# How to get different voltages for SepEx motors



## ElvishWarrior (Apr 10, 2008)

I've seen some SepEx motors listing different voltages for field and armature current. How does one come up with those voltages and control them? Is it a function of the controller? (I would find that hard to believe.) Would it require different battery packs?

Here's an example:
http://cgi.ebay.com/ws/eBayISAPI.dl...item=230246563220&_trksid=p3984.cWAT.m240.lVI


----------



## frodus (Apr 12, 2008)

sepex motors DO actually require sepex controllers, you can't use a PM/Series motor controller with a sepex motor. There are essentially 2 controllers in a sepex controller, one for field, one for armature.

The field windings are usually lower voltage, lower current. They have much smaller diameter coil windings, and have more turns. The armatures are usually very similar, but can handle full pack voltage/and full load amps.

What does this get you? Regen, braking, reversing and field weakening (overspeeding) of the motor. Something that you can't do with series without additional hardware (field weakening has been done, as has regen, but not without design challenges).


----------



## ElvishWarrior (Apr 10, 2008)

I was aware of distinct SepEx controllers, but assumed that they delivered the same voltage to both coils, just with different times of application for driving and regenerating.

Regenerative braking is one reason I'm inclined towards SepEx. If I bought a SepEx motor and controller, is the voltage on each coil something I'd be able to adjust? What I found hard to believe is that a SepEx controller could take a single battery pack voltage and deliver two different voltages without switching to AC and going through a transformer.


----------



## frodus (Apr 12, 2008)

Are you familiar with how a controller works? Essentially it PWM's the FETs inside, to deliver an "average" voltage on their outputs. One is just set to deliver a lower voltage, lower current. One might be at 0-15% of pack voltage while the other can swing from 0-100% of pack voltage.

Its two controllers in one package. You don't adjust the voltages, the controller does that for you, and applies the field when it needs it, or weakens it when needed. 

What application are you trying to go for? You are limited on the sepex controllers (one reason you don't see a ton of them). Especially when you go above 84V.


----------



## ElvishWarrior (Apr 10, 2008)

Well, I thought I did. I thought that it interrupted the voltage in order to reduce the average voltage applied to the motor, but that the voltage the motor experienced was still the battery pack voltage, just less than 100% of the time.

I had the impression that the motor would only work when voltage was applied to both coils on the same frequency and duration; ie if the interruptions of both voltages were not timed perfectly you would be just wasting energy through one coil or actually sending a voltage back through it as regenerative energy.


----------



## frodus (Apr 12, 2008)

ElvishWarrior said:


> Well, I thought I did. I thought that it interrupted the voltage in order to reduce the average voltage applied to the motor, but that the voltage the motor experienced was still the battery pack voltage, just less than 100% of the time.
> 
> I had the impression that the motor would only work when voltage was applied to both coils on the same frequency and duration; ie if the interruptions of both voltages were not timed perfectly you would be just wasting energy through one coil or actually sending a voltage back through it as regenerative energy.


a motor is an inductor, current keeps flowing through the free-wheeling diodes, just like a diode on a relay or contactor. When you shut off the current FROM the controller, the diodes keep the current going. So its constantly going through the coils when you're moving. Both controllers are synkronized as much as they can be, but you never run one without having the other on, it wouldn't move. Both of them are on at the same time, but different levels depending on what the input is, or if you're regen-ing. Its not just 2 independant controllers, they are interfaced and controlled together.

If you need more info, look into the manufacturers of the sepex controllers and see if they have documentation you can use. Also, do a wikipedia search on separately excited motors.


----------



## ElvishWarrior (Apr 10, 2008)

Anyone have any pointers on where one would find a controller approximately 450A, for a motor with a 120V armature and 24V coil?


----------



## frodus (Apr 12, 2008)

ElvishWarrior said:


> Anyone have any pointers on where one would find a controller approximately 450A, for a motor with a 120V armature and 24V coil?


look for a controller for a GEM car on ebay.... they're 400A or som but 72V and up to 30V coil.

