# Overheating Sepex: Motor or controller?



## JRP3 (Mar 7, 2008)

I was talking to a guy with a Sepex in a sailboat, he says it runs for about 20-25 minutes then starts losing power and eventually shuts down. Initially I thought the controller was overheating and shutting down, Alltrax DCX, and I told him to unbolt if from the wooden bulkhead and try a fan on it, but it did the same thing. After he shot them with an IR thermometer he said the motor armature was 320 degrees, (I hope it's class H insulation), while the controller was under 170 I think. It's rated to shutdown at 95C, 203F, so it should be within range, though it's possible that internally it's higher than he can measure. I think he's running it at half throttle most of the time and under constant load in a boat it's not getting enough cooling. I gave him a bilge blower to aim at the brush end to see if that extended the run time at all, which would point towards the motor being the problem. 

What I don't understand is why the gradual slowdown if it is indeed the motor overheating, or if that points more towards the controller gradually limiting power then shutting down?


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## Guest (Aug 13, 2011)

Did he mention what his field amperage was set at? He could be over amping the fields. Seems mighty hot. What is the size of the SepEx? That will be a big issue as well. Some of the early Kaylor Starter/Generator type motors get hot fast. They must be cooled with lots and lots and lots of air. It is a must for the motor to survive. 

What is his pack voltage
What amps does he run at? 
What type of cells does he use? 
What are the settings for the controller. 

Is he pushing his motor beyond it's limits? I highly suspect he is. 
Is he using one of those tiny D&D motors? 
A boat will tax the tiny motors.


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## JRP3 (Mar 7, 2008)

I don't know what the motor is but it's not a D&D, looks about a 7 inch diameter. He's running it at 36V nominal, Odyssey 2150's I think, 3s3p maybe, at half throttle he's pulling 80 amps. I don't know what the field amperage is, I don't think he does either, his son did the setup.


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## Guest (Aug 13, 2011)

Any way you can get some pictures of that motor and setup? Any way to have him find out what his kid used? It would be good to figure this out and fix the issue for him or to at least ease the heat issue. The old Starter/Generator motors are just over 7" diameter. If he used one they are excellent motors but need to have lots of air pumped in and no more than 20 amps to the field. Best to have less.


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## JRP3 (Mar 7, 2008)

Probably be a few days before I can get any more details. I'm hoping the blower cooling will extend the run time, which would point towards the motor being the problem. Then he can regear to run the motor at higher speed for the same load, reducing current and increasing cooling from the built in fan. He says he doesn't get much more hull speed by running the motor much faster than half throttle, which tells me he's near displacement speed for the hull, and geared too high, (numerically low).


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## ken will (Dec 19, 2009)

JRP3 said:


> Then he can regear to run the motor at higher speed for the same load, reducing current and increasing cooling from the built in fan.


See if you can borrow a different pitch prop, probably easier/faster than regearing.


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## JRP3 (Mar 7, 2008)

Maybe not. Re gearing would only involve changing pulleys, a prop change would require taking down two masts and hauling the boat, or getting a diver.


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## JRP3 (Mar 7, 2008)

OK I have some information. It's an ADC Sepex, AN6-4003, and I have photos of the field map and motor specs at the following link.
http://s550.photobucket.com/albums/ii419/JRP3_photos/Motor specs/
This afternoon I'm going to put a clamp on meter on the field wires and see what the current is in relation to the motor current.
At this point I'm working on the theory that the field map in the Alltrax DCX may not be the correct map for that motor, and therefore the motor and controller are very inefficient and producing excessive heat.


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## JRP3 (Mar 7, 2008)

Took the field readings at four different motor current loads, 25, 50, 75, and 100amps. 

Motor Field
25 4.7
50 5.7
75 8.3
100 10.8

Looking at the motor curves all readings are near or above the line for the 25V chart, which should be around where we are at half throttle and lower in a 36V nominal system. Are the readings at 75 and 100 much too high, should they be right on the field map line?


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## Guest (Aug 20, 2011)

That looks just fine. I'd put my bet on the controller not being properly cooled. Controller causing the cut back.


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## JRP3 (Mar 7, 2008)

Yes I'm sure the controller is causing the cutback, but there is simply too much heat being generated in both the motor and controller for the load that's being applied. 80 amps and about 18 Volts, (half throttle), is about 1.4 kw. Getting the motor armature to 320F and the controller to 200F, (the shutdown temp of the Alltrax), means a big loss of efficiency in the system. At 85% efficiency only means about 210 watts lost to heat, that should not be enough to get the armature in a spinning motor to 320F and the controller to 200F.


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## Tesseract (Sep 27, 2008)

Got your PM, JRP3... Unfortunately, I am just as perplexed as the rest of the peanut gallery here. Better put out an SOS to major and hope he replies... 

That said, it does look like the field current is a bit high for the armature current, but not so much that the motor *case* should ever come close to 160C. 

But that, in itself, is the biggest clue here. Transformers will overheat like this - even when unloaded - if there is a short either between turns or across the laminations. Seeing how much ripple current is flowing through the field and armature (should be much less than 20% of the DC current at full load) would be most helpful here, but I realize that's a tall order to fill. 

You should also see if there is any "leakage" between the field/armature terminals and the frame. The obvious test is to measure the resistance between, say, a field terminal and the frame, but a better way is to measure the current (mA or uA scale) that flows between those points when 12 or more volts are applied (disconnect at least one of the cables to the controller when you do this test).

Good luck...


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## JRP3 (Mar 7, 2008)

I did PM Major, no response so far. Would a short in the laminations also cause overheating in the controller as well, at only 80 amps or so continuous? To clarify, the 320F/160C motor temp was taken at the armature with an IR thermometer, not the outer case. Still pretty damn hot.


