Need help selecting LokSound

[GhengisKong]

I am needing some questions answered about decoder selection for my locomotive. I am re-motoring my OMI DDA40X with two Kato SD40-2 motors with flywheels removed on one end each and needing to know if a LokSound Micro V4.0 is capable of supporting 2 motors at the same time? I had seen where someone had tested the Kato N motors as having 1.0A draw for the stall current and the LokSound Micro had .75A of continuous: is that capable of handling two Kato motors? Or will I be needing to move up to the HO standard sized LokSound V4.0 that has a 1.1A continuous draw? Thanks in advance.

Taylor

[jdcolombo]

I have never had a Kato motor draw more than about .75 amp at stall using a 10v DC supply (I test my motors at 10v because I keep my track voltage at about 11.5v; this means that the voltage supplied to the motor after the decoder's bridge rectifier is about 10v).  Free running amperage is about 250ma.   But the best thing to do is test the motors.  If you have a DC powerpack lying around, or can borrow one, and a cheap multimeter, you can wire the motor and multimeter up to the power pack and test its current draw running free and at stall.  Wire the multimeter in series with the motor, do your test, and then you will know for certain.  I have routinely used Micros in HO scale single-motor installations without problems and I routinely see quotes of stall current in HO motors of 1 amp.

Remember that most decoders are rated at a certain continuous amperage draw, with some peak current headroom.  For example, the Micro is rated at .75 amp continuous, 1 amp peak.  If you test your motors and get about .5 amp at stall, a micro probably would be fine, since it is rare to have an N scale engine actually reach stall current.  Instead, the wheels slip.  I suppose that you could hit stall current if something got lodged in the gears to prevent the wheels from turning and you kept turning up the throttle without knowing, but that's about the only real-world scenario I can think of that would result in an N-scale loco reaching stall current.

John C.

PS - note that the HO-sized LokSound Select has a continuous amperage rating of 1.1 amps.  If your motors really DO top out at .75 amps at stall AND you want to be absolutely sure not to blow a decoder with both motors at stall, not even the HO-sized Select will get you there.  Ultimately, you're going to have to take some risk; the risk might be lower with an HO-sized select, but it will still be there.

[RBrodzinsky]

Wouldn't running two motors off one decoder affect the BEMF adjustments?

[jdcolombo]

Wouldn't running two motors off one decoder affect the BEMF adjustments?

Probably - I think we had a discussion of this in another thread somewhere.  But you could always turn BEMF off to run a dual-motor engine if it was a problem.

John C.

[jdcolombo]

Actually, the more I think about it, the better way to do this would be to use a LokSound micro AND a LokPilot V.4.  The two together would take up less room than a regular Select, and since each is rated at 1-amp peak, they would handle whatever stall current there is on the motors.  Then you don't have to worry about the stall current; you don't have to worry about BEMF, and since the two decoders use the same motor control circuitry, getting the two motors to run at the same speed should be trivial - just set CV 2, 3, 4, 5 and 6 to the same values and make sure the BEMF CV's (51, 52, 53, 54, 55 and 56) are also at the same values (they should be that way from the factory, but double-checking wouldn't hurt).

John C.

[peteski]

IIRC, free running amperage of Kato locos with the typical lo-friction mechanism is less than 250mA (0.25A). IIRC it is around 100mA (0.1A). But is has been a while since I measured it (and I didn't take notes). Of course with a long train behind it, the current will be closer to 250mA (which I believe is the spec written on the insert of Kato's jewel boxes).

Also, while it is good practice to use decoder which can handle the motor stall current (at full voltage), when in real life has anybody dealt with a stalled motor at full throttle? I don't think I ever have.  Even if one presses down on the loco, it is not easy to lock up the wheels, unless one presses down *REALLY* hard. Under normal operation (without a giant hand pressing down on the loco), the wheels will start slipping instead of stalling the motor (so the current will always be less than stall).

[jdcolombo]

Also, while it is good practice to use decoder which can handle the motor stall current (at full voltage), when in real life has anybody dealt with a stalled motor at full throttle? I don't think I ever have.  Even if one presses down on the loco, it is not easy to lock up the wheels, unless one presses down *REALLY* hard. Under normal operation (without a giant hand pressing down on the loco), the wheels will start slipping instead of stalling the motor (so the current will always be less than stall).

Agree - as I noted above, I can't think of any real-world scenarios where you reach stall current.  Maybe that happens in HO or O, but in N the wheels slip instead.  Even if you have traction tires.  And I should have specified that the "free running" current draw I measured was with a train behind.  I don't think I've ever measured a Kato motor just bare with no load at all. 

John C.

[GhengisKong]

Thanks for the reply so far guys. Peteski points out the obvious in that I'll never hit stall. This will be with 2 Kato SD40-2s with LokSound V4.0 all the time so it will never be on an underpowered train.

Thanks John for bringing up the point on dual motor BEMF issues, though I am having a hard time finding that thread you speak of. It shouldn't be  much of an issue to spend $30 more on a LokPilot/LokSound combo.

[peteski]

I am having a hard time finding that thread you speak of. It shouldn't be  much of an issue to spend $30 more on a LokPilot/LokSound combo.

https://www.therailwire.net/forum/index.php?topic=40249.0

 

[jdcolombo]

Actually, I was thinking about this thread:

https://www.therailwire.net/forum/index.php?topic=43324

See reply #8 in that thread and subsequent replies.

John C.