GM car alt 120 volts dc.

[Jerry]

I have a costomer at my car stereo store that has 6 batteries wired in sires for a hydrolic system.

Normaly he disconects all the batteries and charges them one at a time. He asked if there was a way to leave all conected as 72 volts and charge them while driving the car.

We discused using an inverter and a home built 72 volt chager....actuly 84.6 volts.

All that seemed rather expencive, ineficient and bulky. One of our SPL compition show cars has three 140 amp alternators on board.

After remembering this and the mods I've made to car alts we decided to go with a modifide 63 amp GM alt.

I did a bench test today on a modifide alt. At 2600 rpm no load it was making 120 volts. Loaded down with a 500 watt halogen bulb the voltage droped to 77v.

This was the Hornet alt with a single NEO. I'm thinking I'll get more power with a stock alt. That rpm was at the alt. In a car the drive pully on the crank shaft is aboutr 6" diameter. The pully on the alt is 2.5".

From this I would expect the alt rpm to be more than 3 times the engine rpm?

I'm thinking that the alt comes stock at 63 amps. This means that each phase contributes 21 amps. Because I've seperated each phase and gave each phase its own fullwave bridge rectifier and a 20,000 UF cap. I've built 3 seperate dc power supplies. Then wired them in sires. This tripels the voltage of one phase but reduces the amperage. So the 63 amp alt now becomes a 21 amp alt but at much higher voltage.

This is the same upgrade I did on the Hornet but with higher voltage caps and of course much higher rpm.

More test to come but looking for 21 amps at 84.6 volts.

                       JK TAS Jerry

[Gary D]

Hi Jerry, depending on how often the fellow uses his hydrolic system, you might have to incorporate a dump load to save the batteries. Or another option would be a disconnect like an a/c compressor clutch disconnecting the alt. shaft on a toggle switch, letting the belt freewheel when the battery bank is full? Love your experiments! Hope this makes sense to you, could be I'm just thinking of a potential problem that won't exist....  Gary D.

[Jerry]

I'm thinking of incorperating a switch to the rotor coil to shut it down.

Will do an amp meter to track power out and maybe a varyable voltage supply on the rotor to adjust output.

                           JK TAS Jerry

[Gary D]

Cool Jerry, glad you are thinking ahead of the bench testing to the real world usage. Thought you would get around to it, just wasn't sure of you're approach... Hope all works out as planned. Gary D.

[electrondady1]

hello jerry , i 'm curious as to the amp capacity of the diodes you used.  can you speculate as to the output if the alternator was turning at 1020 rpm?

[Jerry]

Maybe 1/2 not sure. I think maybe at 12v this configuration might be doing 400 to 500 watts?

During my wind test I saw 540 watts from the GM alt at 40 mph but I have no idea what the blade rpm was. This was direct mounted and at 12v.

                   JK TAS Jerry

[Jerry]

PS the bridges are 35 amp. I  used 3, one per phase.

                        JK TAS Jerry