Automotive alternator question

[MeanListerGreen]

Are automotive alternaters uni directional?  What happens if they run in the opposite direction?

[MacGyver]

The alternator will work fine spun in either direction BUT the cooling fan is optimized for one direction so cooling may suffer if you spin it backwards.

[MeanListerGreen]

Ahh, that is something I didn't think about.  I was considering a project to light a small shed using scrap I have laying around.  I have an old wind turbine roof vent, an automotive alternator, and a cheap convertor so you can see where I am going with this.  It would spin both ways so I just wanted to make sure nothing would get fried if it did.  I wonder how hot it would get just recarging a battery if it was spinning in the wrong direction?  Also I think the alternator has an internal voltage regulator so I'm not sure if that matters much?

[t19]

Automotive alternators are optimized with cooling to run in one direction.  Of course that direction changes when you put the car in reverse, but as that is normally only for short duration it does not bother it in automotive operations.

[MacGyver]

Automotive alternators are optimized with cooling to run in one direction.  Of course that direction changes when you put the car in reverse, but as that is normally only for short duration it does not bother it in automotive operations.

Uhhh.. your alternator turns a different direction when the car is in reverse?  So, ummm, what are you driving these days?

[sid]

O.K// I think///I would like to see that//sid

[MacGyver]

Automotive alternators are usually very inefficient, and the field winding draws a substantial amount of current just to energize the damned things. I doubt you'll get very much (if any) usable power from a turbine wind vent driving a car alternator.

I'd probably hunt around for a nice small permanent magnet generator or motor that you could use instead of the car alternator. I think you'd have better luck.

The good news is at the low power level you'll likely get from a roof vent turbine you wont likely have any problems with alternator cooling, even if the fan spins the wrong way.

[t19]

I was joking.... damn you guys are too serious

BTW my skidoo is a 2 stroke, and to get reverse you press a button, and the engine stops, changes direction

The alternator is working cause the lights and stuff come on

[LowGear]

For real, Global Moderator.

The Skido slips the timing a couple of clicks and runs the engine backwards?  And the starter?

I hate to doubt you after rescuing me from my big mouth this week but what a fantastic wrinkle in the gray matter.  I caught the reversing alternator fan gag and I have seen Bultacos back fart into counter revolutionary operation because the timing was too tight or wrong.  And then there's steam and electric vehicles but this is a really great idea.  I wonder what top speed in reverse is?

LowGear

[listerdiesel]

Two-stroke engines that were stopped and reversed are quite common, and SIBA did a thing called a dynastart that enabled such things to happen.

Alternator cooling:

While a car alternator fan is indeed optimised for one particular rotation, I believe that Lucas and CAV had fans for both directions available. I have also seen these with the fan taken off and turned around and put back on again. Unless you are running at the max output of the device, then it wouldn't be too critical.

Truck alternators have bi-directional fans, just straight blades so run both ways.

We bought a nice AC203 bus alternator a few months ago, that is a sealed unit with fan on the back blowing air over the casing, bi-directional again. 24V 60A or comfortably  over a kilowatt output.

Peter

[LowGear]

You could pull the fan off and stick (literally with epoxy putty) a 12 volt computer fan on the back.

Low Gear

[Grael]

Right now I run a delco-remy alternator in reverse with a elcheap-o 6.5HP engine from princess auto to charge batteries, it works OK. Need to replace it about every year or so because it pushes about 30-40 amps continuously and a max of 60, and we use it daily so its kinda hard on it...

We also have a ski-doo that runs the engine in reverse for reverse...

[ronmar]

There is a reason you don't see too many alternator wind plants.  The only places I have ever seen them used is in really big rotor/fan configurations, or someplace with a real large surplus of wind. 

Unless you have some pretty large blades to generate the torque necessary to gear the alternator up to a useable alternator RPM, I don't think you are going to get any thing out of it.  The alternator needs over 1000 RPM to really start generating, and several thousand RPM to get anywhere near it's rated output.    Most of the folks growing their own wind plants are also making their own permanent magnet generators as they can generate power at lower RPM and don't require a gearbox/gearing to achieve optimum generator RPM.   

Good Luck

Ron

[listerdiesel]

Absolutely true, Ron, but why bother with 200W or so of power?  surely if you're going to the trouble, you might as well go for a kilowatt at least?

I've got the power curve for the AC203 somewhere, it starts pumping about 1300rpm and goes up to 8500rpm, so 3000rpm is probably a good figure to work on.

Peter