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'Mantua' HO Steam Locomotives & Motor Issue
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 Posted: Tue May 21st, 2019 12:51 pm
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2foot6
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A member in our group has a large HO American outline layout,
he has two Mantua steam locos that run well in reverse,
but very slow to not at all in forward.

The current draw in reverse is 600mA, and in forward it is 400mA.
With no load, the motor runs well in both directions.

I'm sort of thinking a diode effect in the wiring,
maybe a dry joint in the armature,
but to have it in both locos, very unlikely.

Is this a common Mantua issue ? ....
any suggestions welcomed.

I think a new motor will be the fix,
but it would be good to find the problem.

......Peter.




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 Posted: Tue May 21st, 2019 02:40 pm
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W C Greene
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Howdy Peter, I repaired locos for many years and know a little bit about them.
Tell me, are these older (open frame) motors or the later can motor locos?
Also, without the motors, can the locos be pushed backward & forward by hand and no binds experienced?
If they are free running (pushing), then the problem could be the motors themselves.
Some years ago, Mantua offered "can motor" replacements for their old locos which had the motor (of course)
but a motor mount (more valuable than the motor itself!) and some assorted screws, etc.
These directly mounted in the older locos and the open frame motors could be trashed.
These MIGHT still be found with some searching.
A strange problem for sure.

I would opt for new motors if possible and pitch the old ones.
These things can be "tinkered" with and obsessed over, to the point of being a mania...
get my drift?

Good luck with this project.

Woodie




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 Posted: Tue May 21st, 2019 09:02 pm
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corv8
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I dimly remember motors that ran at different speeds forward + in reverse,
because the collector wasn't in the proper relation to the fields of the armature.
That was forty years ago, so I have forgotten details.

Maybe you could check the armature for the relation of the gaps to the fields.

As a non native speaker, I hope you understand my brabbling.




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 Posted: Thu May 23rd, 2019 12:19 am
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2foot6
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:wave:  Thank you Woodie and Corv for you replies,
we were hoping for an easy fix, but we didn't think there was one.   :sad:  

The easy fix is to replace the motor for a number of reasons and it will happen.

Just another thing on the .. to do list .. it's getting longer every day ..  :bg:  

.....Peter.




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 Posted: Mon May 27th, 2019 04:28 pm
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Si.
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Hi Peter  :wave:



I moved this Thread from HO/OO ...  :)

... to HERE in 'Technical'. 

:brill:

We are kinda grouping a number of Topics here sometimes, when possible ... like ...


... ' Technical Q&As. Track laying & turntables. Wheels, chassis & couplers. Motors & drive '


Scale independent (when appropriate).  :P



I seem to recall a 'Tri-ang' HO/OO open-frame like you describe, many years ago ...

... Mmm.  L:



Any luck with the Mantua motor ?  ???



:)



Si.




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 Posted: Mon May 27th, 2019 11:51 pm
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2foot6
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Thanks Si for moving this topic to the better area.

The Mantua and Tri-ang motors are very similar,
even using the same type of brushes, although a little bigger.

We have had great progress  :bang:   
decided to replace the motors with something better, like a can motor.      

Does anyone have any suggestions?

..................................Peter




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 Posted: Tue May 28th, 2019 08:30 am
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2foot6
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Well here is a follow up.
I hate being beaten by an electronic or electrical device, including Mantua locos.
I decided to have another go at fixing this darn thing.

With the body off, the motor seemed to work well in both directions,
put the body back and the motor was slow in forward.

I ended up replacing the tender pick up wire, with decoder wire,
because of the smaller size, and it's more flexible,
giving less tension on the brush spring, with the body on, pulling on the wire.

That seemed to fix the problem.
With the body back on, it worked well for fifteen seconds,
then went slow in forward again.

Now I am balder than when I started this a week ago.

In the process of finding the problem,
my hand rested on the tender, and the loco took off.
After investigating the tender,
there was resistance between the bolster and the tender frame.

Dismantled the bogies, cleaned them and re assembled.
I think because of different metals used in the bogie and tender frame,age, 
corrosion and grime had built up in the bogie in one area, causing the resistance.
 
As the loco was used in forward most times for many years,
the grime built up in the one area.
When in reverse the bogie moved a little, getting a better contact.

Well it's my theory, and I'm sticking with it (makes sense to me).

 :moose: :moose: [toast]

All fixed for this loco, now the other one...  :bang:...

Thanks everyone for your replies and advice.

...Peter


Last edited on Wed May 29th, 2019 08:50 am by 2foot6



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 Posted: Thu May 30th, 2019 06:32 pm
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bobquincy
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Good problem-solving skills! :)

Sometimes motor brushes wear primarily on one side,
effectively changing the timing of the commutator vs the magnetic field.

This can cause the motor to run faster in one direction,
but it is usually not as much as what you found.




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 Posted: Fri May 31st, 2019 12:05 am
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2foot6
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Good problem-solving skills!  :) 

Thanks Bob,
high tech skills are involved in this hobby, or luck.  :thumb:

  :wave: 

I have been looking at the other loco,
in the area of the bolster on the tender.

With a magnifier glass I checked the trucks,
and a thin layer of carbon crud had built up,
to the rear of the truck bolster and tender frame.

But towards the front of the trucks there was little build up,
these are very old locos and run forward most times.

So when it moves forward the trucks move so slightly to the rear of the frame,
and with arcing and wear over the years crud had built up.
But in reverse direction, the trucks move so slightly to the front of the tender frame,
with little crud and less electrical resistance, so the loco run well.

The crud problem explains my original comments,
600mA current draw in reverse and 400mA in forward,
the crud causing a resistance (1000 Ohms) in forward,
allowing a 200mA drop in current. 

 :brill:

So to fix the problem it was a matter of cleaning the trucks and bolster,
maybe a strap made of decoder wire, from the tender frame to the trucks,
would stop the arcing but probably an over kill now.

 :dt: 

Now I can sit back and let my hair grow back.

..............Peter.

:old dude: :rah: :glad: [toast] [toast]




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 Posted: Fri May 31st, 2019 04:53 pm
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A strap of wire is a good idea,
I am not in favor of a loose, rotating electrical connection.

I investigated a similar issue where the operator cab of a machine drew 60-80 Amps,
yet the only ground wire was only 10 AWG.
Rarely, but too often, the wire would get hot and damage the connector.

Looking at the four rubber-bushed mounting bolts, two of them had serious arcing marks.
The bolts were carrying most of the current, except when the cab bounced around,
then the wire got the full load, and if it went on long enough the wire got hot.

A braided ground strap corrected the situation.




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