9v motors slowing to a stop after 60 seconds

[Mr Hobbles]

Howdy! So I have a dozen or so 9v motors I use on an infrequent basis. I gave them a good run this evening, and a couple of them are behaving weirdly.

They run fine for about 30 seconds or so, but slowly they come to a crawl then eventually stop moving before 60 seconds is up. If I leave them for a couple of minutes, they start running as normal again, but then they slow down again over the minute again.

This happens whether or not they're running as motor-only or with a train behind them.

Secondly, if I hook up a 9v wire directly to the top of the motor and let it run in the air (ie. not on the track), this doesn't happen. They can go on and on at all types of speeds.

Any thoughts what might be wrong with them? Thanks

[XG BC]

maybe the termal fuse is dead if they have that?

[supertruper1988]

6 hours ago, Mr Hobbles said:

Howdy! So I have a dozen or so 9v motors I use on an infrequent basis. I gave them a good run this evening, and a couple of them are behaving weirdly.

They run fine for about 30 seconds or so, but slowly they come to a crawl then eventually stop moving before 60 seconds is up. If I leave them for a couple of minutes, they start running as normal again, but then they slow down again over the minute again.

This happens whether or not they're running as motor-only or with a train behind them.

Secondly, if I hook up a 9v wire directly to the top of the motor and let it run in the air (ie. not on the track), this doesn't happen. They can go on and on at all types of speeds.

Any thoughts what might be wrong with them? Thanks

As @XG BC said it is likely the thermal fuse. 

Running them without track put the motors in a "no-load" condition where the only friction seen by the motor is in the gears to make the wheels turn. Once it is on track the motor has a lot more load because it has to do work to move the train. 

Are your trains very heavy weight or very light weight? If they are heavy then its definitely a thermal issue. If they are very light weight, then it could be tripping the thermal fuse due to the wheels just spinning in place like a long burnout around the track.

[zephyr1934]

10 hours ago, Mr Hobbles said:

They run fine for about 30 seconds or so, but slowly they come to a crawl then eventually stop moving before 60 seconds is up. If I leave them for a couple of minutes, they start running as normal again, but then they slow down again over the minute again.

And you've ruled out dirty track or bad track connections on your loop, right? You mentioned that you had other motors, so if they run fine then that would be a good indicator that the track is not a factor. Alternately, if the motors always stop in the same place, I'd first check the track.

[Mr Hobbles]

Thanks for the replies!

2 hours ago, zephyr1934 said:

And you've ruled out dirty track or bad track connections on your loop, right? You mentioned that you had other motors, so if they run fine then that would be a good indicator that the track is not a factor. Alternately, if the motors always stop in the same place, I'd first check the track.

Yeah, I mean the track isn't super clean, but out of the 12 or so motors I have only 2 are experiencing the behaviour. The other 10 are clearly offspring of the Energizer bunny.

 

6 hours ago, supertruper1988 said:

Are your trains very heavy weight or very light weight? If they are heavy then its definitely a thermal issue. If they are very light weight, then it could be tripping the thermal fuse due to the wheels just spinning in place like a long burnout around the track.

Not super heavy, no. Metroliner + club car (but with Powered Up battery boxes inside for another purpose). But as I mentioned they also have this problem even when it's just the motor running on its own, with no train.

 

12 hours ago, XG BC said:

maybe the termal fuse is dead if they have that?

Thanks, so is the solution to remove the thermal fuse? I'm guessing there's no way to do that without cutting the tabs and cracking the motor open? :p

[XG BC]

2 hours ago, Mr Hobbles said:

 

Thanks, so is the solution to remove the thermal fuse? I'm guessing there's no way to do that without cutting the tabs and cracking the motor open? :p

not remove but rather replace. if you are removing it you are bridging over it which could lead to the motors dying if used in the wrong circumstances. and yes you have to crack the motor open to do so.

[Toastie]

1 hour ago, XG BC said:

not remove but rather replace. if you are removing it you are bridging over it which could lead to the motors dying if used in the wrong circumstances.

True.

But to be honest: I opened all my 9V motors, removed that naturally aging thermistor (PTC, the hotter, the higher the resistance), and run them simply without ever since. With no problems at all.  However, not with track voltage regulation, but with PF and PUp. 

What is helping is the electronic driver: Back then in the 9V days, a quite powerful voltage regulator (the black thing with the yellow dial) was doing the speed work. When you run your trains off from PWM modulated drivers (RCX, PF, PUp), it is >much< better with regard to overload, as these drivers have their own protection circuits. Not absolutely save, but much better.

Best,
Thorsten

 

[Mr Hobbles]

I tried something based on something you said @Toastie - hooked up my 9v power regulator to a PF IR receiver (via the empty battery box trick) and tried controlling the broken motors via an IR remote.

Guess what - no issues! They run beautifully (maybe 5% slower than the others?). I wonder why - is PWM a little kinder to these motors than the old-school 9v output directly from the regulator? I'm assuming the PF IR receiver is outputting PWM in this setup...?

Picture of setup - https://imgur.com/a/v1Xwxry (Control Lab 9v Output -> Empty PF Battery Box -> PF IR Receiver -> 9v Track)

Edited February 24, 2022 by Mr Hobbles

[dr_spock]

IR Receiver uses PWM. PWM pulses the motor instead of a steady voltage/current out of the 9V train regulator.  I think PWM would put less heat on the thermal fuse than a constant ON state of the regulator.

[Toastie]

47 minutes ago, Mr Hobbles said:

I'm assuming the PF IR receiver is outputting PWM in this setup...?

Yes it does; full DC for a period of time and then 0V for a period of time - depending on your power setting. Full fwd/bwd = 100% PWM duty cycle = full DC on the track (in your setup), as you know.

With focus on the no-load behavior (with load it - well - depends on the load and things are rendered less straight forward): When you go full fwd/bwd using the PF receiver, do the motors show the drop out behavior? Is it even possible to go to that level without derailing the motors all the time? Because at that level having the (constant) output of the 9V train regulator is the same as having the (constant) output on the PF receiver.

When you did not set PF to max. then indeed PWM may lead to a different response of the (still not good) thermistor (PTC). There are two things happening: motor temperature increase due to (unavoidable) resistive heating by the current flowing through the coils; and pulsed current flowing through the thermistor. If the thermistor has aged to a point, where "self-heating" (via P = I^2 x R within the PTC) and thus resistance increase via self-heating is > resistance increase via external temperature increase (the motor housing) than things become rather unpredictable. In other words: Your observation, that the bad motors run with less speed than the good ones, may be because of the aged PTC with an elevated resistance even when cold. When current begins to flow, both the PTC "by itself" and the motor heat up. Ideally you want a cold PTC resistance of 0 Ohm, which is not possible, but would lead to a self-heating of P = I^2 x 0 = 0). There is always a residual resistance in the PTC. The older they get, the larger that "cold state resistance" of the PTC increases. Up to the point that it heats itself up faster than the motor does.

And yes, PWM may help, depending on how much heat is dissipated when the PWM voltage is 0 and how much during full DC. Just on average, 1 sec x 9V + 1 sec x 0V is the same as 2 sec x 4.5V regarding power. But not with respect to power dissipation in the PTC.

Best regards,
Thorsten

       

Edited February 24, 2022 by Toastie