# Effect of motor length on a SepEx motor's performance



## GizmoEV (Nov 28, 2009)

Unfortunately I have to replace my D&D 6.7" SepEx ES-10C motor due to a couple of comm bars lifting. They spring back when pushed down otherwise I'd just have the comm turned.

Early in the motor's life it was over worked due to a high gear ratio for my hill climbing and it didn't have adequate cooling. Doing the postmortem on it shows that it definitely has been overheated. In the 15k miles since it was rebuilt by Jim Husted it has had a better gear ratio 3.75:1 rather than the 3:1 it used to have and for the last 10k miles it has had an external cooling blower on it. I think the early overheating may have weakened the comm bars and then a little too long at high rpm while unloaded allowed the bars to break loose. At least that is what I like to think.

In talking to D&D Motor Systems the engineer suggested that maybe I should go with a longer motor. The existing one is 10.28" long and the replacement would be 12.2" long. All the length increase would be in the armature and casing. The current motor casing is 6.25" long so the replacement casing would be 8.17" long, a 30% increase in length.

Since I won't be changing anything else in the vehicle what will be the performance differences? I understand that there will be more torque for a given current. This should lower the heating of the motor for a given set of conditions. It should also mean that I will have a better start off the line. What is going to happen at the top end? With the original motor top speed was ~50mph at 3200rpm. Will I still have the same top speed since there will be more torque for a given current even though the back emf will be higher which will tend to lower the top rpm?

Any other effects by going to a longer case?

Thanks,


----------



## major (Apr 4, 2008)

GizmoEV said:


> Any other effects by going to a longer case?


Hi Giz,

Generally speaking when it comes to motors, bigger is better, length or diameter  Sticking with length, the longer core increases the flux assuming the designer stays with the same flux density which is probably the case. If he uses the same armature turns (# of conductors) in the armature, then at a given current the increased flux will yield a proportional increase in torque and back EMF (so decrease in RPM). 

So to get equal performance in the vehicle, you adjust your drive ratio. Then it looks the same as before, except the motor turns slower and has increased mass and surface area. Increase in mass and surface area of the motor helps the thermal situation. Decreased RPM hinders cooling for the normal self ventilated motor but with your external blower wouldn't be that much. 

The longer core requires the coils (both armature and field) to increase in length so it increases resistance. But the increase in resistance is less than proportional to core increase because the end turns stay the same. So the overall effect of resistance change isn't a big deal. There would be a change in motor inductance which would likely make your controller a bit happier.

Major lengthening of the core can result in difficulty getting the heat out of the middle, but I suspect it wouldn't be problem with the size you're talking about.

However  if the designer has the option to alter the armature lamination design, then he can change the armature turns. So when he lengthens the core, he can reduce the comm bar count and increase the conductor size and keep the torque/amp about the same. Then you may not have to change the drive ratio. The longer motor would likely provide superior performance. Of course commutation would have to be considered when changing armature design like this 

So, all in all, it is hard to say exactly, but generally, bigger is better. Bigger should give you an increased region for field control with the SepEx (more flux to play with). You'll have to retune the controller. That could possibly enter into the drive ratio selection. Also the possibility to increase battery voltage along with the longer motor.

But....begs the question ....If you think your present motor was damaged early in its life and has been working well with revisions you made......Why change it now? 

Regards,

major


----------



## Salty9 (Jul 13, 2009)

A old book, "Rewinding Small Motors", 1932 (which convinced me that I didn't really want to rewind motors) says "*Estimating the Two- and Three-phase Rating of a Single-phase Motor Frame ..* . . This method makes use of the number of cylindrical inches in the core, using the inside diameter, which is the bore B squared, times the length of the core. Thus (B x B x L) determines the maximum horsepower rating of any frame." 

I think the author was trying to say that the power is proportional to the flux gap area but am not sure.


