# Series/parallel dual motor control



## Tesseract (Sep 27, 2008)

toddshotrods said:


> Does running two series-wound motors, as most of the drag racers are doing, require a special controller?


I assume - though you did not actually say - that you want to switch between the series and parallel configuration, since nothing special is required if the two motors are permanently wired in series or parallel (though some controllers will complain, often through the untimely release of their magic smoke, at the low inductance of the parallel configuration).

The short answer is that nothing special - except for three contactors (rated for the full motor current) - is needed to switch between series and parallel. 

Many drag racers do this manually - that is, they select the contactor configuration with a toggle or pushbutton switch - rather than rely on the automatic s/p switching in, say, the Zilla. I don't know why, as it seems the Zilla - at least - does a very good job of deciding when to switch from series to parallel. Note, however, I have never seen how (or even if) it decides to switch back to series mode again, and that is a far more difficult decision to make. 



toddshotrods said:


> Is a special controller required to do this? We know Zillas can do it, but can Soliton 1; will Soliton Jr be able to? Can you use any old series controller and reversing-type contactors (say a cheapo Alltrax)? What features are necessary in the controller if so?


1. No, unless you want the s/p switching done automatically.

2. Not yet but it is a planned addition. Not too many people that have actually bought a Soliton1 have asked when this will feature be implemented, though, which is why it keeps getting pushed down the priority list... 

3. There's no reason why Jr. couldn't do s/p switching, and perhaps there is more of a benefit in doing so with a smaller controller?

4. Yes, see above - you just need to know what motor current is doing. It would be nice if the throttle signal was automatically suppressed for a couple hundred milliseconds while the contactors change state, but you could always let up off the pedal yourself while "shifting" - something you no doubt are already quite capable of doing 

As for what you need... technically, it can be done with just three SPST-NO contactors(e.g. - Tyco EV200) and a SPDT relay to control them (and a pushbutton or toggle switch to control it). You could also do this with two SPDT contactors, or one DPDT (reversing) contactor. Note, however, that some (not all) of the contactors will need to be rated for the full controller output current.


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## toddshotrods (Feb 10, 2009)

Tesseract said:


> I assume - though you did not actually say - that you want to switch between the series and parallel configuration...


Yup. 




Tesseract said:


> 3. There's no reason why Jr. couldn't do s/p switching, and perhaps there is more of a benefit in doing so with a smaller controller?...


That's the totally aweosme answer I was really hoping for. I don't plan to race this bike, and would prefer to use a (physically) smaller controller. I just figured the series/parallel switch would make it more interesting and fun to ride than say a single motor.




Tesseract said:


> 4. Yes, see above - you just need to know what motor current is doing. It would be nice if the throttle signal was automatically suppressed for a couple hundred milliseconds while the contactors change state, but you could always let up off the pedal yourself while "shifting" - something you no doubt are already quite capable of doing


We used micro-switches on the bikes for the electric shifters. It's a small pressure switch that goes on the actual shifter and kills the motor for a fraction of a second, while you're pulling up on the lever, and allows it to slip into the next gear without using the clutch. The air shifters use an electronic control unit that you can program to kill the motor for a specified amount of time while the air cylinder is pushing on the shift lever. One of those two would work - preferrably the manual pressure switch to keep costs down as this would be a temporary fix until I could upgrade to Jr. Could even put an actual foot "shift" lever on it! 





Tesseract said:


> ...The short answer is that nothing special - except for three contactors (rated for the full motor current) - is needed to switch between series and parallel.
> 
> Many drag racers do this manually - that is, they select the contactor configuration with a toggle or pushbutton switch...
> 
> As for what you need... technically, it can be done with just three SPST-NO contactors(e.g. - Tyco EV200) and a SPDT relay to control them (and a pushbutton or toggle switch to control it). You could also do this with two SPDT contactors, or one DPDT (reversing) contactor. Note, however, that some (not all) of the contactors will need to be rated for the full controller output current.


Sweet, sweet, sweet! Thanks for a very informative reply Jeff. 

If I had to guess, the racers who are manually switching have found an extra tenth or two on the track and/or are the types that don't trust technology, and feel more secure knowing they're in control.


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## EVfun (Mar 14, 2010)

I would suggest some type of blanking circuit for the controller power section during the shift. Basically, a little time delay circuit that shorts the pot box wires (assuming the use of a 0-5k ohm pot) for around 0.1 second when a shift is initiated. This will make sure the controller doesn't see a sudden slight open circuit under full load. A photorelay being turned on by a time delay circuit set for a 0.1 second on time when powered could handle that nicely.


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## Tesseract (Sep 27, 2008)

Just a quick sketch of how you could do s/p switching with three SPST-NO contactors....

Note that with all three contactors off (NO) the motor will be off. With all three contactors on the controller will be short circuited...


