Author Topic: 9 lead to 12 lead (Read 5159 times)

robl · « **on:** June 07, 2006, 06:43:15 PM »

Hi folks

I'm currently running a small (500W) 240V/60HZ crossflow plant with a 1800 RPM C/2C generator. I've just picked up a very nice 1HP 1200RPM 208/430V TEFC motor with a 9 lead (wye) configuration.

Ideally, C/2C conversions want delta windings.

The three-part question is: (1) If I dig into the motor will the 3 common ends be easily accessible, or they likely varnished and buried somewhere in the slots?

and (2) what are the consequences of just running C/2C on the wye configuration.

and (3)possibly a very dumb idea; can I isolate and tape the three individual wye leads and then use the remaining three windings as a delta? I realize I will only get half the current out, but that should not be a problem. I'm more concerned about eddy currents and overheating.

Thanks in advance for help with this! I do have Nigel's book but it doesn't get into that kind of detail.

Rob

Ungrounded Lightning Rod · « **Reply #1 on:** June 07, 2006, 02:11:49 PM »

can I isolate and tape the three individual wye leads and then use the remaining three windings as a delta? I realize I will only get half the current out, but that should not be a problem. I'm more concerned about eddy currents and overheating.

Cutting out half the coils will increase the current and heating of the remaining coils. Depending on your operating speed, magnet size, and mill-to-battery-shack wiring resistance, the increase in heating could be anywhere from slight to as much as a factor of four. But expect it to be at least a factor of two unless your mill-to-shack wiring resistance is very small compared to that of the genny windings.

A genny will "try to provide as much current as you try to draw", but is limited by one of two things:

- Wiring resistance voltage drop

- Flux of the magnets.

If you're limited by wiring resistance voltage drop, cutting out half the coils means the other half are seeing less voltage drop in the wiring from the genny to the battery shack. (It's like you cut the wiring resistance between the genny and the shack in half.) The result is that the current in the winding rises - though not to double. The coil sees more heating - and heating goes with the SQUARE of the current. If the shack wiring resistance was large compared to that of the winding, you can approach doubling the current and quadrupling the heating. If it was very small you will see only a slight current rise.

If you were limited by the flux of the magnets - say, at high wind speeds - and effectively doubling the winding resistance by cutting out one set of coils isn't enough to pull you down into resistance-limited mode, the genny will continue to supply the same current. That means the current through the remaining coils will be doubled and the heating of those coils quadrupled.

robl · « **Reply #2 on:** June 07, 2006, 04:58:47 PM »

Thanks for the prompt reply, Ungrounded.

I've got about a 1000' of mostly #4 (some #6) to the battery shed, where the 240VAC is rectified to 48VDC. Based on my calcs, the wire resistance will not be a big factor at an average 2A@240VAC.

Research elsewhere shows that it will likely be a mess to pull the center of the wye out of the windings for re-connection.

I've got a electronic (MOSFET) current limiter in the DC rectifier circuit already (to keep the present rig from trying to run above rated current) so perhaps I can use that to keep excessive current draw from over-heating the new gennie.

Do you by any chance know why delta is preferred to the wye configuration when using capacitors to excite a 3-phase motor to be a 1-phase generator?

Rob

coldspot · « **Reply #3 on:** June 07, 2006, 07:50:48 PM »

"Research elsewhere shows that it will likely be a mess to pull the center of the wye out of the windings for re-connection"

Just what I used to think, thats USED TO !!!

I was sitting there waiting for machinist to return from lunch

and with only a razor blade as a tool, started cutting straight

across from the normal wires out point and with just a few cuts,

(to cut string that holdes it all together nice and pretty)

And just lifting the papers covering, quess what,

The hidden star conection!!!!!!!!!!

My very first try at doing this !!!!

This was on my

"Gould Century" 2HP 3 Phase, (That for some reason doesn't show in my Diary

But by clicking back to it using the "more Diary's" button about 3 times by now I'd bet

you can see it if you like)

The Baldor 2 HP 3 Phase, that I'd started out with doing didn't look

so friendly so I've yet to try cutting on it but will when I get more #29's in

to use on it now that the other ones ended up on the gould. lol

I borrowed a cool curved needle from girlfriends stash and after covering with black tape, I re-string tied it using my favorite sewing thead-

"Braded Fishing Line", used of course. LOL Man I love that stuff for just about

anything but fishing with, LOL. Re-Inforced All knife sheaths, with it after learning

how hard to cut it is! LOL

l8r

coldspot · « **Reply #4 on:** June 07, 2006, 07:51:33 PM »

Oop's

Forgot

What is

"C/2C"

??

