# Reversal and regeneration for series wound DC motors



## PStechPaul (May 1, 2012)

Most people will say that series wound DC motors cannot provide regeneration, and reversing must be accomplished by means of a mechanical transmission. But I found the following detailed article that provides a proposal on how to do both. It also seems to include a lot of good basic electromagnetic and motor control theory. I'm still not a "fan" of series wound brushed DC motors for EVs, but perhaps this will help some of those who use them for EVs:

http://eprints.usq.edu.au/501/1/DeanTHOMPSON-2005.pdf


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## major (Apr 4, 2008)

PStechPaul said:


> Most people will say that series wound DC motors cannot provide regeneration, and reversing must be accomplished by means of a mechanical transmission. But I found the following detailed article that provides a proposal on how to do both. It also seems to include a lot of good basic electromagnetic and motor control theory. I'm still not a "fan" of series wound brushed DC motors for EVs, but perhaps this will help some of those who use them for EVs:
> 
> http://eprints.usq.edu.au/501/1/DeanTHOMPSON-2005.pdf


Hi PS,

Fork trucks and golf carts have been reversing series wound motors, like, forever  And regeneration is widely known, just commonly viewed as "not worth the trouble" when it comes to series wound motors. But thanks for the reference. You will note that the author leaves regeneration for "further work." In other words, he didn't attempt it 

Regards,

major


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## PStechPaul (May 1, 2012)

So if these motors can be electrically reversed they will need separate field (stator) and rotor connections. And the contactor(s) would need to be rated to carry the full maximum load current of 500A or so, which makes for a rather large and expensive component. So, although they can do this, I wonder how many actually do?

I found another thread from 3 years ago that gets into regeneration:
http://www.diyelectriccar.com/forums/showthread.php/series-wound-control-strategy-36888.html

Here is more information:
http://zone.ni.com/devzone/cda/ph/p/id/53

There was some caution about attempting regeneration on motors with advanced brush settings. I wonder if this also applies to reversing?


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## DavidDymaxion (Dec 1, 2008)

Some of the NEDRA guys use the 12V system for reverse, so those components don't need to have full 500A capability.


PStechPaul said:


> So if these motors can be electrically reversed they will need separate field (stator) and rotor connections. And the contactor(s) would need to be rated to carry the full maximum load current of 500A or so, which makes for a rather large and expensive component. So, although they can do this, I wonder how many actually do?
> 
> I found another thread from 3 years ago that gets into regeneration:
> http://www.diyelectriccar.com/forums/showthread.php/series-wound-control-strategy-36888.html
> ...


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## major (Apr 4, 2008)

PStechPaul said:


> So if these motors can be electrically reversed they will need separate field (stator) and rotor connections. And the contactor(s) would need to be rated to carry the full maximum load current of 500A or so, which makes for a rather large and expensive component. So, although they can do this, I wonder how many actually do?


Ones that are direct drive (without transmission). Most guys keep the tranny in the donor (it is usually there (free)) so don't mess with reversing contactors. And all the available DC series EV drive motors have separate field (S1 & S2) and armature (A1 & A2) terminals. Occasionally you see a guy using a 2 terminal series motor which is usually taken from a forklift pump drive.



> I found another thread from 3 years ago that gets into regeneration:
> http://www.diyelectriccar.com/forums/showthread.php/series-wound-control-strategy-36888.html


Nice to see someone use the search function  Thanks. Not much has changed in this regard over those 3 years.




> There was some caution about attempting regeneration on motors with advanced brush settings. I wonder if this also applies to reversing?


Sure, the brush shift is incorrect when rotation is reversed. But for vehicle reverse (opposed to regeneration), motor voltage, current and RPM are typically low. Backing up an incline can cause comm burning.


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## rmay635703 (Oct 23, 2008)

I wish I would have noticed this thread back in the day.

In any event why re-invent the wheel?

Curtis offered a whole line of "R" series wound controllers in France.

Most were 96v 400amp variety out of some type of french bread truck.
AKA 1221R
http://www.google.com/url?q=http://...QQFjAA&usg=AFQjCNHPymzUoYWpvIrF1XJsZysvnmnfIg

I have been looking for one for a long time but have not seen any up for sale
but they do exist and work out of the box. (though they tend to fail occasionally, not sure if it is any more often than any other Curtis offering though)

From what I was told the "R" variety of Curtis controller was not significantly different than the standard model, used some sort of boost circuit, would be interesting if it could be made into an "add on" to a normal controller for those of us with neutral brush timing.

Ah well.


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## bsamarah (Sep 16, 2014)

Hi.. 
Has anyone implemented the circuit done by Dean Thompson in the university of Queensland ? I have a few questions about the zener diodes used between the LM5101A and IRF1407 MOSFETs. He uses 2 zener diodes back to back and the Vz is 15V. That means he does not turn on the NFET unless the Vgs is > 15 V, right? But his charge pump can only boost up to 12V, am I missing something ? 
Also he uses variable resistors (referred to as MOV or M0V in his circuit) why are these needed?

The circuit is found on page 107. 
I am trying to build his circuit and test it out, also making enhancements as I go along, but I do not understand the variable resistor (MOV or M0V) and the zeners he places there and how it works that way. 