120V might be hard to find. What is it going in?


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> Anyone have any pointers on where one would find a controller approximately 450A, for a motor with a 120V armature and 24V coil?


Hi Elvish,

http://www.saything.co.jp/products/curtis/pdf3/sepex1244.pdf

This shows the basic circuit. Also the specs from this company. I do not think there are standard available SepEx controllers and motors rated for 120 V. Not that it can't be done, just no market at present.

Regards,

major


----------



## ElvishWarrior (Apr 10, 2008)

Thanks a bunch for the info! I'm not sure though how I would get it up to 120V. Highest I saw on that link was 80V

Here's a wacky question - what about using a small, simple controller to set the field at a given voltage and then use a PM controller on the armature? If the field is maintained constant like permanent magnets would, would the PM controller know the difference?


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> Thanks a bunch for the info! I'm not sure though how I would get it up to 120V. Highest I saw on that link was 80V
> 
> *******That's the problem****
> 
> Here's a wacky question - what about using a small, simple controller to set the field at a given voltage and then use a PM controller on the armature? If the field is maintained constant like permanent magnets would, would the PM controller know the difference?


Yeah, Elvish, that would probably work. Where you gettin' the motor? And you had better make darn sure your field supply is there before you power up the armature or it will overspeed at no load or over current at load while producing no torque.

Regards,

major


----------



## frodus (Apr 12, 2008)

I'm just wondering where you're getting that 120V number.... do you already HAVE a motor that runs on 120V? If so, then ask the manufacturer..... they've got to have something to DRIVE it if they're gonna make it. Or are you just saying you "want" to have a vehicle at 120V?

The only sepex i've seen are 72V or below.

As far as using a PM controller on the field, no, won't work. There are curves for armature AND field in the sepex controllers. Also, how are you going to tell the other control to reverse the field to do regen? Isn't that your point of using sepex? Both controllers would have to talk to eachother and the ones out there I've seen, don't do that, and Can't be made to do that. Also, what happens when you are at max armature, and you let off the throttle, whats to keep the field from weakening and your motor running away (high RPM)?

there's a reason the sepex controllers have the guts inside one controller... they NEED to be coordinated in order to work properly and safely.


----------



## major (Apr 4, 2008)

frodus said:


> As far as using a PM controller on the field, no, won't work. .


Hi frodus,

I think Elvish was talking about using a simple fixed supply (controller, if you will) on the field and the PM motor controller on the armature. In which case, it should work, very similar to how a PM motor and controller work. Which can do regen. And, I've mentioned it before, you do not reverse the field on SepEx systems to regen.

True, that approach does not have all the features and benefits of a real SepEx control system, but no reason it would not work. However I am uncertain he would be able to get a PM controller robust enough for the armature of a SepEx motor.

Regards,

major


----------



## frodus (Apr 12, 2008)

I gotcha, I thought he was varying the field... if its fixed, it should be ok, but inefficient... because its always going to be on, whether you're stopped or not.... it'l just act like a normal magnet... With respect to regen, I keep accidentally thinking of it as series... sorry. In series, if the field colapses with the armature current, you have trouble doing regen.

He still has the issue of FINDING a motor for 120V that's sepex... Not saying they aren't out there... just that I haven't seen any.

And you're right, he's going to have to find something pretty robust for a sepex motor. I haven't seen many PM controllers above 72V as well. Seems to be about the cap of the voltage available in the market for EV's.


----------



## ElvishWarrior (Apr 10, 2008)

I think I recently saw a PM controller that was 120V+. As far as the field being on all the time, I was thinking there'd have to be a switch to turn it off at lights. Like maybe something you'd just rest your hand on.

Or maybe there's a far better solution. A 120V sepex controller would be a good start.


----------



## frodus (Apr 12, 2008)

do you have a 120V sepex motor?


