Motor Shorting

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Thornbush
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Motor shorting

Postby Thornbush » Thu Jun 04, 2020 5:30 pm

I am building a Finney/Brassmasters LSWR T3 and have used a gearbox etch provided by Martin using High level 3-stage 54:1 gears with a Mashima 1624 round can motor. Pick-up is via the 'American' method with the loco picking up off one rail and the tender the other. This was working fine and I had the chassis running smoothly. I now have a fault in that both terminals of the motor are shorting to the chassis which means both tender and loco are shorting to both rails even though they are insulated from each other, even though the motor still runs when connected directly to a power source rather than through the chassis pick-up. I didn't have this problem originally otherwise the pick-up method I used would not have worked.

Am I missing something here? Can anyone advise whether it is possible to fix this or do I have to replace the motor? Of course, the problem is sourcing another 1624 can motor.

Thornbush
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Motor Shorting

Postby Thornbush » Thu Jun 04, 2020 5:33 pm

I am building a Finney/Brassmasters LSWR T3 and have used a gearbox etch provided by Martin using High level 3-stage 54:1 gears with a Mashima 1624 round can motor. Pick-up is via the 'American' method with the loco picking up off one rail and the tender the other. This was working fine and I had the chassis running smoothly. I now have a fault in that both terminals of the motor are shorting to the chassis which means both tender and loco are shorting to both rails even though they are insulated from each other, even though the motor still runs when connected directly to a power source rather than through the chassis pick-up. I didn't have this problem originally otherwise the pick-up method I used would not have worked.

Am I missing something here? Can anyone advise whether it is possible to fix this or do I have to replace the motor? Of course, the problem is sourcing another 1624 can motor.

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John McAleely
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Re: Motor Shorting

Postby John McAleely » Thu Jun 04, 2020 5:40 pm

[duplicate removed]

CeeJay60
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Re: Motor Shorting

Postby CeeJay60 » Thu Jun 04, 2020 5:50 pm

Couple of obvious checks to make, if it was all working correctly before: -
- if you have separated the tender from the loco and put them back together, are you sure you remade the electrical connection correctly?
- check that there are no brake blocks making contact with one or other of the wheels;

I assume there is no other vehicle involved that might be causing a problem through the couplings ...

Doesn't sound like the motor!
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Tim V
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Re: Motor Shorting

Postby Tim V » Thu Jun 04, 2020 6:20 pm

Have you tried wrapping the motor at the rear with insulating tape - sometimes the brush terminals do stick out and bridge across the frames giving just this problem.
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Thornbush
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Re: Motor Shorting

Postby Thornbush » Thu Jun 04, 2020 6:27 pm

I will try that. It's all a bit strange, because if I stand the tender on the tracks on its own then it only shorts to one rail. Likewise the loco to the other rail. If I then test the tender connecting wire (with the tender removed) the other end of which is soldered to one of the motor connectors, then that shorts to the loco as well. If I check both terminals of the motor then they both short to the lock, which I why I think that is where the short is. I can find no other shorts.

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Tim V
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Re: Motor Shorting

Postby Tim V » Thu Jun 04, 2020 7:05 pm

A picture of your arrangements might make things clearer.
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grovenor-2685
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Re: Motor Shorting

Postby grovenor-2685 » Thu Jun 04, 2020 7:07 pm

You say the motor runs when power is applied directly to the terminals, so the motor is basically OK and both terminals cannot be connected to the case.
Check connections between the moror terminals and the motor case, neither should be connected.
Note that you will need an ohmeter on a low setting as the resistance of the motor coils is quite low, measure between terminals first to see this value. Both terminals can't be shorted to the casr the motor would not run but one might be, and that one will have to be the one you connect to the loco chassis.
Your symptoms suggest that the motor terminal connected to the tender is the one shorted to the motor case.
Have you recently had the motor out and possibly replaced it the other way round?
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Keith
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bécasse
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Re: Motor shorting

Postby bécasse » Thu Jun 04, 2020 8:01 pm

Firstly and obviously check that no metal part of the motor casing shorts to either terminal (with the motor removed from the loco). If it does that is probably the source of your problem and is potentially incurable, at least without dismantling the motor.

If that isn't the source of the problem, then you would seem to have a short somewhere between the tender body and the loco body. It might be because the insulation on the connecting wire (or connectors or coupling) has worn and that is causing the short. Try applying full power in the dark, one can sometimes see sparks before the cut out operates - if the controller is too sensitive to allow this, you could try using a 9 volt battery instead.

