# Two DC Kostovs - one Solition or two?



## karlos (Jun 30, 2008)

I'm looking at two motors (Kostov 9" 220V 500A) belt driving the rear wheel half shafts (nothing new) but have a choice of using two Solition Jrs (2 x 500A ) or one Solition (1000A) probably driving them in series.
What I understand from the discussions is that using one controller for the 2 motors will better make the system work as a 'diff'?
One of the issues with one controller is motor temperature feedback and would it be OK to feed the temperatures into the controller in parallel so the controller 'backs off' according to the hottest motor?
Any comments on what best to do?


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## Tesseract (Sep 27, 2008)

karlos said:


> ...What I understand from the discussions is that using one controller for the 2 motors will better make the system work as a 'diff'?


Well, it's better than wiring the two motors in parallel, but the best/safest differential action is when you have a controller for each motor with RPM limiting for each. When two motors are wired in series the amps (torque) from each will be the same, but the volts (rpm) need not split evenly between them! If one wheel loses grip for whatever reason it will take all of the voltage, stalling the other motor and probably flinging itself to smithereens in the process. Remember that there is only 1 tach input on the Soliton controllers...



karlos said:


> One of the issues with one controller is motor temperature feedback and would it be OK to feed the temperatures into the controller in parallel so the controller 'backs off' according to the hottest motor?
> Any comments on what best to do?


If you mean can you wire the internal temperature snap switch in each motor to activate limiting in both controllers, the answer is yes. We don't support reading thermistors, however, because it is our firm opinion that the *motor manufacturer* should decide how hot is too hot, and not us. A snap switch changes state at a definite temperature; a thermistor merely tells the outside world what the motor temperature is and it is up to the end user to decide what temperature is too hot. We'd rather not take on the responsibility of figuring out what a safe internal temperature is for every motor in existence...

Otherwise, which way is best - 1 large controller or 2 smaller ones - is a difficult question to answer. If you use two controllers you need to make sure they see the same thermal environment otherwise one will enter thermal derating before the other and that, as you might imagine, could lead to a "surprising" driving experience... With just one controller, however, you have to pick which motor to protect against overspeed, which could be a problem if it is the other motor/wheel that loses traction (and, statistically speaking, that will be 50% of the time  ).

All in all, it's quite a difficult problem to solve, and not one we really imagined when we set out to design what would become the Soliton1 in August of 2008. As usual, the customers have more imagination than the manufacturer...


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## Dennis (Feb 25, 2008)

> Otherwise, which way is best - 1 large controller or 2 smaller ones - is a difficult question to answer. If you use two controllers you need to make sure they see the same thermal environment otherwise one will enter thermal derating before the other and that, as you might imagine, could lead to a "surprising" driving experience... With just one controller, however, you have to pick which motor to protect against overspeed, which could be a problem if it is the other motor/wheel that loses traction (and, statistically speaking, that will be 50% of the time  ).
> 
> All in all, it's quite a difficult problem to solve, and not one we really imagined when we set out to design what would become the Soliton1 in August of 2008. As usual, the customers have more imagination than the manufacturer...


In other controller setups I have seen, dual controllers have a way to communicate to each other such that in the event you are describing will cause both controllers to behave with the same parameters. So basically if one controller goes into REAL thermal limit then it can communicate this to the other controller and put it into artificial thermal limit. This is bi-directional btw, so there is no defined master or slave. It's all about which one goes out of parameters first which gets the priority control over the other. I am sure you guys could come up with a way to link two controllers together by some communication scheme.


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## Tesseract (Sep 27, 2008)

Dennis said:


> In other controller setups I have seen, dual controllers have a way to communicate to each other such that in the event you are describing will cause both controllers to behave with the same parameters.


That's certainly a smart approach, but I wasn't aware that there are controllers for EVs that do this already? Are you by any chance referring to industrial VFDs (many of which can do this)?



Dennis said:


> I am sure you guys could come up with a way to link to controllers together by some communication scheme.


Mmm... the old "how hard can it possibly be?" philosophy...


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## Batterypoweredtoad (Feb 5, 2008)

Wouldn't this be a perfect situation to wire the motors in parallel? IIRC the motors will "Want" to stay at around the same speed with a parallel setup. This would give you behavior similar to a limited slip diff. It seems like keeping the volts high and splitting the amps would be better for the Kostov as well giving you the high volt/500A per motor the 9HV was designed for. (even better if you guys still allowed the 1400A race upgrade for the Sol 1 )


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## Batterypoweredtoad (Feb 5, 2008)

To the OP-If you ended up with the motors wired in series a possible solution would be to fab up a method to place a Viscous Limited Slip between the two axles.


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## glaurung (Nov 11, 2009)

I have been thinking this same issue lately for my 4wd version2 upgrade.
I would go for two controllers, one for each axle. Then i should have power distributed quite evenly all time. If there would be temp problem on either controller/motor it would not brake anything, just stop. Then fix issues until all goes smoothly.
I would go for two Solitons, Two motors.

