# SepEx controller for 48V PMDC setup?



## Pav (Sep 20, 2018)

Hi all,

Apologies if this has been covered, I tried my best attempts at googling and searching and couldn't find an answer.

I'm looking to potentially run an Agni Lynch LEM200/127 PMDC for a simple conversion that doesn't need a lot of power. These are easy to come by. The plan is to run it at approx 48V.

However, I'm struggling to find a reasonably priced PMDC motor controller for the above.


So here comes the stupid question:

Can I use a 48V SepEx controller for the above, and just not connect the field coil outputs? 

Thanks!


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## major (Apr 4, 2008)

Pav said:


> Hi all,
> 
> Apologies if this has been covered, I tried my best attempts at googling and searching and couldn't find an answer.
> 
> ...


Hi Pav,

It can be done. But you need to hook a power resistor to the field output of the controller. If there is no field current, the controller will sense a fault. The power resistor waste the power typically used to excite the field, but fools the controller. Some adjustments are needed in the field map. Wasted power isn't terribly high. Not great, but acceptable for a hack.

I've used this method to power large resistors for controlled current battery load testing. It actually worked very well. I am not sure how it will behave dynamically on a traction application, but don't offhand see a problem.

Good luck,

major


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## brian_ (Feb 7, 2017)

Would a series motor controller work just as well, possible with tunable parameters set appropriately?


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## major (Apr 4, 2008)

brian_ said:


> Would a series motor controller work just as well, possible with tunable parameters set appropriately?


Most likely. I don't recall having seen a series motor controller with tunable motor parameters. IIRC, the Curtis 1231 was sensitive to load inductance and had difficulty with PM. The series field inductance will be several times greater than that of the armature in the wound field motor. The PM motor armature will likely be several times less than that. 

I've used older Sevcon SepEx and Curtis SepEx. Been a while. I think both had settings for armature and field inductance. Not sure. BTW, using the SepEx with a PM, you lose the reverse function and (pretty sure) regen. 

Regards,

major


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## brian_ (Feb 7, 2017)

major said:


> I don't recall having seen a series motor controller with tunable motor parameters.


Ah... I realize that there isn't the same need as there is with AC controllers, but I didn't realize that they were not tunable.



major said:


> BTW, using the SepEx with a PM, you lose the reverse function and (pretty sure) regen.


That makes sense - they presumably reverse the polarity of the field (rather than the armature), since it takes less current so components can be smaller. Similarly, regeneration would be controlled by changing field strength, and there would be no control of that.


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## Pav (Sep 20, 2018)

Thanks both, useful and sensible comments.

Clearly there are limitations with the SepEx, and I would need some sort of strange remote contactor switch to go from forward to reverse?

The thing that it still has going in its favour is that a SepEx controller can be found for £100-120 (1274-5406).

There doesn't seem to be an abundance of PMDC controllers (used) in that price bracket, even if the requirements are *relatively* low. 48V x 400A is plenty for this installation.

Regarding the resistor on the field coil output - I take it there is no way to programme it to disable or mute the error flag on the controller if it's not connected?


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## major (Apr 4, 2008)

Pav said:


> ...
> Regarding the resistor on the field coil output - I take it there is no way to programme it to disable or mute the error flag on the controller if it's not connected?


Hi,

I don't think so, but check the manual.










Was on the shelf in shop. 5 ohm, 250 watt. Probably overkill. But you get the idea.

major


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## Pav (Sep 20, 2018)

Would a series DC controller run a PM DC motor? (e.g. Curtis 1215). 

I appreciate I may not get any regen out of it, but hopefully it won't waste as much energy by not having a resistor as per the SepEx setup above.


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## major (Apr 4, 2008)

Pav said:


> Would a series DC controller run a PM DC motor? (e.g. Curtis 1215).
> 
> I appreciate I may not get any regen out of it, but hopefully it won't waste as much energy by not having a resistor as per the SepEx setup above.


Yes. Of course you need appropriate voltage and current ratings.

major


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