SOLVED 9/02/2022: PS 3 powered locomotive abruptly stops and restarts after 3 minutes running

I’ve never been inside a Koh’s & Company anything, …..too rich for my blood, ….but nonetheless, how is this engine powered by Kohs?…..I see in your write up that this engine was converted in 2019, but that don’t really mean a hill of beans if it’s been a ticking time bomb waiting for 2022 to go off……I’d check mechanicals first, then disconnect the motor(s) from the board set and test them individually. Find out the max amp draw testing the motors on a straight power source,…..somebody might be able to note on here the max draw that board set can handle before it goes wonky……if your locomotive creeps up on or exceeds the allowable amperage being run on straight power, , then it’s game, set, match, time for plan B ……

Pat

Pat

Thanks for your input!  And I am glad you recalled my article!

The "roller test" I did (as cited in my original post) tells me there is nothing funky with the motors, the wiring, or the mechanicals.  I should have also mentionned in my original post that nothing felt warm during the roller test.

But your comment about "somebody might be able to note on here the max draw that board set can handle before it goes wonky" is why I asked the question if the PS 3 board can handle a motor drive of 1.4 Amps. If I am indeed exceeding the limits of the board, than that's the time bomb you have referred to. But if the board capability is more than that, then it would suggest something else is going on

@John Sethian posted:

Pat

Thanks for your input!  And I am glad you recalled my article!

The "roller test" I did (as cited in my original post) tells me there is nothing funky with the motors, the wiring, or the mechanicals.  I should have also mentionned in my original post that nothing felt warm during the roller test.

But your comment about "somebody might be able to note on here the max draw that board set can handle before it goes wonky" is why I asked the question if the PS 3 board can handle a motor drive of 1.4 Amps. If I am indeed exceeding the limits of the board, than that's the time bomb you have referred to. But if the board capability is more than that, then it would suggest something else is going on

How is that chassis powered/driven?…..what motor(s)?….what’s the drivetrain makeup?

Pat

@harmonyards posted:

How is that chassis powered/driven?…..what motor(s)?….what’s the drivetrain makeup?

Pat

Chassis powered by two Pitmann Series 9000 motors one at each end.  Each motor drives a gearbox that powers three axles through worm gears.   There are ball bearings everywhere. The photos below show the arrangement

Here are the specs on the motors, third column over for 12 volt

Since I was not running anywhere near maxium torque in any of my tests, the current I measured for two motors is consistent with the above

I just ran a similar running test with an MTH FM Train Master with PS 3.  Using the same protocols, the motor current draw was only .80 Amps. So I may indeed be up against a PS 3 current limit. But I'd like confirmation of that before changing to more efficient motors.

Thanks again

Ain’t gonna be the motors that are the problem, ….doubt you’ll get any more efficient than the Pittmans it came with……what I see is just ALOT happening under the hood of that GG1!…..don’t get me wrong, it’s a work of art,…even though they’re smaller Pittmans, I’d be willing to bet the 2 are kinda amp hungry given all the machinery that shaft has to go through to transmit power to the wheel sets…..correct me if I’m wrong, but all PS2 or 3 diesels and or electrics that are double motored, are powered by two small Mubachis …..not two honking Pittmans driven through an entire planetary gear arrangement…..😁

Pat

WOW!  I never saw that kind of complexity, that sucker should be a real stump puller!  The PS/3 board should be able to deliver more than 1.4 amps, but then we don't know what's happening with it's on the rails and running.  Pat is right, the MTH GG1 has two 3xx series Mabuchi motors, and they don't have that tortuous path to get to the wheels!

“Since I was not running anywhere near maxium torque in any of my tests, the current I measured for two motors is consistent with the above”

the motors aren’t running out of their intended specs, but I do believe the board set can’t deliver what the motors want via what the tach sensor is telling the board set to do …..the tach sensor doesn’t care if the board set eats itself alive trying to feed two grown adults vs. two small children…..all it knows is more, more, more….meanwhile, the board set is just like Scotty on Star Trek, …..” I’ve given er all she’s got Captain!” …”She’s gonna shake herself to pieces!” ….

Pat

You could very well be correct about the planetary gear arrangement, so I need to look into that.  Incidentally, these are not the motors it came with...those were even longer 9000 series motors.    I also think they are overkill for this (to give Kohs bragging rights, no doubt).   I am sure there are mor efficient motors out there

And you are correct about the MTH set ups.

Again though, I'd like to know the current spec on that PS3 motor drive. Anyone else know?  My tests show 0.64 Amps should be good.

And for that matter, I'd like to know what is actually happening!

@John Sethian posted:

You could very well be correct about the planetary gear arrangement, so I need to look into that.  Incidentally, these are not the motors it came with...those were even longer 9000 series motors.    I also think they are overkill for this (to give Kohs bragging rights, no doubt).   I am sure there are mor efficient motors out there

And you are correct about the MTH set ups.

Again though, I'd like to know the current spec on that PS3 motor drive. Anyone else know?  My tests show 0.64 Amps should be good.