----------



## ElvishWarrior (Apr 10, 2008)

Not currently, but I see them on Ebay frequently.


----------



## frodus (Apr 12, 2008)

Call the manufacturer of the motor and get a recomended controller for the motor... I mean, if its 120V, it has to have a controller to match.

The sepex motors aren't really out there for voltages above 72V... not anyplace I've looked. I wish they were, as I'd love to get some regen out of a car conversion I want to do after my motorcycle. 72V is where I found they maxed out, and that was a GEM motor/controller combo. I currently have a 72V controller if you might need it, but it might be a bit small for a car.


----------



## John (Sep 11, 2007)

I think Zapi make a 96V sepex controller. Zapi SEM3 96V 400A. I heard series motors can be reworked into sepex motors though don't ask me how.


----------



## rebenergy (Apr 18, 2008)

_I'm just wondering where you're getting that 120V number.... do you already HAVE a motor that runs on 120V? If so, then ask the manufacturer..... they've got to have something to DRIVE it if they're gonna make it. Or are you just saying you "want" to have a vehicle at 120V?_

Did you buy the Aircraft Motor (Starter/Generator) off e-bay?
This looks very similar to an Aircraft Motor I have, but mine is rated for 30v. If you did buy this particular motor from e-bay, then what dose the name plate have for a model number?

*This is a high quality motor starter generator for military aircraft. It function was both as a generator and an aircraft engine starter motor. This Electric motor can be used for Forklifts, Electric Vehicles,*
*SPECIFICATION:*
*· 30 HP at 120 Volts DC ELECTRIC MOTOR*
*· 24 HP at 97V with 5,700 RPM approximately*
*· 18 HP at 72V with 4,200 RPM approximately*
*· 12 HP at 48V with 2,800 RPM approximately*
*· 7,000 RPM approximately at no load and 120 Volts DC*


----------



## frodus (Apr 12, 2008)

rebenergy said:


> _I'm just wondering where you're getting that 120V number.... do you already HAVE a motor that runs on 120V? If so, then ask the manufacturer..... they've got to have something to DRIVE it if they're gonna make it. Or are you just saying you "want" to have a vehicle at 120V?_
> 
> Did you buy the Aircraft Motor (Starter/Generator) off e-bay?
> This looks very similar to an Aircraft Motor I have, but mine is rated for 30v. If you did buy this particular motor from e-bay, then what dose the name plate have for a model number?
> ...


Does it say "Shunt wound" or "Sepex" anywhere? or does it say series?


----------



## rebenergy (Apr 18, 2008)

*Does it say "Shunt wound" or "Sepex" anywhere? or does it say series?*
_I've seen some SepEx motors listing different voltages for field and armature current. How does one come up with those voltages and control them? Is it a function of the controller? (I would find that hard to believe.) Would it require different battery packs?

Here's an example:
http://cgi.ebay.com/ws/eBayISAPI.dll....cWAT.m240.lVI_

This is a snip it from the add on e-bay
*If you need a good power source for an electric vehicle project, Then Here is the Electric Motor for you. This electric motor can produce 30 HP continuously at 120 Volts DC and over 70 HP for short intermittent burst of power at that voltage. It is a used 30 HP 120V shunt wound, continuous duty reversible DC Motor.*
It is a shunt wound motor, but I just wondered if Elvish Warrior had bought that motor off e-bay an looking for information about controllers. I too have purchased a similar motor and thought I could assist him. I have had great help from this group and would be egger to help others if I can.


----------



## major (Apr 4, 2008)

rebenergy said:


> _I've seen some SepEx motors listing different voltages for field and armature current. How does one come up with those voltages and control them? Is it a function of the controller? (I would find that hard to believe.) Would it require different battery packs?_


Hi rebenergy,

One could use a separate supply for the field, but the usual set-up has the SepEx controller use a single battery supply. The controller will then supply the armature and field with separate power at the required voltage for each.