Regards, Harri


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## Dennis (Feb 25, 2008)

Tesseract said:


> That's certainly a smart approach, but I wasn't aware that there are controllers for EVs that do this already? Are you by any chance referring to industrial VFDs (many of which can do this)?



I have seen forklift controls that are like this for dual motor setup where the motors are used as differentials to help the forklift steer, although some have a central control module that does all the necessary work, but your controller is not a dumb controller like those analog ones. 



Tesseract said:


> Mmm... the old "how hard can it possibly be?" philosophy...



Now, now, no need to beat your head into a wall and pull your hair out lol. I say take it one step at a time. You already have to do regen for series wound motors so get that figured out. Being an EE means you will soon have gray hair at an early age because of stress.


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## karlos (Jun 30, 2008)

Thanks for all the responses! The picture is a little clearer.

OK, a related question. In the situation of using dual 340V Kostov 11" motors, what is the situation using two Solition 1 controllers (because 1400A is not now and option and the Big Sol not yet availiable) in parallel? What would be best or possibe; conect both controllers in parallel to a bus and then feed the motors or feed each motor seprately with each controller? Once again, I can see issues with the controllers reading the motor temps. This could be as simple maybe as working out which motor is heating first and using that signal to have the controller/s back off?

PM me Jeff if you want me to trial the Big Sol, I'm only 1 ocean away


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## Brute Force (Aug 28, 2010)

Karlos,

I'm running a setup similar to what you're proposing, dual warp9s and dual Soliton 1s, belt drive to each axle. While I do not have a lot of miles on the setup (it's perpetually under construction), I have driven it HARD those miles and have had no problems with the functionality of the dual setup.

I'll share more details later, I'm under the gun getting it ready for the SORC in two weeks.


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## karlos (Jun 30, 2008)

Brute Force said:


> Karlos,
> 
> I'm running a setup similar to what you're proposing, dual warp9s and dual Soliton 1s, belt drive to each axle. While I do not have a lot of miles on the setup (it's perpetually under construction), I have driven it HARD those miles and have had no problems with the functionality of the dual setup.
> 
> I'll share more details later, I'm under the gun getting it ready for the SORC in two weeks.


Thanks, would be very interested in your experiences. Maybe this needs another thread but I have been having a good look at the belt drive possibilities and for 2 x the Kostov 9" HV I would need 50mm wide Cross Morse 8G belts or the Gates equivalent. 
Your C4 rear end set up looks awesome. I've been drawing up something similar but without all the CNC machining but yours looks hard to beat!
All the best getting ready for the race.


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## Tesseract (Sep 27, 2008)

karlos said:


> ...What would be best or possibe; conect both controllers in parallel to a bus and then feed the motors or feed each motor seprately with each controller?


I would strongly advise against connecting two or more Soliton1's in parallel and instead driving each motor separately. Technically, the Soliton controllers operate as true current sources so they should parallel nicely, but I hope you'll forgive me for not wanting to risk blowing up $6k worth of controllers to find this out for you.



karlos said:


> Once again, I can see issues with the controllers reading the motor temps. This could be as simple maybe as working out which motor is heating first and using that signal to have the controller/s back off?


As I already mentioned, most (all?) motors have a bimetallic temperature snap switch embedded in the field windings. If they are NC switches then you can wire them both in series to the 12V supply then feed each aux input configured as a "Throttle Limit" (in 1.4) in parallel. That way if either snap switch opens up it will activate the throttle limit on both controllers. Simple.



karlos said:


> PM me Jeff if you want me to trial the Big Sol, I'm only 1 ocean away


Oh, beta testing $10k worth of cranky power electronics with someone in New Zealand? What Could Possibly Go Wrong?


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## karlos (Jun 30, 2008)

Tesseract said:


> Oh, beta testing $10k worth of cranky power electronics with someone in New Zealand? What Could Possibly Go Wrong?


Thanks Jeff, humorous and very informative as always!
I got a couple of things from you last comments; seems you are still working on the 'Big Sol' concept and are you testing reactions to a possible $10K price tag?


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## Qer (May 7, 2008)

karlos said:


> seems you are still working on the 'Big Sol' concept and are you testing reactions to a possible $10K price tag?


We're constantly juggling around ideas, theories, wishes etc trying to figuring out what is realistic, what we actually can chew on our mini-team and, of course, what would benefit us and what would be economical suicide to go for. Pretty much none of these projects will be chosen during 2011, very few during 2012 and generally even though we do occasionally mention Big Sol I wouldn't keep my hopes high if I were you.


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## Brute Force (Aug 28, 2010)

Karlos,

A few of tidbits I'll pass along:

Use 62mm belts, they're 25% stronger than the 50mm and still easily available from industrial suppliers. Even then they'll be marginal for the application. And run the highest numerical speed reduction you can fit. Don't expect them to be quiet.

Twin motors on a single controller are OK if the shafts are mechanically locked together. If they are mechanically independent, the control should also be independent.

