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Old 23-05-2018, 10:04 PM   #1
Meir
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Default Bachmann GWR Class 57XX motor short

Hi guys

I'm new to the forums so hi .

I wonder if anyone can help with an issue I've got with a Bachmann GWR Class 57XX which I purchased off of ebay as a "good runner"?
A good runner it ain't lol.

It's a DC (non-DCC) unit which, the time I tried it, ran slowly down the track then starting smoking slightly. My benchtop PSU reported a sharp drop in voltage from 12v to 5-6v at over an amp.

Seems to me like a short.

I've stripped the loco down to the motor and get the same result when I apply power across the two terminals.

If I measure the resistance across the terminals then it comes out as a horribly low 4 to 5 ohms.

Anyone got any good advice on the next step? Beyond chucking it in the bin that is. I love the look of this loco and would hate to have to throw it away .
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Old 24-05-2018, 04:33 PM   #2
Mountain Goat
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Seems to me that the motor may have found some oil onto the commutator. It could have run perfectly just after the motor had been oiled, but then as the oil starts to dry you get a slow running smokey motor (With an burning oily smell) and the loco may run for a short while with a lack of power, and then trip the controllers overload cut out.
I've had it in the past quite a few times due to my own error of over oiling the things!

I'm no expert and I can't tell you what the current or voltage will be when the locos do this. It maybe a different reason all together. It is just that it seems to me to follow the pattern of an over oiled motor.

The solution is to clean the motor commutator and the little brushes etc, and see if it makes a difference. Use cleaning alcohol if you can get it. I've used electrical switch cleaning spray, (Not oil based), but be aware that some sprays can discolour paint, so remove the body entirely if trying such a spray. Alcohol sold for cleaning purposes is a much safer option.

Last edited by Mountain Goat; 24-05-2018 at 04:41 PM.
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Old 26-05-2018, 09:43 PM   #3
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Thanks for the reply Mountain Goat.

Could be what you're saying, but it's definitely drawing a huge amount of current. If I set my benchtop PSU to 1amp then it'll go to that and try and take more. If I set it to 2amps then it does the same. It's definitely acting as if there is a short.

the trouble is is that I'm new to model railways and many of the engine cleaning and maintenance techniques are unknown to me. I.e. I couldn't currently tell you what a commutator is, for instance.
I'll go off and do some youtubing etc to see if I can find out .

Thanks again for the advice!
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Old 26-05-2018, 10:06 PM   #4
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Would the motor windings handle 2 amps if it shorted? Most DC 00 gauge controllers supply up to 1.5 amps. Go easy just in case.
Model railway controllers have a form of overload protection as a train jumping the track and shorting the two rails most of us have experienced. It is for events like these that our controllers need the overload protection.
Even my simple controller uses a bulb to protect from damage should I have a short.

I can help you with the terms of the motor. The central bit of the motor that turns (The whole structure that fits onto the shaft that turns) is known as the armature. Part of this armature has a segmented plate that the two brushes touch. This plate is known as the commutator. The commutators job is to supply current to each of the motors coils at just the right moment that it causes the motor to rotate as a coil acts as an electric magnet, and is attracted or repelled by the fixed magnets around the edge of the motor to cause the armature (Which has the coils attached to it) to rotate. [There are other types of motor which are slightly different but the basic principle is similar].
I hope this information helps. You may already know more then I do. I only know just enough to get by in regards to this hobby!
Photo shows my overload protection bulb (12V 15watt (I think its 15)) wired in series. The idea is that if there is a short the bulb takes the power instead and lights up which gives me a visual indication of a short. Modern controllers have much faster overload protection devices then my bulb. I just wanted to make a controller to run from a 12 volt battery.
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Last edited by Mountain Goat; 26-05-2018 at 10:12 PM.
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Old 27-05-2018, 12:41 PM   #5
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I'll go off and do some youtubing etc to see if I can find out .

Be as cautious with the gospel according to u-tube as you are with the Wiki version, both having been posted by people who in their opinion are correct but in true may be talking, writing, spouting a load of old cobblers.
Any ‘ toob ‘ video that is extremely ill prepared without a hint of a script gets nil-points on my scoreboard, especially those where I am expected to watch the juddering out of focus back of someones hand rather than the subject under review they are stutteringly chin-wagging about. If you are going to post a public video then at least try to make it half competent.
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Old 06-08-2018, 08:02 AM   #6
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Mod Note: The content of this post has been removed, it was a direct copy and paste of a previous post #2 made by another forum user. Pasted here as a new post by this forum user.
This is not acceptable forum behaviour.
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Old 06-08-2018, 08:35 AM   #7
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There could be any one of a number of reasons for what you are experiencing but all appear to point to a short of some sort in the motor. This could be oil or, more likely an accumulation of dirt and muck across the commutator segments. It could also be a short in the coils. If you are getting such a low resistance across the terminals I would not apply current again until you rectify the problem as you may do irreparable damage that could, at the moment, be sorted. The good news is that you are getting a resistance reading, a dead short would show no resistance at all, so dirt may be a possibility.

First up is a thorough clean by stripping and cleaning with an electrical cleaner. The easiest are in aerosol cans. Check the commutator has clean and clear slots in it between the segments, scrape out any muck you find carefully without creating sharp edges to the slots. Clean the brushes, make sure the springs are OK and the brushes sit on the commutator properly. You may need new brushes. If the surface of the commutator looks to be badly scored that is a whole new issue but first we are looking to simply identify the cause of the low resistance.

if, after a thorough clean and dressing up the resistance remains low then you could be looking at buying a replacement motor, either second hand or new. Either way the loco will still be fine when you have rectified the problem.
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Old 06-08-2018, 10:47 AM   #8
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What Annaa said above is quite common. The model could have been running perfectly well while the oil is wet and then when it dries it runs terrible if at all. (Avoid getting oil on the commutator if anyone is reading this and doesn't know about it!)
Typical symptoms of an oiled commutator are the loco runs then its motor runs hot and sometimes omits a little smoke (Not always), and then slows down to a stop and often trips the overload cut out. If it does run it will be slow and gives similar symptoms to that of a weak magnet.
Then if one tries the loco again it may run for a short time and then it starts to slow down to a crawl and trips the overload again. (This is why I like to have a decent controller as some of the trainset budget controllers dont give visual or audible warning of when the overload cut out triggers, and one can be puzzled and assume one has had a disconnected wire etc. With a decent controller (Talking about DC) one knows when the cut out has tripped and knows when power is reaching the controller and the track).

[Talking about visual and audible overload indications on a controller, there's nothing like the old Hornby Dublo 3 rail controllers. I dont half jump when something shorts on them and triggers the cut out! Mind you, anyone who has one of these make sure they are checked over by an electrician as they are old things and so probably need a new mains cable etc, which is why the usual recommendation is to buy a modern controller instead].

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Old 06-08-2018, 11:43 AM   #9
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Quote:
Originally Posted by Mountain Goat View Post
What Annaa said above is quite common.
].
Actually MG it isnít what Annaa said it was exactly the same as you said in post #2
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Old 06-08-2018, 11:45 AM   #10
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The Question was asked back in may and the OP has not returned so you may not get a answer
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