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## toddshotrods (Feb 10, 2009)

I think Major is playing in the salt right now.

http://www.diyelectriccar.com/forums/showthread.php?p=255882#post255882


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## major (Apr 4, 2008)

toddshotrods said:


> I think Major is playing in the salt right now.


I'm back  Yep, must be salt contamination 

I'll need more data, and post some pics of the installation. First which comes to mind is ventilation restriction causing the motor (& controller?) to essentially run totally enclosed. Motors of this size will typically carry a continuous rating of one hp or less TE. So reaching that temp in 20 minutes at 1.4 kW sounds like a TE thermal rise.

How does it do no load running same speed for 20 or 30 minutes?

Nice to be home, at last 

major


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## Tesseract (Sep 27, 2008)

JRP3 said:


> I did PM Major, no response so far. Would a short in the laminations also cause overheating in the controller as well, at only 80 amps or so continuous? To clarify, the 320F/160C motor temp was taken at the armature with an IR thermometer, not the outer case. Still pretty damn hot.


Anything that causes the motor inductance to fall will cause the peak-to-peak current to rise (even though average current remains the same) so, yes, that could cause the controller to overheat sooner.

However, that guess was a real stretch so I wouldn't put too much stock into it, ok?

Unless you have an oscilloscope, current probes and the knowledge to use them at your disposal the only practical means of troubleshooting problems like this is to replace bits one at a time. More specifically, I'd start with the motor because there isn't really any way I can imagine where the controller could cause both itself and the motor to overheat yet otherwise work normally, but there are ways I can imagine for the motor to cause both itself and the controller to overheat...


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## JRP3 (Mar 7, 2008)

major said:


> I'll need more data, and post some pics of the installation. First which comes to mind is ventilation restriction causing the motor (& controller?) to essentially run totally enclosed. Motors of this size will typically carry a continuous rating of one hp or less TE. So reaching that temp in 20 minutes at 1.4 kW sounds like a TE thermal rise.
> 
> How does it do no load running same speed for 20 or 30 minutes?
> 
> ...


It's in a boat directly coupled to the shaft, I'm not sure how easy it would be to disconnect it. I had him put a blower on the motor with a duct tape shroud and that helped keep the motor temps lower but the controller still overheated and shut down in the same time frame. I'll have him add a blower to the controller as well. 
Just so I'm clear, you don't see any issues with the motor field current being 5 amps higher than the field map, and the field current does not need to adhere tightly to that line?


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## major (Apr 4, 2008)

JRP3 said:


> Just so I'm clear, you don't see any issues with the motor field current being 5 amps higher than the field map, and the field current does not need to adhere tightly to that line?


That is correct. You just need to stay out of the forbidden zone  Higher is o.k., up to a point.


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## JRP3 (Mar 7, 2008)

OK thanks, I can put that idea to rest and move forward with better airflow all around. 
I realized every time I look at the setup he has everything open so I can see, but I'll bet he closes up all the hatches when running, creating a hot little coffin in there. Time to ventilate.


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## DIYguy (Sep 18, 2008)

Hey guys. Just wondering what rpm he is typically running?? 
A few weeks ago, before I installed the liquid cooling on the truck (Soliton1), I drove it to a city about 45 miles away. It went great on the way there and the energy used was really quite good. Since this was one of my first longer trips, I determined that 5th gear seamed the best for a sweet spot on current draw...at least on the flat areas. I realized why on the way home as the head-wind was wicked and getting stronger. It might have been good for current draw, but I started to notice gradually decreasing power to the point where the Soliton was stopping any acceleration and ability to climb hills with power. It was a hot day. It's nothing new to anyone,...but made me realize how significant the whole rpm vs sustained current vs cooling issue really is. Now I always keep the truck in the gear that will maintain over 2000 rpm and usually closer to 3000 rpm on hotter days. I have a strong blower on the motor also.. and did have at the time. The soliton has 1.4 software with cooling pump on demand. No more issues at all. 

I agree that this gradual cut back is the controller....however, the motor rpm must be kept high enough to do some good wrt cooling. I think ur going in the right direction with the fan cooling. Is there provision for liquid cooling on the controller? 
Finally, I wouldn't really want to improve the controller cut back too much until the motor cooling is sorted out. This really is helping to protect his motor..... assuming that it doesn't already have a short.

Good luck.

Gary


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## JRP3 (Mar 7, 2008)

Yes I do think he's turning the motor at too low a speed and we have been discussing regearing/repitching the prop. Turns out he has an adjustable prop that he can change the pitch on. Right now he's running at half throttle most of the time, which means on a 36V nominal system only around 20V and probably half the RPMs the motor is rated for. I plan to tell him to aim for running about 3/4 throttle for the same speed he's at now, and hopefully reduce current draw plus increase internal fan speed. I think he'll want to run forced cooling on both the motor and controller anyway, and I'm going to have him pull in some fresh air from outside and exhaust the hot air out of the motor compartment. Water cooling the controller would involve building or buying a heat exchanger. One of the nice things about air cooling is there is no winterization to worry about, just pull the boat and park it.


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## JRP3 (Mar 7, 2008)

Airflow did the trick, one blower on the controller and one on the motor let him run as long as he wanted. He'll experiment with prop pitch to get RPM's up a bit more and current down as well. Thanks for all the ideas.


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## major (Apr 4, 2008)

JRP3 said:


> Airflow did the trick, one blower on the controller and one on the motor let him run as long as he wanted. He'll experiment with prop pitch to get RPM's up a bit more and current down as well. Thanks for all the ideas.


Nice to hear what the solution was


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