Ungrounded Lightning Rod · « **Reply #5 on:** June 07, 2006, 08:01:38 PM »

Yes: You get more current out of it and higher efficiency.

With delta all three windings feed your output - one directly (resistance R, providing 2/3 of the current), two in series (resistance 2R, providing the remaining third), for an equivalent resistance of 2/3 R. Heaing for I amps is 2/3 * I^2 * R. One coil gets two thirds of the heat (4/9 I^2 R), the other two a sixth each.

With wye only two coils participate (and take all the heating) with an equivalent resistance of 2R. Heating is 2 * I^2 * R, split equally between the two live coils.

Thus for a given amount of current delivered, each of the live coils in wye gets more than twice as much heating (2 1/4 times) as the hottest coil in delta, while wye loses half again as much power total to heat.

Nando · « **Reply #6 on:** June 07, 2006, 08:59:57 PM »

Y configuration requires lower capacitance BUT much higher working voltage

DELTA configuration requires much greater capacitance BUT lower working voltage

You can run 1/2 Y and 1/2 DELTA windings arrangement

Also, one can rectifier both group of phases and place them series for 12 phase rectification, remember to calculate the sum of the voltages, 1/2 star & 1/2 DELTA.

Also, one can have two separated output voltage and you may use one to ge the C/2C connection as you want it.

2 controllers will be needed in common configuration connection .

I presume that you want to change to 1200 RPM, by changing the motor pulley, RIGHT ?

Why are you concerned with EDDY CURRENTS ?? and Overheating ?.

And why do you want to do such DUAL phase group connection ??

Stay with a single 2 phase, the motor should not be difficult to get the STAR COMMON connection

Nando

Flux · « **Reply #7 on:** June 08, 2006, 01:39:25 AM »

That type of conversion is usually intended for single phase ac loads.

If you are rectifying to charge batteries you would do better to use 3 phase with a 3 phase transformer( or 3 single phase) although it will need an extra wire the results will be better.

You could then use star.

If you want to find the internal star connection it is not generally that difficult, it shouldn't be in the slots, just taped up in an end winding. If you heat the winding to soften the varnish you should manage without too much trouble.

Flux

robl · « **Reply #8 on:** June 08, 2006, 12:24:41 PM »

Wow. Thank you all for your responses. It's like sitting in the cafeteria at school.

No choice now, I am going to crack the case and have a look for that elusive center connection, but will also test the partial connections option and take some readings. I have a crude MG test set available to put this gennie through the various wiring configurations. It uses a series of baseboard heaters as the load.

First, some replies to the questions that came up:

For Coldspot; C/2C is short-hand for converting a three phase motor to a one-phase generator with capacitors. As mentioned in the replies to my question, you put capacitance in parallel with two of the three windings and take your power off one of them. One capacitor on the first winding, twice that on the second, and none on the third.

For Flux; I'm stuck with 240VAC/60HZ because one the of the users runs directly off the plant at night. I've advised against it, but it's worked reasonably well for him the last 15 years or so. A current monitor blows the other 2 users off the system when he draws more than 100W. They're on chargers so they get their power when he goes to bed.

For Nando; I'm currently running a 1800RPM unit at a location that now has a relocated intake with less head. The 1200RPM unit will avoid the need for some drastic pulley ratios. My concern about overheating/eddy currents revolved (pun intended)around the fact that the unconnected Y circuits might negatively affect their neighbour coils even though they were not connected (or vice versa) through induction or whatever.

If you can stand it, I have one more question...

Is it possible to use the Y and D connections in parallel (properly phased of course)? This would be a fall-back if the center point is not accessible. Nando alludes to it, but I may be misreading things.

Rob

Nando · « **Reply #9 on:** June 08, 2006, 01:58:00 PM »

You can not parallel both Y & Delta with rectifiers diodes because the Y is producing 1.73 times the voltage of the DELTA configuration ALSO THERE IS A PHASE DISPLACEMENT between both sets of windings.

One type of 3 phase rectification is to have a Y and a DELTA in series to obtain 12 phase rectification

You may send the voltages separated to charge two different battery banks.

You can rectified each set and present a common negative and have to positive outputs with 3 wires coming from the generator.

You are assuming points that at not needed in your IDEA -- specifically the "unconnected Y windings without termination".

HYDRO NOW:

What is the old head and the new head, as well as, the water volume available the RPM change will be squareroot( head2/ head1)* RPMold & the power loss will be head2/ head1 * WATTSold .

