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Ah, the old big pulse, small pulse trick and we all fell for it! Would you believe...Doug
You might also want to consider running these tests on similar throttles that are not reported to be destructive. You need to get a baseline on what DCC will tolerate in order to possibly identify the potentially damaging behavior of the 1300. Otherwise you won't have any basis of comparison. You may have taken on quite a challenge...Also, maybe this belongs in DCC/Electronics... (ducks and runs)
One step ahead of ya.... I already have an old MRC Tech II 2500 enroute to me as we speak. That one has particularharsh pulses (I know because of the growly sound that motors make when they run on it... I've had one here before).That one hasn't been blowing decoders (at least Rapido hasn't complained about it), so it will be a good one to look at on the scope for comparison.
Mark,The LL GP 18 has a conventional motor in it, which should be able to tolerate the 2500's pulses. I don't like pulses that make motors growl and buzz at low speeds because that means they are probably creating a lot of heat in the motor, which is not good.I have a couple of Troller "Autopulse" units, and they cause that "growling" sound on my locos; perhaps it's best I not use them. Guess I'll stick with the MRC "ControlMasterVI". I would send that up to you for testing, but I'm using it. That's why I personally would avoid power packs like that because the heat and noise are completely unnecessary and over time it will take life off the motor. But unless you left the engine sitting on the track creeping along at low speed, growling and buzzing for a long time, I really doubt it would get hot enough to melt. More likely, something else went wrong. That must have been the case then. The only issue here is whether something ELSE is going on in the 1300 that could harm a decoder when it doesn't seem to affect a loco motor.
From my experience doing extensive testing on devices with small coreless motors and being aware of the often espoused wisdom that coreless motors shouldn't be used with PWM it caused me to question that wisdom based only on logic and to do EXTENSIVE testing using PWM, both high and low frequency. What I have finally deduced from those tests and reading some of the descriptions from those who had problems is that two things are in play. One is trying to remotor a truck with a smaller motor, requiring a small motor do the work of a big, high torque motor due to an unchanged gearing that is WAY too high for the higher RPM's of the small motors, the source of their power. Even if the max supply voltage is at the motor's rating it has them operating at near stall and therefore at an amp draw that is way higher than their amp rating which results in HEAT and, depending on how bad it is, lots of it. If the supply voltage is higher than rated the problem just gets worse by how over the rating the supply is. The closer to stall, the higher the amp draw, the hotter it runs. They don't have brute force (torque) so do it with more frequent applications of their much lower torque (RPM). This also results in the often described starts being very labored and poorly controlled and then at some point, if able to pull it at all, taking off like a scared rabbit to supersonic speed. This action heats the motor badly and is so uncontrollable that even if the motor was at the very edge and didn't cook itself you probably wouldn't want it as it's not controllable and never will be. It plain old doesn't have the power needed.The second problem stems from using a measurably higher supply voltage and then reducing that voltage to a motor using the PWM average only. The speed control will be present but if the supply is over the voltage rating there will also be heat. The problem is, the motor still sees the peek supply voltage in the pulse, regardless of the average output, and doesn't have the mass to dissipate the additional heat that creates. It gets hot. High frequency pulses aren't as bad as low frequency but both will show a higher temperature and depending on how much of a voltage cut is required. In my tests, when the maximum supply voltage was not higher than the motor rating and the gearing did not have the amp draw exceeding its rating (both conditions required with any motor, with or without PWM) there was no discernible heat rise or evidence of a shorter motor life. That is after literally thousands of running hours on various motors with various PWM supplies (including DCC) and running for days at a time from crawl speed to full throttle.That's been my experience with coreless motors.
Is this really PWM we are talking about with those older MRC packs? I didn't think the 2400/2500/2800 were PWM.I thought they just spewed out some sort of square or sawtooth wave pulse to vibrate the motors and keep them running at very low speed.PWM works really well on motors. So now I am very curious indeed to see what comes out of the 2500.
The serious killer of coreless motors is the DCC track power itself. What I mean is that if a DC-loco with a coreless motor is placed on a DCC_powered track, that will likely destroy (overheat) the coreless motor quickly.
Have you witnessed this? I have a friend with an enormous loco roster, with both iron-core and coreless motors. He's run them on DCC "pseudo-DC" (so-called zero-stretching) with no ill effects. He's even let the locos sit on the track, not moving--which would still deliver plenty of presumably destructive DCC pulses to it--for hours without so much as a whimper.
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Topic: Railpower 1300 testing (Read 40947 times)