Regards,

major


----------



## ElvishWarrior (Apr 10, 2008)

Call me nuts, but would it be possible to use a series motor in a sepex config, with the major difference being that the field voltage would be very low? This would probably be another candidate for using a PM controller for the armature and separate control for the field.


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> Call me nuts, but would it be possible to use a series motor in a sepex config, with the major difference being that the field voltage would be very low? .


Hey Elvish,

Not a good idea. Yeah, it could be done. But the field controller would be a bitch. It would be essentially the same current rating as the armature controller, so big and expensive.

Regards,

major


----------



## ElvishWarrior (Apr 10, 2008)

Still beating the horse to be sure it's dead...

What about this setup:
Take a series motor. Use a PM controller with regen.

Hook up the coils such that power runs through the two coils in series with a contactor in the middle that's closed when the vehicle is accelerating. Maximizes efficiency throughout the whole range of speed.

When braking, the contactor would switch the armature coil from the field coil to the power output of the controller. A constant low voltage would then be applied to the field coils to provide the field when regenerating. The field current would be relatively high, but it wouldn't need a separate controller.

Good idea, bad idea?


----------



## TX_Dj (Jul 25, 2008)

I'd suggest you read Otmar's paper on doing similar to what you described above.

As I recall, it makes for a pretty light show and short brush/comm life.


----------



## ElvishWarrior (Apr 10, 2008)

Know where I would go to find that?


----------



## TX_Dj (Jul 25, 2008)

The link is included in the wiki, under regen braking, and the paragraph about regen on series motors.

http://www.diyelectriccar.com/forums/showthread.php?t=8848


----------



## ElvishWarrior (Apr 10, 2008)

I read that article, very insightful. Thanks!

If I understand Otmar's project correctly, my concept is different in the following ways:
1. His version continues to run current in series through the field and armature coils. To me it almost looks like the motor is being run in reverse, like you're driving the motor and then grabbing the shaft and turning it the other way. In my concept, the field and armature coils are disconnected during regen and the armature is connected directly to the power connections of the controller.
2. His version shunts current to "tickle" the field. If I understand it correctly, that is only to start the current flowing and not to actually maintain the field. My concept would excite the field with a separate power source.
3. My concept is basically running the motor in series when accelerating and running it in sepex when regenerating. A PM controller would be used because the field current would be supplied independently of the controller, being constant just like the field of a permanent magnet motor. The field current would be determined by the voltage of the field supply, which would be an auxilliary battery used only to excite the field during regen.

I'm still struggling to figure out how his improvements got rid of the sparking/arcing. My voltage would be 120V max, possibly lower. That puts it above the 108V threshold mentioned in his blog in 2007, but not tremendously.


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> The field current would be determined by the voltage of the field supply, which would be an auxilliary battery used only to excite the field during regen.


Hey Elv,

Yeah, that sounds like that might work. A couple of things........

Typical field resistance for a series wound motor might be on the order of 0.010 ohms. Then a 12 volt source across it would be 1200 amps. Yeah, it'd sag so you'd really only see like what? 8 or 900 amps? You could use a 6 volt battery on the field and get it down to maybe like 500 amps.

So, what you going to use to switch in the battery for the field? Need a contactor. Even low voltage will arc when you open against an inductive load like that field. So you'll have to use big contacts and expect to service them.

Now you have a fairly big battery and contactor just used for regen. And a charger for that battery. What if you took all that cost and weight and just added to your battery pack and lived without regen? You'd probably go further on a charge without all the headaches associated with the convoluted regen scheme. But that wouldn't be as much fun, right?

