# Rewind motor for more torque or hp?



## Paul9 (Oct 2, 2015)

Hi people,

I have come to a point where I am a bit “stuck” as to what improvements I can do to my EV (a Suzuki Swift/Geo Metro 1994). It originally (in 2008) was a 96v system using 8 x 12v, 100 ah, lead acids, 300amp 96v controller and 96v Motor DC F series 2800 rpm 8.5kw continuous. Performance was not great!

In 2012 the lead acids “konked” out and I replaced them with 34 x 3.2 volt 100ah lithiums thus increasing battery voltage to 109v. I was told not to go too much higher than 109v as the 96v controller may not handle 109v but the motor would. This advice, as I expected, proved correct, as long trips in very hot weather overheated the controller. I have since fitted fans and heat sinks to cool the controller.

I am thinking about buying a couple of more batteries to get me up to 120v nominal (I have spare room for them) plus a 120v 600amp controller (same physical dimensions as existing 96v 300amp controller). What I however cannot do is buy a bigger motor due to space constraints.

I am wondering if having the motor rewound/rewired in some different configuration would give me slightly more torque or horsepower?? I am not looking to double the torque/hp but at least get slightly more out of it so the 120v input to the motor doesn't burn it out? Maybe thicker wiring or longer wiring?

There are plenty of motor rewinding businesses around, so if the above is possible, I would like to present them with the motor and a spec (however vague) for them to rewind the motor.

Many thanks in advance,
Cheers
Paul


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## dcb (Dec 5, 2009)

http://www.evalbum.com/2951
1992 Suzuki Swift from OZ

Advanced DC FB1-4001 (is that "F series"?)
144 volts, zilla 1K controller.

"0-80kph is acheived in approx 7 seconds. It wheelspins in 3rd gear!"
"90 MPH "

what are the motor dimensions and model number?


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## Paul9 (Oct 2, 2015)

Thanks dcb,

I just went and measured the motor and all I can tell you is that it is 36cms long. It is a chinese motor made by Zibo Super Motor Co Ltd.

Thanks
Paul


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## dcb (Dec 5, 2009)

what is the motor diameter? Is it possible to put in a wider motor if one is available? (or a longer one, or neither)

edit: and do you know if it is series or sepex? 

any identifying marks on the controller?

I can't imagine the cost of rewinding a zibo is gonna pan out.

edit2:
http://www.motors-biz.com/item/45524/96v-8-5kw-DC-Traction-Motor-for-electric-car.html
11kw & 144v perhaps, 3000 rpm, if it is a Zt8.5-96 242m diameter


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## Paul9 (Oct 2, 2015)

Thanks dcb,

I have just measured the diameter and it comes out real close to 242mm. I also checked the website you mentioned. 

The inscriptions on the motor are worn but it appears the Model number is in fact Zt8.5-96. The kw rating is 8.5kw and the nominal voltage is 96v. Continuous rpm is 2800 and max rpm is 3800 rpm.

Now I am really confused that the spec for that exact motor on the website has, as you noted, a kw rating of 11kw and a voltage of 144v. Why then is the model number Zt8.5-96??!!

Maybe the motor has a max continuous output of 11kw and a max voltage it can handle of 144v???

I assume it is a series motor as it is described on the invoice as Motor DC F series 2800rpm?

Maybe it will handle 120v dc without a rewind??

Thanks for your advice,
Cheers
Paul


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## dcb (Dec 5, 2009)

It seems like it might handle 144v, really no telling though till you try it.

did you keep the transmission in the conversion?


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## Paul9 (Oct 2, 2015)

Thanks mate,

Mine is clutchless and I use the gears to get what little torque there is, onto the ground.

I read your evalbum. Sounds fantastic!! If I knew then, what I know now, I would have gone to at least 120v or 144v like yourself.

Thanks again,
Paul


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## dcb (Dec 5, 2009)

oh, not mine, just a swift with an "F" series motor, before I knew what you meant.