----------



## GizmoEV (Nov 28, 2009)

That helps a little. I knew it was a little complex due to the many factors involved.



major said:


> So, all in all, it is hard to say exactly, but generally, bigger is better. Bigger should give you an increased region for field control with the SepEx (more flux to play with). You'll have to retune the controller. That could possibly enter into the drive ratio selection. Also the possibility to increase battery voltage along with the longer motor.


That shouldn't be a problem. Maybe since I went up to a 64V pack and the motor is 36/48V rated it will be better with the longer motor. The Sevcon PP874 controller has settings for both Armature an Field of current low, mid, and high A, and resistance.



major said:


> But....begs the question ....If you think your present motor was damaged early in its life and has been working well with revisions you made......Why change it now?


The reason to change it now is that the cost difference between sending my current motor to NY from WA and having a new armature installed vs. having a new motor build is negligible. If the longer motor will make it easier to start on some of the hills I have then I have gained some. I hope it doesn't kill my top end too much.

Here is a picture of the armature: https://picasaweb.google.com/lh/photo/rgjKnM8KmvvUaWfjCrulXNMTjNZETYmyPJy0liipFm0?feat=directlink

Here is one of the ends of the brushes: https://picasaweb.google.com/lh/photo/GAddbBpkoyJrUksXkZjhVNMTjNZETYmyPJy0liipFm0?feat=directlink

It is hard for me to know for sure when most of the heat damage was done. I'm assuming before the blower was installed since that was when I routinely smelled the motor.


----------



## major (Apr 4, 2008)

GizmoEV said:


> The reason to change it now is that the cost difference between sending my current motor to NY from WA and having a new armature installed vs. having a new motor build is negligible. If the longer motor will make it easier to start on some of the hills I have then I have gained some. I hope it doesn't kill my top end too much.


You could just buy a replacement armature and assemble it yourself saving shipping west to east.



> Here is a picture of the armature: https://picasaweb.google.com/lh/photo/rgjKnM8KmvvUaWfjCrulXNMTjNZETYmyPJy0liipFm0?feat=directlink
> 
> It is hard for me to know for sure when most of the heat damage was done. I'm assuming before the blower was installed since that was when I routinely smelled the motor.


Looks like the source of the heat was the comm. You said you raised some comm bars. That can result from running a hot comm (and brushes) like uphill and then coming to a stop. The hot brushes set on the hot comm in the same place for minutes with no cooling and distort the plastic around the comm bar inner dovetail which then means a loose bar forever. Once the bar(s) is loose it bounces the brush causing a spark and heat so the comm heat problem worsens.

Forced air (external blower) helps reduce risk of this heat soak but a longer comm and increased brush size would be good, maybe better than increased core length. 

Another thing. I don't know how extensive of a design selection D&D has. It appears you have maybe a 4 inch core with 57 slots. If they go to 5.5 or 6 inch core, see if they can go to a 45 or maybe even a 37 slot armature. Get yourself a kickass motor 

major

ps....Be sure to break in the new armature or motor.


----------



## GizmoEV (Nov 28, 2009)

major said:


> You could just buy a replacement armature and assemble it yourself saving shipping west to east.


That is an idea I hadn't thought of. I'm sure I could find a machine shop around here to do the work for me if necessary.



major said:


> Looks like the source of the heat was the comm. You said you raised some comm bars. That can result from running a hot comm (and brushes) like uphill and then coming to a stop.


That happened quite a bit early on. Maybe my running at higher rpm just finished it off or made the loose comm bars show up earlier rather than later.



major said:


> Forced air (external blower) helps reduce risk of this heat soak but a longer comm and increased brush size would be good, maybe better than increased core length.


