# Ev with Big Sepex motor



## GE11 (Oct 24, 2011)

So I am using a big 10 inch sepex motor with interpoles here are a number of things I have learned.

1. You most certainly can use a series controller however there is a tick to it(get to that latter)
2. The trick is the field. Getting a good voltage regulator to keep the field constant powering off the battery pack. This is key to being able use a series controller.
3. My battery pack is either 48V or 36v. But I want to run my field at 72v. The trick is gettting a good boost regulator to do this! There are weird things that happen when the pack voltage sags, the regulator has to pull more current to keep the field constant at 72 volts!
4. Going in reverse is easy as flipping a small switch... However if you are careless and just flip the switch whilly nealy you are in for a big disaster!!! No I have not tried it but I know what could happen! Big disaster!
Best put this switch in a place where it is hard to get to! 
5. It is very very easy to have a situation where the Motor armature volts be higher than the pack voltage... be careful this does not damage the controller!!’ You have to have a way to shut the field off!!
6. Need a way to shut the field off when the gas pedal is not pushed! In my case when the field is left on it’s burning 365 watts 72V at 5 amps.
7. The setup is like screaming for regen braking it’s ridiculous! Need to find a way to do this!


More to come later !


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## brian_ (Feb 7, 2017)

I don't understand the appeal of using a bunch of equipment not intended to run a SepEx motor to do what a SepEx controller is designed to do... but it should be possible.

The problem with regeneration is inherent with choosing constant-current field control. The obvious solution is to use another controller for the field: the regenerative braking torque would be determined by the field controller's current output, and you could control the field current in coordination with the rotor current. The problem is building the system to coordinate the two controllers (for rotor and field); that's already done for you in a SepEx controller.


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## GE11 (Oct 24, 2011)

brian_ said:


> I don't understand the appeal of using a bunch of equipment not intended to run a SepEx motor to do what a SepEx controller is designed to do... but it should be possible.
> 
> The problem with regeneration is inherent with choosing constant-current field control. The obvious solution is to use another controller for the field: the regenerative braking torque would be determined by the field controller's current output, and you could control the field current in coordination with the rotor current. The problem is building the system to coordinate the two controllers (for rotor and field); that's already done for you in a SepEx controller.


Well Brian,

It’s called using what you have without going out and spending a bunch of money. I have tried both Altrax and Curtis controllers and they both work great... yes it does take some technical understanding and creativity but that’s the things you have to do if you don’t want to have a ton of $$$$$ invested in something like this.
Secondly there is no controller out there that is going to have the field voltage twice the pack voltage. That’s something I have to custom make.
Yes, it boils down to two different controllers not a problem...
Just sharing what I have observed using a sepex machine...

Thanks


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## brian_ (Feb 7, 2017)

GE11 said:


> 4. Going in reverse is easy as flipping a small switch... However if you are careless and just flip the switch whilly nealy you are in for a big disaster!!! No I have not tried it but I know what could happen! Big disaster!


A good point, and that's what interlocks are for. An interlock is anything that prevents an operation based on some condition; it can be done in electronic logic or physical switches and relays. If you are concerned about this risk, you could design the system which allows the field polarity to switch only when the speed is zero.


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## brian_ (Feb 7, 2017)

GE11 said:


> It’s called using what you have without going out and spending a bunch of money.


I get that, but by the time you have assembled all of the required pieces, is it really going to be cheaper? I hope it works out.



GE11 said:


> Secondly there is no controller out there that is going to have the field voltage twice the pack voltage. That’s something I have to custom make.


That is an interesting aspect. Why do you want this high field voltage? Will the voltage supplied to the rotor's controller not drive enough current through the field? It seems like any SepEx motor should be designed so that the rotor and field windings are suitably matched so that the voltage needed is the same for both.


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## GE11 (Oct 24, 2011)

brian_ said:


> GE11 said:
> 
> 
> > It’s called using what you have without going out and spending a bunch of money.
> ...


Well actually the motor was off of a 70V forklift. But I am running a 36V pack so I can drive in the woods. The goal is to go 35 to 40 MPH. I have driven this field up to 120VDC before but after about 20 minutes it gets quit warm from over 1000watts!!! Yikes! The field measures at: 14.2 ohms
I might letter on do some tricks where I control the field or even boost it to 120V when I need real low end Torque. Right now it’s just set at 72V...


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## brian_ (Feb 7, 2017)

brian_ said:


> The obvious solution is to use another controller for the field: the regenerative braking torque would be determined by the field controller's current output, and you could control the field current in coordination with the rotor current. The problem is building the system to coordinate the two controllers (for rotor and field)...


This coordination might not be too bad. I'm not familiar enough with SepEx motors to be sure, but it seems likely that the field current could be controlled in inverse proportion to the motor speed (more speed => less current; called field weakening) while motoring, regardless of the rotor current. While regenerating, the field current would follow the desired braking torque, perhaps divided by a speed-based factor for field weakening.

There may be a better discussion in this forum of someone having done this before (because it's so obvious that it must have been done), but I did note this:


Clipper said:


> I understand I need to keep maximum field to about half the motor's max RPM,
> then weaken the field gradually up to full RPM. I figure I can manually control the field (with an ammeter on it) until I get a feel for what it wants, then try to automate the field control later.


One design approach is good old R&D... and by that of course I mean Ripoff & Duplicate, not Research & Development.  If you know what SepEx controllers do, you know what your system needs to do. I'm pretty sure that's not just constant field current under all conditions. I had a look at the manual for a Curtis 1268 SepEx controller, and (on page 24) it describes parameters for field current control, which appears to be based on rotor current and motor speed.


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