So more volts might help holding torque to higher rpm (assuming the motor can handle it), i.e. 144/96 = 1.5, so you could stay in 1st or 2nd or whatever at full torque to a %50 higher mph.

if you want more torque, then it will take some guesswork as to how much current you can push, i.e. does it have 2 brushes 180 degrees apart or 4 90 degrees apart? How wide and thick is the contact area of a brush? number of commutator bars would be good to know and the cross sectional area of the armature bars and the field winding. You might as well dimension everything, including the laminations and shell if you are up for it. plus pics.

I imagine there are a few people interested in learning about that motor, it is about warp 9 sized and much less expensive, but so many unknowns otherwise.

if shift speed is slowing you down too, there might be some electrical/mechanical motor braking options that could help on acceleration with some practice.

edit: also there might be a different transaxle with a higher final drive ratio, maybe out of a 3cyl metro if yours was a 4cyl, maybe. Are you starting in 1st?

edit: some trans ratios,
http://www.teamswift.net/viewtopic.php?t=23748
the 1 liter has a 4.105 diff, plus some other gear differences. worst case you have a 3.523 diff, and this would give you %17 more torque.


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## dcb (Dec 5, 2009)

fiy, the 1.3 dohc transmission looks to be (according to the link above) a closer ratio box than the 1.0, but might be harder to find and cost more. 

If you never use anything higher than 4th normally (or won't need to with a higher pack voltage), this might be another option, but you might have to sort out faster shifts to take advantage of it (i.e. brief electrical motor brake pulse right after it slips out of gear, it gets complicated) as you will have to shift more to take advantage of it (but also the motor rpm won't have to drop as far between shifts once you are in 2nd)



```
4.105 swift/metro comparison

gear  1l     1.3LDOHC	%torque increase
1st:  3.416  3.416      0%
2nd:  1.894  1.894      0%
3rd:  1.280  1.375      7.5%
4th:  0.914  1.030      12.7%
5th:  0.757  0.870      15%
```
if you decide to go poking about the boneyard, this is what the dohc looks like (again from teamswift)


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## Paul9 (Oct 2, 2015)

Thanks dcb,

I don't mind going for a walk through "boneyards"! And a picture is worth a thousand words so I will know what I am looking for.

Cheers
Paul


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## Yabert (Feb 7, 2010)

Paul, if your motor is a DC series wound, passing from a 300A controller to a 600A controller that will increase *A LOT* the general performance of the car.
You probably don't need to rewind the motor.

Take picture of the brushes with a rule to give us an idea of the brushes size (or mesure the brushes). With this we will be able to know if your motor can safely take 600A.


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## Paul9 (Oct 2, 2015)

Thanks Yabert,

I don't have the equipment necessary to drop the motor out in my garage. I will have to arrange to go to my motor mechanic mate (who helped me build the car) and use his hoists.

I have recently mounted two fans on the outside of the motor to blow air through the vents into the motor casing. I am hoping this may cool the motor sufficiently to allow it to handle 120v with a slight increase in the amps I will be putting through it. Just because I am considering a 600 amp controller doesn't mean I will ever put 600amps through it. I rarely put more than 150amps through the existing 300amp controller.

As "dcb" and I noted on the website, the 8.5kw 96v motor may in fact be able to handle up to 11kw and 144v. IF that is the case, and with the cooling fans in place, the motor may be able to handle the 120v with higher amps without a rewind?

Thanks for your input,
Cheers
Paul


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## dcb (Dec 5, 2009)

150 amps, hmm. amps are basically torque, volts are basically rpm. 300 amps will make it accelerate twice as fast with twice the torque in theory.

make sure you are monitoring motor current (battery current is less), but from a similar sized motor:
"1000-2000 Amps for brief periods, the
9" motors are actually rated at 450 Amps for 5 minutes, 225 Amps for 1 hour, and 190 Amps continuous duty. "

but you gotta look at the construction (i.e. brush contact area and size/number of brush leads for starters) to see if it is really comparable. plus you want to monitor motor (and controller) temps.

fyi a typical 9" performance cooling setup, a shroud and blower that pack the air in and direct it at the commutator









edit: and you gotta keep your new controller cool too. What were the markings/manufacturer on the original controller?


