Re: 1ph - 3ph inverter advice sought

[Guy]

Jon Laughton <jon@eoin.demon.co.uk> wrote in message news:<3DE73887.C9EE0AE@eoin.demon.co.uk>...
> I'm looking to drive the 440 V 3 ph motor on a small lathe via an
> inverter from my domestic 240 V 1 ph supply. The motor is 0.75 kW...
> ... I've done this with
> smaller motors (about 0.25 kW) with no problem, but wondered if there
> are any issues with a motor of this size.

As a general rule you can supply up to 3hp of 3ph motors from a 13A
1ph socket, so you should have no problems. There are no special
issues other than more risk due to higher current. Check out the
multitude of related threads on this group.

> Any recommendations for
> inverter models and potential suppliers (price obviously being a big
> factor :-) would also be appreciated.

An inverter is something else... but anyway, I got a Transwave static
converter <http://www.powercapacitors.co.uk/Transwave/tw%20doc.htm#ststc>
for a mill and found it works very well indeed. A new, more
modestly-sized converter ought to cost you a couple of hundred quid;
there's not much to go wrong inside so it should last a long time.

I toyed with building a rotary converter (about 500+ new, IIRC) but by
the time I could of scrounged enough capacitors, a suitable idler
motor, a transformer (maybe), switchgear and a metal box to shove it
all in, I'd have spent 300 quid in beer and petrol anyway.

Building a static convertor and re-wiring your motor in a delta
configuration (240v between phases so no transformer needed) is the
cheapest option; if you can get capacitors, switches and a box you're
basically sorted.

Guy

[Norman Billingham]

Jon Laughton wrote:
> I'm looking to drive the 440 V 3 ph motor on a small lathe via an
> inverter from my domestic 240 V 1 ph supply. The motor is 0.75 kW, and
> I'm mainly concerned with just getting it going rather than supplanting
> the normal belt and gear speed change system. I've done this with
> smaller motors (about 0.25 kW) with no problem, but wondered if there
> are any issues with a motor of this size. Any recommendations for
> inverter models and potential suppliers (price obviously being a big
> factor :-) would also be appreciated.


I run an 0.75HP motor on my lathe from an inverter
from Eurotherm drives. Can't remember what it
cost but money well spent. Much sommother than
single phase and fully variable speed.

The only issue I found was you need screened cable
from inverter to motor as the converter produces a
lot of RF. Local supplier needed a few days to
get me a couple of metres of 3 core screened cable
with that sort of current carrying capacity.

[Jon Laughton]

Guy wrote:

> As a general rule you can supply up to 3hp of 3ph motors from a 13A
> 1ph socket, so you should have no problems. There are no special
> issues other than more risk due to higher current. Check out the
> multitude of related threads on this group.
>
> > Any recommendations for
> > inverter models and potential suppliers (price obviously being a big
> > factor :-) would also be appreciated.
>
> An inverter is something else... but anyway, I got a Transwave static
> converter <http://www.powercapacitors.co.uk/Transwave/tw%20doc.htm#ststc>
> for a mill and found it works very well indeed. A new, more
> modestly-sized converter ought to cost you a couple of hundred quid;
> there's not much to go wrong inside so it should last a long time.
>
> I toyed with building a rotary converter (about 500+ new, IIRC) but by
> the time I could of scrounged enough capacitors, a suitable idler
> motor, a transformer (maybe), switchgear and a metal box to shove it
> all in, I'd have spent 300 quid in beer and petrol anyway.
>
> Building a static convertor and re-wiring your motor in a delta
> configuration (240v between phases so no transformer needed) is the
> cheapest option; if you can get capacitors, switches and a box you're
> basically sorted.
>
> Guy

Thanks for the converter idea. I thought these were big, expensive things... didn't realise smaller
cheaper ones are available/buildable. I better look into them.


--
Jon Laughton

[Jon Laughton]

Norman Billingham wrote:

>
> I run an 0.75HP motor on my lathe from an inverter
> from Eurotherm drives. Can't remember what it
> cost but money well spent. Much smoother than
> single phase and fully variable speed.
>
> The only issue I found was you need screened cable
> from inverter to motor as the converter produces a
> lot of RF. Local supplier needed a few days to
> get me a couple of metres of 3 core screened cable
> with that sort of current carrying capacity.

Thanks for the screening tip - I wasn't aware of the RF problem.


--
Jon Laughton

[Craig Powers]

In article <3DEB58D5.9000009@sussex.ac.uk>, Norman Billingham
<n.billingham@sussex.ac.uk> writes
>
>
>Jon Laughton wrote:
>> I'm looking to drive the 440 V 3 ph motor on a small lathe via an
>> inverter from my domestic 240 V 1 ph supply. The motor is 0.75 kW, and
>> I'm mainly concerned with just getting it going rather than supplanting
>> the normal belt and gear speed change system. I've done this with
>> smaller motors (about 0.25 kW) with no problem, but wondered if there
>> are any issues with a motor of this size. Any recommendations for
>> inverter models and potential suppliers (price obviously being a big
>> factor :-) would also be appreciated.
>
>
>I run an 0.75HP motor on my lathe from an inverter
>from Eurotherm drives. Can't remember what it
>cost but money well spent. Much sommother than
>single phase and fully variable speed.

