Spindle upgrade
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Hi,
not to my knowledge.
The problem with VFDs is they draw a great deal of current and are likely to severely stress your domestic single phase installation.
Most (reputable) manufacturers regard 2.2kW, about 3 hp, as the practical limit for single phase use, even then a 2.2kW VFD and motor can draw 23A-26A.
Obviously this problem gets worse as the power levels go up.
VFDs with outputs in the 5kW (7.5hp) range are all intended to be run form three phase AC input. You can run them on a single phase input but as you've found with significant
de-rating.
The problem is that three phase VFDs have fewer DC link capacitors than a single phase unit. If you were prepared to add additional DC link capacitors you'd not have
to de-rate a three phase VFD. Adding more capacitors sounds easy....but its not. Firstly the capacitors are expensive, at least for good quality ones, and they get charged up
to 320VDC, if anything goes wrong they go BANG in spectacular fashion.
Some VFDs, particularly those intended for lift service, often have terminals bought to the outside of the unit direct from the DCLink, and thus represent a much easier proposition to
add more capacitors. All VFDs have an 'in rush' circuit or mechanism that prevents a huge in-rush current at power-on which would otherwise certainly trip your breaker.
If you are trying to add more DCLink capacitors you must first ensure that the in-rush circuit will tolerate a doubling or tripling of DCLink capacitance.
Most of the Chinese VFDs I've ever pulled to bits use PTC (positive temperature coefficient) thermistors to limit the inrush.....and they are clever, cheap and if well chosen reasonably
reliable. Adding double or triple the DCLink capacitance is asking for trouble with a PTC. In those situations I prefer a high wattage (10W plus) vitreous resistor, typically 20Ohm to 50Ohm.
Once the capacitors have charged then the resistor needs to be shorted with a relay.....and not a cheap arse relay either, I use an open frame Allan Bradley type, reliability at 50A is
measured in decades, and cost about $100.
Almost all VFDs have a pair of terminals for a braking resistor. One terminal goes to the DCLink +ve, and the other through the internal brake IGBT to the -ve DCLink.
If you don't require or are prepared to forgo the brake resistor you could permanently bridge the braking IGBT and hence the brake terminals on the VFD terminal strip
are permanently connected to the DCLink and could be used for adding additional DCLink capacitance.
The bottom line is that if you are prepared to fiddle with your VFD you can avoid having to de-rate it, allow a few hundred for quality parts. If you don't know what an IGBT is
or what a DCLink capacitor is and what it looks like then it probably not a project you want to undertake without some expert assistance. DCLink capacitors go BANG
and they'll happily blow you into the middle of next week if you are careless.
Craig
Originally Posted by Tckkgk012283
