I know Jason likes to joke around but if they come up with an issue that is shown to cause damage to the locos I doubt that is one of their jokes. Those cheap power packs aren;t well filtered, and they could easily be putting out spikes far higher than the moninal 12 volts - it doesn't necessarily cause problems with the motor (except maybe a coreless motor like in those Kato locos with the truck mounted motors), but with dual mode DC/DCC electronics it could cause components like capacitors to charge up above their rated value and fail.
I do also have a 1370 I got to do DC testing, I should take a look at that along with my Tech IV. If I remember to take it home from work (I used it to run large scale Thomas around the office tree).
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
SeeYou190They also have a note on their DC power pack page that says the 1300 and 1370 might not be compatible with DC locomotives manufactured by Rapido. Is this because the 1300 & 1370 are PWM?
No,
This is because Rapido outright says in their product manuals that they have had damage from customers using these two power packs (as well as trainset powerpacks). Rapido also says, in the same sentence (paraphrasing) that they will not replace the circuit board in the locomotive if you damage it in this way. No idea if they are serious or just messing around (its kinda hard to tell with them), because I dont run DC. I have an MRC Tech II 2500 (I think) for break-in and testing of repairs prior to decoder installation.
gregci happened to see a product review for the MRC Tech II models 1400/1500/2400/2500 in RMC, i believe march april 1980. It showed scope traces. Those traces showed rectified AC. A switch on some of the models controlled whether it was half or full wave rectified.
the may 1980 RMC completed the review of the 1500/2500. It had described the 1500/2500 as having momentum/brake and the 2400/2500 as higher powered versions of 1400/1500.
but the 2500 uses PWM unlike the other 3. The review showed scope traces for the 1500/2500 at 4 throttle settings. PWM pulses are ~16 msec apart, which is the period of 60 Hz. I could see some 60Hz ripple riding on top of the wider PWM pulses.
the article discusses motor heating as a disadvantage of PWM, which it probably is at 60 Hz. I believe modern day decoders use processors that can generate PWM pulse at 200 kHz.
greg - Philadelphia & Reading / Reading
WIsh I still had my 1500 to test, or open up and look. I don't think the circuit was that complex. They were simialr to earlier designs that produced a sine half-wave pulse when the throttle was cracked but as the throttle was increased it either filled in the other half or lowered the level of the pulses (take your pick - the effect is about the same, stronger pulses on startup with little or no pulses at full throttle). Most of the "tech speak" on the packaging and on the units themselves was marketing fluff. Mine worked well, and was a big improvement, but considering what came before it was a simple Aurora Postage Stamp Trains power pack, anything would have been better.
I do have a Tech IV, and I have a set of pretty much every security blade screwdriver bit known to man, so unless they glued it all together, I should be able to take a peek inside. Kind of curious now. I've only used it to run some HO locos back and forth ona test track, and it does have nice smooth control but the locos are an Atlas/Roco S2 and a custom painted BB SW remotored with a Sagami can motor so darn tootin' they run smooth.
SeeYou190I am pretty sure the MRC Tech II model 2500 was a true PWM pack, but I have not read anything about the current production packs being made like this.
i happened to see a product review for the MRC Tech II models 1400/1500/2400/2500 in RMC, i believe march 1980. It showed scope traces. Those traces showed rectified AC. A switch on some of the models controlled whether it was half or full wave rectified.
And that is exactly why decoders all use PWM. There is no room on a decoder (or in most locos) for a heat sink or even a component large enough to handle a watt or more of heat (most HO decoders are rated for continuous 1-1.5 amps, and momentary peaks to 2 amps). By using PWM, even a small surface mount component can easily handle the limited amount of heat generated.
doctorwayneThere's some discussion here about generation of heat, but the portion of this throttle which is to be installed under the layout is equipped with a large heat sink.
the irony is that the throttle has to dissipate more heat at low, rather than full throttle settings in a linearly regulated throttle as shown in the schematic.
when the locomotive is operated at a high voltage, 10V for example, and drawing 1 amp, the locomotive is drawing 10W (10V x 1A). If the supply is 12V, there's 2W ((12-10V) * 1A) of heat dissipated in the throttle.
but if the loco is operated on 2V and let's say 0.5A, the locomotive is dissipating 1W (2V * 0.5A) but the throttle is dissipating 5W ((12-2)V * 0.5A).
this is the beauty of PWM. The throttle either provides max voltage on no voltage, on-off. The MOSFETs in my throttle have an on resistance of 0.04 Ohm, so when on and providing max voltage, they disspate 0.04W of heat when passing 1A.
