Kostov, Kelly Postmortem

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4Springs
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Kostov, Kelly Postmortem

Post by 4Springs » Sun, 26 Oct 2014, 14:25

As described in my build thread, I recently had a couple of failures. They were:

Kelly KDH14800D controller:
This went into a state where it was basically "full on". So the motor went into an uncontrolled vvvrrrroooooommmmm!
Don't know why this happened, it was first thing in the morning so everything was cold. Possible that my precharge was not up to scratch, but seems unlikely.

Kostov 17R (9"):
After the controller failed I bought a new one. The new one was bigger (1000A vs 800A). This worked fine until I got a bit carried away and pushed the motor past its limits. I took the motor to a motor rewinds place who said that it would take a lot of work (1 or 2 thousand dollars worth) to rebuild. Since a new one the next size up costs $2400 delivered, I have now ordered one of those. Hopefully the new one will be less likely to die if I get enthusiastic in my driving.

The title "postmortem" on this post is probably a bit misleading. It sort of implies a level of knowledge which is above me. But I can at least take some photos of the bits:

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This is the front bit (excuse my technical language). I think the motor guy said this was ok. Brushes are in good order and not worn down much in my 15,000km of use.

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You can see some smoke on this middle bit ("rotor" I presume). The guy said that it measures as a short, and so would need to be pulled apart and probably rewound.

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He pointed out the patina on this bit (commutator?) and said that was bad. Possibly due to too high a voltage.

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I assume this is called the stator, and the coils are also burnt out. Maybe not all of them.

The motor guy was a bit dubious at the voltage I was using, he had written down that 124V was the rating of the motor. My controller can potentially give it 160V or so. I'm not sure where he got the 124V from, when I got home I could clearly see the label which says 144V. The Kostov website seems to indicate that voltage doesn't really matter too much except if there is no controller on the motor to stop it over revving (see my entry under "Kelly Controller" above!).
He could also not believe how little this motor cost.   

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And finally, here is a photo of the innards of the Kelly. There is no way that I am going to get it any more disassembled than this short of using a hacksaw. The case is one piece of aluminium - you can only take the ends off. It looks like two circuit boards have been slid down inside with the help of the six yellow spacers. Screws from the outside keep the spacers in place, and possibly some of them go through to the circuit boards. Every one of the 30-odd screws on the outside were covered in epoxy resin. I found that if I heated it it would go brittle and could be prised out of the phillips-head screws.
There are three large aluminium terminals running down between the circuit boards. There are heat-sunk components on the left and right, which have screws through from the outside to attach them to the aluminium casing.
This is the "waterproof" version of the controller. It has been filled with a rubbery stuff which I would say might be silicone rubber. It burns away with a hot knife soldering iron attachment. There are 8 plastic tubes running down the middle for some reason, these are not filled with silicone. To get any further I would have to destroy the case. I may do this someday if I get enthusiastic, but too much else to do right now!

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EV2Go
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Kostov, Kelly Postmortem

Post by EV2Go » Sun, 26 Oct 2014, 19:41

4Springs to give you some context as to how well the Kostov stood up to a blown controller have a look at this short video made by EV Capri (member on the forum) and his experience when a controller went wild with a 144v pack.


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Kostov, Kelly Postmortem

Post by T1 Terry » Mon, 27 Oct 2014, 02:10

Wow, that was some wind up. Would that motor damage on 4 Springs Kostov be due to overheat rather than over voltage? It doesn't look like anything came apart due to over speed but it sure looks like it got real hot.

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Kostov, Kelly Postmortem

Post by EV2Go » Mon, 27 Oct 2014, 02:17

Good question as you can see from the video Kearon's NetGain just let go when it reached sufficient revs. Whereas the Kostov under similar conditions seemed to let go electrically.

There no guarantee if you repeated both situation again that you would get identical results but to me the Kostov does look like it is built beefier and might last longer for it to burn out.

I know which one I would prefer to repair.

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Kostov, Kelly Postmortem

Post by 4Springs » Mon, 27 Oct 2014, 02:28

T1 Terry wrote: Would that motor damage on 4 Springs Kostov be due to overheat rather than over voltage? It doesn't look like anything came apart due to over speed but it sure looks like it got real hot.

I had two separate problems. The initial overspeed one did not stop the Kostov. As far as I know it was fine after that. I asked my wife how long she thought she took to turn off the power when it was overspeeding and she said a few seconds. This sounds longer than the guys in that video. I have a heavy flywheel on mine so I wonder if that helped it to not fly apart.
The one that burnt it out was when I drove too hard for too long with the new beefier controller. I was pushing it with my foot to the floor for a good 30 seconds or more. But there may have been some kind of damage from the initial overspeeding? If so I couldn't tell (it ran fine for about 30km before I decided to go flat out).

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Kostov, Kelly Postmortem

Post by EV2Go » Mon, 27 Oct 2014, 02:30

That is both the stator and the interpoles. Kostov are a bit unique in that the put interpoles between the field coils? to stop them flashing over.Image

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Kostov, Kelly Postmortem

Post by Richo » Mon, 27 Oct 2014, 20:37

4Springs wrote:This is the "waterproof" version of the controller. It has been filled with a rubbery stuff which I would say might be silicone rubber. It burns away with a hot knife soldering iron attachment.


Ah it could be conformal coating.
In it's cured state it's reasonably inert.
Burn/heat it and it will release carcinogenic vapours.
Most of them usually imply infertility, 2 headed monsters and cancer(not in that order).
Even though I'm interested in a stripped down one I'd stay away from it.

Bad luck with it all though Image
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Kostov, Kelly Postmortem

Post by BigMouse » Tue, 28 Oct 2014, 21:45

It's probably silicone potting gel. The same stuff that covers the dies inside of an IGBT brick (if you've ever taken the top off one, you've seen it).

I'm becoming very familiar with the stuff lately.

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Kostov, Kelly Postmortem

Post by Richo » Thu, 30 Oct 2014, 20:46

One of my IGBT 6-packs has holes in the top and so I can see straight in and see the die and the gel.
Handy for when I blow it up later Image
So the short answer is NO but the long answer is YES.
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