volt rotor and bolting it up onto a 24 volt system tractor. When that 24 volt regulator sends field to the 24 volt rotor all should be good.. but I dont know if the 24 volt rotor will talk to the 12 volt stator and make power?

[skenn_ie]

24V rotor will produce the same field strength as the 12V one. Output is proportional to field strength, RPM, and stator windings so you would need to double the RPM in order to get 24 - 28V output from (designed) 12V windings.