It all depends on the motor, if the heat generated by the wated power exceeds the ability of the motor to dissipate that heat, eventually something will melt. As long as you are taking out the same or more heat than is generated, it can run all day.
Interesting that it was originally conceived for N scale, as in the early days of DCC, not only were all decoders expensive, getting ones to fit in N scale locos was much harder. But consider so many N scale locos are big blocks of metal with the motor clamped between them - not a bad heat sink.
Coreless motors have no heavy metal to sink the heat. They are quickly damaged by the heat generated trying to run on DCC power. They are also easily damaged by older/cheap decoders that use a low frequency PWM.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
as others have posted, applying an AC signal to a DC motor results in excessive heat which may damage the motor (melt wire insulation resulting in a short).
i had the impression that this wasn't so bad if the DC locomotive were moving due to pulse stretching which results in a DC component to the DCC signal causing the DC locomotive to move.
But now i'm not sure.
all motors act like generators when their armatures turn. The turning armature, even though a current thru its winding creates a force to push, also generates a BEMF which is a voltage opposing the current pushing the armature (i.e. the motor acts like a generator). The BEMF reduces the voltage across the armature windings which reduces the current due strictly to the resistance of the wire. In other words, the maximum current thru the armature is when the motor is not turning.
DC on a DCC system is the result of an asymetric AC phase where one phase of AC (+/-) occurs for a longer percentage of the time than the opposite phase (-/+). The phase with the longer duration determines the direction and the DC voltage is proportional to the difference in duration.
As with pure DC, the BEMF counters the voltage in the phase with the longer duration. However, during the opposite phase it adds to it!
For example, if the BEMF is half the peak voltage due to a relatively large DC component, during the in-phase phase, the resulting voltage is the Vpk - BEMF, in this case half the peak. During the opposite phase, it is Vpk + BEMF.
if the locomotive weren't moving, it would simply be Vpk all the time, resulting in Vpk * Vpk / Rmotor in wasted power as heat.
during pure DC operation, the voltage across the motor is Vdc - BEMF. However, on a DCC system there is wasted power during both phases and in the opposite phase it's even more than when the loco sits idle, although it is for a progressively smaller period of time,
it seems me that operating a DC locomotive on a DCC system is never a good idea although i doubt anyone has reported long term damage.
greg - Philadelphia & Reading / Reading
gregc ROBERT PETRICK Mark R. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. AC sine wave ?
ROBERT PETRICK Mark R. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency.
Mark R. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency.
The DCC track voltage is very similar to an AC sine wave but at a much higher frequency.
AC sine wave ?
I am so sorry to have chimed in.
When a DC loco is at Address 0 in a DCC system and the throttle is at zero, the burbles that go thisaway are equal to the burbles that go thataway and the train remains still. Singing. When the throttle is increased, there are more burbles going thisaway than thataway and the train begins to move. Thisaway. More throttle -- more burbles and faster speed. When the direction button on the throttle is reversed, the burbles go vice versa the other way around and the train runs backwards.
Clear?
Robert
PS Edit to clarify. When I said more throttle more burbles faster speed, I should have said more throttle bigger burbles faster speed.
LINK to SNSR Blog
Mark R. On a DCC system, there is no form of DC voltage on the rails of any kind. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. The decoder is what converts this AC-like voltage to a usable DC for the motor circuit. When you place a DC engine on a track with DCc voltage, you are in essence applying a low pulse AC voltage to the motor. An AC voltage is an equal pulsing of positive and negative at a very high frequency. So, at speed step 0, the DC motor is receiving small equal pulses of opposing voltages at about 120 time per second. This means the motors armature is occilating back and forth 120 time per second .... this is the buzzing sound you are hearing. What zero stretching does is either increase the positive or negative amplitude of the AC sine wave. The armature is still occilating back and forth 120 time persecond, but it's occilating ever so slightly more in one direct than the other the higher the amplitude is, creating rotational movement. This would be the same as you sitting there and throwing the direction switch on your DC power pack 120 times per second .... not that you could actually do that, but that's what's happening to your DC motor when being controlled by a DCC signal .... not good for it by any means. Mark.
