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Rotary Convertor or Variable Frequency Drive. Which is best?
tilly819 - 10/10/20 at 09:06 AM

Hi All.

I keep hearing this question come up on various facebook groups and web forums. So I have put together this little video in an effort to debunk some of the false information and give people the pros and conns of both devices. My hope is that this will allow home workshopers to make an informed decision so they don't end up wasting money on the wrong solution for their application. Hope you enjoy.

ianhurley20 - 10/10/20 at 08:35 PM

Thank you for making the video Tilly - brilliant and helpful explanation of the options for 3 phase for those who will use it.

big_wasa - 11/10/20 at 06:58 AM

Interesting vid. With just one motor in my lathe it was a simple choice I thought. But It may be worth noting that multi Vfd’s may not be an option any way due to earth leakage.
The Rcd in my last house would only just cope with the one on the lathe. A second one for the coolant pump tripped it out every time. Despite a s/h 1/4hp Vfd only costing me £30 it’s lived in a box for several years.

SteveWalker - 11/10/20 at 12:57 PM

quote:
Originally posted by big_wasa
Interesting vid. With just one motor in my lathe it was a simple choice I thought. But It may be worth noting that multi Vfd’s may not be an option any way due to earth leakage.
The Rcd in my last house would only just cope with the one on the lathe. A second one for the coolant pump tripped it out every time. Despite a s/h 1/4hp Vfd only costing me £30 it’s lived in a box for several years.


We had a similar problem with the RCD tripping due to the number of PCs, printers and accessories, all with mains filters that leak to earth. It was obviously near the limit and randomly tripped every so often - usually at some inconvenient time.

We solved our problem by ditching the RCD and replacing the MCBs for the circuits that it protected with miniature RCBOs that were the same size. Since then, as the various leaky loads are spread across a number of circuits rather than all combined together, we haven't had any trips.

v8kid - 11/10/20 at 01:00 PM

Excellent Video.

Can I suggest some additions to your pro/con lists which may help making a decision.

1. Older machines tend to be designed around HSS tooling which has a lower cutting speed than Carbide. In this case a VFD can double the machine speed bringing the machine up to date and giving much better cutting in some circumstances.
2. Coolant pumps have a low starting torque requirement which makes them ideal for fixed capacitor 3 phase conversion costing less than a tenner including case. Plenty youtube vids on the subject
3. Single-phase motors are not that expensive particularly the smaller sizes and they all have standard frame sizes.
4. Be careful when specifying VFD the majority are for star connected 3 phase motors which only require 240V whilst delta motors require 415V. Not all motors can be converted from delta to star.
5. Another option for traverse motors is to use stepper/servo motors which are cheap (stepper) and operate off cheap SMPS power supplies and controllers. Added advantage of future CNC control.


Cheers!