Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It
says the primary is rated at 240 - 480 V and the secondary at 120 - 240
V. Do you think this might be suitable for a phase convertor if used in
reverse? Perhaps there is some way to reduce the voltage slightly before
feeding it to the idler motor, or perhaps the motors would stand 480 V?
We don't get the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem

Chris

Ignoramus9991 wrote:
On Sun, 7 Aug 2005 12:51:52 +0000 (UTC), Christopher Tidy wrote:

Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It
says the primary is rated at 240 - 480 V and the secondary at 120 - 240
V. Do you think this might be suitable for a phase convertor if used in
reverse? Perhaps there is some way to reduce the voltage slightly before
feeding it to the idler motor, or perhaps the motors would stand 480 V?
We don't get the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem

Chris



I see no reason why it cannot be used as a step up transformer.

I think that it would be much more efficient to just buy a nice used
220V motor, like 7.5 HP or some such, than mess with very high
voltages, heavy transformers, etc etc etc, all to power a puny 2.5 HP
motor, which in the end will end up costing a lot and won't provide
much power. It's 40 pounds starting bid, who knows what it will sell
for, etc.

Let's do the math:

A. Making RPC with your current motor and transformer
- very heavy motor
- not much power
- pay money for transformer
- very heavy setup
- very high (easily lethal) voltages

B. Buying a used 5-7 HP motor
- light motor
- very small size and weight of setup
- not so deadly voltages
- not much more money, all you need is caps and a contactor.

Really, having a 2.5 HP idler will severely limit your options as of
what to run. Like, yesterday I bought a 2 HP compressor, I could not
run it from a 2.5 HP idler, not very well anyway. I am glad that I
have a 10 HP idler. (I am aware that your electric supply does not
permit 10 HP idlers).

I am sorry if this message appears to "rain on your parade", I admire
your skills and determination and the motor you have is beautiful and
historical. But, at the same time, I think that you get a "better bang
for pound sterling", if you use your skills to play with machinery
that you can run off the phase converter. RPC is just a tool to get
other tools running.

It depends how you see the project. Either you just see the RPC as a
tool, or you see it as a fun science project, into which you can
incorporate a cool motor you got free. For me it's the latter. I don't
need the RPC to drive particularly big loads, and I'd like to use it to
do some electrical engineering experiments. I'm also rather fussy about
the way my projects look, and a modern TEFC motor just doesn't match the
looks of that old motor.

You also perhaps underestimate the need for a 415 V convertor in the UK.
If I have a 240 V convertor, every piece of equipment I want to hook up
will need to be rewired for 240 V. And, as I've discovered, it isn't
possible with all motors. I have a good friend who's very serious about
electrical projects (Tesla coil enthusiast, etc.) and he's building a
convertor too. He wants a 415 V convertor so he can reproduce an
industrial supply in his workshop.

I saw a couple of 7.5 kW (10 hp) motors on the demolition site when I
collected the 2.5 hp motor last week. I could probably get one, but
again they're delta connected for 415 V, so I would need a transformer.

Basically I'm in it for the science project, whereas you're in it for
the tool. Just different priorities.

Chris

"Christopher Tidy" wrote in message
...
Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It says
the primary is rated at 240 - 480 V and the secondary at 120 - 240 V. Do
you think this might be suitable for a phase convertor if used in reverse?
Perhaps there is some way to reduce the voltage slightly before feeding it
to the idler motor, or perhaps the motors would stand 480 V? We don't get
the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem

Chris

Chris

The single phase 10 KVA transformer looks like it can be wired to take 240
vac up to 480 vac. Transformers dont mind being reverse connected, as you
probably know, even though the primary is conventially wound closest to the
core. The eBay transformer would be a good choice for your need to use a
480 vac idler to make 480 vac 3 phase from a 240 vac power source..
I asume that you are more comfortable with 480 vac than I am. I hate
480.

Jerry

Jerry Martes wrote:
"Christopher Tidy" wrote in message
...

Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It says
the primary is rated at 240 - 480 V and the secondary at 120 - 240 V. Do
you think this might be suitable for a phase convertor if used in reverse?
Perhaps there is some way to reduce the voltage slightly before feeding it
to the idler motor, or perhaps the motors would stand 480 V? We don't get
the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem

Chris


Chris

The single phase 10 KVA transformer looks like it can be wired to take 240
vac up to 480 vac. Transformers dont mind being reverse connected, as you
probably know, even though the primary is conventially wound closest to the
core. The eBay transformer would be a good choice for your need to use a
480 vac idler to make 480 vac 3 phase from a 240 vac power source..

