MC-60 PWM Controller Modifications

If the DC51 is a true SCR phase control with armature feedback (like the KB controllers) then it's a great deal. I suspect for that price though it may be a simple light dimmer type unit; the motor speed would change somewhat under varying loads
 
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Q. "will this motor controller start where you left the speed at or do you have to start from 0 and got to a setting?"

A (my response). Where the soft start has not been disabled on MC-60 controllers, I defeat the soft start by throwing a drum switch (you could just a dpdt switch instead) between the controller output and the motor. Drum switch allows for reversal of direction and has three positions as follows: R-N-F. When I stop using the lathe in the forward or reverse direction, I stop the lathe by shifting it into "N". Then when I start again, I merely shift the drum switch into "F" or "R" without having a soft start wait.
Just went out and checked the DC-51 I have. As it comes it turns the motor on at about 1/4 turn and works fine from a dead stop to full rpm. Set the speed at 50%, turned off the power switch and waited until the motor stopped and then turned it back on. It started and returned to the same rpm. Slowed it down to maybe 100rpm and did the same thing and it started ok and returned to the same rpm.
 
I also bought one of the DC51 controllers this week just to see if it would work. Wired it up to a 2 3/4hp (1.4hp @ 90v)TM motor and it worked perfect. Soft start is actually better than the MC60 that I have on my mill. Just wondering how long it will last. For $20 ( get a price break if you order more than one) its kind of a no brainer.
Over the past 2 or so years I have purchased and converted around 20 lathes, drill presses and bandsaws to dc motors using dc51 controllers. What I have learned is that they are not all created equal. I would say that around 50% work perfectly but the rest either do not work or do not produce enough torque at low speed to be useful. The suppliers have been very good at replacing (refunding) for the ones that do not work at all. Since they are only rated to 400 Watts, perhaps I have been expecting too much. However the fact that about half of them actually work well is an enigma that I have not yet been able to solve.

What I have done, is use the potentiometer and the box from the defective ones to house a mushroom cap switch and then wired the pot to an MC 60 like I have done here.
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The DC51 may not be well protected against inductive motor loads hence the reliability issues. They are probably intended more for resistive loads like lamps
But for the price they are a bargain even if half of them fail
 
You are correct in that they are a bargain except it would be nice to what is different between the ones that work and those that do not.

My theory is that they are just designed for smaller motors. 400 watts is about equal to 1/2 hp. At full speed there is certainly enough power but at low speeds, the voltage is as low as 10 or 20 volts, so it is difficult to develop enough power. That's my theory for the ones that do not work. The ones that actually work seem to adjust, drawing more amperage producing the power. I had one on a drill press that would actually blow a 15 amp breaker under a low speed load without bogging down the drill.

I have ordered one of the 800 - 1000 watt boards and look forward to seeing how this one performs.
 
Today my 800 - 1000 watt board arrived. It appears to be well made. However after I connected the ac power, motor cables and pot, all I got was a green light indicating that the board was hot. There is a j4 110 220 connector that I do not understand. Any suggestions? Thanks

In the item description is says "need to set j4 conversion"

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It sets your input voltage. If you power the board with 110 volts you would bridge the center pin and the 110v pin, if you are using 220 you would bridge it to the 220 pin.
My board came in the mail today also but I haven’t hooked it up yet.
 
Thanks! I didn't realize that there was a sleeve type connector involved. It came set for 220 and now it is set for 110. It works now and my first impression is that there is more torque than the dc 51's provide at slow speeds, but still not as much as an mc 60. This is just my impression based on how difficult it is to bog down the motor at a slow speed.
 
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While I don’t have an immediate need for it I’ll probably hook mine up this evening just to be sure it works.
 
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