Connections: Y - Delta ?? or ??

[behoof]

Well, after all sorts of issues and life in general I've Finally got the 3HP 3PH conversion in the air. No thanks to one of our horses finding it necessary to play in the guy wires, that hurt progress for a while. Anyway, it's finally up and running now for my question.

http://www.fieldlines.com/story/2007/8/27/51542/1469

http://www.fieldlines.com/story/2007/8/28/51444/7540

So it's in the air and spinning like crazy right now, high winds here.

It's clamped at battery voltage, 24 volt system, but only 3 or 4 amps output with surges to 7 or 8A.

It's wired Y and I'm trying to remember what it was that Zubbly told me about using Y, Delta or Jerry for advantage, but surely can't remember and can't find the notebook with all those notes in it.

So I'm wondering what might be a good course of action to increase output, if I can.

I've got Zubbly's chart from his conversion diary and it's what I use to make my connections.

Don't know much about Jerry connection or how it would apply here, if so?

This is the set up I made for my connections, so it's pretty easy to make changes.

The blade set I made are 12' diameter TSR 6, at least that's the design I used.

Below is a picture of the blades being balanced in the shop.

[Flux]

If it's going like crazy and you only have a few amps you need more volts.

From your figures it looks as though you need 1Y to get the most volts. Not sure what you have now. Going to delta will make it run even faster.

If you have it 2 Y then try 1 Y and see if that loads it more.

If that fails then try it into 12v and see if you can get some decent amps.

These motor conversions seem to have to go pretty fast and perhaps you don't have enough wind to get the sort of speed you need. Can you actually measure rotational speed, it is difficult to judge without some proper speed measurement.

I am not sure you have enough alternator to handle a 12ft prop. There are some things that didn't make sense on your lathe tests but I didn't have time to have a good look.

If I get more time I will have a closer look but you won't want a 12 ft prop doing much over 500 rpm before it becomes frightening.

Flux

[behoof]

HI Flux,

Thanks for the reply.

It is wired 1Y

Was thinking about just splitting the battery banks for charging purposes and continuing to use all my 24volt system as it is?

Matter of fact, I've got my fork lift batteries being constantly charged in sets of 12V banks, been working fine for me. I equalize them occasionally at 24V, seems to be just fine.

These big blades are definately different than my 5 footers on my PMDC's. The 12 footers should have been perhaps 10's I guess? Back when our friend Zubbly was with us he had told me 10' to 12' would be the ticket, so, as with most of us, I went with the 12's and here I am.

We've got some pretty serious wind going on right now and my observation of the blades is that they almost top out (can't give you RPM, couldn't get it to work)at, guessing here, about 200 - 250? Just a guess. Not as fast on the pickup and slow down either, didn't expect they would be, of course.

I remember Zubbly telling me that (I think) Delta, more amps less volts and vice versa with Y... is that correct? and I forget how Jerry or Jerry2 fits this

Skip

[behoof]

Also, I can't remember the formula Zubbly gave me for figuring cut-in on conversions but I do remember him saying and using his formula and arriving at a cut-in around 80 RPM's.

This is certainly not doing that.

[Ungrounded Lightning Rod]

I'd try unloading it momentarily.  If it speeds up more than about 2x then you're in stall from the load and you need to wire it for lower output voltage to raise the cutin RPM and get it moving adequately to stay out of stall until it's collecting a decent amount of power.

Dropping voltage goes in the sequence:

 1Y

 1delta

 2Y

 2delta

Delta may have extra issues from circulating currents (though a conversion may have good enough waveforms that they're not very large).  So I'd jump straight to 2Y and see if that makes the output current higher or lower.  If it improves things I'd try the deltas to see which is better, then try the equivalent jerry-rig to see if your waveforms are bad enough that jerry beats delta for a given voltage.

Jerry-rig consists of unhooking the three coils from a delta, rectifying them separately, and paralleling the rectifier outputs.  It runs at the same voltage as delta and doesn't have the circulating current losses.  But it does produce less current at a give RPM.  So if your waveforms are clean delta should beat jerry, but they're usually bad enough that jerry lets the rig speed up and ends up beating delta.

Of course if going to 2Y makes it worse it's an undervoltage problem rather than stall.  So then it's back to 1Y and solutions like 12V charging, transformers, boost converters, or rewinding.

