Relays for a Delta\Star switch

[Noamsal]

Hi,
i recently got a new motor, 45mm stator and 9x11 winding, doing about 65kmh on 72v 60a
it has slots for wires on both sides of the motor, i'm thinking about getting 6 phase wires (3 from each side) in it and to make a delta\star switch to make it go 80-90kmh
i searched the forum and still cant understand how relays work and how they will change my motor from Wye to Delta in one switch, i would like to hear an explenation
also what relays do i need? i want to have something that could take more than what i give, so there will be no heat problems
Thanks,
Noam

 

[Punx0r]

Star-delta switching is very common for industrial 3-phase motors. Have a look here: http://electrical-engineering-portal.com/star-delta-motor-starter

There are a lot of contacts that require switching.

Two questions before you rewire: Is your motor definitely currently wired in wye/star? Also, in delta, will it have enough torque to actually achieve your desired speed?

 

[Noamsal]

the motor is definetly in wye configuration, on 72v 60a it has lots of torque, it will have enough torque with delta connections also but i rather have it as a 2nd speed so i could lower the power down for technical offroad stuff, i need it mostly for my 15km daily commute on a straight road with not much cars and light
i used to run my old 1000w hub on 48v 50a with delta connections, had little torque but raised the top speed from 38kmh to 60kmh, but i wan't to have torque when starting from a dead stop so i want a switch

 

[amberwolf]

There are a few good threads on how to do this and how it works, including at least one by DoctorBass.

 

[Noamsal]

I've looked all over the forum... i've seen doctorbass thread and i sent him a PM also.. all the explanations i found aren't complete, if i had a base of how a Relay works i might understand it, but i don't have it so...
i tried to make a simple diagram on paint for myself, i'm not sure i'm right with it and there are still some missing links, but for start - is this right?

 

[thewmatusmoloki]

I think from memory this was the first thread to seriously address this topic, but it was "back in the day" a bit now.

Still brilliant info from the doc though. http://www.endless-sphere.com/forums/viewtopic.php?t=9215

Edit , sorry just realized you have seen that thread already.

 

[John in CR]

Everyone who's done it was disappointed with the results, because they don't fully understand what changes. It is not like a gearing change or even close to that effect. The phase-to-phase resistance changes (and inductance too, I believe), which causes the controller to react differently and not deliver the same current. That means the torque difference is small despite the change in Kt.

As far as the relays go, you'd want solid state, not something with springs.

I have some motors with series/parallel switching, a greater effect than star/delta, and the performance difference is small. One is slow and one is fast.

My recommendation instead would be to make your battery switchable instead. There are real performance differences in changing voltage. Low voltage can make it a more efficient climber, and high voltage gives you greater power and speed, along with greater torque throughout acceleration.

 

[Punx0r]

Matt (recumpence) seemed to praise it on his recent motoped build, but that may have been more about taming the inrush current (and resulting torque) when accelerating from rest and low speeds for the benefit of the controller and rider.

 

[Noamsal]

I know how delta mode works, i just don't know how relays work..
i used to run my old motor with Delta connections and 48v 50a, no switch, just delta from start to finish, it took my speed up from 38kmh to 60+ but took lots of amps, i think that with a switch and the right motor (which i have) it could be great. it works better with slower winded motors, since they already have bunch of torque.
i think that with switching to delta at 60kmh it will still have more torque than the 1500w leafmotor i had, after all, its 6 more turns and 10 more mm's to the stator

 

[John in CR]

it works better with slower winded motors, since they already have bunch of torque.

This and similar statements about different turn counts on an otherwise identical motor shows that you're a victim of the common myth. The simple fact is that all the different versions are really just the same motor and make the same amount of heat for the same torque.

Split your battery pack in half and make it switchable between series and parallel for a noticeable real difference that delta/wye switching can't provide.

 

[Noamsal]

i can't do that because half of my li-ion pack isn't strong enough to give the 60a peak

 

[nutnspecial]

I'm interested in delta/star wiring/switching too. For the bht, i think 30kv? (75v 2500rpm)

Now if it's at all possible, I'm even more curious of voltage switching. 72-82 or 36-41 would be interesting to consider. I'm wondering if there's much benefit for my setup tho.
John is there a thread, I have a bunch of questions and scenarios? If not and you wanna start one I'll participate 4 sure, just didn't wanna go ot here.

