Renovating a Hardinge HLV-H

[BillTodd]

Hi Paul,

the Siemens MM150 you use, it appears to be a 240VAC Single Phase input device,

No. The Siemens MM150 VFD I am using is the 1.5kW 500v three phase input version. It is fed from the single phase 415vac output of a step up transformer.

All VFDs run on DC internally, so they do not really require more than one phase to work. High power ones have 3ph input because they need more current and it is easier (i.e. smaller, cheaper capacitors) to smooth the DC from a poly-phase input (like a single cylinder engine needs a bigger flywheel than a multi- cylinder engine) .

There is sufficient capacity in most VFDs to operate on a single phase input without causing any real problems (especially on a lathe with a low duty cycle operation).

Some VFDs have phase loss detection, which would prevent single phase operation, but most newer ones just sense DC bus ripple voltage so will operate fine on single phase input (they will still fault if excessively loaded).

Bill

[pauly45]

Hi Bill,

Thanks for such a prompt reply.

That makes a lot more sense now.
I'm assuming that the risk is that since only one phase is being used to supply all the output power, that it is the rectifier diodes on the one input that risk being over-loaded - all the output power being derived from one phase set of rectifier diodes rather than three ?

Do you just leave two of the input phases disconnected ?

Using a 3 phase 415 input VFD makes the selection choice much larger and cheaper !

Many Thanks - I'll look into 415v 3ph VFD's now !

Regards
Paul.

[BillTodd]

I'm assuming that the risk is that since only one phase is being used to supply all the output power, that it is the rectifier diodes on the one input that risk being over-loaded - all the output power being derived from one phase set of rectifier diodes rather than three ?

True, but since the rectifier diodes are usually integrated with the rest of the power devices, there's virtually no cost to the manufacturer to make the devices very robust (i.e. to use the same spec devices for the smallest and largest power VFD in a range).

The only real issue is ripple current heating in the capacitors.

Bill