Maybe I should install a time delay circuit on my blower where it will continue to run for a few minutes after I turn off the key. I do have an option to have an 8 brush motor built but that would only add about 1/4" to the brush width. The 8 brush motors use a narrower brush. The brushes in this motor are 1.25" wide. Would I still likely be better off with the longer comm of an 8-brush motor over a longer armature 4-brush design? I don't think I can get my cooling blower under the tail on anything longer than an overall 12.2" motor.



major said:


> Another thing. I don't know how extensive of a design selection D&D has. It appears you have maybe a 4 inch core with 57 slots. If they go to 5.5 or 6 inch core, see if they can go to a 45 or maybe even a 37 slot armature. Get yourself a kickass motor


I just measured the core of the armature (the section of laminations, right?) and it is 3.5". Assuming the longer armature adds all the length to this section would make it 5.42".

There are 57 slots. Does a lower number of slots increase the RPM for a given voltage? What does that do for the low end torque? Right now it is (was) a little sluggish until the motor was spinning 2-300rpm then it is (was) like turbo boost kicked in up until around 2500rpm when acceleration noticeably decreased up to maximum speed which usually was around 3200rpm. I would like to get just a little more top speed when the battery voltage is at ~60V and motor rpm is ~3500rpm.



major said:


> ps....Be sure to break in the new armature or motor.


That is for sure. I planned on finding out what I needed to do when I got a motor replaced. It is a little hard to run on 12V being SepEx but I could easily put a zip tie on the throttle trigger and make it run at any rpm needed.

Thank you for the input. I need to call D&D tomorrow with what I want to do so this has been valuable input. I'll have to ask about slot numbers and such.


----------



## major (Apr 4, 2008)

GizmoEV said:


> That is an idea I hadn't thought of. I'm sure I could find a machine shop around here to do the work for me if necessary.


I'd get new brushes and springs also. Check that your brush holders and field coils are in good shape. And of course, new bearings.



> Maybe I should install a time delay circuit on my blower where it will continue to run for a few minutes after I turn off the key.


Good idea.



> I do have an option to have an 8 brush motor built but that would only add about 1/4" to the brush width. The 8 brush motors use a narrower brush. The brushes in this motor are 1.25" wide. Would I still likely be better off with the longer comm of an 8-brush motor over a longer armature 4-brush design?


I kinda think so. Sure looks like comm (and brushes) were the main heat source. But a bit of both, longer comm and longer core, would be best. Ideally the brush would be very narrow and span as few bars as possible, but this then makes for little surface contact area unless you have a real long comm, which presents problems itself. So it is a compromise. But the same contact area with the longer comm and narrower brush and 8 vs 4 (considering 8 springs) would be better.



> I just measured the core of the armature (the section of laminations, right?) and it is 3.5". Assuming the longer armature adds all the length to this section would make it 5.42".


Yep, lamination stack length or core. Just the steel.



> There are 57 slots. Does a lower number of slots increase the RPM for a given voltage? What does that do for the low end torque?


For the same flux, yes. These are single turn or bar wound armatures, so the "turns" is proportional to the number of slots (also = to # of bars) and enters directly to the torque constant which is inverse of the RPM/volt constant. So you increase the core, increase flux, increase torque, decrease RPM but then reduce turns and decrease torque and increase RPM to get back near where you started......BUT you have increased the conductor size of the armature path and therefore the ampacity and reduced the armature resistance so it makes for a more robust motor 



> Right now it is (was) a little sluggish until the motor was spinning 2-300rpm* then it is (was) like turbo boost kicked in up until around 2500rpm when acceleration noticeably decreased up to maximum speed which usually was around 3200rpm. I would like to get just a little more top speed when the battery voltage is at ~60V and motor rpm is ~3500rpm.


This may be a function of the SepEx tuning. You should be able to get constant (max) torque from zero to base RPM. The longer core motor (having more flux) may allow you to further field weaken for increase of top speed if you can get the slot count down. The longer core with same slot count will reduce top RPM and therefore require a ratio change.

Regards,

major

edit: * This could also be due to a programmed ramp on the current at start up. Come to think about it, I notice a similar thing on my tractor with a Curtis SepEx and GE motor. Kind of a delay. Somewhat irritating. Been meaning to try to program it out.


----------



## GizmoEV (Nov 28, 2009)

major said:


> I'd get new brushes and springs also. Check that your brush holders and field coils are in good shape. And of course, new bearings.