How exactly are you concluding actual motor consumption being delivered via the driver portion of the board set?……and can you conclude consumption (amps) when the locomotive is on your layout at the point of failure?……you’d have to correct me if I’m wrong, but if you’re pulling your amp readings from the AC output, ie; reading it from the rails, that’s a different deal than what’s happening between the driver and the DC motors….in other words, the board set might be consuming what’s considered tolerable, but what’s happening between the driver and the motors might not be,……

Pat

@harmonyards posted:

How exactly are you concluding actual motor consumption being delivered via the driver portion of the board set?……and can you conclude consumption (amps) when the locomotive is on your layout at the point of failure?……you’d have to correct me if I’m wrong, but if you’re pulling your amp readings from the AC output, ie; reading it from the rails, that’s a different deal than what’s happening between the driver and the DC motors….in other words, the board set might be consuming what’s considered tolerable, but what’s happening between the driver and the motors might not be,……

Pat

Measuring the current input into the TIU with the motors running and not running, then subtracting the difference.  Unless there are current  multipliers or transformers in the PS 3 board, the RMS current should be continuous. As a check,  the current I got with the roller test where the meter was in one of the leads to the rollers, matched the current input to the TIU.

@John Sethian posted:

Assuming current is continuous.  Are there current  multipliers or transformers in the PS 3 board?   The current I got with the roller test where the meter was in one of the leads to the rollers, mactched the current input to the TIU.

Wellllllllllllll,……it’s not 100% conclusive of what’s actually happening between the driver and the motors, …yes, it’s continuous, but reading the amps on the outside doesn’t really tell us what’s happening on the inside ….( per say )  …..we know the motors are hungry, ….they have to be with all that motion happening….and we know you’re going into fault. So rather than trying to figure out a mathematical ah-ha ….can you perform a couple tests?…is there any way to uncouple one motor, and make that truck in sense a dummy with out having a baby??…or is that gear train just so complex you’d need a degree in Astro Physics to pull it off?….also, I see what looks like two huge weights??…are they super heavy?…does that engine weigh as much as a real GG1 ( I mean we are talking Kohs here) so can we take things away and perform another running test to determine if we’re on the right path??…..it might be too late for the board set, but nothing beats a try but a fail,….If you can run on one motor, and it’s successful, maybe an option ( If space is available) is to add a second board and treat the one engine like a lash up, or maybe John or George could suggest some sort of slave option??…I don’t know 100% but my mind says those two motors just have alot to do and the board set finally said enough is enough…..😉

Pat

@gunrunnerjohn posted:

WOW!  I never saw that kind of complexity, that sucker should be a real stump puller!  The PS/3 board should be able to deliver more than 1.4 amps, but then we don't know what's happening with it's on the rails and running.  Pat is right, the MTH GG1 has two 3xx series Mabuchi motors, and they don't have that tortuous path to get to the wheels!

Thanks John! That current limit is exactly what I need! 

I am not sure this is as tortuous a path as you two think it is. I am not sure there are planetry gears in that tower.  The overall ratio between motor and drive  shaft is 0.875:1.  So I think there are probably just spur gears.  In which case it's a common O scale drive system to have a tower drive from motor shaft to drive shaft, and then a worm gear boxes to transmit the power to each axle.   Think Sunset with spur gears replacing the belt drive.

I have other more efficient motors on hand, which can provide the same torque at 2/3 the current. But if John's limit (and my mesaurement technique)  is correct, I should not be having problems with what I have  So, I can measure the current directly to one of the motors with the roller test. That should answer Pat's concerns. I will report back. Probably won't happen until tomorrow.

@John Sethian posted:

You could very well be correct about the planetary gear arrangement, so I need to look into that.  Incidentally, these are not the motors it came with...those were even longer 9000 series motors.    I also think they are overkill for this (to give Kohs bragging rights, no doubt).   I am sure there are mor efficient motors out there

And you are correct about the MTH set ups.

Again though, I'd like to know the current spec on that PS3 motor drive. Anyone else know?  My tests show 0.64 Amps should be good.

And for that matter, I'd like to know what is actually happening!

How did they fit longer 9000’s in there?…..the stubby motors already look like they’re at the space limits now, ……what’s the full Pittman model number of the OE motors?…do you have that handy?….and why go to the stubby motors in the first place?…what was the criteria for going backwards in motor size?….

Pat

I'm only adding one cent here and I only glanced over your issue.

Obviously there are factors that change what the board can do. If you ran at lower track voltage for example, or if something isn't providing full power to the board, I'd guess that would seem like the board would handle less.

I believe these PS3 boards handle good loads. I have them in other brand one gauge engines that are power hogs without issue.

I had a one gauge engine that had a power path burn out. It was a printed circuit board that carried power from wheel pickups and the actual printed path was burned so that was one less point of power. That engine did not run right until I fixed it.

Of course none of this may apply, I'm only throwing something at you to consider looking at everything.

I've seen MTH board equipped engines stall because the tach didn't get the expected response from the motors. I've had chaffed wires rubbing the frames. Even a missing insulator inside a truck power point causing havoc. An old PS1 Allegheny I upgraded, had an intermittent short from a protrusion touching a smoke unit power pad. Took me near a year to finally find that one. It only occurred on certain turns or shell twists.

I will watch this thread and try to stay out of the way. Good luck and I will try and help with the little I can add.

