Inductance of Coils

[Electrobent]

I visited my local friendly scientific instrument tech and he got out his LRC meter and measured the inductance of the three coils in my 20" 48V front Golden Motor Hub.  The units are micro Henries (uH).

Between Green and Blue: 578 uH

Between Blue and Yellow: 550 uH

Between Green and Yellow: 705 uH

Does this make sense to anyone?

Thanks!

[Leslie]

No!  IMO their is too much difference between the readings.

What model do you have?

Mine all test 850uh almost on the dot and mines is a Model: HBS36R. and its got 200 watts stamped om it.

[Electrobent]

HBS48 with 1000W stamped on it.

[Leslie]

I think blue has a short in it or the winding is paired wrong. 

Stop running this on your controller or it will be the next thing you have a problem with.

[Electrobent]

can you please say more about what it means to be "paired wrong?"

[Leslie]

My motor I believe has 6 enamel windings together that run around the motor in a WYE configuration like this.  You might have 8 per phase.



To make what I am saying easier to understand.

What if we took one enamel wire input from G and one from B and swapped them and joined them to opposite parrallel phase groups


EG. 5 Blue wires paired with one Green wire and one blue wire paired with 5 green wires.  


We then would have a reversed polarity winding going through both G aannd B iron cores and a reversed polarity winding running parallel to the series WYE to blue.

The reverse polarity windings over an iron core from my best guess would hammer down the inductance and give a little back through the series wye to blue.

But your test could indicate something a little more complex going on as the experience is shared on mixed phase wires to a varing degree.

So this pairing problem could be happening half way through the stator on any number of poles and corrected anywhere beteeen the start and the WYE convergence.

[Electrobent]

I did not realize that the arms of the Y were broken.

There are three groups of 8 wires coming together to connect to the 3 phase wires in my motor.

So it sounds like maybe 2 groups of 4 are swapped. 

So my inductance measurements are of 4 coils.  Two in each arm connected through the center.

Two are low and one is high.  So maybe the outer coils (in the Y arm)  of the two low ones are swapped?

Mybe I can fix this with a soldering iron?

[rolf_w]

... Two in each arm connected through the center. Two are low and one is high.  So maybe the outer coils (in the Y arm)  of the two low ones are swapped?

This is not how these motors are wound. As I tried to explain earlier (http://goldenmotor.com/SMF/index.php?topic=1218.0):

• The motor is star connected
• the bundled 8 wires are (0.54mm) strands of the same conductor
• The motor has 46P51S (poles and slots) and the winding pattern is AaABbBbcCcaAabBbBCcCAaAabBbcCcaAaABbBCcCcaAabBbcCcC
• The conductor for each phase is one 'arm of the WYE' and has no internal interruption/connection. All 8 strands are wrapped around the 17 teeth in one go.
  maybe this illustrates it better http://www.youtube.com/watch?v=CabZEejbeKA

Thus I can't imagine that a phase winding is 'wrongly assembled'. But what can easily happen is that the varnish came off and part of the winding is shorted (winding to winding or winding to stator). This might show up in an unbalanced resistance or inductance (have you checked insulation/resistance between phases and stator?). I had the impression, however, that the induced voltages (back emf) of the 3 phases were quite equal (a sign of no winding shorts)? The firing pattern of the Hall elements does look ok but the phase voltages seem not perfectly symmetric.

I briefly watched your video. To me it looks like:
wrong timing or
single phase winding failure

If you have a Magic Controller (or some RC controller) available you could try it in sensorless mode to sort out the wrong timing issue. I would try this anyway to be sure the fault is not some other effect of your controller.
If the coils 'leak' , you better go for a new motor, its much cheaper then trying to rewind (probably GM replaces you the stator for free?).

[Electrobent]

Would not a short from worn off varnish show up on a regular ohm meter between the coil and the stator? 

Mine are wide open on all six accounts "0.L" on my digital multimeter.

What if a letter got skipped or upper and lower case switched in the process of winding the motor.

Explaining the three pretty sine waves I got when running it as a generator is tough--could it be generated in a correctly wound coil and just come back through the center tie point of the WYE?

And my conditions were not exactly scientific--I don't know that the RPMs were the same on the drill but I do know I did not mess with the knobs on the scope between shots.

[Bikemad]

Would not a short from worn off varnish show up on a regular ohm meter between the coil and the stator? 

If the winding was shorted against the stator it would show up, but if it was shorted against another part of its own coils, it would have a reduced resistance as the length of the winding/s bypassed by the short would be effectively removed from its overall length.

