# Best Controller for a pair of Agni PMDC motors?



## stuff_it (Nov 13, 2012)

I was going to go with a Kelly, and just use one that exceeded our needs as many people say that they tend to be a bit under the Amp rating that they claim in practice. 

I have since seen a few places that they also suffer from lag, so I was wondering if there were any other suggestions. 

It is to power/control a pair of Agni 119-R motors (linked together physically and wired in parallel) for a Formula Student car. 

What I need from a controller: 

probably at least 1000A and 100V capability as a minimum to be on the safe side.

Regen not super important due to the low weight of the car.

Minimal lag, due to racing conditions. 

Easy to program with at least two acceleration profiles and easy to install switching between these. 

Thanks in advance.


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## major (Apr 4, 2008)

stuff_it said:


> I was going to go with a Kelly, and just use one that exceeded our needs as many people say that they tend to be a bit under the Amp rating that they claim in practice.
> 
> I have since seen a few places that they also suffer from lag, so I was wondering if there were any other suggestions.
> 
> ...


Save yourself a lot of grief and use separate controllers or run the motors in series.


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## stuff_it (Nov 13, 2012)

major said:


> Save yourself a lot of grief and use separate controllers or run the motors in series.


I've been told this could cause a lot of issues with tuning the motors in series (advice from a lot of forums and from Agni) and we want to run a physical diff rather than an electric one as it's a fairly technical operation to program an E-LSD properly as several other teams have found out in the past. 

My understanding is that using the motor's wired in parallel can cause all manner of problems that our team is not equipped to address. Agni's own motorcycle racing team chose to run in series with one controller, also we have acces to a fairly well respected physical/meatspace differential that it would be nice to re-use.


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## major (Apr 4, 2008)

stuff_it said:


> It is to power/control a pair of Agni 119-R motors (linked together physically and *wired in paralle*l)





major said:


> ..or run the motors in series.





stuff_it said:


> My understanding is that using the motor's wired in parallel can cause all manner of problems


So, you running series or parallel


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## stuff_it (Nov 13, 2012)

major said:


> So, you running series or parallel


Sorry, it's a bit late here - running in parallel. I understand this with one controller is better.


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## major (Apr 4, 2008)

stuff_it said:


> Sorry, it's a bit late here - running in parallel.


Yet you admit:


stuff_it said:


> My understanding is that using the motor's wired in *parallel* can cause all manner of *problems* that *our team is not equipped to address*.


I don't get it


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## stuff_it (Nov 13, 2012)

major said:


> Yet you admit:
> 
> I don't get it


Look, it's late as I already said - I made a mistake. 

I aim to run them in parallel as in this post on another forum: http://www.elmoto.net/showthread.php?1090-Running-dual-Agnis-(or-other-motors)

So that I can use one controller.

I have come to this as a first year engineering student knowing absolutely jack/shit^2 about electric drivetrains, so I apologise in advance about any slip ups with terminology.


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## major (Apr 4, 2008)

stuff_it said:


> Look, it's late as I already said - I made a mistake.
> 
> I aim to run them in parallel as in this post on another forum: http://www.elmoto.net/showthread.php?1090-Running-dual-Agnis-(or-other-motors)
> 
> ...


Get some sleep and read this when you are alert  

http://www.elmoto.net/showthread.php?1932-Dual-motor-setup-what-have-we-learned


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## stuff_it (Nov 13, 2012)

I apoligise for being a bit short, but I am really in a bit of a pickle - the university I am studying at doesn't have a well established team, I am drivetrain manager by default, and the rest of my team are on a scale of 'a bit useless' to ' doing actually nothing'. 

I realise that it's something that I should just google for but despite may fairly awesome google-fu I simply don't have the time to do everything (including my full time degree) so any advice about running a pair of Agni motors off of one controller would be massively appreciated, especially which controller to use that is not a Kelly (due to lag). 

I mostly want to know about alternative controllers. 

I would really appreciate any genuine help, thanks. 

Sorry, I should read when more alert.

It's all very confusing for me as I haven't any proper training for it, or indeed much help from anyone experienced - an electric drivetrain is a first for the team as well as myself.


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## Tesseract (Sep 27, 2008)

stuff_it said:


> ...
> I realise that it's something that I should just google for but despite may fairly awesome google-fu I simply don't have the time to do everything (including my full time degree) so any advice about running a pair of Agni motors off of one controller would be massively appreciated, especially which controller to use that is not a Kelly (due to lag). ...


You really do not want to run two PM DC motors with their shafts locked together in parallel. Series is fine, but parallel is a no-no because the PM DC motor has a fixed relationship between voltage and RPM called Kv which inevitably varies from motor to motor. If the RPM is forced to be the same (because the shafts are locked together) and the applied voltage is the same (because the motors are in parallel) but the Kv value is different, then the motors will both not share the load equally and circulate current between them, leading to higher I²R losses without any tangible benefit.


