Best Dc Motor Controller

If you notice my South Bend lathe thread I just installed a KB SCR drive with braking and reverse. I was using the lathe last night and it works very well. It is only noisy when changing speed. I think this could be a problem on long facing cuts when I might change speed to maintain SFPM. I plan on keeping this controller for now and see how it goes. In the mean time I will look out for a deal on a PWM controller. I will certainly update this thread if I make any changes. I wonder if there would be interest in someone writing a tutorial on DC conversion in general as a reference?

The servo concept still intrugues me. Check this out!
Robert
 
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I like the KB units. I found a new old stock KBIC-125 on Ebay for around 15 bucks, blew the dust out of it, wound up a .035 ohm "horsepower" resistor for it and it works fine. DPDT switch motor leads for reverse (with power off) Yes they do make the motor hum a bit, but I think they are more reliable than the mosfet "treadmill" types. Certainly easier to troubleshoot and repair- simple op-amp feedback, no digital jazz, tried and true. Daytons are similar.
My 2 cents.
Mark S.

Yep. Older KBs on fleabay, cheap, bulletproof, good up to a horse or two. I have several.
 
I am still contemplating various designs. One thing I don't really have a handle on is rotary switches. Can someone help me understand them better? Take a standard 3 pole rotary with 3 positions. I get that each pole has a common terminal that can be connected to terminals on each side by moving the switch. But why are there two terminal connections on the common? i.e typically 2 and 4, 6 and 8, 10 and 12 are really the same terminal? Or do they disconnect when you turn the switch either way? In short, why does a 3 pole double throw center off switch end up with 12 terminals instead of 9? Anyone familiar?
Robert

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It varies depending on the brand and model. You're right, normally you expect 9 contacts but not always. It may be that each pole is actually 2 separate poles inside and they are tied together for extra current handling or reliability.
BTW I don't think you need (or want) to switch the neutral, I would just tie them all together. Just switch the hots. You don't want to compromise the neutral connection if the switch were to fail somehow.
Mark S.
 
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A lot of systems seem to switch the neutral also since it may not be at ground potential. There is no neutral in my 240v system anyway. I was just showing a common switch. I am trying to avoid separate switches for run/brake and forward/reverse with a braking resistor. I really need the resistor connected when the switch is in the center off position.
Robert

Edit: I guess I could do this with a 4 position 2 pole switch. Pos 0=off, Pos 1=forward, Pos 2=brake, Pos 3=reverse.
I would still like to know if 2,4 6,8 10,12 are always connected on the 3 pos switch.
 
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Only way to be sure is to ohm them out with a continuity tester or meter.
MS
 
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