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## toddshotrods (Feb 10, 2009)

Tesseract said:


> Just a quick sketch of how you could do s/p switching with three SPST-NO contactors....
> 
> Note that with all three contactors off (NO) the motor will be off. With all three contactors on the controller will be short circuited...


Awesome - thanks!


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## clintster7 (Jun 29, 2010)

not an expert but i think i know what u are talking about but I was just thinking that it would be nice to have the switch happen when shifting to say 3 rd or whatever gear that is close to what you want to do manually .. like a manual switch that is trigged by the shifter or cable ( or something like that ) a " manual switch that is automatic "


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## TX_Dj (Jul 25, 2008)

clintster7 said:


> not an expert but i think i know what u are talking about but I was just thinking that it would be nice to have the switch happen when shifting to say 3 rd or whatever gear that is close to what you want to do manually .. like a manual switch that is trigged by the shifter or cable ( or something like that ) a " manual switch that is automatic "


clintster, in this application there is no "3rd gear" because there is no transmission. The series/parallel shift changes the torque/rpm relationship of how the two motors work together, somewhat emulating the behavior of a 2-speed powerglide transmission.

This is the same setup that John Wayland has used with great success for several years in White Zombie, which he's pushing over 11 second passes (maybe faster now) under pure electric power (and he uses a controller)


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## clintster7 (Jun 29, 2010)

oh ok . no problem still a good idea .. I have seen the white zombie on you tube and looked at his build 750 lb of torque from the start .. cool car .


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## Dink (Jun 3, 2010)

Tesseract said:


> Just a quick sketch of how you could do s/p switching with three SPST-NO contactors....
> 
> Note that with all three contactors off (NO) the motor will be off. With all three contactors on the controller will be short circuited...


 What is benefit of series/ parallel switching with dual motors? Would you not get better performance using dual controllers of the same rating,(in parallel) as the one used for switching?


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## EVfun (Mar 14, 2010)

Dink said:


> What is benefit of series/ parallel switching with dual motors? Would you not get better performance using dual controllers of the same rating,(in parallel) as the one used for switching?


Sure you would, but at a pretty steep price. I think the top of the line Zilla that is in the White Zombie and Crazy Horse Pinto runs about $5500 each!

If you try to use two Z1k-EHV controllers to replace the single Z2k-EHV then you won't have the launch. At launch the Z2k can push 2000 amps through 2 motors in series. That is 4000 amps worth of torque. The pair of Z1k controller can each push a motor to 1000 amps, for 2000 amps worth of launch torque.


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## Dink (Jun 3, 2010)

EVfun said:


> Sure you would, but at a pretty steep price. I think the top of the line Zilla that is in the White Zombie and Crazy Horse Pinto runs about $5500 each!
> 
> If you try to use two Z1k-EHV controllers to replace the single Z2k-EHV then you won't have the launch. At launch the Z2k can push 2000 amps through 2 motors in series. That is 4000 amps worth of torque. The pair of Z1k controller can each push a motor to 1000 amps, for 2000 amps worth of launch torque.


 I don't understand. How is it that a Z2k that only handles 2000 amps, can push 4000 amps in series mode? It seems to me that you have the same amps either way, a Z1k to each motor or a Z2k to both.


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## Qer (May 7, 2008)

Dink said:


> I don't understand. How is it that a Z2k that only handles 2000 amps, can push 4000 amps in series mode? It seems to me that you have the same amps either way, a Z1k to each motor or a Z2k to both.


Torque is proportional to current. If you have a 2000A controller and connect the motors in series, you get 2000 Ampere through each motor, which gives the torque proportional to 2000 Ampere *per motor*. This is equivalent to connecting the motors to one 2000 Ampere controller each.

If you have a 2000A controller and connect the motors in parallel they have to share the total current and you get 1000 Ampere through each motor. This is equivalent to connecting the motors to one 1000 Ampere controller each.


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## clintster7 (Jun 29, 2010)

so? If the 2 motors start with more amps by sharing the overall low end torque is higher.. But will they draw less amps due to only half the volts.


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## Tesseract (Sep 27, 2008)

clintster7 said:


> so? If the 2 motors start with more amps by sharing the overall low end torque is higher.. But will they draw less amps due to only half the volts.


This doesn't make any sense. Please re-word your post or clarify what you are asking here.


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## clintster7 (Jun 29, 2010)

ok I'll try.. I'll just ask if it works like the batterys do.. ? Series/parralell one way you get twice the amps and the other you get twice the volts. But in a motor from what I understand (may be wrong) , if you only put half the volts will the motor pull less amps (im thinking about the way a motor graph looks) 
example ... A motor with 12 volts will have less amp pull than the same motor with 24 volts because it is tryin to reach a higher RPM/topspeed..

I think I may not be taking into account that the controller is already feeding it's max output.. As we are talking about max accel.. Sory for confuzion...