I just uploaded three more pictures of the field coils brush end: https://picasaweb.google.com/lh/photo/4DEP5wcoOY8-ARzwDI-8P9MTjNZETYmyPJy0liipFm0?feat=directlink

Field coils drive end: https://picasaweb.google.com/lh/photo/v_dXGYyp-5Xl4kg3iQbFQ9MTjNZETYmyPJy0liipFm0?feat=directlink

Inside brush bell end: https://picasaweb.google.com/lh/photo/6v3zgnqNq7CmMV4WpZaAsdMTjNZETYmyPJy0liipFm0?feat=directlink

What do you think? I didn't see anything worse than you see here. I did not try to clean out any brush dust since I don't have an air compressor or a good dust mask for such fine dust.




> For the same flux, yes. These are single turn or bar wound armatures, so the "turns" is proportional to the number of slots (also = to # of bars) and enters directly to the torque constant which is inverse of the RPM/volt constant. So you increase the core, increase flux, increase torque, decrease RPM but then reduce turns and decrease torque and increase RPM to get back near where you started......BUT you have increased the conductor size of the armature path and therefore the ampacity and reduced the armature resistance so it makes for a more robust motor


It sounds like it might be worth doing what I can to go with a longer armature, longer comm (8 brush), and 45 or 37 slots to get a cooler running motor with similar top end rpm. It takes about 8500W (135A battery at ~62V) to push this machine at 50mph with the motor spinning at ~3200rpm. Which number of slots do you figure might get me close to back to the same rpm at that load, 45 or 37? I didn't get a hold of the D&D engineer today so I'll try again tomorrow.




> This may be a function of the SepEx tuning. You should be able to get constant (max) torque from zero to base RPM. The longer core motor (having more flux) may allow you to further field weaken for increase of top speed if you can get the slot count down. The longer core with same slot count will reduce top RPM and therefore require a ratio change.
> 
> Regards,
> 
> ...


That could be. The settings I have are:


Armature current low: 100A
Armature current mid: 150A
Armature current high: 420A
Field current low: 5.00A
Field current mid: 20A
Field current high: 50A
I assume that in general near zero rpm the field is at max and armature current is at max under a full throttle condition and that field current diminishes as rpm increases to the max. At least that is how I interpret this graph from the manual.


----------



## major (Apr 4, 2008)

GizmoEV said:


> I just uploaded three more pictures of the field coils and inside the brush end bell starting at https://picasaweb.google.com/lh/photo/4DEP5wcoOY8-ARzwDI-8P9MTjNZETYmyPJy0liipFm0?feat=directlink
> 
> What do you think? I didn't see anything worse than you see here.


 
Hi Giz,

I can just see the one pic. Looks in pretty good shape. It looks like it has seen some heat. The tape on the lower coil is damaged but doesn't hurt function. I'd say this field has another 50,000 miles in her  If you use it, you might give it a good cleaning and use a high temp motor insulating varnish (like red Glyptal) on the coils for extra measure, but it is probably fine the way it is.

Depends on how much you really want to modify the motor. If the vehicle was working well for you, I'd be tempted to just replace the armature and brushes. But if you change to a different motor design, you have to use what D&D has tooled. I was just guessing at those slot #'s and have no idea if they have laminations designed or coils tooled for those core lengths. Just talk to that engineer there and see what he recommends out of his parts sets and what the cost would be.

As far as the field map settings I don't see anything disturbing. Again, if it was working well and you stay with this motor, leave it alone and get it running and broken in. Then try some subtle changes and test. You say your top steady speed draws about 130A. Lower the field current an amp or two in that area and see if your speed comes up without snap, crackle and pop of comm arcing. Of course, a new motor design means a new tuning process.

At least you got something to talk about with D&D 

major


----------



## GizmoEV (Nov 28, 2009)

major said:


> I can just see the one pic.


