¿ªÔÆÌåÓýWeird fault.? Very uncommon for a transformer primary to die, they often have thermal fuses which fail.? They¡¯re supposed to fail if the transformer overheats (Hey Dave, sound familiar?) but occasionally die just because they feel like it.? ? You¡¯ll find it if you cut away the insulation tape, you might see a little bump.? If the primary is ok replace (or bypass) the fuse.? If replacing remember to crimp in the new one, don¡¯t solder it.? Trap for young players, everyone does it once. ? The MOV isn¡¯t strictly needed.? They suppress spikes by shorting out (and getting warm).? They eventually fail by staying shorted and then take out the fuse.? Spikes shouldn¡¯t bother the transformer but definitely bad for the electronics.? Repeated spikes might have taken out the thermal fuse. ? In theory bypassing the thermal fuse and removing the MOV would get it running again until you can fix it properly. ? Bad switch on the pot is strange as well, might be coincidence. ? If the machine was plugged in but switched off (via the emergency switch), then all of those components would have been isolated from spikes on the line. ? I¡¯ve no idea what went wrong, but good to see you fixed it easily. ? Tony ? ? ? From: [email protected] <[email protected]> On Behalf Of Gary Anderson via groups.io
Sent: Sunday, 2 March 2025 3:40 am To: [email protected] Subject: [7x12MiniLathe] FC350BJ/110V Controller Transformer and Switch Failure. ? I have the FC350BJ motor controller on my Cummins mini-mill.? It is also used on mini-lathes so this applicable to this forum.? It's a second hand machine so I don't know its history.? ?Motor/controller was running as new.? Machine was unplugged and not used for a few weeks.? Plugged her back in and the motor would not turn-on.? The switch portion of the potentiometer/ switch was faulty.? In the CCW position the switch should be closed.? I had ~1 Meg Ohm of resistance.? The transformer for the low voltage +15V, -15V? circuit was open on the primary side.? Luckily LMS eventually had these parts in stock. LMS Part# 2492(Transformer), #1282 (Potentiometer).? ?I am grateful for their sourcing of replacement parts.? After replacing the two known faulty components, the mill now turns-on with full range speed control.? I have not yet tested under motor load. ? I understand that the potentiometer will eventually wear out. The fact that LMS carries the transformer leads me to believe that this is a somewhat common problem with this controller.? I did not find anything on the web about this particular problem.? Hence one reason why I am posting here.? Maybe help out another person that has experienced this fault.? ? Right now, my only brainstorm is there was a power surge when the pot/switch was in the CCW position.? The Metal Oxide Varistor didn't clamp and protect transformer, but it did clamp and drew more current than the pot/switch could handle. I have not yet replaced the MOV on the PCB.? ?I haven't completely thought through the problem, yet here I write.? ? Does anyone here have advice on other components that may be faulty/compromised that lead to burn-out of the switch and transformer?? Or modifications that can be done to make this controller more robust that are worth the time and money??? ? Resources that I used to assist me during my debugging: John Gerling's write-up ? For now, the mill is up and running.? I am still eyeing the KBMD-240D as a more robust alternative. ? Regards, Gary ? |