On a DCC system, there is no form of DC voltage on the rails of any kind. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. The decoder is what converts this AC-like voltage to a usable DC for the motor circuit.
When you place a DC engine on a track with DCc voltage, you are in essence applying a low pulse AC voltage to the motor. An AC voltage is an equal pulsing of positive and negative at a very high frequency. So, at speed step 0, the DC motor is receiving small equal pulses of opposing voltages at about 120 time per second. This means the motors armature is occilating back and forth 120 time per second .... this is the buzzing sound you are hearing.
What zero stretching does is either increase the positive or negative amplitude of the AC sine wave. The armature is still occilating back and forth 120 time persecond, but it's occilating ever so slightly more in one direct than the other the higher the amplitude is, creating rotational movement.
This would be the same as you sitting there and throwing the direction switch on your DC power pack 120 times per second .... not that you could actually do that, but that's what's happening to your DC motor when being controlled by a DCC signal .... not good for it by any means.
Mark.
Right. Thanks Mark. This is the best explanation I've seen describing this situation. Every time I try to explain it, people roll their eyes at me.
One other thing that causes eye roll . . . When a non-decoder engine is operating on a DCC system at Address 0 and is within a reversing section, and another train crosses the gap, the non-decoder engine will suddenly stop and reverse direction. Slamming on the brakes, full speed reverse, coupler tension bucked, loads shifted . . . not a pretty sight.
Thanks again Mark. Old thread, hope you're still around.
NOOOOOOOOOOOOOOOOOOOOOOOOOOOO!
Bear "It's all about having fun."
BigDaddyYou were supposed to laugh
BigDaddythere goes my new stand up comedy career, down the drain
A big heavy Pittman-type motor has a larger mass to help dissipate the heat, a smaller can motor is actually WORSE and more easily overheated. ANd a coreless motor will be destroyed in minutes if not seconds if placed on DCC track. That used to be only high end brass, or remotored locos, but there's at least one new Kato HO loco that had the motors built into the trucks - they are coreless motors and if you set one of those on DCC track without a decoder it won;t take long to damage it. Note sure if they've released any others usign that technology yet.
ANd a few manufacturers have gone to the trouble of adding a capacitor to their DC light board which causes no issues running on plain DC power, but will short out the DCC system, effectively preventing you from running a non-decoder loco.
maxmanBigDaddy "I don't think so, Tim"
"I don't think so, Tim"
You were supposed to laugh, there goes my new stand up comedy career, down the drain.
Henry
COB Potomac & Northern
Shenandoah Valley
As was said, there is a chance of damaging the motor. The two brushes heat up where they contact the armature. About ten years ago I did temp measurements with an infra red temp scanner on a test stand. I could see the hot spots even in a can motor. With the motor armature stopped and DCC still applied, the temp increased.
The gears are not the issue. The buzz is annoying.
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.
BigDaddyThat's why Al Kalmbach invented the CV 29 calculator
joe323What CV disables DC mode on DCC loco and what setting should it be to disable it?
Bit 2 of CV 29
I don't know how to change a single bit and I'll bet you don't either. That's why Al Kalmbach invented the CV 29 calculator
http://www.digitrax.com/support/cv/calculators/
Analog is the highfalutin word for DC
It's part of CV29, bit 2 (so value of 4). Not so simple as just subtracting 4, but common values of CV29 are 38 and 6, for long address or short address. In those cases, making it 34 or 2 will turn off DC operation in the decoder.
Digitrax command statioons also have an option to turn off the ability to run an analog loco. On a layout with only a few trins runnign it doesn't really matter but on a busy layout, running an analog loco using address 00 slows the response of all the others because it works by making every 0 bit in the DCC data stream longer, which means each data packet takes longer to send, so it takes longer for a command to get froom the throttle to a DCC loco. Most clubs disable the analog in the command station for this reason.
Disabling it int he loco means you can;t take your DCC loco and run it on a friend's DC layout, but it also can prevent runaways where when the layout is powered up, the DCC signal isn't fully formed so the loco thinks it is on DC and takes off at full speed. Disabling DC in the decoder stops this.
