BGM-100 not on a wheel grinder

[RickKrung]

The PSI motor controller is variable speed using a potentiometer (pot).  Steve Bottorff says the Viel with the PSI motor and smaller drive pulley runs at 1700 rpm.  I don't know the speed at the lower end, but it is not slow enough for me.  It happens that there are three tiny "pots" in the inside of the controller, on the circuit board, that control the top and lower end speeds.  This first photo shows where they are on the circuit board.


The second photo shows a close-up of the three pots, with letter labels, "L", "H" and "F".  I called PSI technical support and after being told my warranty was "blown up" due to having modified the controller by installing a reversing switch, then I was told what the three pots do.


L = Low end speed
H = High end speed
F = Frequency (I was told NOT to touch this one). 

I adjusted the low end pot when the motor was running in reverse, to as slow as it would run without faultering.  Switched it to forward and it hardly ran, faultering a lot.  So, I don't know why but it runs at quite different speeds on the lower end of the low end, depending on direction.  It works to just turn the main speed control knob up when switching to reverse.  I don't know how much this will matter, as I don't know what I'll try to do with it running in forward.  I also don't know how slow I need or want it in reverse, for sharpening knives.  I do know that it does go slow enough for anything I might want.

Rick

[Ken S]

Rick,
It has been quite a while since I checked my motor speeds. As I recall, I adjusted the slow speed (with the pot) to around 900 RPM. This makes a noticeable difference. I usually use the speed control knob around half.
As you have noted, just switching to the smaller drive pulley cuts the speed from 2700 RPM to 1800 RPM.

Ken

[RickKrung]

Rick,
It has been quite a while since I checked my motor speeds. As I recall, I adjusted the slow speed (with the pot) to around 900 RPM. This makes a noticeable difference. I usually use the speed control knob around half.
As you have noted, just switching to the smaller drive pulley cuts the speed from 2700 RPM to 1800 RPM.

Ken

Ken,

I find that a little curious.  When you say "with the pot", which one are your referring to? 

Are you saying that you use the primary (external) speed control set at around half and that you used the tiny internal "low" speed pot to adjust the lower end speed to around 900 rpm?  This seems incongruous. 

SteveB lists the top end at 1700 rpm.  Speed control set to about half should then be around 850 rpm, but that is hard to know as we don't know the wave form of the speed control pot (linear or tapered).  When setting up VFDs on my Rivett 1020, 6x26 vertical mill and a large Bridgeport vertical mill (not mine), I found the pots often had a very rapid speed increase near the bottom and a fairly slow speed increase over the upper range of pot rotation.  Frustrating. 

Do you mean to say that you adjusted the low end "tiny" pot in some way.  If so, how and what effect it has on the low end speed, on your machine, is unclear to me. 

I adjusted the low end pot to where the pulley turns very slowly, which on the order of 60-100 rpm.  Of course, if I want it faster during use, the primary speed control knob would be used. 

Rick