# Dual, twin, Siamese, multiple motor discussion



## Matej (Dec 4, 2015)

Hello gentlemen,
Sorry if a similar topic already exists, but after searching I only ended up with more questions than I had initially. 

As I pondered my future conversion for several moons, I came to the conclusion that I really want two inline DC motors. I do not necessarily have any specific goals as far as power or range or top speed. My goal itself is having a working twin motor setup, whether it be two forklift motors or a pair of Warp 9's or anything in between. I am fascinated by the twin setups, even though I realize it may not be an ideal 'My First EV' project.

The physical aspect of mating and mounting the motors does not seem terribly difficult. I do however have plenty of questions regarding the controllers, voltage, and behavior of the Siamese setup versus a single motor. Some of the questions are probably quite dumb, but I have not had much luck finding the answers online so far.

For the sake of keeping the numbers simple, let us say we have two 72V motors coupled together:
1. Is it better to use two 72V controllers or a single more powerful controller, or is it simply a matter of preference?
2. If using a single controller with the motors connected in series, should it be a 72V or a 144V controller?
3. If using dual controllers, should the motors still be connected in series or should each motor be connected separately only to its respective controller?
4. Is there any scenario where the motors would be better connected in parallel?
5. Should the battery pack voltage be 72V or 144V with the dual controllers?
6. Should the battery pack voltage be 72V or 144V with a single controller?
7. Will the top speed remain the same as it would be with a single 72V motor, or will it be higher with the dual setup?

Those are the main things I am curious about at the moment. I do not expect anyone to answer all of the questions at once, plus I am sure I will have many more in the future. I would simply love to learn as much as possible about running paired motors, so any input or thoughts are welcome and appreciated.
Thanks in advance!


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## EVfun (Mar 14, 2010)

"1. Is it better to use two 72V controllers or a single more powerful controller, or is it simply a matter of preference?"

It is mostly a matter of choice, but if you go with a higher pack voltage and choose to wire the motors in series then you need to go with a single controller. Motor controllers can rarely be run in parallel.

"2. If using a single controller with the motors connected in series, should it be a 72V or a 144V controller?"

If the motors are in series you need to apply 144 volts for each motor to get 72 volts. Since motors run hotter and less efficient at when under design voltage you should run them at (or even a little above) design voltage. 

"3. If using dual controllers, should the motors still be connected in series or should each motor be connected separately only to its respective controller?"

If you are using duel controller they will be wired individually to 2 controllers.

"4. Is there any scenario where the motors would be better connected in parallel?"

High speed operation is best done in parallel if you do not have sufficient voltage. Each motor sees the full controller voltage at only half the motor current.

"5. Should the battery pack voltage be 72V or 144V with the dual controllers?"

72 volts to insure even discharge.

"6. Should the battery pack voltage be 72V or 144V with a single controller?"

I'd recommend 144 volts with the motors wired in series and a single controller. However, there are few EV motors that are designed for such a low voltage. Resistive losses tend to fall as the voltage goes up because the current needed for any given amount of power goes down.

"7. Will the top speed remain the same as it would be with a single 72V motor, or will it be higher with the dual setup?"

Likely little change in top speed provided the single motor doesn't turn into slag trying. Your peak power level will be mostly dictated by the controllers current limits and your pack voltage.


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## Matej (Dec 4, 2015)

Fantastic information. Thank you for bothering to answer all the questions. I really appreciate it!




EVfun said:


> "7. Will the top speed remain the same as it would be with a single 72V motor, or will it be higher with the dual setup?"
> 
> Likely little change in top speed provided the single motor doesn't turn into slag trying. Your peak power level will be mostly dictated by the controllers current limits and your pack voltage.


To understand this better, if using the two 72V motors connected in series with a single 144V controller and a 144V battery pack (or slightly more than 144V in a realistic scenario), the top speed would be limited to the equivalent of that of a single 72V motor being fed 72V, correct?
Or would it be more similar to a single 144V motor being fed 144V, if I am misunderstanding?

I do not have a concrete parts list picked out yet, though it would certainly be nice if I could reach highway speeds, at least for a few miles at a time. Thus I am trying to determine what would be the smallest individual motor size/voltage that I could get away with using for the dual setup.


