VFD Question

[Chaz]

Thanks, confirms my worry then.

I assume any spindle then just runs at a lower voltage ....?

This was bought to fix the issue - http://www.ebay.co.uk/itm/Transwave-...vip=true&rt=nc - not cheap but that should work.

That's basically a motor being spun up and then 3 phase taken off it I assume.

How do these work? Look like some phase shifting of the transformer output to create a 'fake' 3 phase. Any good? http://www.ebay.co.uk/itm/4kW-Single...3D322379604644

[magicniner]

The things which put me off rotary are the fixed frequency combined with continuous power consumption, if you want variable speed you still have to add a drive, you can feed a drive with one or more transformers rather than rotary if you are going to use a drive.
I use dual voltage motors, retro-fitted where the original is not dual-voltage, and predominantly Siemens VFDs with the odd Hitachi or other major brand unit, if I ever do buy something which must have 415v I'll probably go the transformer(s)/industrial drive route as transformers are bullet proof and industrial drives are cheap second hand and NOS as most hobby users shop for 240v units,

- Nick

[Chaz]

The things which put me off rotary are the fixed frequency combined with continuous power consumption, if you want variable speed you still have to add a drive, you can feed a drive with one or more transformers rather than rotary if you are going to use a drive.
I use dual voltage motors, retro-fitted where the original is not dual-voltage, and predominantly Siemens VFDs with the odd Hitachi or other major brand unit, if I ever do buy something which must have 415v I'll probably go the transformer(s)/industrial drive route as transformers are bullet proof and industrial drives are cheap second hand and NOS as most hobby users shop for 240v units,

- Nick

Thanks. In this case it powers a Knee Mill that doesnt have Variable speed on the motor (mechnical) although we did discuss putting a VFD on but the current control system does not allow speed control (from what we can see). Acu-rite MillPWR.

[magicniner]

doesnt have Variable speed on the motor.

My point was that Rotary and non-electronic static converters don't allow driving compatible 3 phase motor at variable speed, nothing to do with if the machine has some form of variable speed built in or not.
Variable speed to the motor is a facility that those who have never used it rarely comprehend and those that have used it rarely do without subsequently,

- Nick

[Web Goblin]

Single phase 220v to 3 phase 415 volt inverters are available if you have deep pockets, a 3HP one will cost you around £500.

[Chaz]

Single phase 220v to 3 phase 415 volt inverters are available if you have deep pockets, a 3HP one will cost you around £500.

Well, the unit bought up above was £650 2nd hand. They sell for >£1K typically for 5HP.

[m_c]

Rotary phase converters work by using a three phase motor, and powering it on two legs from single phase. The third phase is then generated by the motor. Capacitors are added to help balance the third phase voltage, and for starting (very large rotaries may use a smaller single phase pony motor for starting).
There are plenty guides about if you google for them.

I run my workshop from one, which simply adds a 240-380V transformer to the mix, so I get three phase at the more common UK three phase voltage.

They do use power when running, but certainly not enough to justify the cost of changing to some form of digital inverter. I did price one, and I think I'd have to run the rotary constantly for several years before a digital inverter would pay for itself.