AC from alternator

550Doug · Dec 20, 2011

On a thread below it was mentioned that an alternator produces Alternating current, but the diodes changes it to DC. If the diodes are removed could the AC be used to power a small 120v electric pole saw? If so, then could 2 alternators be installed, one to charge the battery with DC and the other to generate AC?

Bob Huntress · Dec 20, 2011

Intheory, but, I don't recommend trying. First, you would only get 60 hertz at 3600 rpms, allbe it at the alternator. How many amps does your pole saw draw?

David G · Dec 20, 2011

The alternators are 3 phase, and doubt they could handle the wattage or voltage for a saw.

LJD · Dec 20, 2011

There are already dual-power alternators made for that use by Prestolite/Leece Neville. DC and 120 volts AC with voltage controls. Often used in emergency vehicles.

With a standard auto alternator, you can barely get 5-6 amps at 120 VAC.

It is MUCH easier just to use a cheap DC to AC inverter hooked to your battery. The ones that Harbor Freight sells are cheap and surprisingly rugged.

This 1000 watt inverter will do what you want and more. $75. Will handle 3000 watts of surge.

http://www.invertersrus.com/pwrb1000.html

Anonymous-0 · Dec 20, 2011

No,it produces low voltage ac.

Janicholson · Dec 20, 2011

And they make 3 phase, not friendly to a single phase saw.
Ford used a AC output 3Phase alternator on Thunderbirds to make gold film impregnated glass defrost. IIRC they ran 135 to 150 VAC, Jim

buickanddeere · Dec 20, 2011

If it worked and was practical, there would be numerous converted automotive alternators powering "everything".
As previously stated. A beefy 150+amp alternator,deep cycle battery and a high capacity 12VDC inventor to 120AC.

RayP(MI) · Dec 20, 2011

They used to sell a retro-fit kit to take AC off some early alternators. Would only run small motors, and not very well at that - maybe just the thing for a mobile crock pot???? AC wasn't true AC.

John T · Dec 20, 2011

Doug, it can be done, an automotive alternator typically produces a three phase AC output and it can be used to power a small AC appliance BUT THATS NOT WHAT THEY ARE DESIGNED FOR AND THE THE VOLTAGE AND FREQUENCY REGULATION PLUS AVAILABLE CURRENT LEAVES A LOT TO BE DEISRED IN MY OPINION......I used to have an adapter for a car alternator to power a drill etc and it wired to the alternator and had a standard 120 VAC 15 amp NEMA 5-15R receptacle. Seems like I used it once and its probably still hidden somewhere in my shop

A factory 12 VDC to 120 VAC Inverter produces much better frequency and voltage regulated power so if I had to run an appliance from an auto I believe thats the route Id take also.

John T

MarkB_MI · Dec 20, 2011

Why do you think you need AC to run your pole saw? Chances are it uses a brush-type motor and doesn't care if it sees AC or DC.

Now, the AC power from an automotive alternator is three phase, not single phase. Also, I suspect the frequency at typical speeds to be much higher than 60 hertz. So even if you really need AC, you're not going to get 60 cycle single phase power out of an auto alternator. (Well, you could tap a single phase if you wanted to, but the frequency would still be wrong.)

Back in the days before cheap portable generators, it was common to make generator sets using lawn mower engines coupled to car alternators. If you bypassed the regulator, you could get around 90 volts DC, which was good enough to run small power tools. It makes no sense to do this today, when you can buy a generator at Harbor Freight for less than two hundred bucks. (Of course that HF generator is garbage, but it's no worse than the homemade genset.)

old · Dec 20, 2011

If you fry the V.R. in an alternator it can/will produce well over 90 volts and that is enough volts to be unsafe to a human was shown that when I was taking a college course in electronics

greygoat · Dec 21, 2011

I had a kit on my 1965 "Scout",that gave 110
volts A.C. to run a saw or electric drill. I
purchased it from an ad in "Popular Science
Magazine" It was called "Tote-A Volt". Perhaps
they're still around. Sold the Scout in Sept.

