This new relay pair will only change speed (thus disconnecting the VFD) when the VFD is stopped.I may have misunderstood the logic you described, but I believe I might rethink that approach. The plan is to use the interlocked pair of contactors (currently used to control the speed adjust motor) as a new speed selector relay. I'll post a circuit when I've worked out the details.
I could use a microprocessor to control all this but, at the risk of being called a luddite, I intend to use simple relays in the interest of fixability (by others). I'll keep the original speed change lever and switch, but it will be used at 24v to control the VFD. This new relay pair will only change speed (thus disconnecting the VFD) when the VFD is stopped. I'm bidding on a couple of low power (100W) VFDs to run the coolant pump and speed change motors at the moment, with the intention to completely rewire the control box. Meanwhile, I've found another, much smaller and neater, Variable Frequency Drive to power the main motor ( A 1500W Siemans MM150). Progress has slowed while I'm awaiting the 240-415v step-up transformer to arrive from Airlink Transformers. I had to finish the worklight before I could post these :) *(I do this sort of thing for a living, so by bodged, I do not mean unsafe)
I'll draw a diagram of it for your site if you wish. The spindle interlock contactor is wired in a different place it disconnects the 3ph only to the motor and the 1ph control power to the up/down contactorsĪ couple of spare contacts on the fwd/reverse switch are used to break the main contactor coil circuit - so if the fwd/rev switch is changed while running it stops the machine. I found a couple of subtle differences between my machine and the wiring diagram from your site: ( a MG50M2CK1, if you have any in your pockets)
It popped a 600v 20A fuse and killed one of the IGBT modules :( I then realised I'd forgotten to replace the current limit lead (which has to be removed to get at the relay). I stuck it back together only to get no responce at all.
I had to take the VFD apart to find out why (I have no manual for this thing). I powered down to investigate why the relay, which bypasses the resister, was not working. Got the spindle spining in both high and low speed and up & down the speed range.īut, while doing all this, I noticed the slow-start resister on the VFD was smoking (It's an old 5HP Toshiba device and has a softstart to prevent fuses popping on switch on). I then bodged* my 440v VFD on, temporarily using the control transformer as a step-up. Applied power to the thing for the first time.įirst I rewired the control transformer to accept 240v input (instead of 440) then checked the contactors were operating OK.Ĭhecked the power feed controls - they were working OK, except I'd reversed the connections to the variable transformer so high speed was low and vice-versa (easily fixed).