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## EVfun (Mar 14, 2010)

clintster7 said:


> so? If the 2 motors start with more amps by sharing the overall low end torque is higher.. But will they draw less amps due to only half the volts.


As the motor rpm climbs the motor voltage will increase. At some point they will draw less amps due to the lower voltage. At that point the motors are switched to parallel operation. 2 motor in parallel with a 2000 amp controller gives the same power as 2 motors each hooked to a 1000 amp controller.


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## Bowser330 (Jun 15, 2008)

EVfun said:


> As the motor rpm climbs the motor voltage will increase. At some point they will draw less amps due to the lower voltage. At that point the motors are switched to parallel operation. 2 motor in parallel with a 2000 amp controller gives the same power as 2 motors each hooked to a 1000 amp controller.


As EVfun mentioned above...at some point, since the voltage to the motor is half when in series, the motor will reach that max rpm and the amperage draw will reduce significantly, thats when the shift to parallel happens to now give the motor full voltage and full rpm range, however you have to settle for half the amps which would be 1000A in the case of the Zilla2K...

to actually get 2000A of torque from two motors to stick to the ground in a controllable way is the bigger challenge, of course the dragsters can do it because they have dragster class differentials and sticky slicks in the back...a normal EV would spin its way sideways...

1000A should be plenty...in a 9" motor that 250ftlbs of torque instantly @ 0-rpm...with enough voltage, that would be enough for a nice 0-60 in a lithium powered lighter weight EV.


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## Dink (Jun 3, 2010)

Bowser330 said:


> As EVfun mentioned above...at some point, since the voltage to the motor is half when in series, the motor will reach that max rpm and the amperage draw will reduce significantly, thats when the shift to parallel happens to now give the motor full voltage and full rpm range, however you have to settle for half the amps which would be 1000A in the case of the Zilla2K...
> 
> to actually get 2000A of torque from two motors to stick to the ground in a controllable way is the bigger challenge, of course the dragsters can do it because they have dragster class differentials and sticky slicks in the back...a normal EV would spin its way sideways...
> 
> 1000A should be plenty...in a 9" motor that 250ftlbs of torque instantly @ 0-rpm...with enough voltage, that would be enough for a nice 0-60 in a lithium powered lighter weight EV.


 So am I to believe that a given series motor will have the same power, if it is given the same amps at 72v and 144v, until the 72v rpm limit?


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## Qer (May 7, 2008)

Dink said:


> So am I to believe that a given series motor will have the same power, if it is given the same amps at 72v and 144v, until the 72v rpm limit?


Nope. Same torque, not the same power.

power=voltage*current

But also:

power=RPM*torque

and since torque is proportional to current that implies that RPM is proportional to voltage.


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## clintster7 (Jun 29, 2010)

above price $$ was brought up .. So 2 smaller controllers could be used .. How much would a spagetti box cost .. And I'm not sure the spagetti box + 2 controllers would be compatible .. So is the choice 2 controllers or 1 controller+ spagetti box .. ?


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## Bowser330 (Jun 15, 2008)

clintster7 said:


> above price $$ was brought up .. So 2 smaller controllers could be used .. How much would a spagetti box cost .. And I'm not sure the spagetti box + 2 controllers would be compatible .. So is the choice 2 controllers or 1 controller+ spagetti box .. ?


say whaaaaat?


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## clintster7 (Jun 29, 2010)

Bowser330 said:


> say whaaaaat?


ohh sorry .. I was talking about the *hair ball * not " spaghetti box " don't have any Idea where spaghetti box came from .  but hair ball and spaghetti kinda look alike if you are talking about wires. haha 

here is the video I was looking at when I came up with the question ......


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## EVfun (Mar 14, 2010)

Once again, he has a far faster launch in the White Zombie because he uses a single 2000 amp motor controller and series/parallel switching. He can drive up to 2000 amps through *both* motors for launch. If he was using 2, 1000 amps Zillas he could only drive 1000 amps through 2 motors at launch. Then he would need lower gears to get the launch he has not and the speed at the other end of the quarter mile would be lower (and time slower) as a result.


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## Dink (Jun 3, 2010)

Qer said:


> Nope. Same torque, not the same power.
> 
> power=voltage*current
> 
> ...


 Lets see if I understand things correctly. That when wired in series the amps are fully delivered to each motor, but at half the volts. In parallel half the amps but full voltage. So by doing the series/parallel switching, you can achieve more low rpm torque(series) then swich to hp(parallel). Being the volts only limit or control rpm provided that there is constant amps supplied,the motors don't care until that magic volt/amp cross over point. Like 5252rpm is where torque and hp cross in an ICE. That hp don't matter till after 5252rpm.