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## Paul9 (Oct 2, 2015)

Thanks dcb,

That photo of the cooling system makes me green with envy! Obviously way outside my skillset!

Thanks
Paul


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## Yabert (Feb 7, 2010)

Paul, what you need to understand is a 72v 600A controller will give you more performance if you compare to a 120v 300A controller if you consider the same motor.
Amps = torque = acceleration



Paul9 said:


> I rarely put more than 150amps ...


You are monitoring battery amps right? Motor amps are always higher.


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## Paul9 (Oct 2, 2015)

Thanks Yabert

I am learning all this stuff as I go along. I didn't know battery amps and motor amps were different. The little I know has come from my electrician brother and my motor mechanic mate plus asking people on these type of forums (and making a multitude of mistakes!!)

Correct me if I am wrong, you are saying puting 120v into the motor would improve performance at the same battery amp level??

At present I have a battery bank nominally 109v dc. My 96v 300 amp controller draws from that. Say, for instance, my battery amps are 150amps, is my motor getting 150amps at 109v or 96v? If I increased battery bank voltage to 120v and got a 120v controller then I assume the motor would be getting 120v (and performing at a 120v level) even though it is a 96v motor?

I gather from others that motors are more forgiving of receiving higher voltages than controllers? 

Sorry for my slowness and thanks!
Cheers
Paul


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## Duncan (Dec 8, 2008)

Hi Paul

Your controller effectively delivers to the motor the voltage it needs to draw the current that you have selected with your throttle
full throttle = max current
1/2 throttle = 1/2 current

Also your controller is a Power In = Power Out device
So motor voltage x motor current = battery voltage v battery current

Your motor will have a very low resistance so 
when you are stationary it will only take ~ 10v to get 300amps

Stationary Motor 300amps and 10v = 3,000watts = Battery 100v and 30 amps

As the motor spins it develops a Back Electromotive Force (Back EMF)
at 1000rpm and 300 amps BEMF may be 40v

So
1000rpm Motor 300amps and 10v + 40v (50v) = 15,000watts = Battery 100v and 150 amps

And that will go on until the controller is maxed out when Motor current will equal battery current

If you increase the battery voltage you will reduce the battery current and allow the motor to produce more torque at higher rpm


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## Paul9 (Oct 2, 2015)

Thanks Duncan,

I think(?) I am getting the hang of this

If I put what I think you said in my words - the 96v controller doesn't always pull 96v? In fact it only does so when it is "maxing out" (as you put it!)? The local distributor of my controller said, the manufacturer said, it will handle up to 120v but wouldn't be covered by warranty if run at that voltage.

I think if I upped my battery voltage to 120v, my controller would definitely overheat so I should get the 120v controller to ensure no overheating problems? Is that correct?

Really appreciate all the help responders have given me!!
Cheers
Paul


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## Duncan (Dec 8, 2008)

Hi Paul
Your 96v controller always "pulls" 96v from the battery

But it does controller magic and only "pushes" the voltage that your motor needs

Running a controller at the limit is a good way to let the magic smoke out!

Getting a higher current higher voltage controller is a good idea 
If you are worried about too much current it is simple to limit the travel of your throttle
If you only have 1/2 throttle the controller will only give 1/2 current


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## Paul9 (Oct 2, 2015)

Thanks Duncan,

I think the penny is finally dropping! You Kiwis aren't all bad even though you keep beating us at Rugby!!

Thanks a lot!
Paul


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## Duncan (Dec 8, 2008)

About the Rugby
You have got to select your game - with the All Blacks on form? - how about cricket?


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## Paul9 (Oct 2, 2015)

Well the Kiwis are the world champions at Rugby League too! I think we are rated more highly in cricket but not sure of that.


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## galderdi (Nov 17, 2015)

Paul9 said:


> Thanks Duncan,
> 
> I think the penny is finally dropping!


 The penny is finally dropping for me too (Thanks also to Duncan).

I have a similar problem. Trying to squeeze better performance out of my system.

I had a ride in another EV and I was surprised when I saw the amps rising to around 800amps yet the performance was only on par with mine from 240amps. Now I am realising their current was probably being measured on the motor side of the controller while mine is on the battery side.

