120-volt AC alternator ?

Is there such a thing ?
I imagine you would need a pretty sophisticated voltage and frequency regulator.

https://www.youtube.com/watch?v=QHRpA_xeFjM

Didn't watch all the way through, but the thing to keep in mind about that method is the frequency of the output was shown as about 300Hz at the beginning of the video. That may be fine for lighting, but will probably raise hell on anything with a power supply on the front end, like a TV or computer. AC motors aren't going to like it either, but they'll spin REALLY fast.

Depending on what you want to do a heavy duty inverter fed by a high amp 12v alternator is probably a better bet.

Not real cheap though

Exactly. An inverter can produce clean 60hz power. A home generator produces usable power by maintaining specific speed….not realistic for any sort of automobile alternator.

In the 1980s there were several add on 120/240 volt belt driven AC generators sold for pickups and service trucks, but a quick Google search does not bring up any currently sold.

I owned a Honeywell Redi-Line motor generator.
It was a “synchronous 12 volt motor” that was directly shaft coupled to a 1600 watt 120 volt 60 Hz AC single phase generator.
They had 1000, 800 and 400 watt models

It held 60 hz very steadily and the unit would not start running until it “sensed” a 120 volt AC load.

You hooked it directly to the battery terminals so that the battery amp-hours of capacity supplemented the alternator output.

Weighed about 40 lbs.

Worked without a hitch until stolen out of my truck tool box by a thief

When I had my 1985 Dodge Charger, it blew the fusible link. I measured around 120 volts at the alternator - I didn't believe it. Hooked up a 100 watt drop light and it fully lit up. So for sure they can put out 120 volts...............

Interesting, thanks gents.

I was pondering that you could drive any variety of common electric motors/pumps for some purpose.

Electric fan, water pump, maybe oil pump, maybe even A/C.

I'll look into invertors. In any case, all the energy would come from, and be limited to, the high current alternator.

Running an AC motor is VERY frequency dependent without a VFD (expensive) so an inverter is definately the way to go. A battery is likely required to be in the system in order to stabilize the current, but of course that’s already there in an automotive application.

You can't. The frequency is way wrong. I forget how many poles a typical alternator is, but its quite a few. I am repurposing an old Leece Neville 24 volt to do DC motor interpole testing, and our target is to get 400 hz out of it at 100 amps. You can't drive an alternator slow enough to get 60 hz and get any reasonable output.

The only AC motor that might work is a universal AC/DC motor since the speed is voltage not frequency dependent, but it would have to be de-rated due to the higher frequency. Higher frequency = more impedance = more internal motor heating.

So in short……your thread title “120 volt AC Alternator?” Is answered by stating a typical home portable generator HEAD (the part the motor drives) IS a 120 volt alternator, it just has to be driven at constant and specific RPM in order to produce usable power for things like motors and electronics.

PacNWcuda,

Yes I figured a fundamental problem for an engine-driven alternator would be the engine RPM

It all depends on needs. Alternators can be converted to A/C usage. Demand is critical. Most devices need a form of regulation. 60 mhz needs to be by rpm or electronic control. Tractors can run generating units off a three point. It mostly depends on what you want to do?

Bingo in bold. Using a set up like this to power things won't necessarily get you anywhere, since the alternator can still only deliver the same amount of max power. High volts gets you lower amperage, which does get you smaller wires, which can be an advantage sometimes.


Don't forget the guy in the video is using a pair of step-up transformers to get to 120vAC. Coming out of the alternator I would assume it's closer to 30?vAC. By using the step-up transformers, he's trading amperage for voltage. Power drawn remains the same

If given the choice between a 12v water pump directly off the regulated output from the alt, or a 120v water pump with a setup like in the video, the 12v will be more efficient since it doesn't have the conversion losses

I was never a GM fan but, I recall that some late 70s early 80s caddies had fluorescent lights and an alternator that did provide 120 volts to run them. No idea on frequency or amperage.