DigitalGriffin I think we are saying the same thing in different ways. But you do bring up a good point. The base is tied in with the alternating current. That will generate a small 60Hz signal to the track. It's not modulated, it's a fixed pulse width.
I think we are saying the same thing in different ways. But you do bring up a good point. The base is tied in with the alternating current. That will generate a small 60Hz signal to the track. It's not modulated, it's a fixed pulse width.
SeeYou190...Is the momentum always on, or is there a way to turn it off?....
Kevin, there's a screw in the base of the handheld unit which can be used to adjust the momentum feature - I don't care for momentum either, so mine is turned off.There's some discussion here about generation of heat, but the portion of this throttle which is to be installed under the layout is equipped with a large heat sink. As I mentioned, I've run over a dozen locos at a time, and also multiple locos on trains which weighed over 20lbs. and had no problems whatsoever. Ken also stands behind the stuff he builds, and I'm very pleased with mine.
Wayne
gregc zstripe My understanding is that the use of PWM in small DC motors like we have in our trains, heat increases in the armature during slow speed use i don't know of any DCC decoder that doesn't use pulse or PWM to drive the motor. If the didn't and drove the motor with DC, they would need bulky heatsinks DigitalGriffin I'm pretty certain that's standard DC. pre-transistor throttles simply had a rheostat in between the transformer and motor to control the motor voltage. The problem with this is that the more current the motor drew, the more voltage and power were dissapated in the rheostat, reducing the motor voltage. DigitalGriffin The circle on the right is a transistor. The B the input that determines how much power is allowed to go through the transistor to your track. When you have the throttle turned all the way up, the power goes to the ground instead of the base. No power at the base pin, no power going through the transistor. in a bipolar transistor (not FET), the base-emitter looks like a diode with a voltage drop of ~0.7V. The collector-emitter current is proportional (x50) to the base-emitter current. In this configuration, the emitter is the output connected to the track thru the DPDT switch In this configuration, the transistor regulates emitter current to maintain the voltage at the emitter at the base voltage less 0.7V. If the emitter voltage drops, the base-emitter voltage and current increases, increasing the collector-emitter current. The opposite happens when the emitter voltage increase. in other words, the 10K pot determines the voltage at the track and the zener diode, D1, maintains a constant voltage across the pot, independent of the transformer voltage. DigitalGriffin There's a natural resistence to keep the field from collapsing when the power is removed. Whenever you have resistence to something, heat is generated. But this is NO problem for a quality motor as long as you aren't constantly reversing the voltage on it. +/12 V swings can play havok then. Not only are you trying to collapse the field, but reverse it. a current is produced when a wire passes thru a magnetic field. A wire has a resistance, hence a voltage can be measured across the wire or a loop of wire passing thru the magnetic field. This voltage is called back EMF. BEMF results even if a current is forced thru the wire which results in a physical force that moves the wire loop and turns the motor. when a voltage is first applied to the motor when it is not turning, a large current flows thru and a large force (torque) is generated to turn the motor. As it picks up speed, BEMF increases, reducing the effective voltage across the motor windings, the current thru it and the force pushing it. it reaches an equilibrium at some speed. If a load slows it down, there's less BEMF, the current increases along with the torque helping it compensate and reach a new equilibrium. The opposite happens when a motor speeds up when the load decrease such as when it runs downhill. the heat generated in the motor is the dependent on the current thru the wire resistance. This is not the voltage across the motor because of BEMF. Applying an AC voltage to a DC motor doesn't cause it to turn, there's no BEMF hence it draws max current, generating max heat which can melt the wire isulation causing a short.
zstripe My understanding is that the use of PWM in small DC motors like we have in our trains, heat increases in the armature during slow speed use
i don't know of any DCC decoder that doesn't use pulse or PWM to drive the motor. If the didn't and drove the motor with DC, they would need bulky heatsinks
DigitalGriffin I'm pretty certain that's standard DC.
pre-transistor throttles simply had a rheostat in between the transformer and motor to control the motor voltage. The problem with this is that the more current the motor drew, the more voltage and power were dissapated in the rheostat, reducing the motor voltage.
DigitalGriffin The circle on the right is a transistor. The B the input that determines how much power is allowed to go through the transistor to your track. When you have the throttle turned all the way up, the power goes to the ground instead of the base. No power at the base pin, no power going through the transistor.
in a bipolar transistor (not FET), the base-emitter looks like a diode with a voltage drop of ~0.7V. The collector-emitter current is proportional (x50) to the base-emitter current. In this configuration, the emitter is the output connected to the track thru the DPDT switch
In this configuration, the transistor regulates emitter current to maintain the voltage at the emitter at the base voltage less 0.7V. If the emitter voltage drops, the base-emitter voltage and current increases, increasing the collector-emitter current. The opposite happens when the emitter voltage increase.
in other words, the 10K pot determines the voltage at the track and the zener diode, D1, maintains a constant voltage across the pot, independent of the transformer voltage.