[Flux]

Yes it is a bit difficult without rpm figures to know if you are stalled or running away.

My guess is that your cut in may be a bit high and the blades will not run the alternator fast enough to get the load on quickly enough to hold those blades back so it is more likely to be run away than stall.

If the blades are going like crazy and you have helicopter noises then I think the alternator is short of volts. If you try into 12v and things are worse then it may be stall but I really don't think you will get enough load to stall a 12 ft prop with only about 8A. If you can do so then it is incredibly inefficient and you may well need to raise cut in speed and trade low wind performance for higher output.

Flux

[behoof]

Thanks again for the replies.

I did find Zubbly's formula for cut in speeds.

(RPM / max volt) x System Volts = Cut in Speed

So for mine it's:

(1725rpm / 460V ) x 24 Volts = 90 RPM Cut in

That's according to Zubbly.

I've just switched it over to 12V but of course the wind died (naturally LOL)

Will probably lower tower tomorrow and switch to 2Y and see what it does.

If this helps, I counted 66 RPM and was at 25 Volts and I let it freewheel by pulling the fuses and it didn't speed up to any observable degree. Winds not cooperating now, of course.

Skip

[kurt]

did you bench test your motor conversion at a couple known speeds measure open volts in 1Y 2Y 1D and 2D before you put it up??? if not take it down and do so report back. then you can use math to calculate the best wiring plan to hit cut in in the proper speed range for your prop seems like i have had this conversation before about a year ago must have been someone else in irc.

[Ungrounded Lightning Rod]

I like flux's suggestion of switching to a 12V battery for your test.  Much quicker and easier than rewiring for other voltages.

If the problem is too low a voltage the current should (much) more than double and the total power will thus increase.  Then you can work on the too-low-voltage solutions (and never have to pull down the mill unless you decide to get it rewound or change the blades).

If the problem is stalling the current will only rise slightly - less than doubling -  and the total power will decline.  Then you can go back to 24V and try the lower-voltage wiring arrangements.

[Ungrounded Lightning Rod]

Zubbly's formula assumes the magnets produce a field about the same as the operating field of the pre-conversion rotor.  That's a pretty good approximation.

On one hand the Neos on the conversion can drive the stator core to saturation while the motor would normally have run a tad below saturation, which boosts the induced EMF (i.e. the open-circuit output voltage) a bit.  On the other hand the voltage drop from drive current and wiring resistance means the motor's back-EMF was somewhat below the line voltage.  The two work in opposition and come close to canceling.

[behoof]

Just as a side note:

When I shut it down even when the wind was kicking pretty good this thing would allow the blades to BARELY rotate, I mean barely.

Don't know if that means anything in the equation but wanted to mention it?

Skip

[TomW]

Thats normal, behoof.

Without motion on the magnets there is no braking so it must move to be braked. Weird as that sounds.

Just my experience. A few RPM or so.

If you had the cable it might be worthwhile to run the leads down temporarily til you sort it out. Or just getting it on the bench for some controlled tests might be the quickest route to an answer.

Tom

[bob golding]

if you designed it for 24 volts dont make the mistake i made  and try and get too much power out of it at 12 volts. i dont know if this will be a problem with a motor conversion i am not familiar with motor conversions so it might not apply.

cheers

bob

[behoof]

well, got it back up after rewiring it to 2Y.

I have a little bit of wind going on and am watching it and visually comparing the rpm to what I saw before at 1Y.

I've also got it wired as a 12Volt system using 6 100aH SLA's.

I could count on less than one hand how many times I've seen this actually reach cutin.

It just looks like its stalled up there, even in a pretty good wind... we've got 10-15mph gusting to 20mph today so I am getting to see movement anyway.

I've tried while it was spinning at it's fastest to disconnect it both by opening the DC side and by just plain removing the wires from the bridge and didn't see any appreciable difference in rpm either up or down.

Also, doesn't seem to make any difference wether hooked as 24V or 12V (obviously since not reaching cutin anyway).

Also when shutting it down it does stop and only rotate very very slowly.

I guess my visual on it is, " While watching it, when considering the current windspeed relative to the trees and such nearby, it should be moving considerably faster." Of course, I've never worked with blades this large so am not really familiar with what I SHOULD be expecting.

Appreciate any input on this, TIA.

Skip