I can't get my 80sp out of stall

[windyrock]

I have an 80 sp on  24v with 12*800 a'hr batteries, running the house via an outback invertor. The mill runs 3 ph down the pole to the shed, about 50 meters, is rectified with 3*35 amp recitifiers on a large heat sink. From the rectifier, through an amp meter then direct to bank. The c40/60 is wired seperately direct to the battery.

The system normaly generates 18-19 amps.

Something has gone wrong recently and I just cant find it. The mill is currently rotating @ 170 hz producing 5 amp in a strong wind. Pull any one phase wire off a rectifier and it will quickly accerate up to 400 hz generating 18 amp. Connect the phase back in and the machine will holds its revs for about a minute and then die back. This works for any phase. I've changed rectifiers. I've used a car rectifier. The rectifiers all test ok. All wires are checked back to the mast.  The head looks ok. There is no effort to spin the blades. I've crossed/shorted the phases with the mill on the ground and there is definantely alot of resistance which disappears when the test short is removed.

Another thing I could never work out which could be related. When the mill was working properly I was playing around with motor 50 uf 400v capacitors across the phases(all I had). This made the mill die away as well to about 5 amp from 18, which when removed, the mill would reaccelerate.

I live on a remote (windy) Is off New Zealand, own gernerator, big farm, few resources etc.

Several other mechanical problems had developed with my set up, the bearing had spun on the shaft etc. This has all been tidied up, the air gap is right now etc. I'm beginning to suspect the old 2m dia 2 blade wooden prop. It is hard to start, I useually have to give it a spin on the ground to get going. If it does come out of cog on a windy day by itself, it will rotate very slowly in severe stall below generteing range. It will generally sulk for a long time like this, but once a gust gets it into the 150 hz plus range it can accelerate to over 500 hz in furl.

I think the problem is either;

1.   Some sort of phase short that only occurs when current is flowing
   
2.   The rebalanced mill is taking to much grunt and blades cant cope
   
   

I would appreciate some advice if anyboy can see something obvious.

Regards

Windyrock.

PS Your board is incredibly usefull when you live in a remote place.

[TomW]

rock;

Ok, first. Many of us may not know what an 80 SP is [I don't]. This is why it is generally good to never assume your audience knows all the same abbreviations and acronyms you know.

So, first thing you should do is tell us what that is. With that information the chances of a useful answer increase dramatically.

My first guess is shorted bridge. which short the turbine.

TomW

[commanda]

80SP is a Fisher & Paykel, the one wound with 0.8mm wire, re-connected so the series coils in each phase are halved and re-connected in parallel.

Failing all else (having already replaced the rectifiers) I'd be suspecting the cable run, especially in the drop down the tower. Or, if there are any joins in the cable run.

Disconnecting the cable from both ends, attack it with a megger.

Amanda

[windyrock]

Thanks Amanda

Yes; it is a home wired 80SP Fisher & Pykel.

If there was short between phases in the tower (highly likely, the wire is about 15 years old and seen a few windmills out), wouldnt this show up as a high resistance when I spin it by hand?  I've cliped a test wire between any phase and when I turn the mill by hand there is a real resistance. Take it off and it spins (fairly) freely. Is there such a thing as a partial short that gets worse as current flows?

By attacking it with a megger, I understand that I should pull the wire out of the tower, get both ends together and use an ohms meter to check for infinant resistance on each phase?

Thanks for your comments

windy rock

[commanda]

If the cable has been there for 15 years, the chances of it being the culprit is looking more and more likely.

A megger is basically a high voltage ohm meter. Typically they run at 500 volts.

Disconnect both ends of the cable, and measure between each pair of wires from one end.

An ordinary multimeter, with its low voltage, may not show up any fault.

Amanda

[windyrock]

Thanks for that Amanda. I dont have a megga, but will when I next get to NZ. I will pull a new wire through the pole with the old one. It will eliminate one issue.

Thanks

[oztules]

can you explain option2... rebalanced mill.

As an aside: If you use capacitors on this mill it will stall the blades (as you have found). It will generate higher power at lower rpm, and thats why it stalls the blades.. you will require larger blades to balance the new rpm/torque requirements of the new configuration in that case....which is not this problem.

A single coil group with shorts in it may be able to produce this extra load on the mill and pull it into stall.

With 7 groups of windings with 6 poles per group, 1 cooked / shorted pole could unbalance the 42 pole config.

It seems odd that 1 phase can put out the original output of the three without over revving to do it. (when you disconnect 1 phase and it does 18A at the usual 400hz)

.......oztules

[joestue]

Check to see if ONE of the cables is shorted to the tower.

You don't need a megger, this is not an open circuit. Use a light bulb and battery.

[Flux]

I can't help feeling that you have always been very close to stall and something has changed enough to tip you over the edge.

Normally a burnt coil will stall the whole thing but with the F & P with its long poles and high leakage reactance you may still be able to run it single phase with a bit of a short somewhere.

Any change in the air gap from bearing changes may tip you over the edge. I don't know about these things but I thought you could move the magnet forwards partly off the stator so you should get it out of stall if you can do that.