PS Noamsal, that looks like a NICE ride!

 

[amberwolf]

i can't do that because half of my li-ion pack isn't strong enough to give the 60a peak

The pack itself can provide the same current regardless of what voltage it is at, so if you cut the pack's voltage in half teh only thing that changes is the total *wattage* it could provide.

Whether your controller/motor *uses* what the pack can provide at the lower voltage is a whole different thing but has nothing to do with whether the pack can do it.

if i had a base of how a Relay works i might understand it, but i don't have it so...

did you try the question itself?
https://duckduckgo.com/?q=how+a+Relay+works&t=ffcm

 

[Noamsal]

After watching some vids on youtube about relays and looking at some diagrams i managed to come up with this pic below
its a 'diagram' in my private language lol, basicly every black box there is a relay, i took a diagram of a delta\star connection and played on it on paint so i could understand whats going on
and i found these -
http://www.ebay.com/itm/5Pcs-Car-12V-12-Volt-DC-80A-AMP-Transparent-Relay-Socket-SPDT-5Pin-5-Wire-/400697473167?hash=item5d4b6e388f&vxp=mtr
i think those will do good for my use (60a peak) and i already have a 12v converter
thanks guys for helping
and one more question - how much does the relays consume while they're on? couldn't find it on the ebay page..

 

[John in CR]

The relays would need to be rated for something higher than your phase current limit, which can be far greater than your battery current limit, and they need to be rated for your pack voltage too, so an automotive relay won't cut it by a long shot. The ones you'd need aren't cheap, and those I've seen are bulky too.

Again, it's a big waste of money, time and effort. Plus it introduces plenty of new failure points. There have been a number of people who've done it on hubmotors, and to my knowledge not a single one of them still uses it or did it to a 2nd motor. That alone should tell you it's not a worthwhile modification. It's not an easy one either. eg Where would you put the contactors? They won't fit inside the motor, so that means wasted copper length, and more wires to get to the outside and back in.

In the RC world some do it, though not with relays, just a different hard wire termination, and the reason it's valid for them is to get a different Kv to swing a different prop (essentially a change in gearing) without needing to change the pack voltage and controller. With a hubmotor, there is no change in gearing other than changing the wheel size, so changing the Kv accomplishes nothing. Getting up a hill at a given speed requires a given amount of torque, and the motor will make the same amount of heat (ie same efficiency) regardless of the winding turn count or change in phase termination (ie change in Kv).

I'm just offering helpful advice that I learned from the mistakes of others. What you do with it is up to you, but I'm finished with the subject.

 

[Noamsal]

are you sure the relays have to stand the phase amps? not battery amps? it makes sense but no-one said it before in all the threads i've been to..

 

[riba2233]

are you sure the relays have to stand the phase amps? not battery amps? it makes sense but no-one said it before in all the threads i've been to..

Of course they have to stand phase current, look at where they are positioned... It's a dumb idea since motor is always the same, it has same maximum power and torque all the time, no matter how you connect it. You just have to optimize your system and you will be fine with one "gear" (delta wye switching isn't same as gearing).

 

[recumpence]

I have to preface this post by saying I am not an electronic engineer. So, I have to bow to the geniuses on this forum who are. However, I have experience with this and, therefore, I want to chime in.

I really do not want to start an arguement with John. But, I have to say I completely disagree with nearly every statement he made on the subject. That being said, I have only done this on my high RPM RC motors. So, the results may differ in a hub application.

First of all, there is a HUGE difference between Delta and Wye in ridebility, throttle response, heat, efficiency, etc when switching between Delta and Wye. Also, you do NOT want solid state switching. There is too much heat buildup in the FETs. I consulted with Outrider USA on this and they found solid state was very inefficient. Relays work great. Also, my relays are rated for 80 amps. Yet, I pull 330 amps through them without a problem. That is because you are pulling the current through the phase wires in tiny bites, not continuously. I thought for sure I would burn out my relays. But, they run nice and cool and have tolerated months of abuse without missing a beat.

I will agree with John, however, that you can setup your pack for series parallel and get a very similar result. I went with Delta Wye relays because I did not want a doubling of motor RPM (which is what series/parallel would do). I like the 1.71 times increase Delta gives versus wye.