Indiana Ken · Dec 21, 2011

I have an old converter kit that was for use on a vehicle to obtain 120 volts from the alternator to run a drill etc. As stated in another post brush type motors (typical of power tools) will run on AC or DC.

The converter box had two 120 volt outlets, a volt meter and a two position switch labeled; "Tool" and "Auto". In the "Auto" position the alternator regulator sense wire was disconnected from the battery, causing the alternator to go to full output. The procedure was to set the switch to "tool" and adjust the engine RPM to obtain 120 volts or close to it for the load you were trying to run.

The kits were best at 1) burning up your alternator, 2) burning up your power tool or 3) burning up both your alternator and power tool simultanously.

I would part with my kit for a the right amount of cash - currently it is completely fried inside so I know it worked last time it was used.

Anonymous-0 · Dec 21, 2011

A 60 alternator will put out just under 800 watts

A drill or saw use around 6 amps (HD ones more and LD ones possibly a little less - my number for amps is on the low side) at 120 v that equals just over 720 watts running - more on startup.

I guess anything will work for a short while.

Generally electric motors don't like being starved for voltage although some variable speed motors handle it better plus the fact that A/C electric motors in general don't react well to a different frequency.

The result more heat which equals a shorter life for both the generator and the tool.

An inverter would be better as it can draw additional power from the batteries making the drill run cooler at the right voltage and current flow - assuming a big enough inverter.

Bob M · Dec 21, 2011

(quoted from post at 21:22:45 12/20/11) Intheory, but, I don't recommend trying. First, you would only get 60 hertz at 3600 rpms, allbe it at the alternator. How many amps does your pole saw draw?

Bob - I agree - don't try it!

A few comments:

Most (all?) automotive alternators are 14 pole. Running at 3,600 RPM the AC output frequency will be 420 hz. The effect of this high frequency on a motor designed for 60 hz is uncertain - but it definitely WILL NOT be good(!)

Automotive alternators generate 3 phase AC internally. But since your load is single phase AC, somewhat less than 50% of the alternator's rated power output (watts) can be utilized.

Finally voltage regulation will be a problem. In 12 volt DC service an alternator depends heavily on the battery to provide "ballast" that helps regulate output voltage. A custom VR would need to be designed to modulate 12 VDC to the rotor field winding and control the AC output.

DaveK(IN) · Dec 21, 2011

How does an auto alternator produce three phase power? I thought most of them have a single wire output.

jackinok · Dec 21, 2011

you can buy them,also welders made using alternator.BUT theres a reason they are not common,just like other folks say.much simpler to just buy 12v tools,or install a inverter.

JMOR · Dec 21, 2011

(quoted from post at 11:10:32 12/21/11) How does an auto alternator produce three phase power? I thought most of them have a single wire output.

he 3 phase is rectified internally and only the DC is on an output terminal.

Ken Macfarlane · Dec 21, 2011

A few mistakes in the responses:
-Alternators are not single phase, but are 3,4,5,6 phase. I think 6 is the highest I've seen before.
-You can't get usable A/C out of one for running normal a/c stuff
-All those converter box (old style) just allow the voltage to increase to 120 v DC (or what ever you excite it too) so you can run lights and so called universal motors, the ones with brushes like drills and grinders.

leej · Dec 22, 2011

(quoted from post at 21:56:27 12/21/11) A few mistakes in the responses:
-Alternators are not single phase, but are 3,4,5,6 phase. I think 6 is the highest I've seen before.
-You can't get usable A/C out of one for running normal a/c stuff
-All those converter box (old style) just allow the voltage to increase to 120 v DC (or what ever you excite it too) so you can run lights and so called universal motors, the ones with brushes like drills and grinders.

concur on the DC aspect, but a dozen rectifiers??? No $h!t?

AC from alternator

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