I thought you could cycle through the pics but I see now that if I don't have the album up I can only see one.

Here is a pic of the field at the other end, not much difference really: https://picasaweb.google.com/lh/photo/v_dXGYyp-5Xl4kg3iQbFQ9MTjNZETYmyPJy0liipFm0?feat=directlink

A look at the brush end bell: https://picasaweb.google.com/lh/photo/6v3zgnqNq7CmMV4WpZaAsdMTjNZETYmyPJy0liipFm0?feat=directlink

It looks really good compared to just before I sent it the first time to Jim Husted. At that point there was corrosion on the surface of everything, even some of the brush leads had corrosion on them and the surface was brittle. Regular use and a cooling blower bringing in filtered air really makes a difference in this wet climate.



> Looks in pretty good shape. It looks like it has seen some heat. The tape on the lower coil is damaged but doesn't hurt function. I'd say this field has another 50,000 miles in her  If you use it, you might give it a good cleaning and use a high temp motor insulating varnish (like red Glyptal) on the coils for extra measure, but it is probably fine the way it is.


That is what I thought. The tape on each of the coils looks similar. As for 50,000 miles that means it should last me another 10 years if I keep up my ~5000 miles/year. Maybe it will outlast my LiFePO4 pack.



> Depends on how much you really want to modify the motor. If the vehicle was working well for you, I'd be tempted to just replace the armature and brushes. But if you change to a different motor design, you have to use what D&D has tooled.


I was figuring that if I needed to replace it, now would be the time to make some changes. I'm liking the idea of just getting a replacement armature, brushes, springs, and bearings. I'll have to see if D&D will sell me just those parts. Brushes, springs, and bearings are probably standard items but the armature may not be. I assume the armature resistance can be measured without it being on the shaft. I'll need the new value for the controller.



> As far as the field map settings I don't see anything disturbing. Again, if it was working well and you stay with this motor, leave it alone and get it running and broken in. Then try some subtle changes and test. You say your top steady speed draws about 130A. Lower the field current an amp or two in that area and see if your speed comes up without snap, crackle and pop of comm arcing. Of course, a new motor design means a new tuning process.


That makes sense. The only sounds I got out of the motor before was that high pitched whine in the neighborhood of 2600rpm and then only under load. It just dawned on me that since there are 57 slots/bars that the frequency of a bar passing a brush would be 57/60ths of the rpm. I had my son, who is in to music, listen to various frequencies generated on my iPhone and we determined that the pitch we hear is double the frequency of a bar passing a brush. With 57 bars that would mean one set of brushes would be seeing a "new" bar when the other set of brushes were half way across their "new" bar or there a bouts. At that particular rpm maybe the brush arcing is audible. I wish I had field and armature current numbers for that point.



> At least you got something to talk about with D&D


Yes, I feel much better prepared to talk to them about it. I think I'll see if they will sell me an armature, brushes, springs, and bearings. If they don't want to, I think I'll go with the 8-brush design, especially if I can't get a lower slot count, and just do regular inspections of it to see how it is doing. It it looks like it is showing some heat damage then I can look for something else which will be better suited to my use of the vehicle.

Thank you very much.


----------



## Frank (Dec 6, 2008)

When I spoke with D&D re motor temperature their engineer told me that an important reason for going with the longer motor was extended range i.e. more torque with given current therefore lower current for a given output. I can't remember what kind of improvement he was talking about but it may be a consideration for you. We have the same setup and I would have liked to run the longer motor for improved performance, but there's not enough room on my bike.

When monitoring motor temperature it was not unusual to see a 20-40*F rise after shutting things down so adding a timer to your blower circuit would probably do a lot for you.

Frank


----------



## major (Apr 4, 2008)

Frank said:


> When I spoke with D&D re motor temperature their engineer told me that an important reason for going with the longer motor was extended range i.e. more torque with given current therefore lower current for a *given output*.


