building a manual wye/delta switch!

O

olaf-lampe

10 kW
Joined
Mar 27, 2008
Messages
710
Location
Germany
I'm getting some naked 7kW colossus motors these days and plan to wind them with all six phase wires connectable outside the bell.
This way it's possible to use a manually shifted wye/delta 'gear-box' without the expensive relais'.
1st gear ratio would be 1.73:1 and 2nd gear is 1:1
Has anyone built something like that before?
I have some thick copperbars and pertinax plates I will use.
I would hide the box somewhere and mount a remote stick combined with 'throttle interupt-switch' like a suicide shifter for Choppers. 8)
http://www.google.com/images?q=suicide%20shifter&rls=com.microsoft:de:IE-SearchBox&oe=UTF-8&rlz=1I7ACAW_deNL361NL361&um=1&ie=UTF-8&source=og&sa=N&hl=de&tab=wi&biw=987&bih=422

Will make a sketch and post it here soon.
-Olaf
 
Olaf,

A wye-delta switch isn't the same as a mechanical gear change.

It produces a change in Kv, which is equivalent to switching to a different battery voltage. So if you already have enough battery voltage, a wye-delta switch is just like changing the throttle setting.

There are second order effects on controller efficiency and phase current limits, but the main effect is like a throttle and battery change. It doesn't make the motor efficiency at a given rpm and power change.

Another effect is that if you are using Hall sensors, the timing changes.

Nick
 
That's confusing me:

Miles wrote kv= 1/ kt
Which means there is a difference in torque between wye/delta because the kv changes.

And others say there is no difference in torque. Perhaps because of the current limiting controller? But what happens with torque, when the same current goes through 2 coils ( wye) instead of 1 coil ( delta)?

Can someone lighten me up?
Olaf
 
The continous torque potential for a given motor is determined by the copper fill%.

It makes not difference the wind, or the termination.

If your goal is to take a delta motor with too low of inductance and resistance to be powered by an existing controller, then by all means, re-terminate it in WYE to save yourself the trouble of re-winding, and your controller will have a lot better chance at surviving, yet at the cost of a substantial drop in power potential (from the RPM loss), and if you increase the voltage to get the RPM back, then you end up at exactly the same stresses on the controller you had previously in delta.


Totally unrelated to torque production, if you want to eliminate recirculting eddy currents, terminate in WYE. It's a little more hassle because you have to make extra terminations, but if you're going for every last fraction of a percent of efficiency, it's the best termination option. Again though, it's pretty much a toss-up, but if you're going to take the trouble to do your own wind, it's got the best efficiency potential.
 
Hi Luke,
I don't understand this argument of copperfill as limiting factor?! IMHO this only comes in count, if we have unlimited current available...
Plus we usually are not interested in continuos torque numbers. :wink:
In real life our controllers are too small to handle the current demand at low rpm. That's why they have current limitation. But when the motor has already build up revs in wye-mode, the inductance is high enough to safely switch to delta and you get the full potential without changing the voltage.

Question still is:
Does a motor produce more torque in wye at a given current limit and with a given voltage?
In RC world we have a simple rule: terminate in wye and you can use a larger prop diameter. Must be related to torque?

-Olaf

liveforphysics said:
The continous torque potential for a given motor is determined by the copper fill%.
Click to expand...
 
olaf-lampe said:
I'm planning to glue the halls in a 120° angle in the stator.
Is it necessary to mount another set of halls in a different angle and switch between them at the same time as the wye/delta switch? ( I assume switching the 5V for the halls is enough?)

-Olaf
Click to expand...

Yes, you need them offset by 30 edeg, either retarded or advanced (depends on motor setup).

For an equal power input between the two motors, delta or wye makes ZERO difference in torque.

Have Miles or Jeremy explain to you why only the copper fill% determines the torque capability of the motor.
 
I understand what Luke is saying, and he is right, in the context that he defines torque. Olaf's point is that for a given amount of current, the torque numbers will be different in wye, vs. delta, and he is also correct. It is absolutely a valid option to have the motor start out in wye mode, and let the rpm go higher, resulting in a greater amount of starting torque, for a controller-limited amount of current. Once the motor is up close to where it starts to lose efficiency, a switch to delta mode will let you get more top speed, and put the motor back into its sweet spot. Also, since you are already moving, the load in delta mode will be a lot lower.

-- Gary
 
Olaf,

Did you see this thread: http://endless-sphere.com/forums/viewtopic.php?f=2&t=19590 ?

olaf-lampe said:
In RC world we have a simple rule: terminate in wye and you can use a larger prop diameter. Must be related to torque?
Click to expand...
http://www.rcgroups.com/forums/showthread.php?t=1096719
 
Olaf is not questioning the fact that the torque will be constant, regardless of kV, just that the current required to achieve a given torque will be different. What he is talking about is not motor theory, but in a real world setup which uses an input current-limited controller. In this scenario, I agree with Olaf that detla-wye switching can be quite useful. For a fixed current level, wye mode will produce 1.73 times the torque that it will in delta mode.
 