In response to Pat’s concern that I may not be measuring the motor current properly, I added a current meter to the leads to one of the motors:

The meter on the right (set at AC) measures the current to the TIU, the meter on the left (set at DC) measures the current to the front motor. To keep things unambiguous, the rear motor is out of the circuit.  The meter on the right stabilizes at 0.620 Amps

Note this is a roller test

This is what I got

SMPH   One Motor         TIU          TIU (adjusted)

0            0                    .620                    0       

15          0.57             .844                  ,224

20          0.60             .902                  .280

25          0.64             .954                  .334

30         0.68             .975                  .350

35          0.70             1.02                  .400

It appears that measuring the current through the TIU is not an accurate way to measure the current through the motor (Thanks Pat) AND at 35 SMPH on rollers I am right at the limit that GRG cited (0.70 x 2 = 1.4 A), so that explains why I had the drop outs when running on the layout.

As I said in a previous post, I have other motors I can try.

@harmonyards posted:

How did they fit longer 9000’s in there?…..the stubby motors already look like they’re at the space limits now, ……what’s the full Pittman model number of the OE motors?…do you have that handy?….and why go to the stubby motors in the first place?…what was the criteria for going backwards in motor size?….

Pat

Yes.  In order to fit the longer OEM 9434 motors, Kohs had to resort to a "Unique soft universal joint"  which was two discs which engaged each other via nylon pegs. A conventional U joint would not have fit

As you can see above, these pegs break easily.  (Which by the way, is how I got this thing so inexpensively).  Going to a 9232 Pittman allowed me to use a more conventional universal joint:

Given the fact that the motors are driven using PWM, you may not be getting an accurate reading as well.

@John Sethian posted:

Going to a 9232 Pittman allowed me to use a more conventional universal joint:

Have you seen the drive shafts that Pat uses on his Pittman upgrades?  They come in all lengths, and are really a major upgrade from the cheesy dogbone U-Joints.

@gunrunnerjohn posted:

Given the fact that the motors are driven using PWM, you may not be getting an accurate reading as well.

It’d be nice to know the amp draw of the two combined motors without the PS3 board set in play,  …..maybe via a simple rectifier set up, or straight DC track power, and then determine consumption requirements under load on his layout, ….no??

Pat

@harmonyards posted:

It’d be nice to know the amp draw of the two combined motors without the PS3 board set in play,  …..maybe via a simple rectifier set up, or straight DC track power, and then determine consumption requirements under load on his layout, ….no??

Pat

That would be a good approach, set the DC meter on the chassis and run it around and see what the current draw is.  Probably even easier to use DC on the tracks and just measure the current.

Wow, very impressive analysis by the genius train doctors who have posted their brilliant comments above.

Bravo, I hope you fix it! Arnoldo

@gunrunnerjohn posted:

Given the fact that the motors are driven using PWM, you may not be getting an accurate reading as well.

That's why I originally measured just the AC input. I know what the Fluke's algorithms are for a simple 60 Hz sinusoidal waveform.   I don't know how it interprets a pulse width modulation waveform

As for rewiring to work on straight DC and measure that current..  I am not up for doing a science experiment here, and I am not sure it will give useful information anyway. Other motors have a higher Nm/A  (torque per amp), so that seems to me to be the most expedient approach.

Besides John, I remind you of your tagline

@John Sethian posted:

In response to Pat’s concern that I may not be measuring the motor current properly, I added a current meter to the leads to one of the motors:

The meter on the right (set at AC) measures the current to the TIU, the meter on the left (set at DC) measures the current to the front motor. To keep things unambiguous, the rear motor is out of the circuit.  The meter on the right stabilizes at 0.620 Amps

Note this is a roller test

This is what I got

SMPH   One Motor         TIU          TIU (adjusted)

0            0                    .620                    0      

15          0.57             .844                  ,224

20          0.60             .902                  .280

25          0.64             .954                  .334

30         0.68             .975                  .350

35          0.70             1.02                  .400

It appears that measuring the current through the TIU is not an accurate way to measure the current through the motor (Thanks Pat) AND at 35 SMPH on rollers I am right at the limit that GRG cited (0.70 x 2 = 1.4 A), so that explains why I had the drop outs when running on the layout.

As I said in a previous post, I have other motors I can try.

I wasn’t trying to be condescending, let me be clear on that, ….John put it in better terms than I did….beings it’s PWM driven, the meter readings ain’t exactly true …is there anyway you can simply disconnect the entire PS3 board set and rev this guy up on a rectifier, or straight DC power?….with both motors parallel?…thats will tell the true story of the amp consumption by both motors,….beings the board set is constantly adding or subtracting voltage ( in an attempt to cruise ) your Fluke can’t take this into account, …Id think your meter is seeing some float, because by your numbers, everything seems honky dory …..I’ve built a lot of large heavy articulated steamers with gigantic Pittmans, and believe me, id be ok with 1.4 amps raw ( that’s pulling a train BTW) ……most big straight frame engines ( 4-8-2s, 4-8-4’s etc, etc,.) with large 9400’s singles I try to get well below an amp before sending them down the road to have electronics added, ….but I do my testing long before the package is added, …..I use my Z4000’s amp meter as a start, but I back it up with my Fluke, cause Z4000’s can be known pathological liars…I can’t say for sure, but my gut is telling me your Kohs with two Pittmans and a dizzying array of drive train might be tugging closer to 2 amps, or even above ….and that might be too much for the PS3 to handle under load…..