Thanks for the advice. Out of curiousity, why is the primary
traditionally wound closest to the core? This transformer is tempting,
but my concern is that the "official" voltage in the UK is 415 V, so I
will be supplying a somewhat excessive voltage to the motors. What do
you think?

I asume that you are more comfortable with 480 vac than I am. I hate
480.

I'm pretty careful. I only ever once had a shock, and that was off a
capacitor which had held a charge for a while. After that I was very
wary of capacitors.

Chris

What you are trying to do sounds like the Westinghouse 4kva convertor I
have. It has a step-up transformer built in and various taps to allow
380V, 415V, 440V etc. Makes using kit easier as I can just plug it in.
Currently running a Bridgeport, Harrison M300 and a few other items from
it.

Christopher Tidy wrote:

Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It
says the primary is rated at 240 - 480 V and the secondary at 120 -
240 V. Do you think this might be suitable for a phase convertor if
used in reverse? Perhaps there is some way to reduce the voltage
slightly before feeding it to the idler motor, or perhaps the motors
would stand 480 V? We don't get the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem


Chris

"Christopher Tidy" wrote in message
...


Jerry Martes wrote:
"Christopher Tidy" wrote in message
...

Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It says
the primary is rated at 240 - 480 V and the secondary at 120 - 240 V. Do
you think this might be suitable for a phase convertor if used in
reverse? Perhaps there is some way to reduce the voltage slightly before
feeding it to the idler motor, or perhaps the motors would stand 480 V?
We don't get the full 240 V from our supply anyway.

Here is the link:

http://cgi.ebay.co.uk/10kva-Transfor...cm dZViewItem

Chris


Chris

The single phase 10 KVA transformer looks like it can be wired to take
240 vac up to 480 vac. Transformers dont mind being reverse connected,
as you probably know, even though the primary is conventially wound
closest to the core. The eBay transformer would be a good choice for
your need to use a 480 vac idler to make 480 vac 3 phase from a 240 vac
power source..

Thanks for the advice. Out of curiousity, why is the primary traditionally
wound closest to the core? This transformer is tempting, but my concern is
that the "official" voltage in the UK is 415 V, so I will be supplying a
somewhat excessive voltage to the motors. What do you think?

I asume that you are more comfortable with 480 vac than I am. I hate
480.

I'm pretty careful. I only ever once had a shock, and that was off a
capacitor which had held a charge for a while. After that I was very wary
of capacitors.

Chris

Chris

The only reason I know about for winding the primary close to the core is
to give it maximum capability to couple to the magnet core. That would
ninimize the losses even while no load is applied (idling time)

The ratio of IN to OUT voltage as determined by the jumpers on the eBay
transformer is the imprtant factor for you. Can you put 208 VAC single
phase into the eBay transformer?

There is a problem with 480 other than electric shock. 480 has the
ability to vaporize metals and spray it around. I have seen the results of
dropping things across 480 and I'm probably overly 'scared of it.

Jerry

In article ghvJe.9796$WQ.8625@trnddc03,
says...



There is a problem with 480 other than electric shock. 480 has the
ability to vaporize metals and spray it around. I have seen the results of
dropping things across 480 and I'm probably overly 'scared of it.


I'd never heard that before, but it explains why a short in
a 480 box tends to blow the cover off, while a 240 "event"
isn't usually nearly as exciting. Personally, I'm
respectful of 120, very cautious around 240, and just plain
skittish around 480. I have one customer that has a bunch
of 550 volt imported from Canada equipment that I did
control retrofits on that makes me feel much as you -
probably more nervous than I should be.

Ned Simmons

On Mon, 08 Aug 2005 03:09:29 GMT, the renowned Ignoramus9991
wrote:

On Sun, 7 Aug 2005 22:23:12 -0400, Ned Simmons wrote:
In article ghvJe.9796$WQ.8625@trnddc03,
says...



There is a problem with 480 other than electric shock. 480 has the
ability to vaporize metals and spray it around. I have seen the results of
dropping things across 480 and I'm probably overly 'scared of it.