Hi Frank,

If by "given output" you mean power, then it is incorrect to expect reduced current for a given power from a larger motor. Well, possibly maybe 1% or so from increased motor efficiency. You can get more torque per amp but the RPM will be reduced so the output power remains essentially the same for a given input power.

major


----------



## Frank (Dec 6, 2008)

Hmmm, I didn't really think about it. It might be true (er) for PbA batteries. For given power, lower current means less Peukert effect therefore greater range.

??


----------



## GizmoEV (Nov 28, 2009)

I just got off the phone with Vic at D&D and have my replacement motor ordered.  He is building one with the longer armature because he said he couldn't really build the 8-brush design for some reason. I'm not sure if it was because of the Gizmo mounting needs or something else. Like major said, Vic said that the longer armature might drop my top end speed a couple of mph but that I could lower the field current a little and likely gain that back. Field current could probably be lowered down to about 3A. I had it set at 5A for my old motor.

As for top safe RPM he said 6000 would be a safe max. He concurred with me that the comm bars lifting wasn't from overspeed but from prior overheating and thus weakening of the comm. Calculating from the speedometer reading my motor didn't exceed 5500 RPM so I don't feel as stupid as I was afraid I was going to.  I'm still frustrated that I had to replace my motor.

Another thing Vic said was that the resistance settings in the Sevcon controller aren't really necessary. He said they are mostly used for determining if the correct motor is hooked up. That makes sense to me since the controller has current shunts to determine current to the field and armature so I don't really see why the controller would need to know the field and armature resistance.

Another thing to note, D&D does make a SS forced air cooling band for $55. This is cheaper than what it cost me to have one made and I made.

Finally, he is installing a NO thermal switch for me to hook up to my cooling blower so I don't have to use the one I setup that mounts to the side of the motor case. 

So now, I need to figure out a simple timer circuit so that the blower stays on or comes on for a few minutes after the key is switched off. I've thought of some sort of a capacitor setup on the coil side of the relay which would take a few minutes to drop in voltage before the coil bleeds the voltage down to the point it drops out but I'm concerned about the inrush to the capacitors when the thermal switch turns on. Any ideas? Maybe I better start a new thread for this one.


----------



## major (Apr 4, 2008)

Time delay relay.


----------



## GizmoEV (Nov 28, 2009)

major said:


> Time delay relay.


Now that is just too obvious. Thanks, now I have to figure out exactly what I want it to do and how.


----------



## electro wrks (Mar 5, 2012)

I've been using one of the non-contact thermometers from Harbor Freight, with good success, to measure armature temps after a test run. I've found outside case temps to be a poor indicator of armature temps- I'm guessing because of the time delay for the heat inside to migrate out. Does anybody know if it's possible or practical to mount the temp sensor/ fan switch closer to the armature -say on a brush holder?


----------



## GizmoEV (Nov 28, 2009)

electro wrks said:


> I've been using one of the non-contact thermometers from Harbor Freight, with good success, to measure armature temps after a test run. I've found outside case temps to be a poor indicator of armature temps- I'm guessing because of the time delay for the heat inside to migrate out. Does anybody know if it's possible or practical to mount the temp sensor/ fan switch closer to the armature -say on a brush holder?


What I did with my current temp sensor was to get one which turned on at a relatively low temp. It comes on at 100°F and off at something like 96-98°F or so. I figured that having the temp low would likely compensate for the time delay somewhat. It seemed to work just fine. My motor had heat damage from earlier in its life due to high gearing and 450A current every time I climbed my hill to get home. It started smelling nearly every time I got home and eventually started sparking due to the heavy brush deposits on the comm. I sent it to Jim Husted to be revived and he said I had to gear it down a bit. I went from a 3:1 to a 4.09:1 and that made a big difference. When I went to LiFePO4 I went with a 3.75:1 gear (didn't slip when wet as bad) and I added the forced air cooling. After that I never smelled the motor except when I took a "short cut" and ended up having an 1800' hill climb in just a few miles so I think the low temp switch worked ok.