Pat

So in simpler terms, no, I don’t think you’re reading them wrong at all, ….I think you’re being lied to,….being bamboozled, ….led down the brim rose path,….🤣🤣🤣🤣🤣

Pat

@John Sethian posted:

Besides John, I remind you of your tagline

Sure, but I don't have the problem!

@John Sethian posted:

That's why I originally measured just the AC input. I know what the Fluke's algorithms are for a simple 60 Hz sinusoidal waveform.   I don't know how it interprets a pulse width modulation waveform

As for rewiring to work on straight DC and measure that current..  I am not up for doing a science experiment here, and I am not sure it will give useful information anyway. Other motors have a higher Nm/A  (torque per amp), so that seems to me to be the most expedient approach.

Besides John, I remind you of your tagline

A rectifier is 4 wires …6 in your case,….swapping motors is gut the tool box time ….I’d opt for the easier approach…..this will tell the story for sure…..tossing motors at it in hopes of a solution seems like dart board diagnostics…….especially given the testing you’ve already gone through…..

Pat

1.1 to 1.4 A on straight DC

Voltage 10.4 Volts

Power: MRC Pure Power DC

Pickup wires go directly to the motors

PS3 board completely disconnected

Current and voltage measured with Fluke digital Multimeters at the power supply

Loco orbiting the track, no train per previous tests

           25 laps

           10 minutes continuous, no incidents

           Estimate 70 SMPH based on lap times

           This is twice as fast as previous tests in which halts were observed after 3 minutes

           Its also much faster than I would run a train

Conclusion?  (I have my own thoughts, but I shall await input from others)

@John Sethian posted:

1.1 to 1.4 A on straight DC

Voltage 10.4 Volts

Power: MRC Pure Power DC

Pickup wires go directly to the motors

PS3 board completely disconnected

Current and voltage measured with Fluke digital Multimeters at the power supply

Loco orbiting the track, no train per previous tests

           25 laps

           10 minutes continuous, no incidents

           Estimate 70 SMPH based on lap times

           This is twice as fast as previous tests in which halts were observed after 3 minutes

           Its also much faster than I would run a train

Conclusion?  (I have my own thoughts, but I shall await input from others)

Well now you know what the real draw is, ….1.1-1.4 shouldn’t have killed the PS3 board,…those are numbers I ship off custom builds to have electronics added with no fears,…..so you’re not seeing any spikes, any lurching, motors are fairly cool to the touch after 25 laps?…I have no clue how big your layout is, but I go by time, not laps made….I see you went 10 minutes, so if there was something going askew, I’d expect to see it happen within that time frame…..SO before you go bananas ripping out motors, reach out to GGG ( George ) …..his email is in his profile, ….George can do component level repair to those boards when it’s possible…..I don’t know if John does or not, so I’ll let him defer it back to George, or himself if he wants….I’d let George take a look at the board, and see if he can breathe life back into it….those amp draws on that engine with two Pittmans, going through all that rotating mass is way better than I would think……..I surely wouldn’t be doing motor swaps at those numbers…..I doubt you can clean it up much better than that,…..BUT since you’ve got it running on DC, pull your train and THEN let’s see your numbers…….the numbers I quoted you on my builds, are same as yours, but pulling 35 scale freight cars for hours…..😉

Pat

@harmonyards posted:

Well now you know what the real draw is, ….1.1-1.4 shouldn’t have killed the PS3 board,…

GOOD TO HEAR!

those are numbers I ship off custom builds to have electronics added with no fears,…..so you’re not seeing any spikes, any lurching, motors are fairly cool to the touch after 25 laps?…

NOTHING.   VERY SMOOTH RUNNING,  MOTORS COOL

I have no clue how big your layout is,

115 feet per lap

but I go by time, not laps made….I see you went 10 minutes, so if there was something going askew, I’d expect to see it happen within that time frame…

TWICE THE SPEED, FOUR TO FIVE TIMES THE DURATION THAN WHEN FAILURE MODES OCCURRED BEFORE

..SO before you go bananas ripping out motors, reach out to GGG ( George ) …..his email is in his profile, ….George can do component level repair to those boards when it’s possible…

YOU WILL RECALL MY ORIGINAL POST WHERE I ASKED IF COMPONENTS CAN BE REPLACED/REPAIRED.

..I don’t know if John does or not, so I’ll let him defer it back to George, or himself if he wants…

I'LL WAIT FOR JOHN TO REPLY BEFORE REACHING OUT TO GEORGE

.I’d let George take a look at the board, and see if he can breathe life back into it….those amp draws on that engine with two Pittmans, going through all that rotating mass is way better than I would think…

AS IS SAID ABOVE, THAT IS A PRETTY COMMON DRIVE TRAIN FOR 2 RAIL O SCALE.  THAT IS HOW THEY GET SUCH SMOOTH RUNNING LOCOMOTIVES.  A LOT OF THEM HAVE HO SCALE DCC DECODERS IN THEM, SO CURRENT DRAW HAS GOT TO BE SUB 1.5 AMPS

…..I surely wouldn’t be doing motor swaps at those numbers….