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## stuff_it (Nov 13, 2012)

Tesseract said:


> You really do not want to run two PM DC motors with their shafts locked together in parallel. Series is fine, but parallel is a no-no because the PM DC motor has a fixed relationship between voltage and RPM called Kv which inevitably varies from motor to motor. If the RPM is forced to be the same (because the shafts are locked together) and the applied voltage is the same (because the motors are in parallel) but the Kv value is different, then the motors will both not share the load equally and circulate current between them, leading to higher I²R losses without any tangible benefit.


Yes I just looked, I meant series all along - serves me right for posting when I'm 'tired'. 

I always get the two mixed up. 

Please can someone advise about *Controllers* as I keep asking?


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## Tesseract (Sep 27, 2008)

stuff_it said:


> ....
> Please can someone advise about *Controllers* as I keep asking?


You can lead a horse to water...

||||||||||||||||||||||||||||||||||
VVVVVVVVVVVVVVVVVVVVVVVVVV


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## stuff_it (Nov 13, 2012)

Tesseract said:


> You can lead a horse to water...
> 
> ||||||||||||||||||||||||||||||||||
> VVVVVVVVVVVVVVVVVVVVVVVVVV


Thanks.

Just out of curiosity is it possible to store and switch between more than one acceleration profile using this controller? Say if you wanted an 'eco' and a 'sport' mode.


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## Tesseract (Sep 27, 2008)

stuff_it said:


> ...
> Just out of curiosity is it possible to store and switch between more than one acceleration profile using this controller? Say if you wanted an 'eco' and a 'sport' mode.


Nope, but you only need a laptop with an ethernet port and a web browser to change all relevant parameters. Not as convenient as a switch, I'll admit, but we really couldn't think of a way to add this function to the flash memory space we have left to play with and it not be a total kludge. Sorry, them's the breaks sometimes.

Which reminds me... the current/voltage specifications in your first post are way out of whack for two Agni 119-R motors in series. You really want a minimum traction battery voltage of 200V, and a maximum motor current of 500A (~3x the continuous current rating of 170A). Trying to push more current than that through a PM motor can result in demagnetization of the PM field.


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## stuff_it (Nov 13, 2012)

Tesseract said:


> Nope, but you only need a laptop with an ethernet port and a web browser to change all relevant parameters. Not as convenient as a switch, I'll admit, but we really couldn't think of a way to add this function to the flash memory space we have left to play with and it not be a total kludge. Sorry, them's the breaks sometimes.
> 
> Which reminds me... the current/voltage specifications in your first post are way out of whack for two Agni 119-R motors in series. You really want a minimum traction battery voltage of 200V, and a maximum motor current of 500A (~3x the continuous current rating of 170A). Trying to push more current than that through a PM motor can result in demagnetization of the PM field.


Thanks, I know it sounds terrible that I'm so vague on the voltages and stuff but I'm a first year and have ended up drivetrain manager for our Class 2 (Design) Formula Student team pretty much by default. Don't worry I won't be wiring anything up without a lot of help!

I don't know what your browser interface looks like but in theory if it were also controllable entirely by keyboard would it be possible to augment it with something like a Rasbperry Pi (to run scripts to do the switching for you)? Pretty sure that wouldn't fall within the rules for what I'm doing but jut curious.


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## Jozzer (Mar 29, 2009)

I've done series and parallel of twin Agni's, and whilst both CAN work, series is a lot easier and more reliable.
My current favorite method is a Soliton Jnr 500A controller and a 200v pack.
It's very easy to rig up a 3 way switch to give you 3 "torque profiles" using the "reverse" and "valet" modes of the controller to limit power (both in forward direction).

If your going racing, try to get ahold of the Agni 111RDR motor, which is a little more efficient under higher loadings and can utilise 100v (per motor) instead of 84v (max safe voltage/speed for a 95R).

As Tess says above, 500A is about all you'd want to push through an Agni, although the magnets/armature may be able to handle a little more (possibly) the brushes certainly cannot!


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## stuff_it (Nov 13, 2012)

Jozzer said:


> I've done series and parallel of twin Agni's, and whilst both CAN work, series is a lot easier and more reliable.
> My current favorite method is a Soliton Jnr 500A controller and a 200v pack.
> It's very easy to rig up a 3 way switch to give you 3 "torque profiles" using the "reverse" and "valet" modes of the controller to limit power (both in forward direction).
> 
> ...


I was considering 119-Rs though I'm a bit confused about how the continuous output powers are lower at a given voltage. As a 1st year Mech Eng student we're only just starting to cover stuff in class that I could probably have done with being taught months ago as far as this project goes! I've been lurking on this forum for quite some time but still find it very confusing, especially trying to size battery packs. 

Also I know it's fairly standard to have a fixed gear for something like this but am I correct in thinking that for something like Formula Student (with 'fast' and 'endurance' events that I would be better to have two?)


