# Alternator Output Question

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Rane
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Alternator Output Question

Hi, I was wondering if it would be possible to get (or build) an alternator with an output of a somewhere around 70 volts and 250 amps. I've seen alternators with the amp output I'm looking for, however, I've not seen any with a high amount of voltage. How would I go about making an alternator with that amount of voltage? Is it even possible? I'll be honest, I'm really new to this level of electrical stuff... Any ideas, suggestions would be really appreciated.

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Re: Alternator Output Question

17.5kW output? I'm pretty sure no alternator puts out that kind of power...

Alternators are usually 12-14V because that's what cars' electrical systems use.

In theory, you could rewind one with five or six times the number of turns, but then you'd have to use wire with 1/5 or 1/6th of the cross-sectional area, drastically increasing resistive losses. Higher resistance would either mean the thing fries from the heat generated at 250A, or even that it won't be able to generate 250A at all.

What do you want this for, anyway?

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rgx
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Re: Alternator Output Question

Actually, it's not really that complicated, but it will be big, heavy and expensive. An alternator (generator) at 70 V / 250 A works the same as one at 12 V (or 15 V, rather) and 100 A, only it's bigger. I guess you want 70 V rectified output (DC), which means the AC voltage will be around 50 V. Unfortunately, that's not a very common voltage. You might find a synchronous machine built for 110 V AC and 250 A, and use a lower excitation current to get around 50 V AC. That will however be a big machine, perhaps around 100 kg. Also pulling 250 A rectified DC will heat the windings more than 250 A sine wave, so better get something capable of a bit more. Even bigger. At that size, the machines are likely to be three-phase, so look for something like 110 V and 3x100 A 3-phase.

I was also contemplating the possibility to overvoltage a 28 V alternator from a truck (not US, they run 12 V, but the old world has 24 V). That includes a lot of risks though, and alternators for cars in general have bad efficiency. The biggest I saw were 180 A so you would need two.

A motor/generator shop might be able to rewind a 110 V machine to 50 V, so you get something smaller.

Finally, guessing you are contemplating some kind of series hybrid or large battery charger setup, you could let a 110 V machine power a DC motor controller (such as the Zilla). 110 V AC rectified is around 150 V, which should be within reach for many controllers. Even Kelly has one that takes up to 144 V (168 V). Then you can get any voltage you want from 0 - 150 V.

Rane
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Re: Alternator Output Question

Finally, guessing you are contemplating some kind of series hybrid or large battery charger setup, you could let a 110 V machine power a DC motor controller (such as the Zilla). 110 V AC rectified is around 150 V, which should be within reach for many controllers. Even Kelly has one that takes up to 144 V (168 V). Then you can get any voltage you want from 0 - 150 V.

This sounds like what I'm looking to do. Like I said, I'm new to all this, so my comprehension is really fuzzy; to clarify what you said: 110v alternators are available and a controller (man, that Zilla is expensive!(though, that's to be expected)) will be able to regulate the correct voltage to the electric motor as well as control it...? I looked at some 110v alternators, but the sites I looked at didn't specify the amount of amperage they could produce. The electric motors I've seen say that they will take a maximum of 250 amps, which, I'm sure is more than they would or should be fed on average. So (I guess this is where I'm try to go with this), a 110v alternators, run through a controller, should be able to run a decent EV motor (and a car with it)?

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Re: Alternator Output Question

to clarify what you said: 110v alternators are available and a controller (man, that Zilla is expensive!(though, that's to be expected))will be able to regulate the correct voltage to the electric motor as well as control it...?

Not really. He's suggesting you use a motor controller on rectified mains power to charge the batteries. I think. But since it sounds like you're trying to make a series hybrid (gas engine powers electric and charges batteries) that's not going to help you...?

You could used a permanent magnet motor like it was an alternator. But, that's not cheap; an Etek-RT (about the only motor I can think of that would be suitable for this) will run you \$500. You wouldn't need a controller to charge the batteries, though, since you could gear the engine to make the motor put out the right voltage.

And, yeah, the Zilla is quite pricey, but that's a performance controller. Unless you're building a sportscar, you won't need anything near that kind of power.

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