I WILL WAIT TO SEE WHAT JOHN/GEORGE SAY FIRST.

.I doubt you can clean it up much better than that,…..BUT since you’ve got it running on DC, pull your train and THEN let’s see your numbers……

I KNEW YOU WOULD ASK THAT!  THE ONLY THING I COULD EASILY ADD ARE PASSENGER CARS, BUT I DIDN'T WANT TO COMPLICATE THE MEASUREMENTS WITH LIT CARS  (YES, I KNOW HOW TO SUBTRACT, BUT ....)  WHAT I DID WAS SUCH AN OVER TEST IN SPEED AND TIME COMPARED TO WHEN THE FAULT WAS OBSERVED, THAT I DON"T THERE IS A PROBLEM WITH THE MOTORS OR DRIVE.   

.the numbers I quoted you on my builds, are same as yours, but pulling 35 scale freight cars for hours…..😉

UNDERSTOOD

Pat

THANKS AGAIN!

JOHN

MTH one scale that use larger motor have the rectifier heat sunk.  In addition, when they used PS-32 board they added brass heat sink to the motor fets.  PS-3 boards do a have a temp thermistor sensor that will kill power if temp gets too high and it is possible the Flash code may have a temp setting.

A lot of info to read above.  Are you saying this worked fine since 2019 and just started to act up?  If the engine stop but lights and sounds remain on, and you have control which I think you said you do, then the board still has power and I believe the motor fets are overheating, or some component related to motor operating.  That is shutting down the motor and you get the abrupt stop.  G 

Maybe George can take a look at your board, and build it with a little overkill, …add the one scale heat sinks??..and set up a better flash code??…as I recall you did harvest this set up from a Railking engine, so it’s possible what George says rings true ……all the way back to the beginning when we mentioned this might’ve been a ticking time bomb, ….waiting for 2022 to go off!….😁

Pat

I like the idea of "hardening" the PS 3 board!

@John Sethian posted:

I like the idea of "hardening" the PS 3 board!

Click on GGG’s profile and send him an email, he will steer you in the right direction with the board set……George does all of my PS boards….always perfect!…

Pat

Sent GGG an e-mail as soon as I saw his post!

All good stuff here with all of my favorite O scale team members!

I’m following.

- Mario

Nothing is so easy as the job you imagine someone else doing!  Thanks Pat. I can't "harden" the board and the problem is if this worked for a few years, then something happened to the board.  I can test board but chances it will run fine on a test unit which only uses a single HO motor.

I would transplant the board into a MTH PS-3 engine and see how it behaves.  If it runs fine the issue is those 2 big motors.  If it behaves poorly even in a MTH engine, the board did get damaged.  You could solder a test bulb to the DC output of the rectifier.  This is primary PV for the Motors.  Run it.  When it stops see if the bulb goes out.  If it does that mean the Rectifier stopped rectifying.  But more likely is heat generation around the motor fets.  The current draw does not seem excessive, but they put a thermistor in there for a reason, so I assume there is some limitation.  Additionally, only one of the motor fets drive the motor, the other is in there for some fully unexplained reason (when I asked years ago).  Something about controlling heat in the motor drive circuit.

I am out of diesel boards and used up my G scale PS-32 boards.  Which would not be a good fit anyway since they drive bulbs not LEDs and the whole upgrade would need to be modified.  G

Thanks G.  I shall explore my options accordingly

@GGG posted:

Nothing is so easy as the job you imagine someone else doing!  Thanks Pat. I can't "harden" the board and the problem is if this worked for a few years, then something happened to the board.  I can test board but chances it will run fine on a test unit which only uses a single HO motor.

I would transplant the board into a MTH PS-3 engine and see how it behaves.  If it runs fine the issue is those 2 big motors.  If it behaves poorly even in a MTH engine, the board did get damaged.  You could solder a test bulb to the DC output of the rectifier.  This is primary PV for the Motors.  Run it.  When it stops see if the bulb goes out.  If it does that mean the Rectifier stopped rectifying.  But more likely is heat generation around the motor fets.  The current draw does not seem excessive, but they put a thermistor in there for a reason, so I assume there is some limitation.  Additionally, only one of the motor fets drive the motor, the other is in there for some fully unexplained reason (when I asked years ago).  Something about controlling heat in the motor drive circuit.

I am out of diesel boards and used up my G scale PS-32 boards.  Which would not be a good fit anyway since they drive bulbs not LEDs and the whole upgrade would need to be modified.  G

I distinctly used the words “maybe” and “ when possible” ……pretty sure I didn’t commit you to anything!……😉…..or at least I didn’t mean to commit you!…

Pat

John, I just remembered I have small 25mm square 12VDC fans that I bought to keep on hand for just such an occasion of overheating electronics and/or spinning diesel fans. If you want a few I can send you some.

- Mario

Mario

Thanks! I may call on you for these.

In the meantime I have established the board is OK, and that the GG1 won't pull squat with only one motor driving one truck, and the other truck totally free wheeling.   I have also established the Kohs pickups are quite a drag.  And they are on both sides.  Not a good design.  I partially addressed that, and improved the run time.

