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