Regards,

major


----------



## ElvishWarrior (Apr 10, 2008)

The 0.01 Ohm ball-park field coil resistance is helpful to know. That is something I knew I needed to measure on the motor before finalizing the regen circuit design. I wasn't thinking anything more than a few hundred amps for field coil resistance, certainly no more than the current at rated power. So if I want to run closer to 250 amps, I'd want a 3V regen field voltage. A set of NiMH D cell batteries were what I had in mind. It wouldn't have to be huge, especially if it were charged from the main battery pack or the accessory battery (12V).

That's an excellent standard by which to measure its practicality - does the cost, work, and weight gain improve upon the benefits of adding one or two batteries, or using the next size battery up?

Here are some goals and assumptions of my planned conversion that factor in:
1. This EV would be intended for either short range trips with no extender or long range trips that couldn't possibly be achieved without an extender, even with a Tesla or Lion long range EV. Now these trips would not have to be high speed. Many would be on the back roads of PA. Which brings up another detail.
2. The 10% range extension achieved by regen braking would of course be affected by the type of driving. In western/central PA, there are a lot of long hills. Not like the rockies, where a typical EV motor would burn out unless speed were reduced, but long enough that you would spend a lot of energy going up the hills and would hold your brakes pretty steadily going downhill. My assumption, to be evaluated, is that a soft, consistent braking down a long hill would restore more energy than urban acceleration and stopping.
3. Back to the range extender. Another reason for regen braking is to keep the range extender requirements reasonable. I would like the generator to be light enough for two non-athletic middle aged adults or teens to be able to lift it into the trailer hitch without extreme effort. This would also help fuel efficiency in range extended mode.

So in short, regen braking would be used in a fashion that:
1. Is more oriented towards overall vehicle efficiency than range extension, to match the capabilities of a range extender.
2. May provide a higher return than regen normally would due to driving style.

Tentative vehicle specs:
4x4 light truck <3500lb
55mph max highway speed
18-22hp motor
120VDC system
10hp rated range extender generator, so 8.5-9hp available


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> The 0.01 Ohm ball-park field coil resistance is helpful to know.


Hi Elv,

Yeah, that's a ballpark. Depends on the particular motor. May be half that. And will vary with the temperature, maybe as much as 25%.

Driving on hills is a good reason to take a serious look at regen. The battery enters into the regen equation big time. Will it take it for an extended downhill run? Or overvoltage and gas?

And NiMH D cells for field excitation? Charged from the main pack? Not saying it can't be done, but a challenge for sure.

Also wondering what you plan to use for the armature controller. You mentioned a PM motor controller with regen. Is such a thing available for a power level you'll need?

And after all this is done, do you think your series motor will commutate on regen without serious arcing?

Regards,

major


----------



## ElvishWarrior (Apr 10, 2008)

For a controller there's a Kelly 120V 220A. That works out to about 35hp, which is about right for a D&D ES-31B motor.

Battery capability comatibility with regen is something I need to look deeper into for sure. Voltage would be something I'd monitor, gasing is something I need to learn more about.

Another benchmark for the value of regen might be how much more efficiency is gained by using a higher voltage system instead of regen. If going up to 144V over 120V gained 10% or more in efficiency then that would be a big deal.


----------



## ElvishWarrior (Apr 10, 2008)

Ok, trying to subdue any fear of asking stupid questions...

Would going to another type of battery improve the return on regen? Such as NiMH? So that it would act a little less like a sensitive battery pack and a little more like a capacitor?


----------



## major (Apr 4, 2008)

ElvishWarrior said:


> Would going to another type of battery improve the return on regen?


Hi Elv,

Possibly. Different battery chemistries behave differently with regard to charge characteristics. I can't tell you which is best for your application. Certainly the charge/discharge columbic efficiency and internal resistance will play into the equation.

Regards,

major


----------



## frodus (Apr 12, 2008)

ElvishWarrior said:


> For a controller there's a Kelly 120V 220A. That works out to about 35hp, which is about right for a D&D ES-31B motor.


is that continuous rating? I've heard people say the Kelly is actually more like 1/3 the max Current rating, so 600A is really 200A.


----------

