Member postings for Robert Hurst 1

Ok, thanks Dave that all sounds feasible and makes perfect sense.

Yes, aware of SMPS technology, wasn't aware it was now being used in VFD's.

Do you have a link to such a device, as interested to learn more?

Many thanks.

Ok, let me expand a little on my original comments.

Firstly to put things into context I was formerly employed by a UK manufacturer of inverter based GPU's and UPS's so I do have a clear understanding of how the electronics work. I have also installed and commissioned VFD's up to 200kW from a number of manufacturers so aware of application and limitations.

"These offer very good value for money, however the electronics is a bit marginal so I'd recommend buying a unit rated twice that of the motor, especially if running from a single phase supply"

"Sorry but not true and possibly misleading. One should not necessarily double the inverter power over that of the motor. Overload conditions may burn out the motor and then the VFD!"

The Huanyang inverters, whilst very good are built to a price. As a rule of thumb in electronics, for every 10*c increase in temperature you half the lifespan, or put the other way if you can decrease the temperature by 10*c you double the lifespan. They are designed to be run from a 3 phase supply, giving 6 charging pulses per cycle from the rectifier. They can be run from a single phase supply, but this will give only 2 charging pulses per cycle, increasing the ripple current accordingly. This will increase self heating of the reservoir capacitors and reduce lifespan.

Please see; https://www.precision-elec.com/derate-three-phase-vfd-for-single-phase-power/

You should be able to enter the full load current of the motor when setting up the parameters. An overload condition should never endanger the motor or the inverter, but instead reduce torque (current) by reducing the speed (frequency) or shut the unit down.

"Beware of vendors claiming that their unit will step up from 230 V to 415 V, this is simply not true."

"The clear suggestion that inverters cannot supply 415V outputs is tosh. I ran my lathe on a 415V inverter, simply because I was told the star point could not be split to enable delta connection. They DO. But the inverter was rather more expensive than a 230V equivalent.

Most, or all, good manufacturers offer both output voltages in the usual range. Just don’t expect an inverter marked as 230V three phase output to work at full power, if connected to a 415V star wired motor. Power will be down by about 40%."

A VFD works by rectifying the incoming supply to a value roughly equivalent to the peak voltage of the supply, in the case of 230V~ this is around 350V dc, 400V~ around 560V dc. This is referred to as the bus or link voltage. The output stage then converts this back to AC, but the peak output voltage cannot exceed the bus voltage, ie the output (ac) voltage cannot exceed the input (ac) voltage.

My milling machine is fitted with a pole changing motor, so had no choice but to run at 400V. I have a step up transformer supplying a VFD at 400V single phase to achieve this.

Please see; https://inverterdrive.com/HowTo/240V-Supply-to-a-400V-AC-Motor/

There may be inverters on the market with a voltage doubler rectifier which could potentially supply an output greater than the input, but I'm not aware of any. I would have thought suppliers of VFD would push these if they were available, as it's an ever increasing application.

If you know of such, perhaps you'd care to cite a link or provide evidence. Can you back up your comments with some photos of voltage readings whilst in operation? Resorting to rudeness merely weakens your argument.

I've spent some time earlier looking on ebay at some of the entry level offerings, there certainly is a bewildering range and can see that someone unfamiliar with VFD's could be easily misled.

Regards.

Diamond wheels are brilliant and give a really keen edge.

Bit of a fiddle to get them to run true on an off-hand grinder, worth spending the time with a dti to reduce run out as much as possible.

You may find you need to replace the OEM pressed steel cup washers with machined items.

Spent the afternoon pottering about, did a bit more welding on the frame for the 47, sharpened a couple of drills and made a new head for my Thor hammer. Didn't have a suitable lump of copper, so wound one out of some earth strap.

Hi Peter, by generic I guess you mean the units manufactured by Huanyang amongst others.

These offer very good value for money, however the electronics is a bit marginal so I'd recommend buying a unit rated twice that of the motor, especially if running from a single phase supply.

Beware of vendors claiming that their unit will step up from 230 V to 415 V, this is simply not true. Check your motor can be re-configured for 230 V (delta or mesh connection). A 415 V motor will run on 230 V but will lack torque.

Cheers.

Is it possible to scroll through the VFD menu and read the DC bus (or link) voltage?

Cheers, Rob.

Thanks for the welcome guys.

KEM-SAFE L.F is marketed by Kemserv but I'm not sure if it's the same stuff;

http://www.kemserv.com/solvent-based-cleaning-products-northumberland.php

We used PF cleaner when I was working for Balfour Beatty which is brilliant stuff;

https://www.socomore.com/shop/surface-preparation/surface-cleaning/pf-solvent/

These days i tend to use BCE (Brake Clutch Electrical) cleaner available in 5l cans or aerosol.

Cheers, Rob.

Hi all, thought I'd say hello since joining up.

I live in Aylesbury (Buckinghamshire) and am a member of the Bracknell society.

I run a 5" S&D 7F built by my father and am currently building a 5" battery electric class 47.

For those of you on facebook please see my page; https://www.facebook.com/ProjectOdin47/

It's a small world so I'm sure I'll be amongst familiar faces.