I am currently pursuing two options

1)  Go to more efficient motors (my original course).   My goal is to get below 1 Amp, where I know it will run for a long time.

2)  Put a second PS 3 board to drive the second motor and run the whole thing as a Lash Up. Per Pat's suggestion. Space is a challenge, but we'll see

Your fan gives me a third.

Incidentally, I considered dunking the board in a thick copper mini bath tube of fluorinert.

https://www.3m.com/3M/en_US/p/d/b40045180/

Would have solved the problem.  But sealing against leaks would have been a challenge.

John

I'd be looking for more efficient motors, but I'd think the Pittman's would be pretty good.

Have you considered dropping in a different PS/2 or PS3/2 board and seeing if it is actually the motors?  FWIW, the PS/2 board or the PS3/2 board shouldn't have an issue with a couple of amps to the motors.

@gunrunnerjohn posted:

I'd be looking for more efficient motors, but I'd think the Pittman's would be pretty good.

Have you considered dropping in a different PS/2 or PS3/2 board and seeing if it is actually the motors?  FWIW, the PS/2 board or the PS3/2 board shouldn't have an issue with a couple of amps to the motors.

Yes.   I don't want to risk trashing a second board!   I'll make this thing as efficient as I can first!

@John Sethian posted:

Mario

Thanks! I may call on you for these.

In the meantime I have established the board is OK, and that the GG1 won't pull squat with only one motor driving one truck, and the other truck totally free wheeling.   I have also established the Kohs pickups are quite a drag.  And they are on both sides.  Not a good design.  I partially addressed that, and improved the run time.

I am currently pursuing two options

1)  Go to more efficient motors (my original course).   My goal is to get below 1 Amp, where I know it will run for a long time.

2)  Put a second PS 3 board to drive the second motor and run the whole thing as a Lash Up. Per Pat's suggestion. Space is a challenge, but we'll see

Your fan gives me a third.

Incidentally, I considered dunking the board in a thick copper mini bath tube of fluorinert.

https://www.3m.com/3M/en_US/p/d/b40045180/

Would have solved the problem.  But sealing against leaks would have been a challenge.

John

I wouldn’t say a third option; more like a 1b and 2b.  Either way, they wouldn’t hurt. I’d say power them off a unused lighting feed off the PS3 board.  Cab light perhaps?

@CentralFan1976 posted:

I wouldn’t say a third option; more like a 1b and 2b.  Either way, they wouldn’t hurt. I’d say power them off a unused lighting feed off the PS3 board.  Cab light perhaps?

Like I said, an option on the table!

@John Sethian posted:

Yes.   

Yes to what?

@gunrunnerjohn posted:

Yes to what?

Yes I considered trying a new board, but I don't want to risk a brand new board. Unless, of course you'd like to give me one!

Well, if you could find one of the modified PS32 boards for one-gauge, those were beefed up with a heatsink on the motor driver FET, that would probably be one to try if you wanted to swap boards.

If you want to stick with the PS/2 board, adding a heatsink to the driver FET, even if you have to dispense with the plastic carrier, might be a smart move.  I'd also make sure the bridge rectifier has a GOOD heatsink, perhaps a custom one with a better bond to the chassis.  Those are the two high current critical components in the motor drive circuit.

Truthfully, I think just blowing air on it with a tiny fan is going to be a lot less effective than better heatsinking.  Adding the fan as well can't hurt...

@gunrunnerjohn posted:

Well, if you could find one of the modified PS32 boards for one-gauge, those were beefed up with a heatsink on the motor driver FET, that would probably be one to try if you wanted to swap boards.

Not a first choice, as I could not find one, AND I would have to change all the lights

If you want to stick with the PS/2 board, adding a heatsink to the driver FET,

Could I prevail upon you to show me where the driver FET is?

even if you have to dispense with the plastic carrier, might be a smart move.

I had actually considered that, but need to know where the critical components are to make sure I have decent high thermal conductivity path

I'd also make sure the bridge rectifier has a GOOD heatsink, perhaps a custom one with a better bond to the chassis.

Same request about the bridge rectifier

Those are the two high current critical components in the motor drive circuit.

Thanks in advance!

Truthfully, I think just blowing air on it with a tiny fan is going to be a lot less effective than better heatsinking.  Adding the fan as well can't hurt...

Here's the motor driver FET.

A 1mm thick copper strip soldered along this edge and folded under the PCB (with some Kapton tape to insulate the board), would be good.

Can't miss the bridge, it's the big flat component that already has a heatsink.  My point is making that heatsink better as leakage through the bridge when it gets hot can compromise the motor driver FET.

Thank you!

Note that soldering to the tab of the FET is a fairly delicate balance of enough heat to do the job, but not too much as to kill the FET.

You may be better off using thermal epoxy and gluing a large heatsink on the FET instead of trying to solder to the FET.  It's not as effective, but it's much easier to do without killing the board.

@gunrunnerjohn posted:

You may be better off using thermal epoxy and gluing a large heatsink on the FET instead of trying to solder to the FET.  It's not as effective, but it's much easier to do without killing the board.

