alternators in series

robbymax

Hi I need some advice, I have built a DC generator using 2 x 24 volt alternators what would be necessary to hook them together to charge a 48 volt battery bank can they just be wired together in series or would there be a problem both the alternators are isolated from each other at the moment they charge half the bank each but that can unbalance the 48 volt bank please tell me they wont go bang

ChrisOlson

Re: alternators in series

No, you cannot hook them in series. Bridge rectifiers do not work like batteries. To use them on 48 volt you will have to replace or rewind the stators.
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Chris

mike95490

Re: alternators in series

robbymax wrote: »

... please tell me they wont go bang

they go Pooofff

Cariboocoot

Re: alternators in series

Actually, depending on exactly what the alternators are and how they are wired it can be done.

However, it would appear that now you have two entirely isolated DC 24 Volt outputs, one feeding one half of the battery bank and one feeding the other half with a common +&- connection in the middle. As there would be no improvement over this arrangement there's no point in changing things around.

ChrisOlson

Re: alternators in series

I think the question was whether or not robbymax could take the positive output from one alternator and feed it to the frame ground on the other one, and then use the positive from one and the negative from the other to charge at 48 volts. The answer is no. You'll instantly blow the diode trio (used for exciting the field) and the regulator out of the one hooked to the positive side. The other one won't excite at all unless the first one develops a dead short in it, and then you'll blow the diode trio and regulator out of that one too.
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Chris

Cariboocoot

Re: alternators in series

ChrisOlson wrote: »

I think the question was whether or not robbymax could take the positive output from one alternator and feed it to the frame ground on the other one, and then use the positive from one and the negative from the other to charge at 48 volts. The answer is no. You'll instantly blow the diode trio (used for exciting the field) and the regulator out of the one hooked to the positive side. The other one won't excite at all unless the first one develops a dead short in it, and then you'll blow the diode trio and regulator out of that one too.
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Chris

And the difference between this and what he's doing now is that the positive to negative connection between the two generators is made at the same midpoint on the battery bank. Although there are other wiring schemes that will work, as I said; no advantage to changing anything.

ChrisOlson

Re: alternators in series

Cariboocoot wrote: »

And the difference between this and what he's doing now is that the positive to negative connection between the two generators is made at the same midpoint on the battery bank.

Right, and what he has right now is two 24V sources each charging half the bank, so the bank gets unbalanced. Once you remove that midpoint connection, the frame ground is common on the two alternators and the over-voltage wreaks havoc with things. If you want a single 48V source to prevent bank imbalance problems, then the best option is to rewind the stator in one of the alternators, and put a permanent magnet rotor in it to convert it to a 48V unit. This eliminates all the problematic stuff like the wound field (which will draw too much power and burn it out on 48V).

The problem with 48V in small units like a Delco 10SI/12SI frame is the size of the wire you can fit in the stator core for 48V. The largest is going to be 18 AWG with a 14 pole claw-type PM rotor. BTDT before, and they're only good for about 10 amps (500-600 watts). If you got a big Leece-Neville, then you got a real alternator and it can be done and get some real power from it. But be prepared to spend $800+ on a Leece-Neville 24V alternator that can be rewound for 48V.
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Chris