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## EVfun (Mar 14, 2010)

The single motor on 72 volts and the duel motors on 144 volts both result in the motors seeing 72 volts. To get the same power with the single motor at 72 volts you will need 2 times the current (at half the voltage.) Voltage relates to rpm and current to torque. There is a catch. The duel motors will make twice the power above that point where they come out of current limit. That will increase top speed but it won't take much extra rpm to pull the current down to half, thus the power down to half and reach that point where the lack of available power stops acceleration. 

The important thing to remember is that power is power. 746 watts is 1 horsepower (at 100% efficiency.) At low rpm the current will be limited by the controller, so you have a fixed torque as the rpm rises. At some point you "come out of current limit" which means the controller can give the motor full pack voltage without the current exceeding the controller limits. Right there is peak power. Above that rpm the motor rapidly accepts less current at full pack voltage (more voltage would be needed to force more current.) The current (and so torque) falls off faster than the rpm rises, so motor power falls. The series wound DC motors that are commonly used tend to make peak power at a significantly lower rpm than the gas engines they replace. We usually try to run them at as high a voltage as practical. Duel motor EVs are typically over 200 volts.

Duel motors are usually used to eliminate the transmission. In these cases the biggest benefit is the extra commutator area. With a low gear it is you need a lot of motor current to directly create the torque needed for acceleration because you don't have a lower gear. That extra current for extra time could melt down the commutator. A bigger total commutator area means a higher current can be sustained for longer before things start to fail. I pulled this off in my Buggy with one Prestolite MTC motor. I was running around with a 1000 amp peak current limit and driving only in 3rd gear. The Buggy only weighs about 1200 lb. with a 1.32 3rd and a 4.37 ring and pinion. I still managed to melt the leads off of my brushes driving that way. By turning the current down to 750 amps and using 2nd gear so the motor rpm climbs faster (motor current falls faster) the new brushes have not even slightly discolored the brush leads.


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## ferd (Dec 1, 2015)

Our club has built two dual motor EV cars, so please allow me to offer some of our experiences.


On the first car unfortunately I don’t have a lot of information, but I do know it used two Warp 7 motors wired in series, with a single controller and I believe a 120V battery pack (lead acid). I think he used two Warp 7s because he happened to have them available; he coupled them by pressing one long bar through both of their armatures. I was told he experimented with wiring the motors in parallel as well as series, but found better performance with them in series – probably due to the battery pack being required to deliver less current to meet driving loads (while wired in series). 

The other car used two Warp 9 motors that were coupled by pulleys and belts. It had one controller, and a 144V battery pack (lead acid). The owner first built the car with one motor, but added the second assuming he could double both the torque and the battery range. He did improve road performance (although we could not verify that it was twice as good) and he did improve battery range about 25% (but not double). Obviously two motors provided extra torque, which in turn improved road performance. We figured that the range improvement came from operating the motors closer to their most efficient operating conditions – his average current draw fell from about 150 amps to 90 amps, and his peak current draw fell from 425 amps to 400 amps. 

It may have been possible to wring better performance out of each car, but unfortunately neither project was alive long enough before budget and aged battery problems parked them. Since then both builders have preferred to stick with single motor / controller designs.


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## Matej (Dec 4, 2015)

Thank you for the input, EVfun. Great information once again.

ferd, do you by any chance happen to know what the approximate top speed was for the dual Warp 7's and Warp 9's with their respective battery pack voltages? It is always great to have some real world references.
Is there a reason why both owners decided to switch to a single motor? Making things simpler and easier to service, I venture to guess?


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## Caps18 (Jun 8, 2008)

I've wondered about the range improvements with two motors. Regen might be more powerful as well.

Now, the extra cost probably isn't worth it to most people, and the extra complexity in wiring isn't a great thing either. But, I would be interested in seeing a single controller that could control two motors.


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## jwiger (Oct 18, 2014)

Any of the major controllers can run more than one motor, provided they are mechanically connected. The Zilla 2K can pretty easily run two Warp9 motors on the road. EV West's BMW uses an Evnetics Shiva controller to drive two Warp11s in parallel. Their car makes 850 ft/lbs and zips past 100 mph pretty easily.


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## ferd (Dec 1, 2015)

Matej said:


> ferd, do you by any chance happen to know what the approximate top speed was for the dual Warp 7's and Warp 9's with their respective battery pack voltages? It is always great to have some real world references.
> Is there a reason why both owners decided to switch to a single motor? Making things simpler and easier to service, I venture to guess?




