# Can you overvolt a Sep ex motor



## puddleglum (Oct 22, 2008)

Please forgive me if I'm asking a question that has been answered many times already, but I couldn't find it when I searched it. I know that a series motor can take 2-3 times rated voltage. Can you do the same with a Sep ex motor or will you just fry it? I've got a little 24v sep ex motor that I thought might be good for a light scooter project. I'm wondering if I could go to 36 or 48v.


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## major (Apr 4, 2008)

puddleglum said:


> Please forgive me if I'm asking a question that has been answered many times already, but I couldn't find it when I searched it. I know that a series motor can take 2-3 times rated voltage. Can you do the same with a Sep ex motor or will you just fry it? I've got a little 24v sep ex motor that I thought might be good for a light scooter project. I'm wondering if I could go to 36 or 48v.


Hi pud,

You're forgiven  Even if it has been asked and answered many times, it is difficult to search and find. It is a good question and thanks for telling your specific application voltage.

Going to 36 or 48 volts (maybe even 72) on a 24 V rated SepEx will probably work if you retain the original field map. In other words, increase the armature voltage but not the field voltage. How well it works (meaning the degree of brush arcing) depends on the particulars like the original design, the load currents and RPM. You can mitigate the problems by customizing the field map which will involve trial and error. If you do experience excessive arcing, you could advance the brushes but then would have to reduce regeneration levels or run without regen.

Using 36 or 48V on the 24V motor likely will work o.k. if you have a suitable 36/48V SepEx controller and have it properly tuned.

The series motor is unique w/r/t running 2 to 3 times rated voltage because it can be advanced and this alteration in the magnetic pattern, so to speak, stays constant with varying load. And the series motors are not reversed or used with regen. SepEx motors vary field strength, use regen and reverse so the advance doesn't work well. Higher voltage SepEx motors commonly use interpoles to achieve acceptable commutation.

Regards,

major


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## GizmoEV (Nov 28, 2009)

Hi Major,

I have a similar question. I have a D&D ES-10C in my Gizmo. It is a 48V Sepex. I've been running a 20 cell LiFePO4 pack so loaded voltage is around 64V typically. I have it hooked up to a Sevcon PP784 at the moment but I have also run it with the same pack on a PP745 which it came with. The controller has a setting for field and armature resistance but that is it as far a motor parameters is concerned. I can limit armature and field current if I wish.

I've noticed that at around 42mph, which equates to 2700rpm, I get a high pitched whine from the motor which quiets down and disappears at about 44-45mph or about 2800rpm. It will also quiet down at those speeds if I let up on the throttle. When I had my 48V lead acid pack I never could hit those speeds on level road so don't know if it would have happened then or not.

Do you have any idea what might be causing it? Is it just the rate that the commbars are passing the brushes or is there maybe arching at that point which changes when load and/or rpm moves out of that range?

When the pack is warm and I'm on level road with no wind I can generally top out at 55mph or about 3500rpm. Do you have any idea what the highest safe rpm is for this motor being it is only a 6.7" motor?

Thanks,


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## major (Apr 4, 2008)

GizmoEV said:


> Hi Major,
> 
> I have a similar question. I have a D&D ES-10C in my Gizmo. It is a 48V Sepex. I've been running a 20 cell LiFePO4 pack so loaded voltage is around 64V typically. I have it hooked up to a Sevcon PP784 at the moment but I have also run it with the same pack on a PP745 which it came with. The controller has a setting for field and armature resistance but that is it as far a motor parameters is concerned. I can limit armature and field current if I wish.
> 
> ...


Hi Giz,

Noise at 2700 RPM?????? Might just be some resonance, electrical or mechanical. I doubt it is arcing, but can you put an eyeball on it to confirm? Can you duplicate the 2700 RPM noise with wheels jacked up?

D&D builds a pretty stout armature. I doubt there would be a problem at 5000 RPM. Maybe even up to 8000  But don't go that high on my say so 

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

In addition to what Major said:

On my sepex motor, I found the amount of overcurrent the field can take to be rpm dependent. The internal fan was much better at cooling the fields than an external electric blower. I could run about 50% higher field currents at speed (about twice the power, P = I^2R) than at 0 rpm, even with an external blower going the whole time.

Also, some sepex controllers are designed to temporarily overcurrent the field at a value that would overheat the fields if done continuously.

My Kostov is spec'd for 144 V on the armature, so far I have only run 96V. On 96V I managed to cook the brushes by running at 1000A for around 30 seconds. Anyway, current is probably the more important number for your rather than Volts (within practical limits).


major said:


> ... Going to 36 or 48 volts (maybe even 72) on a 24 V rated SepEx will probably work if you retain the original field map. In other words, increase the armature voltage but not the field voltage. How well it works (meaning the degree of brush arcing) depends on the particulars like the original design, the load currents and RPM. You can mitigate the problems by customizing the field map which will involve trial and error. If you do experience excessive arcing, you could advance the brushes but then would have to reduce regeneration levels or run without regen.
> 
> Using 36 or 48V on the 24V motor likely will work o.k. if you have a suitable 36/48V SepEx controller and have it properly tuned.
> 
> The series motor is unique w/r/t running 2 to 3 times rated voltage because it can be advanced and this alteration in the magnetic pattern, so to speak, stays constant with varying load. And the series motors are not reversed or used with regen. SepEx motors vary field strength, use regen and reverse so the advance doesn't work well. Higher voltage SepEx motors commonly use interpoles to achieve acceptable commutation. ...


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## GizmoEV (Nov 28, 2009)

major said:


> Hi Giz,
> 
> Noise at 2700 RPM?????? Might just be some resonance, electrical or mechanical. I doubt it is arcing, but can you put an eyeball on it to confirm?


I wish I could put an eyeball on it but I can't reach opposite ends of my rig at the same time  That would be a sight, however.  I'll have to try recording a video or audio when I'm driving sometime. Maybe a video of the speedometer so that sound can be matched to RPM.



> Can you duplicate the 2700 RPM noise with wheels jacked up?


I'll have to try that out. I don't remember hearing it then, possibly because the load is rather light with the rear wheel jacked up. I know when driving that the intensity of the sound is proportional to the load.



> D&D builds a pretty stout armature. I doubt there would be a problem at 5000 RPM. Maybe even up to 8000  But don't go that high on my say so


I should be ok then. 5000rpm is about 98mph and 8000rpm would be 156mph 



DavidDymaxion said:


> In addition to what Major said:
> 
> On my sepex motor, I found the amount of overcurrent the field can take to be rpm dependent. The internal fan was much better at cooling the fields than an external electric blower. I could run about 50% higher field currents at speed (about twice the power, P = I^2R) than at 0 rpm, even with an external blower going the whole time.


That is then why the motor would overheat so easily with relatively slow start & stop driving with very little time coasting or stopped. My external blower pushes about as much air out with the motor stopped as the internal fan does at around 2500rpm. With a 70mile range with a LiFePO4 pack I had to add the external fan. Since then I haven't been able to smell the motor except for the time I took a straighter route home and discovered that it came with an 1800 foot elevation change. 



> Also, some sepex controllers are designed to temporarily overcurrent the field at a value that would overheat the fields if done continuously.


The range in the controller is 50A down to 5A and is based on armature current so I assume the field is at 50A at full armature current and it then drops to 5A at some point.

Thanks for the feedback. When I get a video or audio I'll post a link to it. Maybe I should take some pictures of the comm and post them too.


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