RailPro > RailPro Specific Help & Discussion
Walthers F7 (Factory DC) LM-2S Install and Question
melarson:
Having received an ABBA set of Walthers Great Northern F7s for Christmas last year (my wife always knows what to get me ;)), earlier this year I set about installing LM-2S modules in them. Initially I thought all was good as they seemed to run well. But quickly I discovered that as they ran, they kind of sputtered. They would occasionally, randomly, stall briefly for a fraction of a second. They would stop motion and the sound would cut out, then quickly recover motion and eventually reset the sound. I thought at first that it might be a problem with the pickup system (though they have 8-wheel pickup) which didn't please me, but recalled that per Walthers recommendation I ran them each for an hour to break them in, on DC and prior to the LM installation, and they ran perfectly.
I made sure both the wheels and track were clean and yet they still sputter. Not all at once mind you, but individually, at different times and places. There was a time when I thought it might be related to unpowered frogs (at our club layout) but the sputtering was so random and inconsistant I had to rule that out as well.
So, last weekend I took them to my DCC installer guy (whom I go to for difficult installs like brass steamers) and we investigated pretty much everything we could think of. He went through one of the B units from top to bottom, cleaning, adjusting, aligning, you name it. Still it sputtered. Finally, and based on my responding to his question that they ran perfectly on DC, he removed the LM-2S and plugged in a Digitrax DH-123. The engine ran perfectly with no sputtering.
So now we're curious. The only theory we can come up with is that perhaps, for some reason, the LM-2S doesn't get along well plugged into the factory board (where the 9-pin connector originates from). He's thinking perhaps there is some sort of weird feedback situation going on that affects the LM but not the DH decoder.
So my question to you all is, has anyone here experienced this in any of your installs where you plugged an LM into a factory board?
In the mean time, of course, I am having him remove the factory board and hard-wiring a 9-pin in the test B unit. I expect to hear from him soon on the success or failure of that solution and will report back when I do.
Here are some pictures of how I installed the LM originally so you can get an idea of what all is in this thing. The pics are of the lead A unit but all the units are essentially the same (save for the lack of lights in the Bs).
The unit fresh out of the box with the shell removed:
(the factory board in question is the one in the middle, mounted above the motor. The board at the rear of the unit is just the 9-pin version of the jumper connector that allows DC operation)
With the speaker enclosure removed and the components gathered:
Feeding the speaker wires through the enclosure access and soldered to the speaker:
Speaker enclosure reassembled:
Enclosure reattached to chassis, 9-pin connector rerouted, and LM plugged in and secured:
--Michael
Alan:
There appears to be a choke (coil) in series with the motor. Why? What does it do? Seems to me a series inductor might play havoc with RP PWM.
melarson:
--- Quote from: Alan on November 09, 2016, 01:57:53 PM ---There appears to be a choke (coil) in series with the motor. Why? What does it do? Seems to me a series inductor might play havoc with RP PWM.
--- End quote ---
Alan,
Interesting observation! Not sure if it is in series with the motor just from looking at the pic but if it is then yes, why would it be there? What would be the purpose of filtering out higher frequencies from the motor when, as you say, it's bing controlled by PWM. A really good reason to dump the board and wire direct. Makes me wonder about why the Digitrax decoder works fine, though. Does not DCC also use PWM? Maybe RP uses a higher frequency? Maybe RP is just less forgiving of such a device?
Anyway, good catch, thanks!
--Michael
Alan:
I think RP uses a higher frequency PWM than DCC. Basis for their claim of 1000 speed steps whereas DCC is 128. Just guessin'.
G8B4Life:
The choke (and associated capacitor/s, they'll be there somewhere) are for reducing RF interference to your everyday household electronic devices.
Back in the good old days of open frame and especially pancake ringfield motors you could actually hear the RFI being generated by the motor on close by radios, and TV's would have wonky noise bars. Quite a few countries required some sort of RF filtering on models and it's carried over to this day. Now, this RF filtering can (and does) cause all sorts of problems for decoders. How badly I guess depends on the quality of the decoder, some seem to cope with the RF filtering and some don't. RailPro it seems could be in the doesn't category. I have a Walthers loco so I might chuck a LM-2S into it can see what happens.
My advice, and you'll find this repeated everywhere on the net is on any model that you can see RF filtering (choke/s inline with the motor and capacitor/s across the motor) get rid the RF filtering. Modern quality decoders should do any RF filtering needed. RP should do this filtering as well.
- Tim
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