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

[Scaramanga F25]

UPS et all deliver worldwide.

[phorvati]

All your answers are here.

https://documents.pub/document/alter...dbook-ocr.html


Once you digest whats written in this book you will have all your answers. You will probably realize its easier to get a 24V alternator.

[lvictorlucas]

Originally Posted by SVSAVANNAH

are you saying just hook it up to a 24v regulator and it will just work????????

the alternator part just generates ac voltage which is rectified by some diodes. The voltage regulator which are external on some alternators and internal on others selects the voltage. Almost all voltage Regulators will put out a lot more voltage then 24 volt. Back when we used to bypass the voltage regulator to power some power tools. The major problem is overheating so keep an eye on the temperature.

[Mike Banks]

Simply put a 1:2 transformer before the bridge rectifier and voltage regulator. Even simpler is to fit a 24 volts voltage regulator.

Simple is not always good though.

But you would be better to get a 24 volts truck alternator from a wreckers and marinise it if necessary. Most are of marine quality bearings and windings anyway. Lots more amps and much more reliable. Get one that has a remote adjustable regulator, so you can easily fine tune it to suit whatever kind of batteries you are using.



.

[trikola]

There are also options for voltage doubling by some clever circuit with diodes and capacitors. Requires that you bypass the internal rectifiers of the alternator. Ref https://en.wikipedia.org/wiki/Voltage_doubler.
(May be this has been mentioned before - I just dropped inn before reading the whole thread)

[Cadence]

Originally Posted by trikola

There are also options for voltage doubling by some clever circuit with diodes and capacitors. Requires that you bypass the internal rectifiers of the alternator. Ref https://en.wikipedia.org/wiki/Voltage_doubler.
(May be this has been mentioned before - I just dropped inn before reading the whole thread)

That is BS for his intent.

[lvictorlucas]

Originally Posted by Cadence

That is BS for his intent.

This is ONLY practical for very low current, nothing close to what he needs.

[Reefmagnet]

The whole thing is impractical. It's like trying to convert a 120VAC alternator generatore to 240VAC. Possible? Maybe. Practical? No.

[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.

[billgewater]

How is it that you have a 12 V DC alternator on a boat that is wired for 24 V DC? This seems rather weird to me. 24 V DC wiring is certainly a bit unusual.

These Balmer series alternators are rather expensive but they do make a 24 V D 140 Amp model (9504-24-140) See internet. But there are many manufacturers. Mounting is usually the main problem to be solved and the independence of the earthing as most marine systems try to avoid earth loops. Matching pulleys/belts etc. are also an issue.

If the boat has a 12 V DC alternator installed and you are just pursuing 24 V DC for an instrument, then there are voltage-doubler circuits available. These can be rather simple or sophisticated but generally they have low current levels.

If it is an instrument issue maybe you should check its power requirements. Many instruments will run on 12 VDC up to 36 VDC. Read the fine print!

However, if you have two 12 V DC batteries you can charge them (using the 12 V DC alternator) in parallel i.e. each battery is connected to the incoming 12 V DC supply. This means that the positive terminals of each battery are joined together and each negative of both batteries are also joined together. If you then "rewire" these two charged batteries so that they are in series then you will get 24 V DC. This requires that the negative of the first battery is connected to the positive of the second battery. 24 V DC will appear across the positive of the first battery and the negative of the second battery. If you do this then the switching needs to be done very carefully and I would definitely consult an expert who will be able to provide the specialist switching. (Multiple pole heavy duty switches may be needed.)
If the 24 V DC is only needed for something like an anchor winch, then this method may be applicable.
I certainly would avoid playing around with the innards of any 12 V DC alternator. Rewiring is a specialist business and there are thermal issues. involved as well.

[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.

[wingssail]

Originally Posted by SVSAVANNAH

Thanks all, I have my answer: more but thinner windings.

For me it is about using something that I happen to have.

Sometimes it does not make sense to plow ahead with an idea which, on further investigation, turns out to be a bad one.

You might get an alternator shop in Indo to rewind it. I did just that in, Pedang, Indonesia, (Sumatra). It was a dirt floor shop but supposedly the best guy in Sumatra. But you are unlikely to get satisfactory results. I didn't. The number of windings may be wrong, the size of the wire wrong, or several other things may foul up the results. In my case the alternator worked but the output was about 60%, and I wasn't trying to change the voltage. Later, In Mauritius, I had it done again and that time it worked.

So, in the best case, you'll find a shop, they will do something, and it will work and produce 24 volts.

And in a few months it will fail and you'll be back where you are now; you'll need to find a used 24v alternator from a bus, they have them in Indo.

Worst case it will never work.

In either case you are probably wasting you time and money.

Notice these log book entries: Sept 19 Alt rewired in Indonesia, November 20, alternator failed in Mauritius, Dec 22, rewired in Mauritius, and it worked.

[Wotname]

Crikey, there is a lot bad advice and nonsense spouted so far in this thread; so much so that I won't even bother to address any of the dross floating around.

A couple of good salient points have been made but (IMO) by far the best advice is that below from wingsail.

If the OP reads it, they should heed it!

Originally Posted by wingssail

Sometimes it does not make sense to plow ahead with an idea which, on further investigation, turns out to be a bad one.

You might get an alternator shop in Indo to rewind it. I did just that in, Pedang, Indonesia, (Sumatra). It was a dirt floor shop but supposedly the best guy in Sumatra. But you are unlikely to get satisfactory results. I didn't. The number of windings may be wrong, the size of the wire wrong, or several other things may foul up the results. In my case the alternator worked but the output was about 60%, and I wasn't trying to change the voltage. Later, In Mauritius, I had it done again and that time it worked.

So, in the best case, you'll find a shop, they will do something, and it will work and produce 24 volts.

And in a few months it will fail and you'll be back where you are now; you'll need to find a used 24v alternator from a bus, they have them in Indo.

Worst case it will never work.

In either case you are probably wasting you time and money.

Notice these log book entries: Sept 19 Alt rewired in Indonesia, November 20, alternator failed in Mauritius, Dec 22, rewired in Mauritius, and it worked.

[Boatwright]

I see this thread started with you in Indonesia.

Unless you are far away from any engine repair at all you might find it worthwhile to ask around. Countries that are far from 1st World sources of supply are usually very good at fixing things with what they have on hand. As other posters have mentioned 24V systems are common on large diesel equipment (bulldozers, large fishing boats, etc.).

I once saw some guys in a small Mexican village fixing an old-style voltage regulator using a big nail connected to a battery as a soldering iron.

[RaymondR]

The question was "can you make a 12v alternator into a 24v alternator".

The answer is yes but it may nor make a very good 24v alternator.

Some of us cruise in places where an extensive range of parts and services is not available. Being able to source a commonly available 12v auto alternator and have it put out say 20 amps at 24 volts for battery charging might prove a capability worth having.

I use a motor speed controller to control the speed of two 12v auto radiator cooling fans which I have in plywood pieces which fit into my deck hatches. I have used motor speed control devices in parallel with the regulator in an alternator to regulate output voltage and current. If I was to blow a regulator I would be able to use it to manually regulate battery charging.

Sometimes one just has to be a little unorthodox to get by and in that case it does not hurt to have a little knowledge of the possibilities.

I have used a 2.2 kw AC genset and an inverter welder to crank my engine on my previous boat. It would start the engine but blew the capacitor each time. Sometimes you just gotta innovate.