I’d check to see if it’s tab is soldered to the board, and if it is, see if they’re using thermal vias to get the heat to the bottom of the PCB. If it’s not soldered, then I’d try bending the legs up and get it to stand and then you could attach a larger heat sink to it. I wrote a paper based on lab work I did soldering these to heat sinks for Rockford Fosgate way back in 06, before they moved production out of Arizona. They were driving so much power through there that they used tin plated copper bus bars as heat sinks. I’ll see if I could dig up my presentation. As for the bridge, last build I did I mounted the board upside down and used thermal tape to use the frame as the heat sink. Good times.
- Mario

@CentralFan1976 posted:

I’d check to see if it’s tab is soldered to the board, and if it is, see if they’re using thermal vias to get the heat to the bottom of the PCB. If it’s not soldered, then I’d try bending the legs up and get it to stand and then you could attach a larger heat sink to it.

It's clearly soldered to the board, it's a D-PAK surface mount part.  The only connection to the center pin is the pad.

@gunrunnerjohn posted:

It's clearly soldered to the board, it's a D-PAK surface mount part.  The only connection to the center pin is the pad.

Here's some of the report...

Ahhh... the good old days.

Thanks!

- Mario

I eliminated the stop/start cycling of my dual Pittman driven Kohs GG1 by enhancing the cooling to the PS3 circuit board.  It now runs for at least 20 minutes (whereas it used to run only 2-3) and pulling more passenger cars. I have no reason to believe it could not run much longer

The enhanced cooling was accomplished with the following

1. Raised the PS3 board, and opened up both the plastic carrier board and the brass mounting plate so air can flow freely underneath the board
2. Added commercial finned heat sinks to the two FETs under the board and to the bridge rectifier aluminum heat sink.  These were attached using Thermattach: an aluminum mesh with an adhesive applied to both side.
3. Re-applied thermal paste between the factory heat sink and the bridge rectifier, and improved the thermal connection of the heat sink to the chassis
4. Added twin miniature muffin fans to blow air onto the underside of the board, and specifically to the new FET heat sink.  (Thanks Mario for the idea!)

Details and photos to follow, so everyone will know

HOW I DID IT…….

I built this from the bottom up, so I started with the fans. The Kohs GG1 came with twin speakers sandwiched between the chassis and the interior floor.  Both are made from brass.  The speakers were too small and tinny, so I chucked them and used my own speakers mounted behind the grilles on the shell.

The fans I used were from Amazon:

Operating voltage: 5V Current: 0.2 A

• Brushless DC fan
• Fan dimensions: 30mm x 30mm x 8mm
• Adafruit 4468
• UNSPSC Code 43201619

https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1

Here is what one looks like:

I bored out two 1 1/8” holes for the fans in the chassis, using a hole saw and a 3/8” chuck adapter for my precision drill press:

If you look through the sawdust (which came from drilling into the underlying wood support I needed to hold this chassis) you can see the original speaker holes. Everything cleaned up rather nicely, but I painted the chassis with VHT Satin paint just so it looks nice.   Here is the chassis all cleaned up with the holes for the fans in the floor.  You can see where the speaker holes were, and in some places they guided my drill to a different spot than I had intended:

Here the fans have been screwed in place. They fit in the location of the original speakers (which I could not use because they were the wrong impedance and fairly poor quality):

Here is the underside view of the floor.  Note I managed to keep the Kohs nameplate:

I cut a rectangular hole in the interior floor.  Those cylinders are tungsten weights added for traction. You can just see the cab seats at the extreme right and left of this photo

As you can tell, I ended up having to pull the outboard retaining screws for each fan, as they interfered with the truck rotation. At this point the running gear has been installed.  The green and white wires go the motors, the black and white wires that protrude through the two holes just below the fans go to the electrical pickups.

The good news is the fans only stick up about 1 mm above the false floor, so I am not compromised for height.

I installed the brass mounting plate for the PS3 board on the chassis with four aluminum stand offs.  The mounting plate is about 0.150” above the fans

The brass plate has been hollowed out to allow the free flow of air. I used NT-H1 Thermal Paste at both ends of the vertical standoffs, and I cleaned the paint off the chassis underneath the standoffs. Anything to encourage heat to leave the boar

In this photo the plastic carrier board has been installed on the brass mounting plate.  I cut out most of the cross supports in the carrier board to encourage air flow.  I later even cut out the bar at the left end, and replaced it with a .040" Phosphor Bronze wire  The green and white wires are from motors, black and white from the pickups, and the red and white are for fans:

This is the underside of PS3 Board.  The two large square black units, Q201 and Q 309, are the FETS which will get the heat sink

I applied Kapton tape over the components next to the FETS, so the heat sink can’t possibly short them out. It shouldn’t anyway, but no harm being sure

I used Thermattach #411 to make good contact between the FETs and the heat sinks. It is essentially an etched aluminum sheet with adhesive applied to both sides

It available from Digi Key.  This is what the Thermattach looks like.  In this photo one of the protective sheets has been removed, and the heat sink attached (DIGI-KEY #TGH-0220-04,  Aluminum Heat Sink 22 x 22 mm).  The heat sink has been trimmed to just cover the FETs and to clear the board carrier:

The Thermattach was trimmed to match the heat sink, the other protective sheet was removed, and then the heat sink attached to the FETs.

