I recently bought an older HO Athearn BB SW7 with an open frame motor. I am planning to add a decoder and run it on DCC. I have read about the limited space available under the shell of this and other switchers, so I was looking for a small decoder. I came across the DZ123 on sale at Walthers. It is rated at 1 Amp (2 Amp PEAK). This is where it gets interesting…I have read that the open frame motors draw considerably more current than the newer can motors. I believe I read that the start up current is about 1.5 Amp, and stall current even more…I haven’t yet received the loco, so I can’t confirm the current draw.
My questions to you all are:
Would it be a safe assumption that the DZ123 would sizzle and fizzle in a tiny puff of smoke if I tried to run it with this motor? What is the significance of the PEAK power?
Does anyone have experience with this motor and DCC? (what basic, “inexpensive” -2 FX decoder has worked for you in this application?)
is there anything else I should be aware of (motor isolation aside) when switching this to DCC?
You could very easily repower with a decent can motor. I think you would be much happier with the overall performance and the decoder will work without worries.
I hadn’t thought of that. I’m really not looking to invest too much in the loco. How much would a “decent can motor” run me? Is it much of a job to swap out? Things like this always seem to get infinitely more difficult to me once I am in the middle of them![D)]
IIRC, the Athearn SW7 would draw slightly less than one amp in full slip, so the decoder should be OK - especially if you clean up and lube the drive system before putting it into service.
One of them has a TCS MC4 and the stock motor. The decoder is tiny and to be honest, I still had a hard time getting it to stay nice in the cab and route the wires neatly so I could install the body. Yes, the big issue is to isolate the motor on the bottom. Before installing the decoder, I cleaned the motor up and lubed it. May have even put a shot of CRC 2-26 on the com. I also completely cleaned and relubed the gearboxes. At full slip, it pulls a little over .6 amp.
The other one I remotored with a Protopower kit (should be able to find for around $35 or less). One of the advantages to this is you end up with more room. The can motor takes less room that the stock open frame. I was able to install a Soundtraxz LC series decoder, putting a 3/4 inch speaker in the cab. Not sure what the current draw is on this one, but it RUNS better. On this one, I use a Cary SW1500 body.
Don’t decoders have any sort of current limiting? I really know nothing about them, but you’d think it would be a good idea, considering that DCC is used with a rather high-current supply (often much higher than cab control) and a load that can draw quite high currents when stalled.
I have an old athearn sw7 that I am using with an NCE D13SR decoder with no problems. My recommendation is to tune the loco, clean the wheels, commutator etc before you install your decoder, Replace the brushes if they are very old. If you have a DC ammeter you can test the loco to se what the stall current draw is. I found different locos to be significantly different. Mine was just over an amp at stall.
After you install the decoder you will need to fine tune the performance, the starting voltage will need to be set pretty high and the top voltage lowered to about 50%. The loco by it’s limited traction and weight won’t pull too many cars so by limiting the top speed you will limit the current draw.
I don’t remember exactly what the current draw running under DCC but I know it maxes under .5 amp on my RRampmeter. It draws a lot more than any other loco I have but still way under one amp.
Thanks to all who responded. I feel better about the possibility of the DZ123 working for this application. I will do as was suggested and clean 'er up and check the current draw. Hopefully I’ve got ane that draws on the lower end. I bought it on eBay as NOS, so I’m hoping it won’t require too much of a rebuild.
Also, if you have more than one look at how noisy or quiet they are. I’ve found that some of athearn drives tend to be quieter than others. They also tend to run smoother. I have a number of old athearns that I’ve repowered with cans and they do make a big difference, but not an absolute necessity for DCC.
Not sure how much it contributes to noise or anything, but one area that always comes to my attention on the OLD BB Athearns is those junky flywheels. Todays seem to be mostly turned brass. On the old ones I have, most flywheels seem to vibrate and wobble. Seems like the newer flywheels also contribute quite a bit to smooth and quiet operation
The SW& showed up last week and I started working it over. (My cheapy multimeter[banghead] only measure up to 250mA, so no idea what the stall current is yet) I disassembled the whole unit and cleaned it up a bit. It looked like it had seen very minimal use. It made one hell of a racket when I test ran it (prior to the overhaul). It ran fine, but took quite a bit of juice to get it moving. Upon disassembling it I discovered that one of the motor pads has hardened a bit, and wasn’t properly seated in the mounting hole. This is allowing a whole lot of “play” in the drive train, and there is evidence of the flywheels rubbing on the shell. I have to pick up some motor pads on my next trip to the big city, and I assume that will go a long way towards quieting things down. Just watching it run without the shell it looks like things are a bit off balance, probably due to the flywheels as mentioned above. The truck seem to roll free and easy when removed from the frame - no binding or chatter, so the noise is likely the universals chattering (it is REALLY LOUD with the shell on, and flywheels rubbing!) due to the bouncing flywheels?
My questions is this: Does anyone know who makes replacement flywheels to fit this model? I found flywheels in the Walthers catalog by Timewell Precision (part #712-1033) to fit SW12/SW1500’s, but I’m not sure if they would do the trick. Are there others out there?
There is a good clinic in the Yahoo Group “RPMclinics-RickBell”. It’s in the files area labeled Athearn Blue Box.pdf. Rick goes over a tuning an athearn engine as well as installing a decoder.
Thanks for the link. Just so I am clear, the current “old school” shaft is 2.4 mm? I’m all set to order, but I want to make sure I’m getting the right part.
Boy am I glad you posted this comment. I humbly apologize, but apparenty posted incorrect information. It looks like the shafts on the old style Athearn open frame motors are actually 1/8 inch, which ends up slightly over 3mm. I’m surprised that no one caught my mistake. I got a litttle confused, most of the flywheels listed are specifically for can replacement motors. I’ve been playing with several locos, cleaning, re-motoring and such. Seems like the majority of the can motors are 2mm, with a few of them at 2.4 mm.
It looks like the Timewell you found are direct replacements. If you are not changing the motor as well, they may be a good idea.
You say it takes quite a bit to start the motor. That they do. A can replacement starts at a much lower voltage, thus better starting and slow speed operation. If you rummage around (http://www.1stplacehobbies.com/cgi-bin/prod.asp?pn=116-80321), you’ll find the repower kits for under $40. That takes care of several issues. Isolating the brushes, fixing flywheels, high start voltage. It’s an easy job, pretty much just use silicone and glue a new motor in place.
The other small benefit is the can motor is slightly smaller, allowing just a little more room to mount a decoder and wiring.
Thats interesting, I have 8 or 9 old athearn locos from the 70s’ and 80’s and they are all 2.4mm. I also have a few Stewarts with athearn drives and they too are 2.4 mm.
That’s interesting. I felt like a real putz, posting info that I was unsure of. Last night I measured the shaft on two locos, a GP9 and F45, both vintage of the late 70s. In both cases, the shaft measured 0.125 inch. I guess maybe I should pull the body off the SW7, since that’s the one being questioned anyway.
When I was working on the SWs, I could have also sworn that the shaft was 2.4. But then again, the larger locos have a longer motor.