| Author |
Message |
Bill Gerrie (209.50.74.134)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 19, 2004 - 10:02 am: | |
Hi Guys
Does anyone of the electronic crowd out there know what would happen if you were to use a 24 volt rated alternator on 12 volts. Would it work as if it were a 12 unit because it is only getting 12 volts or would it just not work as it should. I have a 24 volt unit and was just curious what would happen or would I be better to get a 12 volt unit. Thanks for your help. Bill |
TWO DOGS (65.179.208.155)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 19, 2004 - 11:34 am: | |
12 volt g.m. one wires are$150.00 for a 140 amp... |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 19, 2004 - 12:55 pm: | |
The big difference between a 12 and a 24 volt alternator, if you aren't talking about current capacity or the regulator, is that the rotor winding has a lot more turns in it, thus it takes a higher voltage going to the rotor to create a given output voltage than would a 12 volt alternator.
In simple terms, this means that on a 12 volt alternator, it might only take an excitation voltage of 4-5 volts going to the rotor winding to get 12 volts out of it at full load. But on a 24 volt alternator it might take 9-10 volts or even more on the rotor to get 12 volts out of it at load.
Bottom line, if the alternator is an "internal regulator" style, don't even try it because 12 volts won't even get the regulator going and even if it did it wouldnt work properly. But if it's an "external regulator" style and you stick a 12 volt external regulator on it, there's a fair chance it might work. If it doesn't, nothing would be harmed.
Cheers
Gary |
DonTX/KS (66.82.9.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 19, 2004 - 1:24 pm: | |
I went to a rebuilder with three used Delco 12v alternators, they converted them to 24v one wire for a little less than $50 each. I used one for an emergency backup run off the cam pulley, one on the genset for no really good reason other than I had it laying there.
As stated, I think a 24v rotor was about all they really had to change. |
Bill Gerrie (209.50.74.122)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 19, 2004 - 5:50 pm: | |
Thanks Guys. I just got a rebuilt 24 volt GM 300 amp alternator with a separate regulator from a guy and I just wanted to know if I could use it in place of the 12 volt one on an 8V71. It just seemed a shame to put it on the shelf to collect dust. Bill |
Phil Dumpster (24.16.243.37)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 20, 2004 - 7:03 am: | |
Both the rotor and the stator are different between 12 and 24 volt alternators. This is not including the voltage regulator.
Given two alternators of the same power output, the rotor on a 24 volt alternator will have about four to eight times as much resistance as the rotor on a 12 volt alternator, so that the field power remains the same, all other things being equal. Hence, where the 12 volt unit might get excited at 4 to 5 volts, it will take 8 to 10 volts on the 24 volt unit. For exact numbers, you'd have to do a bit of math to compute ampere-turns multiplied by the number of turns to get the same field strength in webers.
Also, the stator on the 24 volt unit will have twice as many turns as the stator on the 12 volt unit. It will use wire half the cross-sectional area of the 12 volt unit, and be rated at half the current.
If you need to rebuild an alternator, you can rewind it for 12 or 24 volt operation. Hell, you could rewind it for 240 volts if you really wanted too.
As far as using a 24 volt unit at 12 volts, yes, you can do that but you have two issues to deal with. You will only get half of the power output that the unit is rated for. That is, if you have a 300 amp 24 volt alternator, which normally produces 7200 watts, you can run it at 12 volts but still have to obey the 300 amp rating, giving 3600 watts. You will also need a regulator which can supply the higher voltage needed by the rotor to produce an equivalent magnetic field. Older mechanical regulators could usually do this, but it's a crap shoot whether a newer solid state unit can.
You'll have to try it to see if it will work. |
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