PDA

View Full Version : VFD Question



Chaz
14-01-2017, 07:40 AM
I bought one of the 'cheap' Huanyang VFDs on Ebay some months back in preparation of me using this for Thor as a Spindle speed control mechanism. I did not buy the spindle at the time but had a 3 Phase Vacuum Pump motor I wanted to turn with it. I did get the motor to turn but it always ran hot which might be explained below.

The unit is a 4KW 5HP 380V unit which can take both single and three phase input.

Yesterday, I tried to use this unit to power a friend's new (secondhand) kneemill. We had some success but I later realised that the issues we were having were voltage related. I measured the output at 50HZ and saw no more than around 260V out. I checked the settings, I think parameter PD005 is max voltage, and this was set to 415V. I reduced it to 380V.

When the unit was running, it was reporting 380V although I was measuring 250V (on average).

What I now assume is that it will only make 380V if it has a suitable three phase incoming power. I had believed before this, that I would convert 220V single phase to 380V three phase with this unit. Should I be able to? Did I miss something? I believe the reason the pump motor ran hot was low voltage means higher current = heat.

Thanks

Neale
14-01-2017, 09:34 AM
I have a similar problem. My lathe uses a 3HP motor that is not rewireable to delta from star to run on 240V 3-phase, and it is so built into the machine that it would be major surgery to remove/replace. I found that inverters will only convert single-phase in to three-phase out at the same nominal voltage - no voltage conversion. Basically, they rectify incoming A.C. to D.C., then chop that to generate the output. So, you need to use a transformer to bring single-phase 240 to 400 or so to feed the inverter. In my case, someone kindly offered me an inverter that had been hacked to change the input circuit slightly. At heart it is quite a good ABB inverter, but the input is now a single-phase input voltage-doubler rectifying arrangement to give a higher voltage on the D.C. bus, which then gives me an appropriate output voltage. Works ok, but as I crank the lathe speed up via its variable-speed pulley arrangement, motor load goes up, and the D.C.bus voltage starts to sag - the capacitor is being charged at only 50Hz because of the voltage doubler but is being discharged at 150 Hz, in effect, so the voltage drops during input cycles and eventually the inverter protection kicks in and complains about input voltage faults. The original input circuit uses a full-wave rectifier so that even with single-phase you get a 100 Hz input. Like you, I need to look out for a 240-400V transformer!

magicniner
14-01-2017, 01:21 PM
The long and the short of it is that you can buy a (much more expensive) unit that is an Inverter Drive which will take lower input voltages, do the magic internally, and drive high voltage motors, just don't expect anything just billed as a VFD, Variable Frequency Drive or Drive to do that unless you get it in writing that it will drive a 415v motor on a 240v supply,

- Nick

Chaz
14-01-2017, 03:11 PM
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-Rotary-Converter-5-5hp-4kW-Single-to-3-Three-Phase-240v-to-415v-/322379604644?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=OTLEsFGTqymwgVUH4krHdRhMNvM%253D&orig_cvip=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-to-3-Three-Phase-240v-to-415v/282318185693?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%2 6asc%3D40760%26meid%3Dca4642aa554649e0896b13506d86 16a2%26pid%3D100011%26rk%3D1%26rkt%3D12%26sd%3D322 379604644

magicniner
14-01-2017, 03:39 PM
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
14-01-2017, 03:46 PM
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
14-01-2017, 04:52 PM
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
14-01-2017, 05:14 PM
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
14-01-2017, 07:29 PM
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
14-01-2017, 08:41 PM
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.