I need some information on DC motor controls.
I got 3 controls that don't work. They are Dayton (Grainger) 2M171E controls for a 90 volt armature. They control speed and direction. The controls have 2 power SCRs and 2 power diodes in a bridge configuration. Several of the SCRs have broken leads (TO-220 packages and the leads broke at the entry into the epoxy).
The boards are relatively simple, with only one IC on it - an LM324, and one resistor array made by Dale, a bunch of various Rs and Cs and
4 other signal transistors and one programmable unijunction. I doubt either of these parts are bad. Also the boards show no signs of smoke or anyone screwing with them (thank God for that - 3 virgin boards). One unit has been somewhat cannibalized but not that badly. I can pick up the switch, pot and other minor stuff for it.I did talk with a tech service fella at Grainger who was quite willing to talk with me but he, also, didn't know anything about these SCRs. He did mention that the controls cost about $450 so they are worth fixing tho he did mention that that if the defect is in the high power control side of the circuit, the cost of repair might be prohibitive. As we talked, I did find out that he's a ham (so am I) and that I might be able to sub another SCR to make it work if he can't find out what generic part number it actually is. The part numbers on the SCRs are 'house numbers' (I hate that) so I will have to start with the manufacturer for them, unless a garden variety SCR will work without too much noticeable degradation. Get one of them running, I'll experiment with substitution on the others. The Grainger-ham told me who makes the control so that's progress and he's willing to query them on part numbers.
Opening the case, I found that there is a terminal strip marked for connecting to the armature and another one to connect to the field. Must be a DC motor but I don't know anything about DC motors and not all that much about other motors, either. Apparently, I have to use a motor that I normally don't seem to have handy here at home. And I don't plan to hook the thing up to just any other motor.
Can any of you shed light on this kind of speed control ?
The fella who wants me to fix these things didn't seem to know much about them (makes 2 of us) so I'm pretty much at a loss to start working on them. The reward for me if I can fix them is that he is willing to give me Hobart engine driven welder he no longer uses. He says that the motor needs rings but that's not a big deal. Sounds like a fairly simple rebuild.
John
Cut,grind,weld,measure,recut,reweld....