De-rating 3 phase inverters - Update

Following on from my query about this I picked up a cheap 5HP 3 phase
400-440v inverter. Wired it in to the "real" output of the Transwave
transformer (ie single phase 415volt-ish). Looped the 3rd phase into
this. Runs fine until I try to run the lathe at top speed, at which
point it indicates an over current fault.
The conclusion is that a 5HP inverter wired in this way isn't up to
the job of a fully loaded 3HP motor in a CVA lathe - which is really
what Rob said in the original post.
A 7.5-10HP 3 phase 400-440 volt inverter should do the job - just
need to find one cheaply.
Reply to
Charles Ping
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charles i dont know if this helps .
i now have a running 1024 smart and brown lathe ,using a transwave 5h staic inverter running a 3 hp idler motor ,and the terminals for th lathe are connected to the idler motor terms ,amps on the transwave meter are around 5 running just the idler ,and 8 running the 2.5 h lathe motor on high speed. you could check to see if an idler motor would help ,and also chec your voltages ph to ph on the 3 ph , they should be around 5 % of eac other. regards rober
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If it is a proper drive he is using then the phase-to-phase voltages should be more or less smack on with eacher other. If not then there is something seriously wrong with said drive, and will go bang. If is an open loop drove (ie, without a rotary encoder) then there may be something wring with the current feedback.
One thing about running smaller motors than the drive is rated for, is that it can cause severe speed stability problems, particularly when unloaded, as the signal to noise ration of the current feedback begins to affect the machine control, if the drive is suitably advanced.
One thing you could try is that if you have the choice, you can re-wire the motor from star to delta, making the mnotor effectively a 230V machine. Of course to deliver the horses, the current has to increase, so your back to square one.
Hope this helps a bit. Just so you know, I used to design drives for Control Technqiues.
Reply to
Robert Wilson
Rob Thanks for the suggestion. To avoid any doubt I'm using an inverter that is driven from a 240-415 tranny. No idler motors or any of the other tricks that are associated with a traditional converters. What sort of scale of small motors causes a s/n problem. A factor of 2, 4, 6 or 8 under the spec?
Reply to
Charles Ping

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