Julian Roberts
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Re: Motor Shorting

Postby Julian Roberts » Fri Jun 05, 2020 2:45 pm

I don't know if the above has already solved your problem. This is really only to repeat one part of what others have said in more detail -

I had problems on my Compound which has a similar electrical arrangement. I was baffled until I found that there were two issues with the motor lead tags on which you solder the connecting wires.

First, the tags can twist round so that they touch the motor casing. Second they can touch the loco itself. In either case you may get a short. In my case it was an intermittent short.

The problem is you can't see what may be happening when the motor is in the body. The tags may be slightly moved by something or other. Bits of tape to insulate places where it is possible something touches solved it for me, and making sure the tags are firmly screwed down.

Has the problem been solved already? Hope you're getting it sorted!

DougN
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Re: Motor Shorting

Postby DougN » Sat Jun 06, 2020 9:02 am

Julian, that's a good heads up as I am just working through installing gearboxes and motors. So I think I will use some shrink wrap around the tags, one one and the other has a portescape but I think it might be a good idea to insulate the connections also.

Doug
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John Bateson
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Re: Motor Shorting

Postby John Bateson » Sat Jun 06, 2020 9:19 am

Heat Shrink Sleeve.jpg
Heat Shrink Sleeve to cover the tags


Just a thought, but I use heat shrink sleeve over the motor tags, these help to stabilise the position of the wire as well as insulating the bare ends. Use the tip of a soldering iron, cose but not touching, wavinving it over the joint area until the sleeve has shrunk.
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David Thorpe
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Re: Motor Shorting

Postby David Thorpe » Sat Jun 06, 2020 9:59 am

If you have a metal drawbar between loco and tender, could that be causing any problems?

DT

Thornbush
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Re: Motor Shorting

Postby Thornbush » Sat Jun 06, 2020 10:02 am

Thank you for all your answers and suggestions and sorry for not replying sooner, but other commitments kept me away from the workbench until this morning.

As requested, I have attached some photos of the arrangement. One terminal of the motor is connected to the loco chassis using a split pin through some brass tubing so it can be removed easily. The other terminal is connected to the tender in the same way.

This morning I check everything through again:-
- with the lead to the motor removed the tender only shorted to one rail
- the loco only shorted to other rail
- the lead from the tender shorted to the loco which means when it is connected to the loco the tender shorts to both rails

I then:-
- removed the motor from the chassis and checked for shorts between the terminals and can but there were none.
- checked the resistance across the terminals which was 19 ohms.
- checked the terminals for any stray shorts, metal filings or flashes of solder and cleaned them with a soft brush
- powered the motor and it ran ok.

I then fitted everything back together and it all seems to be working again.

So I am confused but happy it now seems to be working - at the moment!
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Andy W
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Re: Motor Shorting

Postby Andy W » Sat Jun 06, 2020 11:59 am

"So I am confused but happy...." a perfectly normal state of mind for members of this forum.

"...I use heat shrink sleeve over the motor tags..." a great tip John.
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David Thorpe
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Re: Motor Shorting

Postby David Thorpe » Sat Jun 06, 2020 12:39 pm

That looks like a beautifully built kit.

DT

IANATEXTON
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Re: Motor Shorting

Postby IANATEXTON » Sat Jun 06, 2020 3:26 pm

Glad to hear that the loco is now working. What are you using for the drawbar between the loco and the tender?

I have found that when using the American system you have to be careful to ensure that there are no shorts between the loco body, which will be live to one rail, and the tender body, which will be live to the other.

The fall plate is always a potential problem, even if one insulates the front of the tender where it lands with thin plasticard. I had a shorting problem when a loco was going round sharp curves, with the edge of the fall plate shorting out against the tender brake standard.

Ian

FCA
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Re: Motor Shorting

Postby FCA » Sat Jun 06, 2020 3:42 pm

If you can it's best not to have any of the bodywork live because current can pass through the buffers to other vehicles. Insulating the chassis from the superstructures is recommended. Your photos suggest that this could be a bit of a challenge on this loco!