Direct drive will have disappointing performance if you don't have 1000 amps on tap. Go for dual Soliton 1s to push your dual Kostovs.


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## karlos (Jun 30, 2008)

Brute Force said:


> Karlos,
> 
> A few of tidbits I'll pass along:
> 
> ...


Thanks for that! Have a 2.8:1 reduction drawn currently, 6500rpm motors, 1690mm wheel circumference which gives a theoretical top speed of 235kph/146mph. I don't want to max out the revs at the end of a 1/4 mile, maybe a little higher ratio its required. Any opinions?

Still would love to see more pics of your project


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## rochesterricer (Jan 5, 2011)

IIRC, the Commuter Cars Tango uses a single Zilla 2k to run 2 motors that run the wheels independently. I don't know any details of the setup beyond that though.


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## EVfun (Mar 14, 2010)

rochesterricer said:


> IIRC, the Commuter Cars Tango uses a single Zilla 2k to run 2 motors that run the wheels independently. I don't know any details of the setup beyond that though.


The Zilla has 2 tachometer inputs. I don't know if the motor are wires in series or parallel in the Tango.


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## brainzel (Jun 15, 2009)

Don't know exactly if I understood right, but here is a belt driven dual-kostov build with one Soliton 1 from RebirthAuto click this link.


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## Bowser330 (Jun 15, 2008)

rochesterricer said:


> IIRC, the Commuter Cars Tango uses a single Zilla 2k to run 2 motors that run the wheels independently. I don't know any details of the setup beyond that though.


+1

http://www.commutercars.com/specs.html



> *Controller: *
> Zilla Z2K motor controller, providing up to 2,000 Amps at 350 Volts (600 kW).
> Designed and built by Otmar Ebenhoech at Café Electric LLC in Corvalis, OR.
> 
> ...


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> 2 Advanced DC FB1-4001 9" motors, one driving each rear wheel with over 1,000 ft-lb of combined torque at low rpms. 8,000 rpm redline.


Since the WarP-9 delivers about 250 lb-ft at 1000A and it is quite similar to this ADC motor, this implies the two motors are wired in series. That is to say, each motor sees 2000A and delivers ~500 lb-ft of torque, for 1000 lb-ft total.

On a separate note, I can't imagine those poor little motors like seeing 2kA - that's drag racing current, except this is supposed to be a commuter car (literally).


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## Bowser330 (Jun 15, 2008)

Tesseract said:


> Since the WarP-9 delivers about 250 lb-ft at 1000A and it is quite similar to this ADC motor, this implies the two motors are wired in series. That is to say, each motor sees 2000A and delivers ~500 lb-ft of torque, for 1000 lb-ft total.
> 
> On a separate note, I can't imagine those poor little motors like seeing 2kA - that's drag racing current, except this is supposed to be a commuter car (literally).


I wonder if they have the series-parallel "electric shift" in the Tango....


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## Brute Force (Aug 28, 2010)

Brainzel,

The Rebirth Auto unit has the motors mechanically locked together via synchronous belt, so they are effectively a single unit.

Don't get me started on the Tango. Somewhere buried under all the marketing horse crap is a nice car, but too much fiction around it for my tastes.


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## rochesterricer (Jan 5, 2011)

Brute Force said:


> Don't get me started on the Tango. Somewhere buried under all the marketing horse crap is a nice car, but too much fiction around it for my tastes.


Yeah, that tends to happen when you are trying to attract investors.


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## EVfun (Mar 14, 2010)

Have either of you ever driven a Tango? The performance is positively abrupt -- as in *abruptly* you aren't "there" anymore!


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## rochesterricer (Jan 5, 2011)

EVfun said:


> Have either of you ever driven a Tango? The performance is positively abrupt -- as in *abruptly* you are "there" anymore!


I never said otherwise. We are talking about the amount of hype the owner puts out about the car. Honestly, it doesn't bother me that much though. It always exists with startup companies trying to find investors, so I never have a problem looking past it.


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## Brute Force (Aug 28, 2010)

Driven a Tango? Nope, doubt I ever will. From all reliable accounts it has astounding performance. But 800 horsepower and 2500 lb-ft of torque from a pair of FB-4001 and a single Zilla? An "estimated" 12 second quarter and an "estimated" 135mph top speed? Two words: Horse crap!


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## rochesterricer (Jan 5, 2011)

Brute Force said:


> Driven a Tango? Nope, doubt I ever will. From all reliable accounts it has astounding performance. But 800 horsepower and 2500 lb-ft of torque from a pair of FB-4001 and a single Zilla? An "estimated" 12 second quarter and an "estimated" 135mph top speed? Two words: Horse crap!


I can tell you the 1/4 mile time is not estimated. There are multiple videos of Tangos running mid to high 12's. Part of the reason they have to say "estimated" for those numbers is because they allow the customer to choose the final drive ratios, and that will obviously change the possible performance numbers.


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