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## Qer (May 7, 2008)

Dink said:


> Lets see if I understand things correctly. That when wired in series the amps are fully delivered to each motor, but at half the volts. In parallel half the amps but full voltage. So by doing the series/parallel switching, you can achieve more low rpm torque(series) then swich to hp(parallel). Being the volts only limit or control rpm provided that there is constant amps supplied,the motors don't care until that magic volt/amp cross over point. Like 5252rpm is where torque and hp cross in an ICE. That hp don't matter till after 5252rpm.


Here's a small article Otmar has written about series/parallel shifting.

http://www.cafeelectricpress.com/blog/?p=40

What he doesn't write is that the torque curve is flat up to the hp-peak where the torque starts to drop. Then, after the shift to parallel, the torque curve becomes flat again (but at half the level as before) until it starts to fall off again after the new hp-peak.


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## evnz (Jul 24, 2010)

Tesseract said:


> Just a quick sketch of how you could do s/p switching with three SPST-NO contactors....
> 
> Note that with all three contactors off (NO) the motor will be off. With all three contactors on the controller will be short circuited...


just interested what was f1 and f2 in the drawing please
thanks 
owen


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## major (Apr 4, 2008)

evnz said:


> just interested what was f1 and f2 in the drawing please
> thanks
> owen


Tess seems like a morning person so I'll give it a shot tonight and he can chime in later. I believe f1 & f2 represent the series fields in motor 1 and motor 2 respectfully.


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## Tesseract (Sep 27, 2008)

evnz said:


> just interested what was f1 and f2 in the drawing


F1 & F2 are the field windings of the motor. That was just to make it extra clear that this should only be used on *series field* motors. Not PM motors, not SepEx, not shunt, etc.


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## Frank (Dec 6, 2008)

I hope you do this (switching) as I'm interested in your impressions on a street machine. I would like to point out though that with a higher voltage and stiffer pack it's not really necessary, as long as the sagged pack voltage is as least as high as twice the voltage limit of a single motor.


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## evnz (Jul 24, 2010)

white zombie use s/p so what is the best ?
if i put two motors together series give a through you in your seat torque and then parallel gives ?


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## dcb (Dec 5, 2009)

There's a few posts on it, but basically if you assume the controller is limiting the current, then series gives you full current to each motor and 1/2 voltage (till the rpm and back emf of both motors builds up to pack level).

Then parallel applies full voltage and half the current to keep the rpms climbing.

White zombie controller turned on a relay to switch between them.


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## dougingraham (Jul 26, 2011)

evnz said:


> white zombie use s/p so what is the best ?


I think I read that in the last season they were running it they eliminated the series/parallel switching because there was no advantage.


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## Frank (Dec 6, 2008)

S/P switching was developed because of the tremendous sag of lead-acid batteries. With a very stiff pack there's no advantage


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## dcb (Dec 5, 2009)

looks like the blog entry is here:
http://www.plasmaboyracing.com/blog/?p=206

the s/p circuit was acting up so they left it in series and got better results.

There is a little more area under the curve with series/parallel on the low end, so someone might find it useful in the right circumstances, but lightweight, high power for short duration doesn't look like it with the current state of technology.


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## EVfun (Mar 14, 2010)

If your pack voltage is sufficiently high there is little advantage to switching the motors to parallel mode. Parallel mode is available to increase the motor voltage so the motors will make more power at higher rpms. Most of the DC motors we are using can take less than 180 volts across the terminals. A stiff 360 volt pack can supply that to both of them in series.


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## evnz (Jul 24, 2010)

So i could set up two forklift motors in series on a 140 volt pack and limit the controller to say 600 amp and each motor is getting 70v and 600 amps 
Correct? 
So a drifft car needs tyre spin would you get more from series or parallel?


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## dougingraham (Jul 26, 2011)

evnz said:


> So i could set up two forklift motors in series on a 140 volt pack and limit the controller to say 600 amp and each motor is getting 70v and 600 amps
> Correct?
> So a drifft car needs tyre spin would you get more from series or parallel?


Max power is limited by the battery voltage in this case which is 140. Current is limited by the controller setting of 600 amps. Assuming no voltage sag your max power will be 140*600 = 84000 watts or 84 kw or 113 hp. Series and parallel don't enter into it for this number. Torque is directly proportional to the current each motor sees. To maximize the torque you want to series the motors. That way both motors see the full 600 amps. The downsize of this is now each motor only sees 70 volts which will cut the max RPM at which you get this torque in half. This may not be a wide enough torque band to get you what you want. Your best bet to maximize power is to put in as high a voltage pack as your controller can support effectively and then work your way up in current and voltage to find the limits. In your example you want a 280 volt sagged pack so both motors see 140 volts when in series. If your controller will only do that 140 volts at 600 amps then use two controllers, one for each motor. In this case you would need a battery that can source 1200 amps at peak.

Hope that helps.


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