Posted by DC31k on 24/07/2019 17:24:38:
I hesitate to mention it here, but the 5hp 240v in, 415v out inverter sold by Drives Direct will do the job but it is rather expensive and it does involve switching downstream of the inverter's output, which seems to be verboten with extreme prejudice on this forum.
Well my Drives Direct 10 HP 415 volt out plug and play box hasn't gone pop despite direct switching on the output. Yet! Date on the label says July 2005. I've had it 10 years and it still seems to be running OK. Although its really due for new capacitors which, apparently, should be considered consumables on any inverter over the longer term. Not cheap in this case. Need to have another go at finding an electrician to hook up my three phase incomers. The Drives Direct box was only supposed to be a temporary expedient. Nowt so permanent as temporary!
Spins up the 3 hp two speed wartime vintage motor on my P&W Model B 12 x 30 lathe a treat on both fast and slow via a splendidly steam-punk set of oil immersed switchgear.
That said I've been very conservative with my rating. No motors above 3 Hp and a set of smoothing chokes on the output which should keep the spikes down.
My view about selecting a motor for VFD control on a lathe is to go by the low speed power and torque requirements. Large jobs run slower and need the oomph. Small fast spinning work rarely needs much power in absolute terms. Give serious consideration to a arranging things so that simply twiddling the VFD potentiometer can substitute for mechanical speed changes over the most used speed ranges. So much easier. Worth changing the pulley sizes to do this. Although a tachometer is fine and dandy a graduated knob is perfectly satisfactory in practice. Low tech reliability and you can see what you will get before starting. Glue a table to the machine to convert knob graduations to speed in the various gear ratios.
Although my Smart & Brown 1024 has a continuously variable mechanical speed control from 40 to 2,300 rpm in two ranges the vast majority of the time its run between 300 and 800 rpm. YMMD.
Clive
PS Simon posted whilst I was typing. Nice to know I'm not alone.
Edited By Clive Foster on 24/07/2019 22:23:48
Edited By Clive Foster on 24/07/2019 22:25:24