Appreciate your help in advance. 

Thanks

Basem.


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## PStechPaul (May 1, 2012)

The MOVs are Metal Oxide Varistors, used to limit the amplitude of inductive spikes that might otherwise damage the MOSFETs or other components.

The 15V zener diodes from the drive outputs of the LM5101A are puzzling and probably an error. Here is the spec sheet for the device:
http://www.ti.com/lit/ds/symlink/lm5101a.pdf

The polarity of the second 15V zener to the low side gates is wrong. As shown, it limits the gate voltage to +0.7 and -15V.

Here is the datasheet for the IRF1407:
http://www.irf.com/product-info/datasheets/data/irf1407.pdf

I am not much interested in series wound DC motors, so I only skimmed through this paper. Note that the field must be reversed to get reverse drive, and this may be difficult for some motors. It may be better to supply a variable current to the field, and drive the armature with an H-bridge which allows electronic reversing, and eliminates the high current electromechanical DPDT contactor. Alternately, an H-bridge could be used to replace the contactor.


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## bsamarah (Sep 16, 2014)

Hi.. 

Thanks for your reply. Still have a couple of clarifications.. 
1. I've never seen anyone use Zener Diodes back to back to protect/limit voltage to the MOSFET gate, is what he is doing correct ? 

It seems to me tha the back to back zener diodes should be connected between gate and source, right? 

When you say the 15V back to back zener diodes are connected to the gate are probably an error, do you mean they should not be there, or they should be of lower voltage, like a 10V or 12V? 

For the datasheets (which I looked over many times now) not sure if there was something in particular you are referring to that you wanted me to see.. Still new and trying to figure out what things mean on the datasheet, so I take any opportunity to learn. 
I am currently using this paper as a learning vehicle to design a DC motor controller. I am currently only using half bridge (no reverse). My issue is that I keep burning the LM5101A. So, I read up quite a bit about protection and looked at several designs, but I can not get this off my head, I want to really understand why he is using zener, is there any advantage to it than using resistors and diode in parallel.. I even looked for Dean Thompson online to see if I can contact him so I can understand (I am unable to find him but contacted the university and waiting for a reply). 




Really appreciate your help and response. 

Thanks

Basem.


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## PStechPaul (May 1, 2012)

Zener diodes back-to-back are often used to protect the gates of MOSFETs and IGBTs. IGBTs are often driven with both positive and negative signals to achieve a harder turn-off. It is not as useful for MOSFETs so a single zener can be used as shown in the schematic.

The zeners in series from the gate driver to the MOSFET gate should not be there. In some cases, a small series resistor (1-20 ohms) is used to reduce the dV/dt of the device to reduce ringing, EMI generation, and high voltage spikes. It may be better to use individual resistors on each MOSFET gate as well, to reduce the peak current. 

The multiple MOSFETs in parallel may present too much capacitive load for the driver, which may account for its demise. A zener and capacitor across the device power supply rails may also help. Layout is important, too. And you may find that adding a fast SiC or high voltage Schottky diode across the motor may be helpful. The internal diodes are sometimes not fast enough.


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## bigmotherwhale (Apr 15, 2011)

a good trick is neon bulbs can be used to protect switching devices, series them together so their ignition voltage is just over the supply voltage, then if you have an inductive kickback into a transistor it helps limit the voltage, it works well.


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## bsamarah (Sep 16, 2014)

PStechPaul said:


> Most people will say that series wound DC motors cannot provide regeneration, and reversing must be accomplished by means of a mechanical transmission. But I found the following detailed article that provides a proposal on how to do both. It also seems to include a lot of good basic electromagnetic and motor control theory. I'm still not a "fan" of series wound brushed DC motors for EVs, but perhaps this will help some of those who use them for EVs:
> 
> http://eprints.usq.edu.au/501/1/DeanTHOMPSON-2005.pdf


Hi I tried the circuit suggested in Dean Thomson's paper. It does not work. I managed to do some modifications onit, and got it to drive the series wound Dc motor connected to the car's flywheel. However, I am still not able to get the car moving with my own made controller. 
I am looking for some help from a person experienced to review my design and suggest some enhancements or updates in order for me to understand why the controller keeps failing. 
Any help is greatly appreciated, I've been on working on this for about 5 years now with very little progress. 

Your help is greatly appreciated. 

Thanks

Basem.


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## bsamarah (Sep 16, 2014)

major said:


> Hi PS,
> 
> Fork trucks and golf carts have been reversing series wound motors, like, forever  And regeneration is widely known, just commonly viewed as "not worth the trouble" when it comes to series wound motors. But thanks for the reference. You will note that the author leaves regeneration for "further work." In other words, he didn't attempt it
> 
> ...





major said:


> Hi PS,
> 
> Fork trucks and golf carts have been reversing series wound motors, like, forever  And regeneration is widely known, just commonly viewed as "not worth the trouble" when it comes to series wound motors. But thanks for the reference. You will note that the author leaves regeneration for "further work." In other words, he didn't attempt it
> 
> ...


 Yes, I agree, from my experience, I can see that regen with a Series Wound Dc is probably too costly and ineficient. As for reversal, you will need to control field and armature separately to do that.


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