The harsh pulses of DCC driving a DC loco actually worked out for me once - had an old Bowser PRR T1 that had never been run after being built, and none of the DC packs I had could get it ti run and keep running, they didn;t have enough power. Put it on the DCC track using address 00 and it was able to move and keep moving long enough to finally start breaking in, gradually got faster and smoother. The big heavy motor in that wasn;t in much danger running on the DCC track, but to leave it sitting there NOT spinning would eventually overheat it or any motor.
What CV disables DC mode on DCC loco and what setting should it be to disable it?
Joe Staten Island West
geomodelrailroaderIf it is a kit convert it as soon as possible. You should never place a DC locomotive on live DCC track the only place you place them is on insilated programming tracks or on a section wired to DC. If you place a DC locomotive of DCC track it will blow up same thing happens to older locomotives.
5-year-old thread; and your reply is not fully correct. Some DCC systems (like Digitrax) do allow most DC locomotives to operate without harm for a short time. The programming track has nothing to do with DC operation.
Layout Design GalleryLayout Design Special Interest Group
If it is a kit convert it as soon as possible. You should never place a DC locomotive on live DCC track the only place you place them is on insilated programming tracks or on a section wired to DC. If you place a DC locomotive of DCC track it will blow up same thing happens to older locomotives.
jalajoie Personally I don't run a DC loco on a DCC system, however at my club we had a member that never installed a decoder into his engines. He ran analog locos on our Digitrax system for 10 years without any ill effect to ether his locos or the Digitrax system. In fact he was so good at running his trains that he could even run through a reversing loop with ease. He knew the exact time he had to reverse the direction on the throttle to achieve that feat. This member never had any failure to his roster running constantly analog locos on a DCC system.
Personally I don't run a DC loco on a DCC system, however at my club we had a member that never installed a decoder into his engines. He ran analog locos on our Digitrax system for 10 years without any ill effect to ether his locos or the Digitrax system. In fact he was so good at running his trains that he could even run through a reversing loop with ease. He knew the exact time he had to reverse the direction on the throttle to achieve that feat.
This member never had any failure to his roster running constantly analog locos on a DCC system.
Notice he said running not sitting still while on DCC.
I have run DC motors on DCC and the armature was cooler while running. The armature got hotter, the longer the motor was sitting still. I used an infra red temp scanner for the measurements.
Remember, your mileage will vary.
DCC puts a constant AC voltage on the tracks. The rapid reversal in direction of a DC loco, 60 times a second, is hard on the gears.
Thanks.
Russell
csxns jalajoieHe ran analog locos on our Digitrax system for 10 years without Is this Digitrax,wireless?
jalajoieHe ran analog locos on our Digitrax system for 10 years without
Yes it is a DCS200 8amp. wireless system. It was installed at the club in 1999 and has been working like a swiss clock ever since.
Jack W.
aj1s Randy, Thanks. I understand the stalled rotor heating problem. That's not the root of my question (but thanks for the explanation, since it may help others). Pardon my ignorance, but most people suggest disabling analog mode on mobile encoders to avoid issues with runaway locomotives sometimes occurring at power-on. Is this because DC track voltage is NOT always maintained at zero at startup, or something else? Are boosters required to automatically maintain track voltage at 0 volts DC unless/until they have a viable control input? Do any boosters maintain 0 VDC in the absence of a valid control bus input? While the motor overheating will not "instantaneously" destroy a loco, running at very high speed could cause the loco to take an unplanned route down an extreme grade, and destroy it quickly enough that it might as well be considered "instantaneously"! Such a scenario might not be the fault of a DCC component per se (more likely a bad wiring connection, broken/disconnected connector, etc.), but running a DC loco on DCC removes one of the "safeties" inherent in the system. Just like the ground wire in (US) electrical systems. that extra measure of safety is never needed unless something else goes wrong. Also, another message thread here just brought up the issue of reverse loops, AR controllers, and DC locomotives on DCC layouts. They don't play nicely with each other. You can't exit an AR controlled reverse loop into a non-AR controlled district with a DC loco. As an NCE camper, naturally I'll add that to my "list of reasons running DC locos on DCC power is a bad idea" Andy
Randy,
Thanks. I understand the stalled rotor heating problem. That's not the root of my question (but thanks for the explanation, since it may help others).