I don't know what the top speed was for the dual Warp 7 conversion, although its builder told me he mostly drove it on secondary roads (where the speed limit was 45 mph). He was limited by his controller (an older Curtis unit that would trip if he tried to get more than about 350 amps out of it) and his batteries (which were old lead-acid that were well past their expiration dates). I think his car could have handled modern highway speeds if he replaced the controller and batteries.

As far as I know, the dual Warp 9 conversion was also only driven on secondary roads, usually never faster than 45 mph. We did take it to a couple of EV challenge events, but those tested battery range instead of top speed. This car also suffered from lead-acid batteries that were past their primes. It also suffered from a poorly thought out and executed installation that included sectioning out a piece of one frame rail - making the car flex and probably unsafe. 

The owner of the dual Warp 7 conversion might still have that car, but I don't think it has been running for years. His budget was spread too thin to afford replacing batteries, and his time was spread too thin due to trying to launch a business (non-EV related). I might try to track him down and see if I can revive his conversion - it potentially could be a fun project (it’s a Triumph TR7 convertible).

The owner of the dual Warp 9 conversion finally realized that his car was unsafe, so he stripped out the EV parts for other projects. He's back to single motors because, as you suspected, it's less complicated. One of the motors went into a Factory Five '33 Hot Rod kit car, and the other into an Allison dune buggy kit car. He still has and uses the Allison, but the '33 Hot Rod is gone (not sure if those EV parts went with it).


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## Matej (Dec 4, 2015)

Another thing that I have been wondering about is whether the two motors need to be identical. Obviously everyone uses two of the same motor because it is easier to set up and control that way. However, I am curious what would happen if two different motors were connected.

For example, let us say we attach a Warp 7 to a Warp 9.

Version 1:
We wire the motors in series to be controlled with a single controller. Would the smaller motor act similar to a supercharger on an ICE, or would it do the opposite and just hinder the performance of the larger motor?

Version 2:
We use a separate controller for each motor. Could the controllers be programmed in such a way that the power/torque curves of the motors complement each other throughout the rpm range?

Thanks for any insight.


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## jwiger (Oct 18, 2014)

If you are going to link DC motors, you want them to be as close to identical as possible due to the rpm of the torque knee. This knee is caused by back EMF (Electo Motive Force) it has to due with the motor acting as a generator and pushing back on the voltage supply from the controller. It's the principle that makes DC series motors spin an RPM almost directly proportional to their input voltage. 

This occurs at lower RPMs in larger diameter motors if all else is the same. The warp 7 needs to spin faster than the warp 9 to hit its max HP. But the RPM would be limited to the slower 9" motor. I think some people are pairing warp9s with Impulse9s. The difference is the length if I recall. 

I'm planning on experimenting with a warp9+UQM (dc+ac combo) in the future. But that's way off.


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## WolfTronix (Feb 8, 2016)

For another data point.

The Solectria E10 runs two motors in parallel, each driven by their own 144V controller.

Each motor has a pulley which belt drives a larger common pulley on the drive shaft to the differential.

Motors and belt box:
http://www.wolftronix.com/E10/images/P4280346.jpg

Inside the Belt box:
http://www.wolftronix.com/E10/images/P4210300.jpg

I am a fan of the dual parallel drive, when you have one motor or controller go down, you can still make it home. 

More info:
http://www.wolftronix.com/E10/index.html

Hope that helps, 
Wolf


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## mizlplix (May 1, 2011)

To get as much satisfaction you can from your project first figure out the biggest pack it can fit in. THEN figure how much you want to spend on a pack.

That will determine everything else.

Miz


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## Matej (Dec 4, 2015)

To revisit this thread, I have a follow-up question regarding using two controller versus a single controller.

For example, how would using two 144V 500Amp controllers compare to using one 144V 1000Amp controller for both motors wired in series?

Which configuration would be more efficient and which would be more powerful? Or would the performance be similar?

Thank you.


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## Matej (Dec 4, 2015)

Would the setup pictured below be functional? Or would the controllers and motors just fight each other?

It is a very crude diagram with only the main components, but basically both controllers and motors would be on their own separate circuits, only sharing the main traction battery and throttle input.


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## Matej (Dec 4, 2015)

Another question related to the diagram above.

In the future, could I add a second identical battery pack to increase range and current, so that each motor/controller would have its own separate battery pack?

I assume it would primarily be a matter of somehow keeping the two packs in perfect balance, if that is even possible.


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## PStechPaul (May 1, 2012)

I think much depends on the type of motors and controllers. I assume the two motors will be mechanically connected on a single shaft. 