DigitalGriffin There's a natural resistence to keep the field from collapsing when the power is removed. Whenever you have resistence to something, heat is generated. But this is NO problem for a quality motor as long as you aren't constantly reversing the voltage on it. +/12 V swings can play havok then. Not only are you trying to collapse the field, but reverse it.
a current is produced when a wire passes thru a magnetic field. A wire has a resistance, hence a voltage can be measured across the wire or a loop of wire passing thru the magnetic field. This voltage is called back EMF.
BEMF results even if a current is forced thru the wire which results in a physical force that moves the wire loop and turns the motor.
when a voltage is first applied to the motor when it is not turning, a large current flows thru and a large force (torque) is generated to turn the motor. As it picks up speed, BEMF increases, reducing the effective voltage across the motor windings, the current thru it and the force pushing it.
it reaches an equilibrium at some speed. If a load slows it down, there's less BEMF, the current increases along with the torque helping it compensate and reach a new equilibrium. The opposite happens when a motor speeds up when the load decrease such as when it runs downhill.
the heat generated in the motor is the dependent on the current thru the wire resistance. This is not the voltage across the motor because of BEMF. Applying an AC voltage to a DC motor doesn't cause it to turn, there's no BEMF hence it draws max current, generating max heat which can melt the wire isulation causing a short.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
zstripeThe link I provided has a different opinon on PWM.....pertaining to heat and what PWM actually does
not sure where there's a difference of opinion on how PWM works.
one thing several quick searches pointed out is that there's a difference between running PWM at a low vs high freq (same duty cycle) and why.
the inductance of the motor resists a change in current. So at low frequency (100 Hz), the current thru the motor increases to max during the PWM pulse and has a chance to drop to zero when the pulse is off. This translates to more resistive heat being generated during the pulse at max current.
at higher freq (150 kHz), the pulse switches off before the current has a chance to change much and similarly, does not decrease much when the pulse switches off. In other words, the current is relatively constant, although varies, with PWM at high frequency. This means the motor can see a current and voltage similar DC with PWM at higher freq.
i believe todays decoders operate PWM at higher freq (200kHz).
monitoring BEMF allows the decoder to make adjustments to provide good low-speed performance
i don't know enough to understand the heating effect differences with PWM freq. I couldn't access the IEEE article referenced at the bottom of the link.
let's assume the motors do run hotter with PWM. I don't believe it is cumulative in the sense that it wears the motor out. I believe increased temperature can cause the wire insulation to melt and is only a problem if there is a short. Until there is a short, there is no loss of performance.
i don't know what is the melting temperature of the wire insulation is nor how close to that temperature our locomotive motors are getting due to PWM.
the fact of the matter is that motors are being driven with PWM and presuambly running hotter because of it and there doesn't appear to be an unacceptable increase inb failure rate.
rrinker The key with PWM is it depends on the frequency of the pulses. Even coreless motors, which have no nice solid metal armature to dissipate heat, are fine with PWM - as long as it's of a sufficiently high frequency. ALL DCC decoders put out PWM. The ones that say they are 'silent running' or 'supersonic' use PWM frequencies above human hearing, and are capable of driving a coreless motor safely. Not many off the shelf locos have coreless motors though - some high end brass, and those new Kato locos with the motors integrated in the trucks. Old decoders in the early days of DCC didn't use high frequency drive, those could and did make motors bizz, particularly types where the magenets weren't glued in, like Athearn ones with the tan/gold case. It was cautioned not to use these types of decoders with coreless motors as it would overheat and damage them. Higher PWM frequency prevents the motor heating, but the downside is it causes the motor to develop much less torque at low speed (short pulses). Decoders include a 'kick start' to increase low end torque (some brand call is torque compensation). There's no reason a DC throttle circuit using PWM couldn't also do all of this. Also, while most DCC decoders can operate with DC or DCC, if set that way, they often are confused by DC PWM control, the PWM square wave looks too much like DCC and the decoder thinks is is on DCC track, not DC. So a PWM throttle is not a good option if you want to run locos that come from the factory with DCC decoders in them. For best results, the decoder should be removed and bypassed. --Randy
The key with PWM is it depends on the frequency of the pulses. Even coreless motors, which have no nice solid metal armature to dissipate heat, are fine with PWM - as long as it's of a sufficiently high frequency. ALL DCC decoders put out PWM. The ones that say they are 'silent running' or 'supersonic' use PWM frequencies above human hearing, and are capable of driving a coreless motor safely. Not many off the shelf locos have coreless motors though - some high end brass, and those new Kato locos with the motors integrated in the trucks. Old decoders in the early days of DCC didn't use high frequency drive, those could and did make motors bizz, particularly types where the magenets weren't glued in, like Athearn ones with the tan/gold case. It was cautioned not to use these types of decoders with coreless motors as it would overheat and damage them.