I am tempted to put a meter on both sides so I really know what is going on.

Its really interesting stuff.

In my case I am seeing around 240amps at about 150 volts on the battery side under maximum load. So the overall power should be similar on the motor side (36KW-any inefficiency losses). Am I correct in understanding: my foot is all the way to the floor = maximum volts to the motor?


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## Duncan (Dec 8, 2008)

_my foot is all the way to the floor = maximum volts to the motor?_

No
That will give maximum current - 500amps or whatever the controller is set to
The controller will do its magic and give the motor the voltage it needs to get the 500amps

So at zero rpm you will only need about 15v so the controller will be 90%OFF 10%ON - even at full throttle
As your revs rise you will need more motor voltage to get the same current until the controller maxes out at 100%ON - the battery voltage = motor voltage


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## dcb (Dec 5, 2009)

galderdi said:


> Am I correct in understanding: my foot is all the way to the floor = maximum volts to the motor?


you are correct in the power into the controller ~ power out part. 

controllers typically limit current though, so they don't self destruct, and to make it more like driving a car. The peddle is more of a current (torque) command, so that you get maximum motor current at wide open thottle. But if the rpm is low the back emf (motors are also generators) is low, it cannot go %100 duty cycle without overamping the controller, so the duty cycle increases (still at full throttle) as the motor rpm comes up, effectively raising the motor voltage.

so for example, in the following, since torque is relatively flat, as it battery voltage, at least until 4000 rpm, you can infer that the motor amps stayed pretty flat (roughly equal to 722 amps), and the motor effective voltage ramped up to to a point where back emf prevented the pack from delivering 722 amps (probably at about 100% duty cycle at the turn there, motor volts/amps = pack volts/amps) then it kept accelerating as back emf rose and current (and torque) declined.

so while the torque was flat, pack voltage was constant, pack current was rising, motor current was constant and motor voltage was rising. Till it hits 100% duty cycle, then pack voltage = motor voltage, pack current = motor current, voltage stays same, current declines with rpm.


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## Paul9 (Oct 2, 2015)

Hi galderdi

I am under the impression that full throttle equals full current (amps)? 

Anyway, if you are trying to improve your vehicle's performance, I assume you have looked at various aerodynamic modifications and rolling resistance reductions?

Things I have done to reduce rolling resistance include:
1) Low Rolling Resistance tyres
2) Thinner tyres than the vehicle originally had (16cm wide down to 15cm)
3) Tyres pumped up high (mine at 45psi)
4) Swapping out lead acid auxiliary battery with 12v lithium battery (weight saving of 16kgs).

Things I have done to improve aerodynamics:
1) Blocked off entire front of car to reduce engine bay turbulence
2) Wheel spats in front of front wheels to reduce wheel bay turbulence
3) Kammback on back of car to reduce trailing vortices (made a noticeable difference particularly at speed)
4) Removed all mudguards
5) Changed to flat wheel covers
6) Removed radio antenna (reception didn't change)
7) Low profile windscreen wipers (don't know if they help)
8) Filled all gaps around front of car

Other changes:
1) Solar panel on roof feeds auxiliary battery (dc-dc converter no longer required - auxiliary battery no longer topped up from main battery bank)
2) Changed all lights to LED’s to reduce drain on auxiliary battery

Of course, swapping from lead acid batteries to lithiums saved me 160kgs (a big help) and increasing the voltage from 96v to 109v also helped!

Cheers
Paul


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## Duncan (Dec 8, 2008)

Hi Paul,

Galderdi and I are singing to a slightly different hymnbook, - 

We are intent on driving like hooligans around a track - so we have slightly different priorities

Good list but less useful on a race track


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## Paul9 (Oct 2, 2015)

Fine Duncan,

I see that our hymn books are slightly different. Another penny drops (I'll be rich soon).

People such as yourself and galderdi would have obviously investigated all the mods I listed to see if they were appropriate to your objectives. And I appreciate your advice.

Cheers
Paul


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## dcb (Dec 5, 2009)

fwiw Paul9, I frequently proselytize about aerodynamics (and rolling resistance, and driving technique/planning)


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