For series DC motors, speed is proportional to voltage, and current is proportional to torque. Two PWM controllers with matched output voltages will run the motors at the same speed, and I think the current will balance to get equal torque from each, to some extent. It may help to se current sensors to assure balance, and speed sensors to maintain good control.

PM DC motors will probably work in a similar manner. BLDC motors are speed-controlled by frequency, so they should be more easily balanced.

AC induction motors may be most easily controlled this way, as their speed is mostly controlled by frequency, but they also have some degree of slip which depends on torque.

I don't have specific experience with such connections, so I may not be correct. Pretty much anything _can_ be done, but good control may require some extensive (and expensive) electronics and sensors.

[edit] Adding a second battery pack would not require them to be perfectly balanced, although if not, one may run down faster than the other. Probably best to use one larger pack in parallel or series, for both controllers and motors.


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## Matej (Dec 4, 2015)

PStechPaul said:


> I think much depends on the type of motors and controllers. I assume the two motors will be mechanically connected on a single shaft.


Thank you for the information and taking the time to reply to my never-ending questions. 

The controllers are two Curtis 1253 80V 600A units. I know a single one would be less than ideal for an EV conversion, but I happened to buy two brand new ones for a steal, and I think using two of them could actually make the car driveable with a transmission. Plus the low voltage is probably a good thing for a first time conversion.

As for the motors, I have an ADC 9" series wound, though I am undecided if I should look for a second ADC, or just sell it and buy two Warp9's which are the easiest to find new and used. Ideally I would prefer two Warp7's or 8's, but it is hard to justify buying them new when they cost almost as much as a new Warp9, in fact some places do sell the 9 for cheaper.

The reasoning behind a second pack was primarily that both controllers probably cannot draw 600A from the same pack simultaneously (I will be using Leaf modules), but they could draw 600A each from two separate packs. Though of course I may be wrong about that, plus it is of secondary importance at this time, as I will be starting out with a small single pack anyway.


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## dougingraham (Jul 26, 2011)

Matej said:


> To revisit this thread, I have a follow-up question regarding using two controller versus a single controller.
> 
> For example, how would using two 144V 500Amp controllers compare to using one 144V 1000Amp controller for both motors wired in series?
> 
> ...


The two controller setup is almost certainly more efficient when operated wide open. In this case the more efficient setup would be the more powerful one. However since you don't operate at wide open throttle very often the difference in normal street operation is not going to be much.

Since you are talking about dual motors the typical options are:

1) Single 340+ volt 1000 amp controller with motors wired in parallel. Set the controller to output 172 volts and 1000 amps and you will see the current share between the motors and you will have 172kw input to the motors or ~160 hp output power.
2) Single 340+ volt 1000 amp controller with motors wired in series. Set the controller to no limit on the output voltage because it will be ok at batt voltage / 2. Current limit to 1000 amps and you will have ~300kw input to the motors or ~ 280 hp output.
3) Dual 144 volt 500 amp controllers with reworked leaf battery to 144 volts. You should see peak input power to the motors of 144 kw and output power of ~135 hp.

For normal street use a two seat sports car might take around 20 kw to hold 60mph on the level. So any of these setups will easily do highway speeds assuming you keep the transmission so you can select an appropriate gear.

Your real limiting factor in the above is going to be the battery. A Leaf battery is setup to do ~120 kw. You can do more than this but at a cost in the life expectancy of the pack.


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## Matej (Dec 4, 2015)

dougingraham said:


> Your real limiting factor in the above is going to be the battery. A Leaf battery is setup to do ~120 kw. You can do more than this but at a cost in the life expectancy of the pack.


Thank you for answering my questions.

If using a separate Leaf module pack for each motor/controller, could they theoretically do up to 240kw?


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## dougingraham (Jul 26, 2011)

Matej said:


> If using a separate Leaf module pack for each motor/controller, could they theoretically do up to 240kw?


Shouldn't be a problem. I would probably parallel the packs but you wouldn't have to.


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## electron bom (Dec 4, 2014)

dougingraham said:


> TA Leaf battery is setup to do ~120 kw. You can do more than this but at a cost in the life expectancy of the pack.


Where are you getting the 120kw figure?


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## Matej (Dec 4, 2015)

dougingraham said:


> Shouldn't be a problem. I would probably parallel the packs but you wouldn't have to.


This is an embarrassing question, but would paralleling the packs increase the maximum instantaneous current limit in the same manner as each motor/controller having its own pack would?