Pardon my ignorance, but most people suggest disabling analog mode on mobile encoders to avoid issues with runaway locomotives sometimes occurring at power-on.
Is this because DC track voltage is NOT always maintained at zero at startup, or something else?
Are boosters required to automatically maintain track voltage at 0 volts DC unless/until they have a viable control input? Do any boosters maintain 0 VDC in the absence of a valid control bus input?
While the motor overheating will not "instantaneously" destroy a loco, running at very high speed could cause the loco to take an unplanned route down an extreme grade, and destroy it quickly enough that it might as well be considered "instantaneously"!
Such a scenario might not be the fault of a DCC component per se (more likely a bad wiring connection, broken/disconnected connector, etc.), but running a DC loco on DCC removes one of the "safeties" inherent in the system. Just like the ground wire in (US) electrical systems. that extra measure of safety is never needed unless something else goes wrong.
Also, another message thread here just brought up the issue of reverse loops, AR controllers, and DC locomotives on DCC layouts. They don't play nicely with each other. You can't exit an AR controlled reverse loop into a non-AR controlled district with a DC loco.
As an NCE camper, naturally I'll add that to my "list of reasons running DC locos on DCC power is a bad idea"
Andy
Andy, there's a good reason for dis-abling the analog (DC) mode on a decoder. When a decoder is first powered up, there's a process the processor goes through called "check sum". This process checks all the parameters of the decoder and happens in just a fraction of a second. This process also checks to see what kind of voltage is present on the rails (DC / DCC / Motorola / etc.) and will then acknowledge this as the voltage configuration to be used. There is no DC voltage on the rails of a DCC system of any kind.
If this check sum process hiccups and doesn't see the DCC voltage, it will automatically default to a DC voltage. Seeing as how most DCC systems have around 14 volts (generically speaking) on the rails, the engine takes off at what the decoder thinks is 14 volts DC. By turning off the ability of the decoder to run on DC, the check sum process will not default the input signal to DC if it misses the DCC signal in the start-up process.
The same happens to momentary losses of power no matter how instantaneous - upon re-application of power, the check sum checks the track input. Again, this takes a very small fraction of a second to do this. Again, that's why an engine will just take off for no apparent reason - you hit a small piece of dirt, the check sum process missed the DCC signal, told the decoder it was DC and the engine took off.
If you regularly run your engine on DCC, turn the analog mode off to prevent this. It's easy enough to change CV29 by one digit if you want to run it on a DC layout any time.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
On initial power up, the DCC signal may not be fully formed for a few cycles - if the decoder is set to do analog conversion, it might see this as DC and take off. I've not had this happen, but I started disabling DC in the decoders anyway _ I'll never run them with DC, so I'll proactively avoid any potential problem.
As long as address 0 is at a non-zero speed, there is a DC potentical to the track signal and a DC loco will start moving, just like when you don;t turn the power pack throttle to stop.
It's really only dangerous to leave a non-decoder loco sitting still and not turning. That's when it will heat the most. When the armature is turning, there's some airflow to help cool it. Only coreless motors cannot handle any operation like this, those motors will be quickly destroyed. But they will also be destroyed with a decoder installed if the decoder is not a high frquency or silent running type. Most any current decoders are, but the Bachmann motor only ones generally aren't, and many older deocders did not have this feature, the sharp low frequency ulse drive from those decoders causes the same sort of heating in a coreless motor.
For those that have systems that support analog locos at address 0, what happens if you do not command address 0 to speed zero before you put a DC loco on the track? Do these systems always zero-stretch to maintain zero volts DC on the track, unless/until non-zero speed commands are issued to address 0?
Just curious. I'm in the NCE camp, so naturally I think it is a practically useless and potentially dangerous feature that could even put your eye out! :)