Miles said:
Olaf,

Did you see this thread: http://www.rcgroups.com/forums/showthread.php?t=1096719
Click to expand...

The guy is talking about iron saturation and max. allowable copper heat loss. I think with our huge motors/small controllers we are far from that.
Most of the HXT motors here on ES haven't been more than 'luke warm' as their owners reported.( eg. AJ has killed his motor, because the winding isolation was damaged)

-Olaf
 
I will give my experience using a manual switch to switch from Delta to Wye. I have it on my mountain bike and I really like it. Here is why.

In wye my Kv is lower so therefore my speed range is lower. In delta top speed is 30 MPH in Wye is 20 MPH. This makes my throttle resolution better in Wye. This is very important to me as the bike is mainly for off-road trails riding, and it makes speed control much more refined. Also in Wye it reduces the load on my controller. I use a Turnigy 100 Amp RC ESC. My max reading of amps in Wye according to my CA is 110 Amps. This is doing some street riding, pulling wheelies, but mostly trail riding. In delta the Max I have seen is 173 Amps. I have never actually read that high of amps while riding, but looking at max amps screen.

Acceleration is by the seat of my pants the same for both, the difference being that in Delta it just keeps accelerating to 30 MPH instead of topping out at 20 MPH.

So basically I use the switch as this. I ride on the street for a few miles to get to my local trails using delta, most of the trails or low speed and so I switch to Wye and have better control and lower amp use. Occasionally I go to an off-road area that allow for faster speed and go back to Delta, however I am careful with the throttle so as to not overload the ESC too bad.
 
GGoodrum said:
Olaf is not questioning the fact that the torque will be constant, regardless of kV, just that the current required to achieve a given torque will be different. What he is talking about is not motor theory, but in a real world setup which uses an input current-limited controller. In this scenario, I agree with Olaf that detla-wye switching can be quite useful. For a fixed current level, wye mode will produce 1.73 times the torque that it will in delta mode.
Click to expand...


Gary- Even for the same battery current and voltage set by the controller, the torque between delta and wye are identical. The delta wind just gets the phase current multiplied in the controller by 1.73 times more for the same rpm.
 
It seems to dawn on me that the formula for power is related to phase current: :idea:
power=torque x rpm => P=kT x I x rpm
where I is not the battery current but phase current. (Iph_rms?)

That would result in a lower input power in wye mode, making it still useful for huge motors vs small controllers.
Beside the equal max. torque it would still feel like a boost when you switch over to delta at higher speed.
Because torque in wye gets lower and lower above the 50% rpm mark, right?

-Olaf

@drewwjet
Do you have pictures or anything about your delta/wye switch, pleease :)
 
olaf-lampe said:
That would result in a lower input power in wye mode, making it still useful for huge motors vs small controllers.
Click to expand...

Yep, the advantage is if your controller is too wimpy to handle the phase current to develop the torque in delta.



olaf-lampe said:
Beside the equal max. torque it would still feel like a boost when you switch over to delta at higher speed.
Because torque in wye gets lower and lower above the 50% rpm mark, right?
Click to expand...


If you just leave it in delta (or if you're winding your own, just wind it in WYE for the KV you actually want), then you get identical torque and speed performance. For the same power in, the first half of delta will be roughly exactly the same as the first half if the motor were in wye.

The choice is simply a matter of choice towards which you feel is the better option. A more robust fet stage, or an external switching setup. They both have roughly identical performance in the end.
 
Part of the biggest advantage of winding your own IMO, is being able to choose exactly the KV you want for your indivdual voltage/controller/reduction options/tire size etc. When you get to do the wind yourself, you can bypass the need for the band-aid type work around things IMO, and go for the most simple, reliable, efficient option.
 
olaf-lampe said:
@drewwjet
Do you have pictures or anything about your delta/wye switch, pleease :)
Click to expand...

There may be some pics of it in my build thread. http://endless-sphere.com/forums/viewtopic.php?f=28&t=16705

It really is nothing more than a 3 pole double throw switch. It is rated at 15 amps, but as I said, I have seen 173 amps on the CA. So far it is holding up with over 200 miles on it. I picked it up at a local electronics surplus shop for $5.00

I bought 3 double throw single pole relays that were rated for 40 amps, again $5.00 a piece, but they were a touch too big to fit inside my enclosure, so I stuck with the switch
 
Remember that for a mechanical switch, there is a difference between carrying capacity and switching capacity.

If you are using the switch for reconfiguring the circuit and only changing it when no current is flowing, then you can get away with a lower rating.

Nick

PS. I still don't think its a good idea.
 
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