I know the amp hours will double, but I am curious how paralleling batteries affects the maximum amps that can be drawn, strictly from a performance standpoint.


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## electron bom (Dec 4, 2014)

Matej said:


> This is an embarrassing question, but would paralleling the packs increase the maximum instantaneous current limit in the same manner as each motor/controller having its own pack would?
> 
> I know the amp hours will double, but I am curious how paralleling batteries affects the maximum amps that can be drawn, strictly from a performance standpoint.


Discharge current is a function of the cell design, chemistry etc. Motor controllers are limited in the amount of power (or energy per unit time) they can draw from a battery, but the battery has its own energy and power limitations as well. 
In ICE terms: an ICE has a factory assigned power rating (300kW V8), but the fuel it combusts to generate that power has a finite amount of energy within the chemical bonds that comprise the hydrocarbon itself (1 gal pump gas = 1.3x10^11J). The rate at which that bond energy is translated into kinetic energy (referenced as torque/hp at the flywheel) describes the ICE power rating. 

All else being equal, Maximum C rate and capacity correlate directly. 

Copied and pasted from mit.edu:
_A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this battery would be 500 Amps, and a C/2 rate would be 50 Amps. _

Read more: http://web.mit.edu/evt/summary_battery_specifications.pdf
Good resource:http://batteryuniversity.com/


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## Matej (Dec 4, 2015)

electron bom said:


> All else being equal, Maximum C rate and capacity correlate directly.


Thank you for clarifying.
The only threads on the topic I could find were on RC forums, where half of the members would say paralleling batteries only doubles amp-hours but the C-rate remains constant due to battery chemistry, while the other half claimed that C-rate is doubled is well.
That only led me to being more uncertain than I was before. 

So translating this to an EV application, even Leaf or Volt batteries could be utilized for a 1200+ amp performance application despite having very low discharge rates, as long as enough of them are paralleled together, correct?


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## electron bom (Dec 4, 2014)

I've read MANY different opinions/claims on what power levels the LEAF cells will support. Doug has claimed 120kw above, but I'm not sure how he arrived at that number. Jack Ricard has a video of some LEAF modules discharging at 700A, but he later burnt up his building with those modules (no BMS). Electricwiki cites a Nissan claim that the cells have a power density of 2.5kW/kg, which almost sounds too good. One thing is for sure, the cells DO handle the 80-90kW LEAF power rating. 
Link: http://www.electricvehiclewiki.com/Battery_specs

Just for fun, this is what I get for max C rate based on electricwiki's number:
Each module weighs: 3.8kg 
3.8kg x 2.5kW/kg = 9.5kW per module 

Each module has a nominal voltage of 7.6V
9.5kW/7.6V = 1250A
1250A/66Ah = 18.93 C 

However, I sense it would be disastrous to pull this much current from a LEAF pack and there would undoubtedly be some serious sag.


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## WolfTronix (Feb 8, 2016)

The Leaf Pack BMS reports back the real time KW that can be safely drawn from it.

Mine reports back that is has 110kW available:
https://youtu.be/e6CroYIOoas

As it heats up / discharges, the KW value goes down.

110kW / 360V = 300A, but the fuse in the Leaf pack is rated at 225A...

But I am sure its I2t value lets it handle 300A for a few seconds without popping.


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## electron bom (Dec 4, 2014)

Thanks for sharing!


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## dougingraham (Jul 26, 2011)

electron bom said:


> Where are you getting the 120kw figure?


Glad you asked. I messed up. Leaf does 80kw, not 120kw. So paralleling two would allow 160 kw, not 240 kw. And this would be for short periods of maybe as much as 30 seconds, not extended runs.

Can the batteries do more? Probably. Just depends on how long you want them to last. If you treat them the way Nissan does they will hold up pretty well.


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## Frankenfiftyfour (Jul 22, 2019)

Matej said:


> Hello gentlemen,
> Sorry if a similar topic already exists, but after searching I only ended up with more questions than I had initially.
> 
> As I pondered my future conversion for several moons, I came to the conclusion that I really want two inline DC motors. I do not necessarily have any specific goals as far as power or range or top speed. My goal itself is having a working twin motor setup, whether it be two forklift motors or a pair of Warp 9's or anything in between. I am fascinated by the twin setups, even though I realize it may not be an ideal 'My First EV' project.
> ...


 Hi, Im looking to do something like this, did you ever come up with a solution?


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