The RPM of the BANKI needs to be "CALCULATED" to the new site parameters and the pulley size accurately defined to PEAK th power output of the generator.

Many do not do such work and the systems under perform by many % points -- many !!

Nando

robl · « **Reply #10 on:** June 08, 2006, 03:04:39 PM »

Blush. You've got me there Nando,

I did do the calculations, (lately I've been using the Excel spreadsheet available from The Microhydro group on Yahoo) but I admit to also buying three sizes of pulleys for the first install. I don't have the calculations with me now, but I expect I'll be swapping pulleys/measuring wattage once again for the new generator.

The thing I have the hardest time measuring/calculating for, is the average flow available. The rains in this part of British Columbia (Canada) are so variable that a 100% (or even a 300%) change in flow in less than two weeks is not unusual. Of course, at that point the head goes up as well. That's a huge change in power available. That's why I have a current limiter on this system; to keep from popping the generator breakers. I don't want to over-size the system for the peaks, since everything has come in by wheel-barrow or back-pack.

Regards

Rob

Nando · « **Reply #11 on:** June 08, 2006, 10:18:53 PM »

I see in your site that you have a 4 inch pipe down to the turbine.

Can you state the head1 and the the head2, and the SIZE of the Nozzle -- can you supply the Nozzle profile ?.

Your pipe defines the maximum water volume in conjunction with the Banki Nozzle and if you have a variable volume, you should have the Banki divided with different Nozzles for the variable water levels to keep the pipe filled all the time under all conditions and produce the proper RPM with the reduced power defined by the water volume changes.

So set your system to have different Nozzles for different water volumes.

The Nozzles should be sectional, like full, 3/4, 1/2, 1/4, 1/4 to accept what water level is available to maintain the right RPM and of course to limit the power drawn as the water volume determines .

Nando

robl · « **Reply #12 on:** June 09, 2006, 03:12:42 PM »

Nando,

To simplify my design I used a single manually operated flap/vane in the nozzle instead of partitioning both the nozzle and the runner and using multiple flaps. If time permits, I would really like to build a partitioned runner and nozzle. In the mean-time, I'll send the info and drawing you requested in the next day or so.

Regards

Rob

robl · « **Reply #13 on:** June 10, 2006, 12:11:39 AM »

Just a quick thanks for the help so far. It took about 10 minutes to find the center connection once I had the generator apart. After rewiring the 12 leads to delta I could actualy get almost 1 volt out of any of the two connections if I wrapped a bit of rope around the shaft. That was without any excitation. More appropriate testing to follow...

Nando · « **Reply #14 on:** June 10, 2006, 08:06:06 AM »

It seems that you have a motor with good remnant magnetization for easy C-2C capacitor configuration.

You can have two DELTAs working independent with one DELTA with bias capacitors.

My suggestions is to have both D in parallel, though you may not use the full power capabilities.

AN Induction motor as a generator may produce around 60 % power of the rated power as a generator .

Nando

robl · « **Reply #15 on:** June 10, 2006, 05:35:52 PM »

Well, that's that. Thank you for your help folks. Hopefully, I will be able to pass on the collective wisdom to the next person.

Per Nando's request...

H1: 20 feet (gross)

H2: 18 feet

Flow: 0.7 CFS average at H1

Pipe: 360 feet of 6" Schedule 40 PVC

Wheel: 12" Dia. by 7" wide

Approx H1 RPM: 300, gear belted to deliver 1800RPM/240VAC/60HZ

Nozzle profile below as low-rez jpg and available as a hi-rez psd in my files area.

G'day

Rob

robl · « **Reply #16 on:** August 31, 2006, 06:01:57 PM »

For archive purposes, I thought I'd update this thread.

I rewired the motor. belted it up to a 1HP variable speed 120VDC motor and fiddled with the capacitances.

Ended up with 10uF (C) between L1 and L2, 20uF (2C) between L2 and L3. At 240V, and very lightly loaded by a TRIAC diverter connected to a 240V 300W baseboard heater, the current into C was 1.25A, and into 2C was 2A.

The diverter was set to trigger at 240VAC. Frequency stayed between 60 and 65HZ, from no load to 500W. However the homemade DC motor controller may not have been too stable, so I'm not sure how that will translate to a real-world situation.

At no load (no diverter), at 1200 RPM, the voltage climbs to well above ~300VAC. Didn't fully test at that voltage because I did not want to blow up my 440VAC caps. The actual control box has 2A and 3A circuit breakers in the cap excitation wiring.

HTH

Rob

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