hub motor delta to wye conversion power consumption changes

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mpb
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hub motor delta to wye conversion power consumption changes

Post by mpb » Aug 09, 2016 4:07 am

Hello all I figure now is a good time for me to post a few questions and get some confirmation from the pros befor i make any fatile mistakes with my very expensive motors...

I am currently building an electric mountainboard (5th one) this one however will use diy hub motors... mechanically i have everything worked out but electrically... well this is where i need assistance as bl motors are wierd...ish

anyhow my motors i am working with are 4x t-motor u8 135kv pros...
it had 37 teeth and 42 magnets
http://www.rctigermotor.com/html/2013/E ... 9/176.html
and the original version has the same stats as the pro just not listed on the pros link so here's the original one http://www.rctigermotor.com/html/2013/E ... 28/94.html


I will be using this in conjunction with 8"wheels witch i have had past success with.
now I realize that 135kv is pretty darn high for my use of a hub motor however I purchased them due to the fae i got them at 1/5th the original price. I figured re wiring the motor from delta to wye would solve my problem and lower the kv to around 80ish wich is right about my goal. i will also be installing hall sensors into the motor at 120 degrees apart as usual after i have gotten the motor speed and general torque worked out.

HERE IS WHERE MY QUESTIONS FOR YOU ALL COME IN.

1. how is rewiring from delta to wye going to effect my power consumption? obviously i want to get as much torque as possible while preserving my range. I read somewhere that going from delta to wye I would half to double the voltage to get the same amount of amp draw as a delta to achieve original torque or power output is this true??
2. do you believe 4x of these motors will work well enough on this board? my last board used an 80-100 motor at 180 kv geared 4 to 1 on the same size wheels and the power was fantastic with sensors added. in my mind four of these these skinnier motors (8626) would add up to just over an 80100 motor just by there physical size which from my understanding is where allot of an outrunners power comes from am i right in this thinking?

Im sure ill have more questions but these are my two main ones currently.

thank you all for your help

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Re: hub motor delta to wye conversion power consumption chan

Post by Punx0r » Aug 09, 2016 8:08 am

Reterminating from delta to wye won't make any difference to the motor as you still have exactly the same amount of copper (and hence the same potential torque and efficiency), the only effect is on the current & voltage demands placed on the supply (your controller).

The difference in voltage and current between delta and wye is √3 (1.732).

At 135kV I would see what the rotational speed of your wheels is at desired top speed, add 20% and see what voltage this requires and see if it's sensible. You could also approach it from a torque perspective and see how much current you'd need. Either way it's seeing if a controller is available to run your motors as they are, changed to wye-configuration, or not at all.

mpb
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Re: hub motor delta to wye conversion power consumption chan

Post by mpb » Aug 09, 2016 1:57 pm

Ok so if the original voltage is 6s and it consumes 30amps max at 6s in delta. And i re terminate from delta to wye what would the new power demands be since i only want it to rotate at 1.73 less than the original speed?

Wouldnt going from such a high kv to almost hakf the kv and keeping the same voltage mean it will only consume 17 amps at 12s thus resulting in less start up power??

The goal here is to lower the kv without having to rewrap to allow the motor to not studder so much on startup and reach my desired top speed. (My desired sop speed is achieved at 80kv ) as the original kv is almost twice my desired top speed wich is a nono due to the amount of studdering i have on startup....

So in simpler terms. Delta wind at 12s is 135kv and consumes 30amps max. It also produces x amount of torque

What would the wye wind then require to pull the 30 amps and prosuce the same wattage and the same x amount or torque??? Would it require 1.73 more voltage to pull the original 30 amps from the delta wind? Or will it still pull 30 amps at 6s?

Will going from delta to wye help it not studdee on startup aince the kv wont be so high?? I was always told the lower the kv the less studdering i will encounter.

Thanks for the help

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Re: hub motor delta to wye conversion power consumption chan

Post by amberwolf » Aug 10, 2016 2:59 am

In delta, you have a single phase coil (set) between each bridge output of the controller.