When I get my new motor from D&D I'll report where they mounted the thermal switch. FWIW, the D&D engineer did say I would be better off mounting the temp switch to the aluminum BE bell rather than the case above one of the pole shoes.


----------



## GizmoEV (Nov 28, 2009)

D&D Motors has awesome service. I talked to Vic in engineering almost a month ago about what I should do for a repair or replacement of my ES-10C motor. I told him at that time I would have to wait a little while to pull the money together for it. At the time he told me that they were about 3 weeks out to be able to build a motor. Since it takes a week to ship across the US I had resigned my self to waiting 4 weeks for a motor after I placed the order. I called him Monday morning to place the order and he said he had set aside the parts and he would try to get it put together this week. This morning, Tuesday, he calls me and asks about my tire diameter, gear ratio, and to verify performance requirements and nominal pack voltage. He had already built the motor and had it on the dyno! I'll have it my next week!

He sent me an engineering report on it showing what I would need to get my desired 50mph top speed that I had with the old, shorter motor. You can see it at: https://picasaweb.google.com/lh/photo/Ai6VXI4SneLThAH_qH30QdMTjNZETYmyPJy0liipFm0?feat=directlink

The motor is an ES-32 MOD-15. Now I just have to program the controller for the new parameters and I should be ready to go. I'm wondering if major or someone could help me understand how the field and armature current settings affect performance. My current settings are as follows:


Field Low = 5.00A
Armature low = 100A
Field mid = 20A
Armature mid = 150A
Field high = 50A
Armature high = 420A
I note that the values are not evenly spaced, ie 5A to 20A = 15A where as 20A to 50A = 30A. Why?


The recommended new settings are:


Field Low = 4.50-5.00A
Armature low = 110A
Field mid = 12A [updated]
Armature mid = 250A [updated]
Field high = 20A
Armature high = 420A or controller max [updated]
What would be the best values to place in the ????? Also, any idea why the max field current is 20A rather than the former 50A? Does a lower max field current decrease the starting torque?


He said that if I need to I could probably lower the field min to 3-4A if I had to. Will this mean more current in the armature as a result or just a little higher speed?


I asked about the thermal sensor and he said it is set to 180°C. Vic figured I could get by without an external cooling blower and suggested that maybe I should hook the thermal sensor to a light in the dash to come on when it got too hot. The engineering report says that the thermo sensor is installed under the brush. I'm not sure if this is the brush lead or if it is physically in the brush it self. I'll definitely post pics when the motor comes in.


----------



## GizmoEV (Nov 28, 2009)

My new motor arrived! 








Sorry for the blurry pic. It is hard to hold still with an iPhone when it takes a pic at 1/15th of a second. Naturally the upper motor is the new one. It is an ES-32Mod-15 which basically means it cost a bit to get the Gizmo mounting holes where they had to be. Most likely only the ones added to the brush end. The lower case is from the ES-10C which came with my Gizmo. It was just geared a little high and couldn't stand the abuse it got during the first 6000 miles or so. It did go another 15,000 after re-gearing it and then adding a cooling blower. D&D felt I likely won't have to do external cooling on the new one. The internal fan does look a little smoother than the other one so it may be more efficient.

You can see the two yellow wires coming out of the brush screen. Those go to a 180°C NO thermal switch. It is mounted "under the brush" as can be seen in this pic.








The best I can tell is that a slot was machined into the brush-ring holder and the switch was mounted in that. I wondered what "under the brush" meant and now I know.

I don't have a weight yet but I do know that UPS ground was nearly $100 to ship the 80 lb package.

Major, would there be any damage to run this motor with the same settings as the old one to see what the performance differences are? I did get recommended values for the other items to program in my controller which I updated my prior post with.


----------



## major (Apr 4, 2008)

GizmoEV said:


> Major, would there be any damage to run this motor with the same settings as the old one to see what the performance differences are?