Higher PWM frequency prevents the motor heating, but the downside is it causes the motor to develop much less torque at low speed (short pulses). Decoders include a 'kick start' to increase low end torque (some brand call is torque compensation). There's no reason a DC throttle circuit using PWM couldn't also do all of this.
Also, while most DCC decoders can operate with DC or DCC, if set that way, they often are confused by DC PWM control, the PWM square wave looks too much like DCC and the decoder thinks is is on DCC track, not DC. So a PWM throttle is not a good option if you want to run locos that come from the factory with DCC decoders in them. For best results, the decoder should be removed and bypassed.
Randy has covered this very well, I was short on time earlier.
And he brings up an important point about dual mode decoders not liking PWM DC throttles.
No DCC loco I have ever tried on the Aristo Train Engineer worked correctly or ran smooth. A great many DCC locos would not run on the Train engineer at all, they would just sit and hum.
Some where, I have some technical info on the frequency that the Train Engineer uses, and that data in on the web, I simply don't have the site bookmarked or handy, but it is a high enough frequency that heat is not an issue.
Obviously I do not use any decoder equiped locos, I do not use sound equiped locos of any kind.
I have removed all sorts of decoders and rewired locos for straight DC operation.
Poor as they are, I was always able to sell those basic Bachmann decoders on Ebay.......
Sheldon
The link I provided has a different opinon on PWM.....pertaining to heat and what PWM actually does. Who is correct? Click on the link and scroll down to " Pulse Control and Motor Heating". Not doubting anyone's opinon on what I said.......just how it is accomplished and the results.
I personally use MRC CM 20's on my layout.....the newer ones without the fan and never had any problems with them...including their hand held, with a spare, that I never had to use. I also run DCC engines with sound on the layout, mostly for the Grandkids......I can live without DCC.
Take Care!
Frank
How the Aristo Train Engineer works:
Momentum is preset, not quickly changed. I keep mine on zero because even the "zero momentum" setting has a "ramp up/ramp down" speed as the throttle is push button, not a rotary knob.
Hold the Faster button train accelerates, hold Slower, train decelerates.
If you reverse the direction while the throttle is active, it will first ramp down to zero, slight delay, change direction, ramp up to previous speed setting.
It has an "emergency" stop button, kills the signal pretty quick.
Throttle does not come with a power supply, you choose voltage and amperage suitable to your scale. It will handle 20-24 volts, 10 amps. I use 13.8 volt regulated at 4 amps. You must have a seperate power supply for each throttle - no common rail.
With most locos it will light headlights at full or nearly full brightness before train moves.
One a loco moves, they virtually never stall. Slow speed starts are very good, similar to DCC, very smooth start/stop.
I did a lot of testing before adopting them for my layout. I use them as part of an Advanced Cab Control system with signaling and CTC.
zstripeMy understanding is that the use of PWM in small DC motors like we have in our trains, heat increases in the armature during slow speed use
DigitalGriffinI'm pretty certain that's standard DC.
DigitalGriffinThe circle on the right is a transistor. The B the input that determines how much power is allowed to go through the transistor to your track. When you have the throttle turned all the way up, the power goes to the ground instead of the base. No power at the base pin, no power going through the transistor.
DigitalGriffinThere's a natural resistence to keep the field from collapsing when the power is removed. Whenever you have resistence to something, heat is generated. But this is NO problem for a quality motor as long as you aren't constantly reversing the voltage on it. +/12 V swings can play havok then. Not only are you trying to collapse the field, but reverse it.
zstripe My understanding is that the use of PWM in small DC motors like we have in our trains, heat increases in the armature during slow speed use......as much as 5 times more than plain DC variable throttle, there by shortening the life of the motor and brushes. If You have the time.....read thru this link.....talks about PWM and all kinds of power packs/throttles: http://www.scottpages.net/ReviewOfControllers.html Take Care! Frank
My understanding is that the use of PWM in small DC motors like we have in our trains, heat increases in the armature during slow speed use......as much as 5 times more than plain DC variable throttle, there by shortening the life of the motor and brushes. If You have the time.....read thru this link.....talks about PWM and all kinds of power packs/throttles:
http://www.scottpages.net/ReviewOfControllers.html
The output of DCC decoder is PWM, and I (and a number of my friends) have been using the Aristo Train Engineer in PWM mode for over 20 years with no ill effects.
