How to slow down a DC loco


malibu43

malibu43

Active Member
Hi all.

A few years ago, the motor died on my IHC 2-6-0 Mogul. I found a new one on ebay and succesfully replaced it. Here is a post that gives some background: http://www.modelrailroadforums.com/...move-shell-from-IHC-Mogul&p=260593#post260593

As I noted in that post, the locomotive with the new motor runs MUCH faster than the old. In fact, I've found during very infrequent use over the last couple of years that it actually is running TOO fast. I run a small DC oval with my MRC Tech II controller. I increase the power up to about 20 (which is about how high I have to turn it before most of my locos will start moving), and the locomotive jumps from 0 to "pretty fast" instantly. If I go any higher than 50, the loco actually runs so fast it will fly off the rails. Essentially there is now a very small power band where the locomotive is usable. Prior to the old motor burning out, this is not how the locomotive ran. it was always one of my smoothest runners, and would actually run slowly very well.

It seems to me that the replacement motor was not actually identical to the original. It seems as though it's wound to run at a higher RPM at the same voltage level.

I'm looking for simple and cost effective ways to slow the locomotive down for use around the tree this year. I could try and find a worm gear with higher pitch, but I don't know how easy it will be to find one that fits the same shaft and is the correct diameter to mesh correctly with the rest of the gears.

Or, is it possible to add a resistor or something in series with the motor to reduce the voltage delivered to the motor?

The other option I've thought of would be to invest in a DCC system, convert the locomotive, and then adjust the speed range in the controller (which I assume is a possibility). I'd go this route if I had a ton of time on my hands and $300 for a DCC system and a decoder. But I don't really have either of those.

Lastly, I could try to just order another motor off of ebay and hope the one I have now is faulty. This one is quite a bit of a gamble and I think would most likely be a waste of money.

Any thoughts or suggestions would be much appreciated!
 
I doubt that the new motor is faulty. It probably is just wound (number of turns on the armature) so that it does what it does, which is running faster. Yes, you could probably find a resistor value that could be placed in series with one of the pickup wires between the track and the motor. Alternatively, you could try to find a motor like the one that died. Look on ebay and search for the same type of motor. You might find a junker IHC Mogul that still has a good motor, but is otherwise a wreck.
Of course DCC would be an option, although expensive. If you have other DC locomotives, you could go for an MRC Tech 6 6.0, which can switch back and forth between DC and DCC. That way you wouldn't have to convert all your other locomotives. That is what is I do, as I have far too many DC locos obtained over 60 years to convert to DCC.

Best of luck! Happy Holidays!
 
what kind of motor was the old one? Can? Still have the old motor? Take some pics of it, one side, other side, worm side/ other side. I'm hedging on something here.
 
The headline made it seem like it was the start of a joke thread! DC? The speed is determined by the amount of power. Just turn the power down? Is that too simple?
 
Thanks for the responses guys. The motor I bought on ebay was supposed to be a direct replacement for the original. In fact the vendor is still selling replacements: http://www.ebay.com/itm/like/171962316617?ul_noapp=true&chn=ps&lpid=82 The motor I bought came without the worm gear (it was much cheaper and I was able to use the worm off the original). It looked identical the original motor, and identical to the motors pictured in the ebay item I linked. Unfortunately, I no longer have the original. But again, the original and replacement I bough look identical to the ones in the ebay link I posted.

One thought that has crossed my mind is that perhaps the replacement motors are wound differently and possibly intended to be used with a different worm gear as well. This would be an issue for me since I bought the motor without the worm and used the old worm gear. They look the same to me, but it's hard to tell for sure in the ebay listing. I could just go ahead and buy another motor for $30, but I'm not confident that that would resolve the issue.

What do you guys think?
 
new guy said:
The headline made it seem like it was the start of a joke thread! DC? The speed is determined by the amount of power. Just turn the power down? Is that too simple?
Click to expand...