In wye, you have two, so twice the resistance. So it would take twice the voltage to force it to use the same current. I'm not able to think well enough to figure out what the resulting torque and speed would be. :)

(unless I have messed up my math, which is possible as tired as I am :oops:)

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Re: hub motor delta to wye conversion power consumption chan

Post by mpb » Aug 10, 2016 3:17 am

ok so if i rewire it from delta to wye and im getting say 20 miles out of my pack(6s 2p) in delta will i now get 10 miles out of my pack in wye since i will be cutting my existing pack in half and running (12s 1p) will i then get 10 miles as a result? or will i get the same 20 miles ? to me what makes sence is it would go from 20 miles to 10 since i have less mah and the same amperage....

however if i go go from 6s to 12 s to retain my origional 30 amp draw wont that then put it back up to the original rpm thus defeating the purpose of my rewire??

the only reason i would want to keep the 30 amp draw is to keep the power that was produced with it. so i guess what this all ads up to is even though the motor will only pull 1.73 amps less than in delta at 6s will it still produce the same power and or torque to get going and accerate as it would at 6s 30 amps??


thank you for the help i cant find any of this info anywhere

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Re: hub motor delta to wye conversion power consumption chan

Post by amberwolf » Aug 10, 2016 3:59 am

I don't know the answers...but if you look up delta wye switching here on ES, you'll see threads by people like Doctorbass who experimented with this sort of thing on bike hubmotors, and probably documented performance before and after.

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Re: hub motor delta to wye conversion power consumption chan

Post by mpb » Aug 10, 2016 4:09 am

I found a little bit of info on http://www.recumbents.com/wisil/e-bent/ ... torial.htm . it was a little bland but it seems to hold some truth.

These need to be arranged one of two ways, "Delta" or "Wye". Generally Wye (also called "star") is more efficient. Wye has 1.73 times less KV than Delta (slower speed per volts), but 1.73 times more torque. In general it's a good idea to stick with Wye configuration for electric bikes as e-bikes need slower motor speed, higher torque, and high efficiency.

does this mean that with going from delta to wye will allow me to not only lower my rpm but gain torque at the same voltage while using the same voltage??? :D :D

it would make sence to me due to the fact that instead of the power going through one phase and then exiting it goes into one and back through another phase befor then leaving the motor. am i correct in my findings??? this would be utterly fantastic if this is true.

hope someone can hop in and confirm this thank you for the help im going to keep searching.

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Re: hub motor delta to wye conversion power consumption chan

Post by Punx0r » Aug 10, 2016 5:36 am

This is getting confusing. Let's see if we can pick it apart...

Your current configuration is 6S and 30A into a delta-wired 135Kv motor

We'll assume it's a li-co battery and that 30A battery current is also the phase current (it won't be, but...), so: 6 x 3.8 = 22.8V @ 30A

We don't know Kt, but let's say it's 1-"torque" per amp

At zero rpm you have 30-torques and at top speed the motor will be doing 3078rpm(!)


If you reterminate to wye and keep the same controller and battery:

Kt will increase by 1.732 times, giving you 51.9-torques
top speed will reduce by 1.732 times, giving you 1777rpm

Efficiency is essentially the same.

The increase in torque will give you greater initial acceleration, but this will soon tail off as BEMF from the motor will rise faster than before.

It's all a simplification and you might find you have less torque at higher speeds in wye than delta, not more. Especially when you consider the phase current from your controller is not fixed at 30A and varies according to what the motor is currently doing.

In general you could say that compared to delta, wye will reduce the load on your controller at start up. It will also reduce the speed. If you look at delta-wye in industrial motor this is exactly what it's used for.

The stuttering/jerkiness is probably the normal problem of a sensorless controller trying to start a motor under high mechanical load (slow start compared to a propeller). It might get a little better with a wye configuration as the motor will initially spin up faster.

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Re: hub motor delta to wye conversion power consumption chan

Post by mpb » Aug 10, 2016 6:07 pm

Fantastic this is just the answer i was looking for. Thank you very much for the explanation. My top speed is only going to be 35mph and i usually cruise at 15 or so. So higher end torque is not as important for me as start up torque I believe with this configuration paired with hall sensors will give me just what i am looking for. Hopefully thebhigh speed traveling and cruising will not be more unefficient than it was when it was wired in delta.... if this becomes too much of a problem i suppose a wye delta (switch) gear changer would be a future option for me. Thank you very much for the adsistance.

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