Will Removing the Load From a Generator Allow it to Cool?

[forsailbyowner]

Ive built a windgen from spare parts and a pma alternator (generator). Its a 10si with 7 magnets. In the closed case the delco 10si is rated for 20 amps continuous output. Im concerned about burning up the stator in high winds. Ive installed a 20 amp breaker that trips at 27 amps. My question is if the load is taken off the generator (breaker trips) will this allow the generator to cool? or will it burn up like an alternator will? I think its the diodes that burn up in the alternator. Im more concerned with the stator. also considering installing the same pma on the engine with an open case and wonder what happens if the load is disconnected at full charge and engine is still running. I did some searches online but havent seen the answer. Thanks

[scoobert]

if there is no load on a wind gen in high wind, it will freewheel, and burn up. if high wind situation, you will need to stop the rotor.
in the engine, it will harm nothing.

[colemj]

Those Delco's are not closed cases - they have a fan that drives air through the case. I assume you have removed the fan to make the windgen, but it seems that the wind would simply blow through the case instead.

Mark

[Zil]

If you don't turn the blades out of high winds the whole thing will disintegrate into many small parts.

[forsailbyowner]

Ok first off the case is a factory closed case. Its standard on bobcats and some other industrial applications. Second the delco 10si is capable of withstanding 8000 rpm and simply spinning it fast is not going to send parts flying. As I understand it When an alternator is disconnected from load it makes big power that runs through the exciter circuit and burns out the diodes and or regulator. Im not worried about overevving the assembly. The blades are warranteed to 140 mi per hr wind speed so I dont think there will be problems there. If there is no problem in the engine compartment then I imagine there wont be a problem on the tower, I guess time will tell. It seems to be putting out just as I was hoping for. I get 7-10 amps at 15kts wind. At 20-25 Im thinking I will be putting out the 20 amps Im looking for. Heres the link to the closed case I purchased.

10SI Alternator Frames Hardware Wind Generator | eBay

heres a pic of the windgen so far. Still have to build a cone.



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[Jim Cate]

G'Day FSBO,

What AirX does for shutting down is not to unload it but to short out the output. Drops the rotation speed way down and does not hurt anything. I did the same thing on our old homebrew wind gen that used a DC permanent mag tape drive motor as a generator. IF the wind speed gets high enough I guess it might speed up enough to generate some power and overheat, but in really strong winds tying off the blades is a good idea just for safety reasons.

The very high RPM that you would get unloaded in high winds would at the least be noisy, the blades would be a hazard to anything near them and there would be bearing wear to consider as well as the possible voltage spike when unloading... all in all not such a hot idea .

Cheers,

Jim

[colemj]

I didn't know the 10si had a closed frame option. The normal ones have airflow through them. Catalog

Regardless of the max rotor speed and wind limit for the blades, have you ever been around a free-wheeling windgen in just 40kts? The blade tips and edges are screaming like banshees and the whole thing is shaking the boat.

You may be OK physically free-wheeling, but you aren't going to sleep well and the neighbors are going to be angry.

Shorting it like Jim suggests is good for up to some certain wind limit, but depending on your blades, bearings, etc you will still want a simple way to stall it or tie off the blades. Not really hard to do - just a piece of rope.

Mark

[forsailbyowner]

Yeah I lived with the airx with no regulation or braking and it got quite unnerving at times. When it cooked the stator the winds were gusting to 50kts. I am planning on making it possible to brake the windgen via shorting the leads manually with a switch but havent done the research to set it up for automatic braking. I have a diversion regulator and a solenoid I need to figure out how to make the solenoid shut off the power and short the leads, The longer blades spin much slower than the air x did. It may have a lot to do with more drag caused by the larger generator assembly taking more energy to turn it thus turning much slower at the same wind speed.

[OceanSeaSpray]

Disconnected alternators don't burn up, it is a misconception. What happens is that the open circuit voltage shoots sky high with no load and no current to keep it down. There is no power being generated, it just blows the diodes by exceeding their maximum reverse voltage rating.
In order to burn the stator, you need to run a heavy current through, i.e. attach a load. If you short the output, it will slow it right down and drastically reduce the amount of power it is able to produce - that is the underlying logic. However, if the wind gets high enough, then it could burn out. It is a question of whether it can get there or not.
If you open-circuit it, it will cool down, because it is not producing power, but the voltage will get extremely high. It needs to be able to withstand it. The insulation could fail arguably, even though I have never seen it happen myself.
Heating is largely produced by the current, it is the windings resistance multiplied by the square of the current. No current, no heating basically.

[goboatingnow]

I am aware that shorting a PM generator will cause braking. But surely with self excited alternators all that will happen will be the magnetic field will collapse and the alternator will not see any braking

Dave

[colemj]

The OP stated that he is using a PM alternator.

Mark