Richard

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Re: Motor Shorting

Postby davebradwell » Sat Jun 06, 2020 7:38 pm

It's interesting to reflect that the vast majority of 4mm scale loco models have normal pick-ups despite these things performing poorly and sometimes being very difficult to install. All the "greats" use them and always have. Whatever their problems everything else can throw up that biggie. Perhaps it's because with so much of the model live you're only ever 1 fault away from disaster. Pick-ups may be terrible but you generally need 2 faults before it all comes to a grinding halt or with DCC, blows up the decoder output stage.

It's a very good thing that your model is running again and it looks a fine piece of work but you don't know what the fault was and it takes a considerable amount of faith to believe that you'll never know. In the meantime you'll perhaps be adding an assisting locomotive to a train and, bang, where did the coupling go. Sometimes it's good to just step back from an issue and ponder in a constructive way......

I bet it was the brakes!

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decauville1126
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Re: Motor Shorting

Postby decauville1126 » Sat Jun 06, 2020 9:15 pm

Interesting in that Dave Bradwell mentions the brakes.

I've found this sometimes when opposite sideplays make contact, often with brake shoes, sometimes even on straight track. I found that running a loco in a totally darkened room can show up various sparky points, often intermittent.

Thornbush
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Re: Motor Shorting

Postby Thornbush » Sun Jun 07, 2020 8:25 am

I have used the longer drawbar from the kit and dog-legged it to pass under the front of the tender where a plastic pin engages with it. I have faced the rubbing plates on the loco drag beam with masking tape and, so far so good, it is all running fine. I will also put masking tape or plastic card on the two faces of the drawbar that could possibly touch the tender just in case. As for the fall plate, I had thought about making one from plastic card but may also try trying to insulate the brass one with plastic card.

FCA is right, trying to isolate the body from the chassis is not an option on this kit, especially as an afterthought.

I decided on the American method for pick up as there is precious little space on the chassis to fit wipers and I have never like plungers. I have to say that as a form of current collection it is great - as long as you get all the relevant insulation right!
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Paul Townsend
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Re: Motor Shorting

Postby Paul Townsend » Sun Jun 07, 2020 1:07 pm

Thornbush wrote:I have used the longer drawbar from the kit and dog-legged it to pass under the front of the tender where a plastic pin engages with it. I have faced the rubbing plates on the loco drag beam with masking tape and, so far so good, it is all running fine. I will also put masking tape or plastic card on the two faces of the drawbar that could possibly touch the tender just in case. As for the fall plate, I had thought about making one from plastic card but may also try trying to insulate the brass one with plastic card.

FCA is right, trying to isolate the body from the chassis is not an option on this kit, especially as an afterthought.

I decided on the American method for pick up as there is precious little space on the chassis to fit wipers and I have never like plungers. I have to say that as a form of current collection it is great - as long as you get all the relevant insulation right!


I tried it and don't like it as you are throwing away half your wheels for electric reliability.

I reckon advocates of wiper pickups, faced with lack of space for them should give split axles a hearing.

Too late for our OP tho' :(

Thornbush
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Re: Motor Shorting

Postby Thornbush » Sun Jun 07, 2020 3:13 pm

There are pros and cons to all pick-up methods. I have used split pick-ups on a tank engine before but found it a bit of a struggle. The thought of trying it on this kit, with representative working inside Stephenson valve gear - well, it would be a non-starter in my book. That said, you can't really see the valve gear on the fully assembled locomotive so i am sure some would ask why, although I know it is there! Time will tell whether I have made the right choice.

FCA
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Re: Motor Shorting

Postby FCA » Mon Jun 08, 2020 8:37 am

That is a beautiful model of a fine engine.

Dave Bradwell makes a good point about the brake shoes. I now make these from Paxolin ( sleeper strip) to guarantee elecrical isolation on my split chassis models. Scrape away the copper once the shoes are fixed to the hangers.

Richard

Thornbush
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Re: Motor Shorting

Postby Thornbush » Tue Jun 09, 2020 12:10 pm

Well, I can confidently report that it is not the brake shoes. However, I am getting intermittent shorts from the front bogie wheels touching the splashers (an elegant feature from Adams but impractical from a modelling point of view). As you can see, it is all very tight on the chassis and there are clear scorch marks on the wheel rims. Other than a thick coat of paint on the inside of the splashers I'm not sure what I can do about it - trying to insulate them with plastic card will reduce the radius curve that the loco will negotiate, which is already about six feet. There is no side-play on any of the axles so I cannot gain anything there either - perhaps that is why Drummond removed them!

I have put a thin piece of plastic card under the fall plate and that is working fine.
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