Alan
 

[Electrobent]

but what would cause a coil to rub against another coil?  It looks like they are wound pretty tight without room for flopping around.

[Leslie]

Im rewinding a motor today.  I knew about the star wye and I had a post ready to go but I have this damed PC soft off next to my enter button and shut down the computer before I posted it.  Its happened to me a few times.  Ive removed the key now.

It looks worth rewinding them to me, as I have found motor winding copper for $30 a KG.

AaA BbBb cCc aAa bBbB CcC AaAa bBb cCc aAaA BbB CcCc aAa bBb cCcC

Is that correct?

The A stands for one direction turn and the a stands for the opposite?

I notice there is and big A and big B together and there is a one AaAa, aAaA BbBb, bBbB CcCc, a cCcC  series strings in there.  This seems odd but not from looking at the windings.  I get lost as you can imagine and wil;l mark it as I go.

I'm ordering a sensorless controller today and wondering which is the best way to rewind this hub for the best results.

I can get any diameter copper.  ATM my hub has 6 X .5mm strands wrapped around the cores with space left for another when added makes 3mm.  I was thinking maybe I could use 7 strands and do the winding carefully or maybe 5 strand of .62.

Ive read that the thicker copper allow for more room on the poles.

But maybe thicker windings will be more difficult to wind or have less thermal disipation.

Any ideas as what I should do?

[muzza.au]

G'day Leslie,

I found the following on ebikes.ca and I think it is relevant.

On the Crystalyte website, you'll see a large number of motors listed and characterized like 406, 408, 409, 4011. The last digits refer to the number of turns of copper around each stator pole. So for instance, a 406 has 6 turns, the 4011 has 11 turns.

The torque that is produced by one of these motors varies in direct proportion to the total current flowing around each pole. So in the above case, a 406 motor with 15 amps flowing through the winding has a total of 90 amps around the pole. The 409 motor would need just 10 amps to have 90 amps around the pole and hence the same torque output.

One false and oft-repeated conclusion is that therefor the 409 is a higher torque motor than the 406 because it can produce the same torque with fewer amps, or likewise more torque with the same amps. This is not the case. All 400 series motors can deliver exactly the same torque at exactly the same efficiency. The lower winding count motors just need more current to do this, but because they have fewer turns of a shorter length of heavier gauge wire, they can handle high currents with minimal loss. To use a concrete example, lets compare a 404 with a 408. The 408 has twice the number of turns than the 404, so the copper wire in the windings has 1/2 the cross sectional area and twice the length, for a total of 4 times the winding resistance of the 404. For a given torque output, the 408 needs only 1/2 the amps, but because it has 4 times the resistance the net electrical loss (I2R) is exactly the same.

Another consequence of having a larger number of turns around each stator is that the voltage induced in the winding by the passing magnets is increased in direct proportion to the number of turns. So for instance, at a certain speed of rotation, the 408 motor will produce twice the back-emf voltage as a 404 motor rotating at the same RPM. To power a motor, the battery pack voltage needs to be greater than the back-emf voltage, and so the 408 motor needs twice the voltage to spin at the same speed as a 404. However, it will only draw 1/2 the current, and you can see that the net power input (Volts * Amps) remains the same.

You have to decide if you want a speedy or torquey motor.

Muzza.au

[e-lmer]

I have this damed PC soft off next to my enter button

I hate where the home key is on my work keyboard, I keep
hitting it when I mean to backspace.

I took a paperclip and bent it to fit under the key so it's more
springy than the adjacent keys.

I did the same thing for caps lock.

Now I can use them, but I have to really want to and hit them hard.

[Leslie]

Ok that was handy.

 

It reads same torque for all motors and says nothing about speed.  I am guessing that it just a speed increase at the expense of efficiency and the lower turn motors run well on lower volts.

Because the wife has almost toasted this motor with shopping I think I will go for more turns and same thickness coil.  I read somewhere if you can get the turns tighter you can get the same speed and more efficiency due to the higher inductance with the more turns.

The heat is what I am concerned about and I will settle for a few less KPH for a more efficient motor.  The higher resistance should slow the current flow up somewhat and keep the heat down.

By using a rubber mallett I may be able to squeeze one more turn on this baby.

The controller I will be ordering be a 48v 1000 watter so I am also considering an extra parallel winding too.

What if one was to wind 6 tuns on the fist pole 5 turns on the second and four on the third pole?

Or would this make it run rough as hell?

Would this in effect give more grunt at the beginning of the firing and give more speed at the end?