Can you get a resistance on the old field and new field? It may be that the new motor has higher resistance (smaller gauge wire &/or more turns) and therefore requires less current and more field voltage. I'd just set it for the new recommended values. If you do try the older (higher current) settings, don't run for very long. Maybe measure the field resistance and do an I²R calc. Don't run the field at too high wattage for long.

edit: Neat idea for sensing brush temp


----------



## electro wrks (Mar 5, 2012)

go to a 180°C NO thermal switch. It is mounted "under the brush" as can be seen in this pic.










Asked and answered: can you mount the temp sensor to the brush holder? I should be a motor designer! I've cooked enough of them.


----------



## Frank (Dec 6, 2008)

This is excellent, I didn't realize how short your original motor was. You're going to love this.


----------



## GizmoEV (Nov 28, 2009)

major said:


> edit: Neat idea for sensing brush temp


I thought so too. I looked at the brush ring in my other motor and it has the same slot too so I think that D&D has a sensor as a standard option. I'm sure the cost of getting the thermal switch isn't too much and it looks like it might even be able to be installed by only removing the brush cover. I've attached a picture of it.


----------



## GizmoEV (Nov 28, 2009)

major said:


> Can you get a resistance on the old field and new field? It may be that the new motor has higher resistance (smaller gauge wire &/or more turns) and therefore requires less current and more field voltage. I'd just set it for the new recommended values. If you do try the older (higher current) settings, don't run for very long. Maybe measure the field resistance and do an I²R calc. Don't run the field at too high wattage for long.


The resistance of the old motor's field is 0.76 Ohms according to the programming in the controller. My meter reads 0.8 Ohms so that seems right. The field resistance of the new motor is reading 2.6 Ohms. Since the case is about 1.75 inches longer it makes sense that there is quite a bit more wire in the field even if the number of turns is the same. At 50A and 0.76 Ohms I²R = 1900W for the old motor. At 20A and 2.6 Ohms I²R = 1040W for the new motor. Maybe that is why D&D said I probably wouldn't need a cooling blower. At 27A the new motor would put out 1900W from the field.

I'm probably just best to program in the recommended settings and adjust from there.


----------



## GizmoEV (Nov 28, 2009)

I got the motor installed last night and went out for a drive. Definitely a different feel. More torque at the low end and less at the top end.

Even though the D&D engineer said that the resistance values programmed into the controller don't matter on this Sevcon PP784 controller it does make a difference. I don't know how this controller uses the values but it does.

I started with the recommended new settings:


Field Low = 4.50A
Armature low = 110A
Field mid = 12A
Armature mid = 250A
Field high = 25A [this is the lowest the controller allows for this setting]
Armature high = 420A
I found that the top speed wasn't what I needed and that the torque dropped off rather quickly. At these settings I was getting more upper end out of the smaller motor. Unfortunately, I don't know what the combination of field and armature currents were.

Playing around with the field resistance I found that when I set it low there was very little power out of the motor. When set at the max of 2.50Ohms there was significantly more torque at low rpm but lost torque rather quickly and topped out at a leisure 35-40mph when I had a solid 50mph with the old motor under the same environmental conditions.

Does anyone have an idea of how the Sevcon PowerPak controllers use the field resistance values? I thought the manual said that there were internal shunts for the field and armature current measuring but I'm beginning to wonder. Why does it need to know the field resistance?

I'm going to try these settings since the Field current vs. Armature current graph looks similar to what I used with the old motor.


Field Low = 2.50A
Armature low = 110A
Field mid = 10A
Armature mid = 160A
Field high = 25A
Armature high = 420A
Field resistance = 2.20 Ohms
What would the problem be of setting the field current this low? Is it that the armature current would have to be set proportionally higher to get enough torque at high rpm's?


Thanks for any input.


----------



## major (Apr 4, 2008)

GizmoEV said:


> Field Low = 2.50A
> Armature low = 110A
> Field mid = 10A
> Armature mid = 160A
> ...


Looks O.K. to me. Your previous setting low was 10% of the high, so 2.5 A is in line.


----------

