Motor/TSU-750 compatibility?

[tbdanny]

Hi all,

I'm in the process of installing a TSU-750 into the tender of a brass HOn3 C-25 locomotive, and need to replace the motor as the stall current of the current one is enough to blow the decoder - 1.3 Amps.  I'm considering using a Mashima M-1624, and I was wondering if anyone has previously used this decoder/motor combination, and if there were any issues I need to be aware of?

Thanks in advance,

tbdanny

[locoi1sa]

   tb.

 The motor may not be the only problem. While some old open frame motors drew some current to turn the armature. I would also look for free rolling wheels and axles, Side rods and quartering issues. Throwing a new motor may be the ticket but 1.3 amps is a lot of power. Something is keeping it from rolling easy.

  I thought I might have to re-power my old Bowser open frame motors but it turned out they draw as little if not less then some old BB Athearns I have.

  Test the loco with the drivers spinning and also starting a heavy train and this is the reading to use. Stalled current is always high but how many times does a loco stall without spinning its wheels?

      Pete

[tbdanny]

loco1sa,

Thanks for the advice.

The 1.3 amp current mentioned was measured with my fingers holding the motor shaft in place on the old can motor - the maximum current that a motor will draw under any load.  The loco itself is a rather smooth runner - I spent a couple of days tuning it up and tweaking it to get performance that was equivalent to a modern, ready-to-run loco.

Cheers,

tbdanny

[fwright]

I'm not familiar with the Mashima M-1624.  However, can I suggest a couple of alternatives to consider?

NWSL currently has a very nice low speed, very high torque motor that is smaller than a 16x24.  I forget the model number, but if you call them, they should be able to help you.

The stall current of the bare motor (the way you are testing) is a measure of the resistance of the armature coils and brushes - and nothing else.  In other words, you are not testing the mechanism load or the torque of the motor, although you could notice the torque by how much effort it takes to stop the shaft.  True, the stall current at 12 volts should not be possible to exceed, but if it causes you to re-motor with a motor with too little torque to stay inside the Tsunami decoder rating when stalled, what have you gained?

If you use the slip current as installed in the model for the decoder rating, you still have a decent, but not as large, safety margin.  The drivers should start to spin before the slip current is exceeded.  It's very hard to imagine a scenario where the drivers are somehow prevented from spinning, yet the model is making good electrical contact with the track.  And you sit there and do nothing while the motor and/or decoder overheats.

Final thought - replacing the magnet in an open frame motor with a rare earth magnet stack will often gain you 90% of the benefits of re-motoring with less than 10% of the effort. Usual cost for the rare earth magnets is less than $5.  If the bearings are still in good shape, and the brushes reasonable, the increased magnetic field of the rare earth magnets will make the motor noticeably more efficient (significantly reduce current and less heat for the same load) and run at a lower RPM.

Of course, if you heart is set on a can motor, ignore the above.  I re-motored with Roundbell's 24V coreless motor in my HOn3 FED 2-6-0 and couldn't be happier.

Fred W

[cacole]

Stall Current was a gimmick thought up by decoder manufacturers in the dark ages when decoders cost $75-$100 each to keep people from blaming them because a decoder burned up, and is not realistic.

How likely is it that you will ever press down so hard on a locomotive that the drivers can't spin?  Or hold the armature with your fingers that it can't turn?

A more realistic measure is pulling a heavy load uphill until the drivers just begin to spin.

[rrinker]

 It can and will spike that hard on initial startup - which is why you often see 2 ratings for a decoder, a continuous and a peakl value, say 1.5 amps continuous 2 amps peak, which menas the decoder can handle those momentary spikes as long as during normal free moving operation the motor stays under 1.5 amps.

And from what I've been reading, the Micro Tsunami is rather delicate, 3/4 of an amp and it doesn't seem to like any spikes at all. If the stock motor draws 1.3 amps stalled, the 750 won't last long.

 What makes this all see like a lot of marketing BS is twofold - first, the peak capacity issue, and second, a lot of those older locos that people just ASSUMED they MUST use more than 2 amps don't really draw that much. Remember we still have people thinking they need an 8 or 10 amp DCC system to run more than 2 sound locos. Yet look at the tests in MR and MRN and see how most of the modern sound locos are 1 amp or less at stall. Oh yeah, another factor - a lot of those old power packs were over rated - so when the supposed 3 amps MRC power pack couldn't run 2 Athearn locos it was assumed that 3 amps was insufficient. Except they never had 3 amps to begin with. MRC was famous for that.

                                  --Randy