Likewise I have also have 0.75kW 1ph to 3ph converter from Eurotherm. It
works well.

This creates the phase shift required for the extra two phases but the
phase to phase voltage is only 240v and so the motor needs to be rewired
as delta to retain the normal power output. Not difficult providing that
motor has all delta and star connections available at the terminal box.
Most have, except for very old ones. e.g. The Brook Crompton motor on my
Boxford BUD was easier to re-jig. 10 minute job.

However the 240v wasn't enough to hold in the 3ph contactor and so I
bypassed it and just use the stop/start available from the inverter.

No problems in 3 yrs of use.

Craig Powers

>
>The only issue I found was you need screened cable
>from inverter to motor as the converter produces a
>lot of RF. Local supplier needed a few days to
>get me a couple of metres of 3 core screened cable
>with that sort of current carrying capacity.
>
>

-------------------------------------------------------------------------------
Craig Powers craig@real-time-sys.demon.co.uk
-------------------------------------------------------------------------------

[Guy]

Jon Laughton <jon@eoin.demon.co.uk> wrote in message news:<3DED3A19.6C09E052@eoin.demon.co.uk>...
> Guy wrote:
>
> > Building a static convertor and re-wiring your motor in a delta
> > configuration (240v between phases so no transformer needed) is the
> > cheapest option; if you can get capacitors, switches and a box you're
> > basically sorted.
>
> Thanks for the converter idea. I thought these were big, expensive things... didn't realise smaller
> cheaper ones are available/buildable. I better look into them.

They *are* big - about 3-4 times the size of an inverter - and heavy
if they contain a transformer. On the other hand they're entirely
passive, except for a start-capacitor relay to get the motor up to
speed, so should last far longer and produce no additional
interference.

Guy

[Prepair Ltd]

On 5 Dec 2002 03:56:16 -0800, spam@guy.griffin.freeuk.com (Guy) wrote:

>Jon Laughton <jon@eoin.demon.co.uk> wrote in message news:<3DED3A19.6C09E052@eoin.demon.co.uk>...
>> Guy wrote:
>>
>> > Building a static convertor and re-wiring your motor in a delta
>> > configuration (240v between phases so no transformer needed) is the
>> > cheapest option; if you can get capacitors, switches and a box you're
>> > basically sorted.
>>
>> Thanks for the converter idea. I thought these were big, expensive things... didn't realise smaller
>> cheaper ones are available/buildable. I better look into them.
>
>They *are* big - about 3-4 times the size of an inverter - and heavy
>if they contain a transformer. On the other hand they're entirely
>passive, except for a start-capacitor relay to get the motor up to
>speed, so should last far longer and produce no additional
>interference.
>
>Guy

We have an Ashina drilling machine, made in Hiroshima (glows in the
dark!) with a 3-phase delta/star motor. This has run since we bought
it in the 1970's with a single capacitor, no switches or relays etc
etc., with the motor wired in delta 220V phase to phase.

It may be because it is only a 1/2hp motor, but I seem to remember
that you can run just with the capacitor up to a couple of HP with no
ill-effects.

It has the added 'advantage' that it stalls before anything breaks if
the drill catches, but still handles 1/2" drills in steel with no
problem.


Kind regards,

Peter

Peter Forbes
Prepair Ltd
Luton, UK
email: prepair@easynet.co.uk
home: diesel@easynet.co.uk

[Bob Minchin]

I normally reckon on 40 microfarads per hp to generate the third phase with about 5 to 10 times that value
for starting. Low torque applications can sometimes need little or no starting capacitor.

Bob

Prepair Ltd wrote:

> On 5 Dec 2002 03:56:16 -0800, spam@guy.griffin.freeuk.com (Guy) wrote:
>
> >Jon Laughton <jon@eoin.demon.co.uk> wrote in message news:<3DED3A19.6C09E052@eoin.demon.co.uk>...
> >> Guy wrote:
> >>
> >> > Building a static convertor and re-wiring your motor in a delta
> >> > configuration (240v between phases so no transformer needed) is the
> >> > cheapest option; if you can get capacitors, switches and a box you're
> >> > basically sorted.
> >>
> >> Thanks for the converter idea. I thought these were big, expensive things... didn't realise smaller
> >> cheaper ones are available/buildable. I better look into them.
> >
> >They *are* big - about 3-4 times the size of an inverter - and heavy
> >if they contain a transformer. On the other hand they're entirely
> >passive, except for a start-capacitor relay to get the motor up to
> >speed, so should last far longer and produce no additional
> >interference.
> >
> >Guy
>
> We have an Ashina drilling machine, made in Hiroshima (glows in the
> dark!) with a 3-phase delta/star motor. This has run since we bought
> it in the 1970's with a single capacitor, no switches or relays etc
> etc., with the motor wired in delta 220V phase to phase.
>
> It may be because it is only a 1/2hp motor, but I seem to remember
> that you can run just with the capacitor up to a couple of HP with no
> ill-effects.
>
> It has the added 'advantage' that it stalls before anything breaks if
> the drill catches, but still handles 1/2" drills in steel with no
> problem.
>
>
> Kind regards,
>
> Peter
>
> Peter Forbes
> Prepair Ltd
> Luton, UK
> email: prepair@easynet.co.uk
> home: diesel@easynet.co.uk

