Adding decoder to old Bachmann Northern


cdouglas

cdouglas

Member
I recently got an OLD HO Bachmann 4-8-4 with one of the pancake motors in it. Is not even one in the plastic housing, its built into the metal of the frame and has copper strips that run parallel to the frame from screws on either side of the main shaft to provide power.

After a tuneup, its actually running really well. Now I want to put a decoder in it. Does anyone have any tips on doing this? It looks I just need to cut the copper strips going from the frame to the motor, secure them somehow so they do go flying out with the brushes, and wire in the decoder.

Thanks
Chris
 
Last edited by a moderator:
Before installing the decoder I would recommend jacking up the boiler and driving a Bowser chassis under it (if you can find one) Bowser made kits to do this, and like bnsf971 said, thise pancake motors don't do well on DCC. I had one unhappy experience with one years ago. It lasted just a few minutes before the factory installed smoke was let out of it, and once you let the smoke out, it won't work anymore! :D
 
Out of curiosity, why would a decoder fry a motor if its feeding it the same 0-14v dc? I've always heard that if it runs good on DC, it should run good on DCC. I am not doubting you guys, just wondering why.
 
Wondering as well

cdouglas said:
Out of curiosity, why would a decoder fry a motor if its feeding it the same 0-14v dc? I've always heard that if it runs good on DC, it should run good on DCC. I am not doubting you guys, just wondering why.
Click to expand...

As far as I know you(cdouglas) are right and DC is DC even if it comes out of a DCC decoder motor lead.

Perhaps we should trust Alan, he is in sales :D

take care ,,, ken
 
That's because you're not taking into account the amps. The decoder will still give the same voltage, but the motor will draw a higher amperage than newer can motors.

This is why all manufacturers clearly state the amps continuous, and the amps peak on each decoder. They also state the maximum milliamps on the function/lighting outputs so that you don't blow them.
 
So shouldn't the decoder fry and not the motor? That makes perfect sense to me that the decoder would fry due to motor pulling more amps than what decoder is rated for.
 
The pancake motors are physically incapable of handling the voltage pulses of a DCC decoder. The motor will burn up from the generated heat in short order.
 
The problem is that these aren't very good motors. Go ahead and do the install. Just don't expect much of a service life out of the motor. Pancake motors are generally found in Chirstmas train sets you might find in Wal-Mart. If the same tabs that transfer power to the motor from the frame also hold in the brushes, that complicates things as well.

I predict if you can get it isolated and wired that it will work...for a little while ;)

Good Luck!
 
Before putting a DCC decoder in any engine you must measure the current draw of the motor while it is stalled. If this current draw exceeds the decoder's current rating then the decoder will burn out.
 
Thanks guys. I will either keep it dc or try to put a newer can motor in it. I'll measure the current draw just so I know.
 
waltr said:
Before putting a DCC decoder in any engine you must measure the current draw of the motor while it is stalled. If this current draw exceeds the decoder's current rating then the decoder will burn out.
Click to expand...

Ahhh, the infamous stall current test! :D Great for decoder manufacturers who want to keep their warranty claims low, but that's about it. This will probably jack the thread a little, but I never do this. Can you think of an operating condition where your loco will actually stall?

There are two that I can come up with. First: it's underpowered. When pulling a heavy train the wheels actually stop. You need a bigger motor here. The other will happen with steamers if at all, and can be caused by running gear (rods) coming loose and jamming the mechanism. This is usually followed immediately by a derailment.

Most modern can motors will not draw more than .25-.5 amp at full load. It's hard to find a decoder rated for less than 1 amp. I usually tie down the loco, or hold the coupler and measure the current when the wheels slip. That's what I use. Older open frame motors are replaced. I never stall test and have never lost a decoder to amp draw in some 15 years of operating with DCC. Go over to the Digitrax list on Yahoo and you'll see lots of discussion on this in their archives.
 
I stand corrected

bnsf971 said:
The pancake motors are physically incapable of handling the voltage pulses of a DCC decoder. The motor will burn up from the generated heat in short order.
Click to expand...

Always good to stand corrected and forced to learn or remember stuff I should have known in the first place.


bnsf971(Terry's) statement about pulsed power explains my misunderstanding and the statements about motors not playing well with DCC.

Read the DCC power Wiki for an explanation of how the decoder motor output is pulsed.

Current/amperage discussions, while important, are a side note to the pulsed power issue.

take care ,,, ken
 
Espeefan said:
Ahhh, the infamous stall current test! :D Great for decoder manufacturers who want to keep their warranty claims low, but that's about it. This will probably jack the thread a little, but I never do this. Can you think of an operating condition where your loco will actually stall?

There are two that I can come up with. First: it's underpowered. When pulling a heavy train the wheels actually stop. You need a bigger motor here. The other will happen with steamers if at all, and can be caused by running gear (rods) coming loose and jamming the mechanism. This is usually followed immediately by a derailment.
Click to expand...

Good point Alan and probably a much more realistic measurement of current draw. None of the engines I have actually stall the motor when stopped, they all just spin their wheels.
 
waltr said:
Good point Alan and probably a much more realistic measurement of current draw. None of the engines I have actually stall the motor when stopped, they all just spin their wheels.
Click to expand...

Just and FYI, the stall current is important because when the decoder first supplies voltage pulses to the motor, it is essentially at a dead stop, or stalled. That's why the stall current is important, not because anybody is going to stall the motor itself.
 
bnsf971 said:
Just and FYI, the stall current is important because when the decoder first supplies voltage pulses to the motor, it is essentially at a dead stop, or stalled. That's why the stall current is important, not because anybody is going to stall the motor itself.
Click to expand...

Ummmm...Nope. Stall current is the same as locked rotor current. That's how motor manufacturers define it. Granted you'll get an amperage spike when breaking the rotor loose to start it turning, but if that were defined as the stall current, why would they have us test for it by applying maximum voltage while holding the rotor immobile? That simulates stalling under full amperage load, not breaking the inertia of a mechanism at rest. Interesting thought, but I've never heard of stall current defined that way by anyone before you. In my prefessional life I've spoken with folks from GE, Baldor, US Motors and others, and none of them ever defined stall torque that way. Yeah, those are the big ones in the real world, but they all run on the same set of rules :D
 
I don't know if all decoder manufacturers do this, but my Digitrax DZ125 decoder is rated 1 amp continuous, 2 amps peak. The Bachmann powered truck (not a pancake motor, but an open frame motor) that powers the little critter draws about 1.8 amps continuous. I've been running it around for a while now and the decoder has not smoked yet so I would say that it is safe to use the peak measurement when picking a decoder for your engine.
 
Back to the original item, 2 thoughts.:)
First,my experience with the pancake motors is they are noisey POS train set motors that are not worth the time to convert. DCC will not help a bad design improve.:(
second, look around,search ebay for a Bowser repower kit.
I have a GS4 that has had the kit added, it runs great now,even with a DCC friendly Pittman motor.:D

your mileage may vary,
 
You must log in or register to reply here.



Back
Top