Your reluctance to start also suggests that the prop is low in torque and perhaps slight damage to it such as erosion on the leading edge may have aggravated the problem.

I have a feeling that you have always been in stall but in the past you had enough torque to get up to the region where reactance comes in and you got through it.

If there is winding faults it will get worse, otherwise I think a better 3 blade prop will help all round.

Tom is right I had no idea what an 80sp was, always give all the details.

Flux

[oztules]

one other thing,

Have you recently tidied up your wiring, used heavier cables or anything else which would inadvertently lower the line resistance of your system?

If you have, try a small resistance in the line and see if that solves the problem.

.....oztules

[windyrock]

The mill ran through a 60 knot plus wind the other day, as it was home made I left it up to see how it would go. Real dumb. I wont do that again. It survived but a phase came off in a connection in the mast, the bearings spun on the shaft, two wires came off in the windings and the leaves and twigs that went through the blades made some decent chips etc. It was taken down, bearings packed and glue, the stator re soldered and re centred, wires up the pole to the head rerouted, tied off etc. After this the mill spun silently and I suspect capable of more power as the bearings were probably an issue for a while.

I was looking at the stator this afternoon, wondering how I could test it for faults on the pole, as you know there are 42 home made soldiers that vibrate/ rub etc...

What I didnt mention is that I had a 100 sp mounted whilst I was doing all this. As it was a new head, all the performance changed. The funny thing was the capacitors worked better on this stator, probably as the blades were going faster/more power as you pointed out. The cut in speed was to high so I went back to the 80 sp and the fault was immediate. I put it down to the 100sp blowing the bridges, so changed all that etc.

I will now look hard for a shorted cooked pole but it isnt obvious. In terms of the output, as the mill accelerates with a phase wire off it is going through 15 plus amps when I hook the 3rd phase back on and it jumps over 20 amps, settles back to 18 for a bit and then dies off. Goes for any phase wire removed ie it will duplicate this with any two phase connected to the bridge, the third pulled off. Would the mill behave this way with a group shorted?

If one of the groups disconnected or shorted would the mast vibrate more or make a noise?

Thanks for your help.

Regards

[oztules]

I think Flux has it nailed.... try a bit of resistance in the line and see if all comes back to normal, and then perhaps some blade maintenance/mods.

[windyrock]

Thanks Flux; You are right about the prop, it is off a very old whisper 600, a single piece two blade without enough root to get it going. I will buy some 3 blade chinese ones from ecconovation this week. However when it does get going it can really move, clocking over 800 hz whilst I was playing around with my furling system a while back. I use a tilt back, now furling around 400 hz (circa 800-900 rpm). I did tidy all my wiring up, it was all over the place and this fault generated a lot of house keeping. The problem is I have used a shotgun fault analysis and with so much change I've lost my way forward logically.

So in summary it is a busy day tomorrow. Change the wire in the tower, iot eliminate internal shorts and shorts to the tower. I don't want to pull the stator off as it is difficult to get it back with the right gap, but I will if the rewire down the pole doesn't work. I hate the thought off totally re soldering it. Maybe I will put the 100 sp back up at that point and see if the problem persists.

Sorry about the termination, I'm using ecconovations terms for the F&P, I wrongly assumed they were used outside Australasia.

Regards

[windyrock]

By a bit of resistance, is this before or after the rectifiers and how many ohms would you suggest trying. I have some old 20 ohm coils off an old lister alt.

Thanks

[oztules]

After the rectifier,before the battery bank.

 1 ohm will drop 20v@20A. so you don't need much just to tip it out of stall, but may be enough to allow you to beat the stall.

This bit i haven't got up to personally, just aware of the theory... I have not required it.

Flux would know how much to experiment with to see if it can temporarily get you out of stall till you fix the prop.

[wpowokal]

One should add here for the un initated, a meger places a high voltage across two wires that are not connected. In the case of a motor or generator between a winding and the frame.

If there is a short, ie connection because of a fault (breake down in insulation etc), the higher than normal voltage (typically double that which the cable/motor normally runs at) at low amperage will show on the metre.

Further if one is using a meger only the cable or in the case of a motor the motor windings should be tested. Disconect all controls, capacitors etc or you will very likly loose the magic smoke.

allan down under

[windyrock]

Thanks everyone for your help. It turned out to be the blades. I put a variable resistor (big wire wound version off a lister alternator battery charger) in line on the positive dc side. Strong wind here at the moment and the mill eased up to 12.5 -15 amps with the blades going in and out of furl @ about 800 rpm.

Volts are up to 40 ac. The resister is hot, in excess of 220 deg c on my IR gun.

It runs fine there, if I jumper lead the resistor out of the circuit, volts drop back to 23 ac and amps are up around 19 dc. The mill will hold this indefinately until the gust goes by and drops back into stall. Violent gusts wont get it back up until the resistor is put back on line. The battery is sitting around 24.4 v and the house is using 1.4 amp @ 240 v. I have a new set of blades on order.

Regards

Tony