[Jon Laughton]

Craig Powers wrote:

>
> Likewise I have also have 0.75kW 1ph to 3ph converter from Eurotherm. It
> works well.
>
> This creates the phase shift required for the extra two phases but the
> phase to phase voltage is only 240v and so the motor needs to be rewired
> as delta to retain the normal power output. Not difficult providing that
> motor has all delta and star connections available at the terminal box.
> Most have, except for very old ones. e.g. The Brook Crompton motor on my
> Boxford BUD was easier to re-jig. 10 minute job.
>
> However the 240v wasn't enough to hold in the 3ph contactor and so I
> bypassed it and just use the stop/start available from the inverter.
>
> No problems in 3 yrs of use.
>
> Craig Powers
>
> -------------------------------------------------------------------------------
> Craig Powers craig@real-time-sys.demon.co.uk
> -------------------------------------------------------------------------------

I've looked at the Eurotherm inverters and they seem reasonably priced for their
functionality, and have RFI suppression (to hark back to an earlier point.) Shame
about the contactor (I may be in a similar situation) but I guess there are ways
round this... which I may need to investigate.

--
Jon Laughton

[John Stevenson]

On Fri, 06 Dec 2002 00:34:20 +0000, Jon Laughton <jon@eoin.demon.co.uk>
wrote:

>Craig Powers wrote:
>
>>
>> Likewise I have also have 0.75kW 1ph to 3ph converter from Eurotherm. It
>> works well.
>>
>> This creates the phase shift required for the extra two phases but the
>> phase to phase voltage is only 240v and so the motor needs to be rewired
>> as delta to retain the normal power output. Not difficult providing that
>> motor has all delta and star connections available at the terminal box.
>> Most have, except for very old ones. e.g. The Brook Crompton motor on my
>> Boxford BUD was easier to re-jig. 10 minute job.
>>
>> However the 240v wasn't enough to hold in the 3ph contactor and so I
>> bypassed it and just use the stop/start available from the inverter.
>>
>> No problems in 3 yrs of use.
>>
>> Craig Powers
>>
>> -------------------------------------------------------------------------------
>> Craig Powers craig@real-time-sys.demon.co.uk
>> -------------------------------------------------------------------------------
>
>I've looked at the Eurotherm inverters and they seem reasonably priced for their
>functionality, and have RFI suppression (to hark back to an earlier point.) Shame
>about the contactor (I may be in a similar situation) but I guess there are ways
>round this... which I may need to investigate.

I'm going to jump in here on the side of the invertor.
I fit literally hundreds of these per year, no exaggeration.
Many on this list have bought the older units off me as equipment has been
upgraded.
It's now got to the price point where you can buy new invertors for a lot
less than you could a few years ago.
To be honest now unless you can get a second hand one for peanuts, don't
bother. The newer drives have far more features on them and are far more
efficient than the older drives.
Go for the invertor, you should be able to get a good deal on the more
simpler of the invertor range. A 0.75 hp invertor COMPLETE should cost no
more than £120 less the dreaded VAT.
When I say complete be careful as a lot of invertors have the programming
panel as a separate unit costing anything from 40 to 80 pounds extra.

Totally ignore the contactor. With an invertor it's not needed, period,
full stop.
Chuck it at next door cat.
Invertors need a very simple start / stop / reverse switch and a pot to
control speed. A total of 6 wires max and all at from 10 to 24 volts and
milliamps load. No chance of electric shock and you can mount the switch
box just where you want it, not in some obscure place where dwarfs live.

Suppression isn't the problem it was a few years ago. Getting the invertor
close to the motor helps as does screened cable. Most of the new ones have
suppression fitted as standard.
A note with screened cable. Only earth one end. Earthing both ends forms a
loop that's worse than having no screeing at all.

Once you go onto an invertor drive you will never go back.
Convertors are useful in some cases where you have special motors and you
can't get off the 440v setup. Downside is these are only a two phase stop
gap measure and cause motor problems in respect of them being lumpy and
noisy.

---
Regards

John Stevenson
Nottingham, England