Again, I have not done this with a hub. So, I do not know what the difference in performance would be. However, for the most part, a brushless motor is a brushless motor in that you should see similar results with a hub.

Lastly, it may be that the others who have tried this a stopped using Delta/ Wye may have been doing something wrong or their specific preference for performance did not lend itself to Delta Wye and they gave up on it........?

That is my take on it. I have been running Delta Wye for months (very harsh use) and in my application, it works fantastic.

Matt

 

[John in CR]

LOL! I didn't realize you were a believer the The Myth, ie a higher turn count motor can make more torque. If you see less motor heat then the controller is reacting to the different electrical load and the motor is making less torque. "Rideability" is also an indicator that's what is happening, which may go further in that at high power and torque a touchy throttle can result in a lot of waste heat due to less control over the throttle.

Delta WYE falls in the same classification as other changes in Kv, which has been fully hashed out before with involvement of LFP, Justin, Miles, and others. I'll stick with their side of the line, because it's supported by the real physics, not anecdotal evidence without meaningful analysis of the causes of what you see. FWIW, in low speed with my series/parallel switching motors, it has smoother operation similar to what you're saying, and that's because the way the controller behaves after just a couple of rotations of the wheel torque gets lower more quickly. The exact same result can be accomplished with use of a 3 speed switch, and no motor mods at all are needed.

John

 

[recumpence]

I NEVER said the torque increased. Don't put words in my mouth.

What I like is the different speed range from being able to switch from Wye to Delta. It also eases the load on the controller in Wye versus just limiting throttle end point.

You can say whatever you want, but the fact of the matter is, I am actually RUNNING this setup and speaking from my own personal experience. Personal experience and actual data collected is not anecdotal. It is reality.

Matt

 

[John in CR]

A change in the wiring of a motor doesn't change the motor. It still makes the same heat for the same amount of torque. That means any benefits you see result from the controller doing something differently and/or not handling the more difficult load well with the speed wiring. If changing the physical wire terminations of the motor is the solution for RC, then that's a shortcoming of the RC controllers used. With a programmable ebike controller the solution is simple, and even with a fixed setting controller a few dollar part in the form of a 3 speed switch should solve the low speed issue. It's a shame they don't work on systems like yours.

The OP isn't trying to solve the same issue. He's starting with what is a too steeply geared motor, and wants to add a lot more to the top speed with a switchable termination. ie No change in power input, no change to improve gearing, but increase top speed by almost 40%. I make factual statements about why it won't achieve what he thinks it will, and you come in and say you disagree with every point without any real understanding of why your own systems behave differently in WYE vs Delta.

I'm sorry I brought up the Myth stuff, because in actuality what you're using the Delta/WYE to accomplish is pretty much the opposite of what believers in the myth think the change in termination would do. Haven't the RC controller guys come up with a way to limit current yet? That's all you need to make your Delta/WYE switching unnecessary, and I'd love to be able to use those tiny controllers that deliver big power.

FWIW you friend just needed more mosfets in parallel and proper a heat sink for his solid state relay.

 

[Lebowski]

I agree with John, delta wye switching is a load of cow manure. De facto delta is bad (has to do with harmonics) so always use WYE.

 

[Punx0r]

Are BLDC motors a special case? Because induction motors run just fine in delta...

Taking the OP's example, he wants to increase motor speed while retaining the same pack voltage and gearing (wheel size), so he has no option but to rewind the motor for a higher KV or reterminate in delta. Whether the motor has enough torque to achieve the top speed in delta, or whether it would be better of permanently wired in delta remains to be determined.

 

[riba2233]

Yeah but higher speed needs more power (exponentialy), and that requires stronger motor and controller. If he's not going to change that, he wont accomplish anything.

 

[Noamsal]

As i told before - I have tried delta connections before, with no switch, on a 48v 1000w with 50a controller, it got me from 40kmh to 60kmh, from 16a continues to 35a, and a really hot system
i know its not perfect, thats why i want the switch, i already know the losses in delta mode and i think the losses i knew with that delta motor would have been much less with a delta\wye switch
also who knows, i might not even use it...
i basiclly want to try this, whatever there is to lose, i just want to try things, why isn't that good?

and BTW recumpence thanx for the help, i was going to give up when i started searching for 200-300a spdt relays lol, good to know 80a will do