# Yikes! Motor burned up--why?



## lownote (Jan 3, 2008)

I had made a consolidation out of an aristo mikado drive. I has installed ball bearing wheels in the tender, and a QSI card. The loco ran just fine for weeks. Today I went out to run it and the light came on but no motor. I looked at the loco and heard the sounds of shorting. Took it off the track and noticed smoke--the QSI card had burned up--very badly, melted components--and the motor was hot. Took it and put it on the bench, with straight dc--the lights come on, the motor does not turn, it just gets hot. Yes, the motor is completely burned up. I took it out.


The wheels all turned freely, it was not any kind of a gearbox jam. 



So any one have any diagnostic ideas? The loco ran fine for several weeks--flawlessly. No signs of shorting. Today, it suddenly failed for no apparent reason. 


Could something have gtten inside the motor case to cause a short? Could it have been a defective motor? This motor ran for a while inside an aristo mikado--it was not a sudden failure

Any ideas?


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## lownote (Jan 3, 2008)

Also any ideas on where to get a replacement motor?


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## Greg Elmassian (Jan 3, 2008)

Aristo has motors... 

Your motor shorted, and it could be many things, you could pull the motor apart and test the commutator segments to see what is up, is it a dead short right now? Check this first. 

There is also the possibility of a similar problem to what I believe happened to some GP40's, but it's unlikely. If you want to investigate, I'll work with you offline, don't want to put out any misinformation about Aristo failures. (believe it or not!). 

Regards, Greg


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## lownote (Jan 3, 2008)

The commutators look fine, but the really there's a LOT of melting--the fan melted and left plastic lava everywhere. The rotor/coil is fused. I took the motor apart 

The loco was stored in our shed. When I noticed it didn't come out, I looked in and saw the lights were on, and the whistle blew, so the QSI card was working properly. In this loco the decoder was in the tender, but the light in the loco were fine. So I'm ruling out a short in my wiring. 

I wonder if something got into the motor? I'll email you


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## aceinspp (Jan 2, 2008)

Could it be that you had a loose voltage regulator. If so poof magic smoke. Ask me how I know. You need to keep calling Navin as he never returns calls or send him a e-mail. Once in a while he will answer those. Later RJD


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## lownote (Jan 3, 2008)

There's no voltage regulator in there, unless it's on the QSI card--I tore the guts out of this thing and wired it directly. I'm 100% sure the wiring I did is right. I suppose it could be the now-deceased QSI card, but there's only 20 volts available on the track. 

Navin called me back and they have a motor in stock, it's on its way.


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## Greg Elmassian (Jan 3, 2008)

motor shorted, melted output transistors. 

It could have locked up mechanically, is there any chance you have a slipped driver that locked up the mechanisim. My 0-6-0 dropped a connectring rod and locked up and melted a QSI. 

Greg


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## TonyWalsham (Jan 2, 2008)

Doesn't the QSI card have any short protection?


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## Greg Elmassian (Jan 3, 2008)

They used to have a polyswitch, but it was removed from production because it tripped prematurely. I think putting in a higher value one is a better idea. It does sense overheating, but that is by a copper trace conducting heat from the output transistors to the microprocessor. 

I think I'll put some 4 or 5 amp polyswitches back in mine. 

Regards, Greg


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## TonyWalsham (Jan 2, 2008)

I have found with polyswitches they work best as ultimate overload protection rather than dead short protection. 
To make them work faster I often double them up. For example if I want to fast trip at 2 amps I use two 1 amp ones in parallel.


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## Greg Elmassian (Jan 3, 2008)

It may be faster acting because you are really only operating on one 1 amp unit... most of the the current will go through the lowest resistance one... so you should begin tripping around 1 amp... I did read somewhere that you can parallel them... maybe it's sort of an equalizing situation... current goes through the one with slightly less resistance, it heats up and trips and the current goes to the other.. and trips... 

I need to read up some more on using them in parallel... 

But I give credence that it must work, coming from you Tony.. 

Do you know where such a set up starts to trip? like just under 2 amps? or more like 1.5? 

Thanks, Greg


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## TonyWalsham (Jan 2, 2008)

Sorry Greg. 

I agree it is relying on there being variations in the tolerance of two components for the idea to work. 
A single Polyswitch will trip pretty quickly but not as fast as a fast blow fuse. 
I have no actual data. Just anecdotal evidence that two in parallel trip faster than one single Polyswitch. 

I use two 3amp ones in parallel for a 6 amp ESC. It holds 5 amps without tripping and I have never had any component failure when a short takes place. 
I guess the actual point at which two trip depends on the mismatch of the two.


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## Hagen (Jan 10, 2008)

Fuses in parallel is simple "add them up math" since you effectively double (or triple or whatever) the leads.
I was a bit surprised the first time at a hydro powerplant where I saw several 100A fuses in parallel in a rack. That was the main fuse for that turbine. Several hundred Amperes.

Seen it since as well in much more "normal" applications.


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## Greg Elmassian (Jan 3, 2008)

Thanks Tony, it's what actually works that is really important. 

Seems to not make complete sense, but I did read on the Raytheon site you can do it. I'll give it a try, and do some experimenting. The QSI output transistors are supposed to be good for 5 amps... I know that 10 amps will met them.. don't ask me how I know! 

Greg


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## Hagen (Jan 10, 2008)

"_Derating is necessary because two fuses in close
proximity radiate heat less effectively than single fuses. As a general rule, IPD
recommends a minimum reduction in rated current of 10% for 2 fuses in
parallel (20% for 3 or 4 fuses in parallel) and the combination assigned a rated
current of nearest preferred number from R10 or R20 given in AS2752; for
example 2 X 800A fuses in parallel = 2 X 800A X 0.9 = 1440A (= 1400A nearest
__preferred number)."_

Not entirely certain lack of ventilation means that much on our scale.

http://www.ipdgroup.com.au/WMS/Upload/Resources/Fuses in Parallel.pdf


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## TonyWalsham (Jan 2, 2008)

Rune. 
Over current is not the same as a dead short. A binary metal strip detector is OK to tell the electronics to reduce the output but they are not good at short circuit protection. They cannot react fast enough. 
Polyswitches are not perfect but in my opinion it is better to have some protection than none at all. 
Using two polyswitches in parallel relies on the two being not exactly the same. One will trip fractionally before the other. 
I can't prove it but I reckon they trip slightly faster than one fuse rated the same as two smaller ones.


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## Hagen (Jan 10, 2008)

Tony
Precisely, one will "go" first pulling the other down with it. But not before you have reached "about" the trip current over both.so if one of them will trip at 0.9 instead of 1.0A then both should trip at about 1.8A (total) still way within any design criteria for a protection circuit.


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## Dan Pierce (Jan 2, 2008)

When one poly switch starts to heat up, the resistance increases slightly, and then the other starts passing more current as it has lower resistance, sort of like 'hunting' a term used by autotransformers. These should self balance unless a short occurs.


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## Greg Elmassian (Jan 3, 2008)

Actually, you need to study the mechanism of the poly switches, they do change resistance slightly, but they shut down pretty quick when the insides melt, and it happens pretty much all at once (otherwise your loco would slow down gradually, not just stop suddenly)... 

apparently the resistance between two of them is close enough that they share the load pretty equally. 

Regards, Greg


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