To encourage air from the fans to flow from right to left, I oriented the heat sink fins along the longitudinal axis.  In the photo above you can see the aforementioned Phosphor Bronze wire in place of the left hand slat.   Here is the board installed:

You can see the finned heat sink attached to the factory supplied rectifier heat sink.  This side view shows the fans and the FTE heat sink right above them.

Not the most optimal aerodynamically efficient design, I’ll admit.  But there should be enough airflow past the heat sinks…..

I had to install a main bus (made from two HO rails) to distribute AC power from the track:

Connections are (from left to right): harness to the number boards (they are always lit and powered by one of those John Will LED drivers), AC to the DCS board, AC to the fan driver circuits, and AC power from the track via the pickups.   Obviously with this arrangement the fans are on whenever track power is applied. But I did not want to draw any more current through the PS 3 components than needed.  Besides, the fans are designed to be on all the time.

This is the other side, showing the fan wiring.  Note the fan rectifier is attached directly to the chassis. Not that I expect any cooling issues with only 0.4 A going through it.  You can also see the buck convertor that drops the 18 Volts DC from the rectified track power down to the 5 Volts DC needed for the fans

And that’s about it.

I still need to put the shell on, but I don’t see any problems.  The Kohs has real photo etched cooing vents on both sides and both ends just like the real GG1, so there should be no problem getting the hot air out. If there is, I have two additional fans I can add to extract the air.

A few more notes:

1. Per my original thinking. I found two high efficiency Faulhaber motors and tried them out. The good news is they dropped the current by about 0.3 Amps.  The bad news, they are substantially lighter than the Pittmans (a full 5.2 oz), so I had to add weight back to the chassis to climb an uphill curve. Which, you guessed it, caused the draw to go right back up to within a statistically insignificant range of the Pittmans.
2. Readers may recall that the GG1 ran fine for several years,  and only recently started this stop/start cycling.  It was postulated that this may have been caused by the board going bad.  The real culprit is much simpler… I reversed the directions of my Sunset GG1-pulled Congo passenger train and this Kohs GG1 pulled passenger train. Running in this new “direction” the Kohs-pulled train had to traverse an uphill super elevated curve, whereas in the original direction the uphill was shallower and straight.
3. When I installed the fans I hoped they would be loud enough to give the GG1 the sound of real blowers.   No such luck. They are too quiet.
4. My sincere thanks to everyone who offered helpful suggestions, advice, and ideas in this thread.  Most notably
5. 1. Gunrunnerjohn
   2. GGG
   3. Harmonyards
   4. CentralFan1976
   5. Engineer-Joe

With that the saga ends, and I am ready to go on to less challenging problems.  Like developing a clean, plentiful, compact source of energy.

Seriously great work, John.

Irrelevant at this point since you solved the problem, but I'd think this would scare off anyone else thinking of using a PS2 or PS3 board to drive a non-MTH chassis.  I only scanned this thread and forgive me if I missed it, but I did not see discussion of the body-diode heat issue in the motor FETs.  That is, a motor current of 1 or 2 Amps should be NO SWEAT for the FETs MTH uses.  They are rated for tens of Amps!  How can they overheat with 1.4 Amps?

Answer: when pulsing FETs at high-frequency PWM like the PS2/3 boards, the so-called body-diode can actually warm up substantially since this diode turns on each motor pulse.  I'm not saying this is/was your problem, but I recall MTH modified the design of some higher power engines with an external body-diode.  Understood, this is techno-babble and has to do with the inductance of the motor windings and flyback energy in PWM circuits.  But when I read that this was being installed in a non-MTH motor chassis, the flag was thrown on the field.

Bottom line.  For the next guy looking at using a stock PS2 or PS3 board to drive a 3rd party motor/chassis, if you have a heat problem in the motor FET, consider using an external body-diode with lower power dissipation (such as a Schottky).  They are less than $1 and arguably less work than installing fans and heatsinks.

Another issue is the main bridge rectifier.  Many of the std-gauge engines use a tethered bridge to keep the diode bridge from overheating and causing excessive leakage which will kill the FET's.  Lots of early Legacy engines used a tethered bridge on the DCDS as well for the same reason.  Jon Z. mentioned this several times for the ERR products, he specifically told me that the limiting factor is usually the bridge rectifier.  I recently used the ERR Cruise Commander to drive the six motored K-line A-B-A set using a tethered bridge.  I used a 12A bridge and bolted it to the chassis for heatsinking, the FET heatsink on the Cruise Commander barely gets warm.

As I Remember from my experience over 30 years ago, Shottky diodes have a very low reverse voltage rating. In an application with 18 VAC and lots of transients, They may not survive. Be aware of the problem.

@gftiv posted:

As I Remember from my experience over 30 years ago, Shottky diodes have a very low reverse voltage rating. In an application with 18 VAC and lots of transients, They may not survive. Be aware of the problem.

Schottky diodes are available in higher voltage ranges nowadays, but they do still have lower reverse voltage ratings than traditional diodes.  Remember, Stan was talking about the internal Schottky diodes in the FET, so you're dealing with that limitation in any case.