Capacitors and coasting: Premier vs. RailKing vs. upgrade kit(s)

The capacitors for the most part are part of the power supply and sound circuits.  The acceleration, braking and coasting are, set by the PS2 boards software which controls how much power is increased/decreased over a given time thus how fast or slow the engine and its train moves.  So unlike the old HO DC throttles that did depend on capacitors to charge/discharge to control speeds, the Lionel/MTH etc are software controlled.

The energy stored in a spinning flywheel determines the coasting distance when power is removed.  If you "do the math" the size of a capacitor to provide equivalent coasting distance to a typical flywheel would be gigantic.  The capacitors you are seeing are primarily used for other purposes but do add a bit of coasting distance, but without doing the math I'd guess 1% or less relative to the spinning flywheel.

It doesn't matter how tall the city water tower is, if your faucet turns off no water comes out.   If you look at the middle of a PS-1 there are two large 1000uf capacitors in series, if I remember correctly.  Bigger than anything on a PS-2 board.

Type of gearing, smoothness or lack of friction in drive train, motor and flywheel all drive this, along with the load the engine is carrying unless the circuit board is designed with a momentum or coast type function.   G

I am an electrical engineer, not a mechanical engineer (and run into that problem quite often at work), but I believe there is also an issue with the type of gears. Certain gearing types work better in letting motion go in the reverse direction. It might be that worm gears are not good at it.

There is something called a "Torsen" that is used on the HMMVV, Lexus, Audis, and other vehicles that take advantage of this for 4WD vehicles. If a wheel slips, some how power can get routed to the other wheel on the differential, and its all mechanical, no computers or electronics involved at all.

I appreciate the input and interest so far.  But with all due respect I disagree with the responses which have been posted, and I don't believe my original question has been answered.

From my own observation: 20-3028 (PS1) and 20-3071 (PS2) have the SAME motor, SAME chassis, SAME flywheel, and SAME gearing.  In both cases the drive is self-locking (wheels cannot turn the motor.)  Both locos are running down the track at the same speed.  My nephew walks through the room and kicks the plug out of the wall.  The PS2 Berk coasts, the PS1 Berk does not.  In another version of this story, a ham-handed operator presses "DIR" on the CAB-1 or transformer while the loco is at speed.  Same results.  PS2 coasts, PS1 comes to a sudden, rod-graunching halt.

Conclusion: whether it's capacitors, software, etc., the design factor enabling the PS2 loco to coast is electronic, not mechanical.  To follow up on GGG's analogy, even if the city water main broke and cut off supply to my house, I could still do the dishes because of what's in my home's hot water heater (tank.)  My neighbor who has a tankless system would be out-of-luck.

Since the coasting behavior is conferred by the electronics, I can get that same behavior in a mechanically-identical PS1 loco by means of a PS2 upgrade, or transplant.  So observations aside, the gist of my original question:  Are there any differences in capacitance, current handling capacity, motor control waveforms, etc., at the board level, between RailKing PS2, Premier PS2, and the universal upgrade kits formerly offered by MTH?  Also, any differences in Steam vs. Diesel.  Which would be the best "donor" loco for a project like this?  Thanks!

The PS/2 boards are identical between RailKing and Premier, so if the electronics is contributing to the coasting, it should contribute to both model lines equally.

I have two PS/2 diesels, two PS/3 diesels(one RK), and a PS/2 RK steam engine. If I cut power at the transformer, they all stop dead. Should they be different?

Not to my knowledge John, I've never seen a difference between the product lines.  I also see a sudden stop when I cut power.

 Years ago  an electronics  person build me a throttle with a train brake and engine brake.He used toggle switches  capacitors , resistors . transistors  to create the feel of operating a train (slow momentum starting and slowing down) .   The engine  had  it's own brake feature  with a  spring loaded toggle.   Fun at the time and  it can be done., but not by me. 

Ted Sowirka posted:

...

Conclusion: whether it's capacitors, software, etc., the design factor enabling the PS2 loco to coast is electronic, not mechanical.   

The energy for coasting is from the spinning flywheel.  If your PS1 and PS2 engines are identical in all ways, then something "electronic" on the PS1 board is stealing the energy from the spinning motor causing it to dynamically brake.  That is, if you place a load across the 2 wires to your spinning motor, it will brake the motor.

At the board level, the trick is to electronically disconnect itself from the motor when track power is lost.  At the component level this is easier said than done but fortunately we are talking at the board level or the discussion will get bogged down.

If I were doing it, I'd first want to confirm the mechanical performance of your PS1 chassis wrt coasting.  Many ways to do this - such as running DC directly to the motor (no electronics), pulling the power and comparing the coasting distance/time relative to the PS2 chassis starting at the same speed.

Then decide whether to troubleshoot the PS1 board or just go with a PS2 board.  Since PS1 was designed back when conventional control was the only game in town it stands to reason the electronics could handle loss of track power from DIRECTION button presses.  That it abruptly brakes the motor seems there might be an issue with your PS1 board.

On the other hand, when I press the emergency stop button, which has the same effect as unplugging the transformer, I want the locos to stop fairly quickly. 