Most of my locos run very well in the 20% - 80% power range, and I can vary the power within that range to get a wide range of speeds. However, this re-motored locomotive runs so fast that it jumps to life moving very quickly at 20% power and is at risk of flying off the track over 50% power. Essentially the usable power range for this loco is very narrow, and its difficult or nearly impossible to get it to run at scale speeds now. That was not the case before the re-motor.
 
malibu43 said:
Most of my locos run very well in the 20% - 80% power range, and I can vary the power within that range to get a wide range of speeds. However, this re-motored locomotive runs so fast that it jumps to life moving very quickly at 20% power and is at risk of flying off the track over 50% power. Essentially the usable power range for this loco is very narrow, and its difficult or nearly impossible to get it to run at scale speeds now. That was not the case before the re-motor.
Click to expand...

Ah, so, I am a newb and all DCC so my DC 'savy' is WAY out of date!
 
get a millimeter measuring stick and check the length, flat thickness, rounded thickness, post that info here.
you might have a motor designed for the wrong voltage. (like 6 volts). Regardless you don't want that motor, I suggest returning it to the seller. Because I reccomend a NWSL motor and the cost won't be much differrent.
 
Next time I have the loco out I can take those measurements. It seem unlikely though that it would be sized incorrectly, as it dropped into the existing mount and fit perfectly. I will check anyway.
 
I will throw out something else here to check also . Could it be that your wheels have oxidized slightly? You say you don't run it much . I know that would not make a difference with the top speed portion of the problem but it might make a difference when the loco "jumps to life" as the oxidation may be acting as a bit of an insulator . Just putting something out there that might possibly have a little to do with it and would be an easy fix , were it the problem.
 
dinwitty said:
you are clearly not happy with the motor whether its correct or not. Its giving you improper speed.
Click to expand...
That is correct. I am not happy with the new motor. I checked out the NWSL website and the prices lookbreasonable. I'll get the measurements if I can and look into a replacement.
 
I guess no one mentioned the power source. It is possible your power source does not have good control over the lower voltage range. I would test it with a ammeter and see what kind of voltage output you get from your powerpack and see if there are any "jumps".
 
Some good suggestions here. We're getting our xmas tree tonight, so I'm sure my HO and this loco with come down from the garage soon as well. Once I get it setup, I'll take some measurements and report back.
 
NWSL is a really good choice. Perhaps get a smaller motor with flywheel to replace the speedy replacement you have now.
 
Took the measurements today. I only had a ruler on hand, but I'm pretty sure these numbers are right.

Length 14mm
Flat to Flat 8mm
Round to Round 11mm

This is smaller than anything on the NWSL website that I could find. Not sure how to interpret that though...

Any thoughts on next steps are appreciated.
 
Could also be that that replacement motor is only a 3 pole armature. Takes more "juice" to get them going and they're not as smooth or controllable. (or worse it may only have 2 poles)
 
Would that also result in the motor running at a higher rpm for a given voltage?

It may have been lost in my attempt to describe the issue but the real problem is not the loco starting suddenly. The issue I'm trying to resolve is the loco running too fast, which I think is a result of the replacement motor running at much higher rpms than the original.
 
If the voltage needs to be high to get the armature turning, then high speed is what you'll get. Is this N scale? 'cause an 8mm wide motor for HO is very narrow, most would be double that, although with a steam loco, would depend where it's placed, Can motors usually only have 2 field magnets (or any small motor for that matter) but the wider they are, the better they wrap around the armature. Also why a 5 pole armature is better than a 3 or 2 pole. (think V8 power smoothness against a 4 cylinder car engine)
 
malibu43 said:
Took the measurements today. I only had a ruler on hand, but I'm pretty sure these numbers are right.

Length 14mm
Flat to Flat 8mm
Round to Round 11mm

This is smaller than anything on the NWSL website that I could find. Not sure how to interpret that though...

Any thoughts on next steps are appreciated.
Click to expand...

I'm still doing some digging, NWSL has smaller motors as I got one for a tiny Climax from them.
Check your space in the engine for the smallest motor there. 10/12/15 mm (flat/diameter/length)
see if there is room, its not that far off. If some framing material needs slicing off for fit, you may have a winner but do nothing yet but measurements. I am still poking around.
 
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