When I was wiring factories 30 years ago, all the fine speed DC motors for production lines were PWM controlled.
SeeYou190 I do not run DCC. The title of the forum also says "electronics", so this seemed like the right place for this question. . Is there a DC power pack currently made that has a Pulse Width Modulated output (PWM) to control the trains. I am pretty sure the MRC Tech II model 2500 was a true PWM pack, but I have not read anything about the current production packs being made like this. . I would suspect that some must be. PWM is used to control fan speed on your car's A/C blower, actuator position for fuel pressure regulators, and all kind of other things. I just cannot seem to find verification. . I found a couple packs that say their output is "pure filtered DC", but that is only half of what I want. I also want the DC not to be variable voltage, but PWM. . Does anyone know for certain? . -Kevin .
I do not run DCC. The title of the forum also says "electronics", so this seemed like the right place for this question.
.
Is there a DC power pack currently made that has a Pulse Width Modulated output (PWM) to control the trains. I am pretty sure the MRC Tech II model 2500 was a true PWM pack, but I have not read anything about the current production packs being made like this.
I would suspect that some must be. PWM is used to control fan speed on your car's A/C blower, actuator position for fuel pressure regulators, and all kind of other things. I just cannot seem to find verification.
I found a couple packs that say their output is "pure filtered DC", but that is only half of what I want. I also want the DC not to be variable voltage, but PWM.
Does anyone know for certain?
-Kevin
This is offered with a PWM base station, and is wireless handheld:
https://www.revoelectronics.com/
It is offered with a trackside base station for HO.
I use the older Aristo Craft Train Engineer radio wireless throttles, they too are PWM.
Not the best picture, but I have 10 of these. They work great, but are no longer made.
I'm pretty certain that's standard DC.
The circle on the right is a transistor. The B the input that determines how much power is allowed to go through the transistor to your track. When you have the throttle turned all the way up, the power goes to the ground instead of the base. No power at the base pin, no power going through the transistor.
gregche schematic below for the 780 describes a simple transistor throttle, meaning regulated output. It also leaks some of the 60 Hz AC waveform into the output.
Thanks Greg, you are certainly better at understanding schematics than I am. That was all very good information.
Living the dream.
Wayne,
That sure looks like what I am looking for.
Is the momentum always on, or is there a way to turn it off? I really do not like operating with momentum and/or braking. I know it is more realistic, but I like to be in control.
i know this doesn't confirm your question specifically for the MRC Tech 2500. I didn't find anything search for MRC and PWM.
the schematic below for the 780 describes a simple transistor throttle, meaning regulated output. It also leaks some of the 60 Hz AC waveform into the output. As you probably know, these pulses help overcome motor resistance at slow speed.
one characteristic of PWM throttles is that there is no need for a heatshink and they can be a very simple circuit board
Kevin, I'm also running my layout DC, using an MRC ControlMaster 20. Rather than the throttle that came with it (adequate, but not much finesse), I use a hand-held PWM throttle from this guy. Mine is the 3 amp version, with the same handheld as shown in the first picture. It offers great speed control and I've operated over a dozen locos at a time using it (my grandkids got a kick out of seeing them chasing each other around the layout).
I do run heavy trains with multiple locomotives, though, and the set-up handles it with ease. I've done mine so that I can use standard 'phone jacks as plug-ins on the layout's fascia, in various places, and have a 30' springy-type handset cord that I use to connect the throttle. The circuit board will run from either an AC or DC supply. I picked mine up in-person, as his workshop is only about 15 miles from here.
Pulse Power is not the same as true PWM output.
MRC advertises the Tech-7 packs with "Accutech" and "Proportional Tracking Control", but I cannot find a description.
They also have a note on their DC power pack page that says the 1300 and 1370 might not be compatible with DC locomotives manufactured by Rapido. Is this because the 1300 & 1370 are PWM?
I really would like to know.
Who else makes DC power packs?
I just did a Google search for MRC packs and all the photos I see show pulse on/off switches for those that have pulse power.
Very rare to see DC packs online anymore.
I use to make my own at one time. Quite easy. A 555 chip gave me true PWM. At least it worked like that for me. I could vary the width of the pulse.
Check Amazon or ebay or Google.
Edit.
You might search this forum. I remember railpower controller. I think. 60 Hz.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.