Best way to slow a 9v motor down a little

[davidb_54]

Hello,
I am using a commercial quartz controlled 9v motor supplied with a very high ratio reduction gearbox giving with a potentiometer and some other stuff etc in the control circuit it comes with 1 rev per 11 mins at the gearbox output end on slowest pot setting.
This is JUST too fast for what I need to do.
What is the best way to slow the output down by about 10% without losing torque etc ??
the system works great with oits 9vPP3 battery, torque is very good, battery life 20 hours etc BUT iot is just a tiny bit too fast !!
very frustrating
any help much apptecieted
davidB

 

[sadams04]

How about building a 7.2v battery pack instead of using 9v?

 

[davidb_54]

Thanks for the suggestion.
Using the commercially available 9v duracell PP3 is by far the best and easiest for this application for me.
I feel that I need to reduce the voltage just a littlle bit more than the existing built in controller circuit (which comes with the motor/gearbox setup) , does.
I am not a electronics guy, just an astronomer with an electronic problem .......
the controll board has a couple of resistore, a big black square bug with multiple legs and what looks like a small potentiometer to vary the speed.
Could the pot be altered say by adding a furthur resistor across it and thus shifting the range of its adjustment ??
sorry if that is a silly queation !!

davidB

 

[Petrofsky]

Any specific information you can supply might make it possible for me to help you---manufacturer and model number for the controller, all numbers printed on the "bug", any writing or other symbols on the potentiometer, schematic, hi-res color photos of both sides of the PCB, etc. It having quartz in it means it uses a reference oscillator for speed regulation, so changing the supply voltage is not an option. It might be possible to change something to move the reference oscillator's frequency to where you want it, or it might be possible, as you suggest, to move the control voltage zeroing by changing a resistance in the divider.

 

[davidb_54]

Hi and thanks for your input
here are some images and the symbols on the individual components

the sole power to both motor and board is from a single 9vPP3
the motor does not slow down noticeably when running under load and battery is low, rather finally just stalls under load and stops, with the power light still illuminated
10uf & -25 volts on the round thing with a white top
so331 on the other black cylinder near the 8 pin IC
and on the IC
CHM
CM358N
KQF974
Thanks again for your time
davidB

 

[Petrofsky]

Those pics are nothing but thumbnails, but I was able to track you down over at allaboutcircuits and look at them there. Even those were blurry and small. I can see that there is a lot of stuff in the way preventing you from providing a picture of the trace side of the board, which makes my job here impossible, I'm afraid. Also, I agree with that other guy---I don't see a crystal, either. I was unable to find the CM358N online.

If you can see the other side of the board, see if there is a resistor to ground from one of the pins of the pot. Try soldering a same-ohm resistor across it to halve the resistance. If that doesn't do it, try replacing it with one double the value. If those changes change the motor speed, you could put a pot in place of the resistor of the appropriate value and use it to set zero. Stab in the dark.