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## Jozzer (Mar 29, 2009)

stuff_it said:


> I was considering 119-Rs though I'm a bit confused about how the continuous output powers are lower at a given voltage. As a 1st year Mech Eng student we're only just starting to cover stuff in class that I could probably have done with being taught months ago as far as this project goes! I've been lurking on this forum for quite some time but still find it very confusing, especially trying to size battery packs.
> 
> Also I know it's fairly standard to have a fixed gear for something like this but am I correct in thinking that for something like Formula Student (with 'fast' and 'endurance' events that I would be better to have two?)


 111 motors turn slower at any given voltage, but produce more torque for any given current - yet are capable of taking the same current as the 95r (they use the same thickness of copper). So power at any given voltage/current is actually more or less the same, but the motor can take a higher voltage so can produce more power at full speed.

2 gears is a tradeoff - you might gain in some area's (especially off the line), but you lose efficiency and simplicity..and have something new to break!


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## stuff_it (Nov 13, 2012)

Jozzer said:


> 111 motors turn slower at any given voltage, but produce more torque for any given current - yet are capable of taking the same current as the 95r (they use the same thickness of copper). So power at any given voltage/current is actually more or less the same, but the motor can take a higher voltage so can produce more power at full speed.
> 
> 2 gears is a tradeoff - you might gain in some area's (especially off the line), but you lose efficiency and simplicity..and have something new to break!


These are all issues I need to look at, I don't want the car to be rubbish in the acceleration and sprint events but also don't want to end up one of the many new teams that doesn't finish the endurance race when we build it next year.


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## puddleglum (Oct 22, 2008)

Tesseract said:


> You really do not want to run two PM DC motors with their shafts locked together in parallel. Series is fine, but parallel is a no-no because the PM DC motor has a fixed relationship between voltage and RPM called Kv which inevitably varies from motor to motor. If the RPM is forced to be the same (because the shafts are locked together) and the applied voltage is the same (because the motors are in parallel) but the Kv value is different, then the motors will both not share the load equally and circulate current between them, leading to higher I²R losses without any tangible benefit.


Slightly off topic, but does this only apply to PM motors or to series and sepex motors as well. Are other styles of motor more forgiving since the magnetic field can vary?


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## major (Apr 4, 2008)

puddleglum said:


> Slightly off topic, but does this only apply to PM motors or to series and sepex motors as well. Are other styles of motor more forgiving since the magnetic field can vary?


The series motors would be stable in a parallel connection since the field increases with increasing load (armature current) and that increases the armature back EMF which tends to decrease armature current. Perturbations or differences between the two motors would not cause a worsening situation but rather be self correcting or at least stable. 

Since the SepEx can be controlled to mimic the series motor with field control, it can be stable also, but would rely on proper control. That might mean separate field control for each of the two motors with the armatures run in parallel. I've never tried it with SepEx and not seen it done 

If the motors were simply shunt motors or connected with fixed field voltage in parallel, I'd expect stability difficulty similar as with the PM motors.


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## gunnarhs (Apr 24, 2012)

stuff_it said:


> I was going to go with a Kelly, and just use one that exceeded our needs as many people say that they tend to be a bit under the Amp rating that they claim in practice.
> 
> I have since seen a few places that they also suffer from lag, so I was wondering if there were any other suggestions.
> 
> ...


Look at this http://www.electricmotorsport.com/store/ems_ev_parts_kits_agni_sigma72.php
On the bottom of the page you see the specification. It seems that 80V per controller is maximium Voltage but maybe they have higher. Most interesting is this:
"Dual traction applications can be easily and
effectively addressed by connecting two controllers in a 
master-slave configuration. The speed
output of each is then determined by the steering
angle of the vehicle. In this mode of operation,
there is a great deal of flexibility offered by a
number of specialist programmable parameters,
thereby ensuring smooth comfortable control
under all conditions. "


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## winzeracer (Apr 3, 2012)

Congrats on your Build. It is a lot like my build, I am running a Agni 111rdr (from Jozzer) and a Soliton Jr. I went through months of deciding which Controller to choose from. My options were, Soliton, Kelly, and Synkromotive.

Here was my thread chosing btwn the Soliton and Kelly.
http://www.diyelectriccar.com/forums/showthread.php/soliton-kellyi-75741.html

In my eyes the only thing kelly had going for it was regen braking. However after ordering a kelly and looking at what the factory had done to "repair it" ( it was new but did not work and had to be fixed). The work was terrible and after reading many threads of failed Kelly Controllers and the fact that they are SEVERELY overrated in terms of thier power rating, I decided to go with the Soliton. The Soliton was my first chioce all along, but I liked the idea of regen and the kelly was smaller and fit on my kart better. The Soliton really is the best featured controller for the job in my search for the perfect controller. It can handle the currents at or near 100% duty cycle with liquid cooling, kelly could never dream of 100% duty cycle. The software that controls the Soliton is also much better than the kelly, with far more features and variables. I know this sounds like a sales pitch, but I spent countless hours researching this topic. This is all to say nothing of the amazing customer experience with Evnetics. Jeff is on this forum almost every day, and has also been helpful by email.

I did consider Synkromotive, which has what seems to be a great product they were unable to be helpful, because they are only a one man company( or so it seemed).


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