I'd never heard that before, but it explains why a short in
a 480 box tends to blow the cover off, while a 240 "event"
isn't usually nearly as exciting. Personally, I'm
respectful of 120, very cautious around 240, and just plain
skittish around 480. I have one customer that has a bunch
of 550 volt imported from Canada equipment that I did
control retrofits on that makes me feel much as you -
probably more nervous than I should be.

I would not try to run anything 480v. Especially with a kid at home.

i

Industrial fault currents can be a lot higher than what you otherwise
run into. 10kA can do a lot of damage. Even 240V in an industrial
situation can do impressive things if you short it, unlike in a home.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

In article ,
Ignoramus9991 wrote:

[...]

Yeah... Check out ogrish.com for some industrial accident pictures.

i

Eww, last time I went there I saw a dude squeezed in between dual
tires of a truck. His innards had become outards, and it looked like
they went through the top of his skull to get there. Lovely stuff.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

"Christopher Tidy" wrote in message
...
Still thinking about a phase convertor...

I've just seen this transformer on eBay which is rated at 10 kVA. It
says the primary is rated at 240 - 480 V and the secondary at 120 - 240
V. Do you think this might be suitable for a phase convertor if used in
reverse? Perhaps there is some way to reduce the voltage slightly before
feeding it to the idler motor, or perhaps the motors would stand 480 V?
We don't get the full 240 V from our supply anyway.

Here is the link:


http://cgi.ebay.co.uk/10kva-Transfor...7535991085QQca
tegoryZ71391QQrdZ1QQcmdZViewItem


Just one word :

Buck / boost..

Google is your friend.

--

SVL

On Sun, 7 Aug 2005 17:44:36 +0000 (UTC), Christopher Tidy
wrote:

snip
Thanks for the advice. Out of curiousity, why is the primary
traditionally wound closest to the core? This transformer is tempting,
but my concern is that the "official" voltage in the UK is 415 V, so I
will be supplying a somewhat excessive voltage to the motors. What do
you think?

I asume that you are more comfortable with 480 vac than I am. I hate
480.

I'm pretty careful. I only ever once had a shock, and that was off a
capacitor which had held a charge for a while. After that I was very
wary of capacitors.

Chris

It's more than tradition. The winding closest to the core has
the shortest mean turn length so the copper loss of an inner winding
is less than that of an identically wound outer winding.

Best efficiency occurs if the winding handling the highest
power (the primary) is the inner winding.

Because this results in the lowest total copper loss it also
yields the best voltage regulation.

Power transformers are efficient devices and it's usually OK to
use an outer winding as a primary and accept a pretty minor drop in
efficiency.

However it reverses the design corrections for the voltage drop
resulting from winding resistance. This will alter the apparent full
load voltage ratio. For example:-

With 1% copper loss in an inner winding and 1 1/2% copper loss in an
outer winding a 1:1 full load rated transformer would need 2 1/2%
extra turns on the secondary to compensate for the voltage drop.

If this outer winding is now used as a primary the OPEN CIRCUIT
output voltage is now only 97 1/2 %. The full load voltage drop will
reduce this to 95% so that the nominally 1:1 transformer is now only
1:0.95

Perhaps a more useful way of assessing this is to allow for a
voltage error of twice the rated no load to full load voltage drop

Jim

On Sun, 7 Aug 2005 17:44:36 +0000 (UTC), Christopher Tidy
wrote:


The single phase 10 KVA transformer looks like it can be wired to take 240
vac up to 480 vac. Transformers dont mind being reverse connected, as you
probably know, even though the primary is conventially wound closest to the
core. The eBay transformer would be a good choice for your need to use a
480 vac idler to make 480 vac 3 phase from a 240 vac power source..

Thanks for the advice. Out of curiousity, why is the primary
traditionally wound closest to the core? This transformer is tempting,
but my concern is that the "official" voltage in the UK is 415 V, so I
will be supplying a somewhat excessive voltage to the motors. What do
you think?

I asume that you are more comfortable with 480 vac than I am. I hate
480.

I'm pretty careful. I only ever once had a shock, and that was off a
capacitor which had held a charge for a while. After that I was very
wary of capacitors.

Chris

Its not the shock so much as the tendency to form a nice plasma cloud
which can really **** up your whole day.

Anyone need transformers, I have em up to 45kva.
Single and 3 phase.

And 3 phase motors up to 5 hp coming out my ass.

Gunner, California