Ted Sowirka posted:

I appreciate the input and interest so far.  But with all due respect I disagree with the responses which have been posted, and I don't believe my original question has been answered.

From my own observation: 20-3028 (PS1) and 20-3071 (PS2) have the SAME motor, SAME chassis, SAME flywheel, and SAME gearing.  In both cases the drive is self-locking (wheels cannot turn the motor.)  Both locos are running down the track at the same speed.  My nephew walks through the room and kicks the plug out of the wall.  The PS2 Berk coasts, the PS1 Berk does not.  In another version of this story, a ham-handed operator presses "DIR" on the CAB-1 or transformer while the loco is at speed.  Same results.  PS2 coasts, PS1 comes to a sudden, rod-graunching halt.

Conclusion: whether it's capacitors, software, etc., the design factor enabling the PS2 loco to coast is electronic, not mechanical.  To follow up on GGG's analogy, even if the city water main broke and cut off supply to my house, I could still do the dishes because of what's in my home's hot water heater (tank.)  My neighbor who has a tankless system would be out-of-luck.

Since the coasting behavior is conferred by the electronics, I can get that same behavior in a mechanically-identical PS1 loco by means of a PS2 upgrade, or transplant.  So observations aside, the gist of my original question:  Are there any differences in capacitance, current handling capacity, motor control waveforms, etc., at the board level, between RailKing PS2, Premier PS2, and the universal upgrade kits formerly offered by MTH?  Also, any differences in Steam vs. Diesel.  Which would be the best "donor" loco for a project like this?  Thanks!

 

 

With All due respect Ted...  Your first question really honed in on capacitors assuming that was the difference.  And it is not.  Now you have opened up the door to other electronics while closing the mechanical.  Which I do not think you can.  2 similar trains of different vintage do not have to have the same gear ratio, and I believe for steam they do not.  So take your same car and turn off ignition in 1st gear, and then do it again in 4th and see which one goes further before stopping.  Let alone Stan's points.

My analogy was about how the circuit board handles any residual electric power.  If the  FET is commanded to not conduct it doesn't matter how big the capacitor.  It is disconnected from the motor.  Seems like a change occurred with PS-3 too, because they stop abruptly now,  so even with a large flywheel the board can put the brakes on via software control of the FET.   MTH or Lionel would have to tell you how they program it.  Clearly MTH has battery power to control processors and chip, but no real source of power to keep driving the motor.  G

The PS/2 locomotive is pretty easy to explain, if you hit the reverse button, the programming slows it down at a controlled rate, that's the way they all work.

Right John, that's what I've been trying to say...

Premier steam, running in CONVENTIONAL mode:  If you press DIR, a PS2 will gradually stop.  However a PS1 will halt abruptly, often derailing the consist and possibly damaging the mechanism.  Not kid-friendly at all.  The flywheel is very small and doesn't do much if anything.  The gears are self-locking.  I have yet to find a significant mechanical difference between the PS1 and PS2 versions of Premier steam locos.  All of the tooling was carried over from PS1 (except possibly an added "guard" for the flywheel.)  The increased momentum is somehow conferred by the electronics.

I often see RailKing steam and diesels go for $1xx on a popular auction site.  For that price it might be worthwhile to buy one and cannibalize it for an upgrade.  But I wanted to know whether the Premier locos needed a "heavy-duty high current" board, larger capacitors, etc.  Your first response answered my question.  Thank you!

If the motor control waveforms were in fact different, that aspect would be built into the sound and "personality" file.  Since they produced PS2 versions of most PS1 steam locos, those sound and personality files are readily available, and I'm pretty sure if I get the tach tape right, the speed readout will be accurate.  We'll see!

The slowdown when you hit DIR for PS/2 has nothing to do with capacitors and everything to do with programming.  When you press reverse, it uses it's deceleration settings to slow down to a stop.

OTOH, if you cut power, the motor drive immediately stops.  There isn't any capacitor on those boards with enough storage to rotate the motor more than a few revs, certainly not enough to achieve a controlled slowdown.  I think that's the reason there is some disagreement in the thread, we're talking two totally different scenarios.

The PS/1 and PS/2 boards were identical in RailKing and Premier product lines, so if you find a nice Premier locomotive for a good price, you could use the boards.  Note that I recommend staying away from the older 5V PS/2 boards, they aren't as robust as the newer 3V board sets.

Way confusing.  First.  PS-1 is a conventional engine with totally different electronics.  One is constant voltage applied the other is PWM motor control.  Regardless of Premier or RK the electronics are the same PS-1 to PS-1  or PS-2 to PS-2.  The only difference in steam is large steam have larger motors (Pittman Style) and RK have smaller motors and sometime 2 vertical in large steam vice one Pittman.

As everyone has said a Command engine is programmed to  coast for direction change.

I just turned off power on my PR N&W MTH J PS-1.  It coast about 8 inches from 10VAC.  No jerk reaction.  No cars being pulled either.  But the way the circuit works there is nothing electronic you can do unless you build a separate circuit that continues to power the motor on a power loss.  The PS-1 circuit board won't do it.

Also it coasted the same 8" in reverse.   G