Myford 3 phase motor upgrade

Thats just a cheap inverter, granted.

There are plenty of 'Plug and Play' inverters around designed to supply a workshop or individual machine exactly the way it would be sent by your electric supplier. I use one.

The reason is that the inverter is a much less 'stiff' supply than the mains. Drop the load of one puny 25kW motor in or out and the national grid doesn't notice.

Suddenly cut the load from an inverter and the output could potentially be damaged. Even more likely is damage if the inverter is running and the motor is suddenly switched in.

That's why they advise that switching is before not after it.

neil

Perhaps working on small machines, I did not take into account the possibility of an accident by the motor starting unannounced although when using the mill I always switch off because the main switch is alongside the controller. On the Myford, not had a problem yet but you never know, when I go into the shed tonight, will ensure that the supply is switched off.

For many years I had a big old Southbend lathe. It was about 9" centre height and 5ft between centres, driven by a 11/2 hp motor using flat belts. I look back and now believe that this was the best lathe I have owned. That was a great metal cutter but a house move meant that because of space restrictions it had to go and was eventually replaced by a Warco BG600. What a contrast, there were no safety features on the Southbend where as the Warco has micro switches which cut the power to prevent accidents.

Going back to the inverters, I plan to fit one to the Warco and wish to retain the safety features and plan to wire in the inverter to the motor terminals on the existing loom. I will then be able to power up using the existing starting lever, making adjustments for speed etc., on the inverter remote. This will mean that when ever the lever is put into the stop position or any of the guards opened, power will be cut to the inverter. Hopefully, this will not be frequent since I would normally use the inverter control to stop for measuring but can anyone tell me if cutting the power to the inverter will do any harm.

Neil is spot on with his comment, if you break the load form a running inverter or connect a motor to a running inverter output you can damage it.

If you cut the power to a running inverter it should not damage it though you will lose the useful feature of the inverter ramping the motor down to a standstill, there is a recommended limit to the number of power ups that should be applied per hour normally stated in the manual.

I am a bit short of time just now, I will post a reply a little later on what might be the best way to modify your Warco.

Regards,

Michael

Ray I wouldn't keep cutting power to the inverter, I scrapped a £650 one in 1hr 25mins.

If its wired in right any stop, start and control functions will work so if levers off the inverter cuts power so would any useless guards and other controls on trips. A 1ph to 3ph 220v inverter to run the BH600 would run off domestic mains so use that to switch off and isolate when working inside or on the electrics but not for repetitive measuring where stop start levers good.

Hi Ray, if you haven't watched it yet a YT video from Shadon HKW called "2 speed motor VFD application" might help you to show how to safely keep your safety interlocks, just ignore to part where discusses two speed. and drum switches.

chriStephens

I have to give a direct reply to Russells post, I have not persued any statistical reports for accidents by the unsafe installation of inverters because I am frankly aware that if any of the operators at my place of work were injured by any inadequecy of the installation, I would probably end up in court with the possibility of a sentence.

If you check out my article here:

3-phase-conversion-and-other-alternative-methods-of-powering-a-mini-lathe

You can see my approach to having soft stop and start as well as 'emergency stop' all done through the inverter.

If I decide to fit auto stops, then they will only need to be normally closed (low voltage) microswitches in line with the e-stop button.

Neil

Even with three phase supply, vibration can still be evident. It may be caused mechanically rather than electrically.

My oriental lathe, replacing a ML7, (to get a Norton box, and a big bore mandrel) was fitted with VFD prior to delivery, and is very satisfactory. The pendant looks like one of the commercially available ones.

From the safety aspect, a microswitch will break the 24volt supply to the contactor if any of the covers to Gears , Belt, or Chuck Guard are opened..

The original twelve speeds, became six (single sheave pulley on the three phase motor because of space considerations, in place of the two sheave on the original single phase unit), but with variable speed on each range.

However, at maximum speed, (higher than standard, since the invertor allows the motor to be run up on 60Hz rather than to UK and European standard mains frequency of 50Hz), some vibration is evident. This is ascribed to the Bull Wheel being unbalanced by the pin used to lock the bull wheel to the shaft).

I always slacken the secondary (Countershaft to Mandrel) belt when not in use, so unlikely to be the V belt taking a set.

Howard

Just a quick Thankyou for all your advice.

Got a unit from transwave in the end, cheap as chips in comparison to others, piece of cake to fit and program so pleased as punch with it..

Used a metric motor and just made a simple fixing plate..

Still have a knock from somewhere..need to investigate but that's another story.

thanks again

Just wondering for those members that have gone the DIY route and fitted a 'metric' motor what frame/size did you go for ?

Cheers H

It was an 80 frame motor..

Simple plate added to allow fitting and a new pulley..

Many thanks

H