On 2008-07-18, DrollTroll wrote:
"Ignoramus31221" wrote in message
...
On 2008-07-18, DrollTroll wrote:
"Ignoramus20788" wrote in message
...
My phase converter holds voltage better than 5%. That's not because of
some magic, but because the two idlers are big and they have
capacitors attached to both legs.
If you have a big idler, and properly sized run caps, that apply to
both legs, it will have great regulation.
For $100 or $200 you can have a great phase converter.
Run your 10 HP Baldor just like you did, but put 80-100 uF run
capacitors between legs 1-3 and 2-3. Very likely, the output of that,
at low loads like 3 HP, would be extremely well behaved.
Hey Ig,
Leg 3 is the wild leg, right?
I do not like the word wild, but yes.
How big are your idlers?
10 and 7.5 HP
I forgot to mention perhaps the weirdest thing: the wild leg off the
Baldor
is LOWER than the 240 V input!! Izzat possible? I'll have to check it
again!
No surprise
In googling diy rpc's, I saw one with 3 panel volt meters. How cool is
DAT??
very cool, I have one and want to install one too.
Cupla Q's:
I've got a bunch of caps, and of course none are suitable. Do you have a
source for caps? And analog panel meters?
The caps should not be expensive on ebay. I do not think that I have
any oil filled run caps.
I'd like to monitor all three leg-leg voltages as well, possibly in
different locations--at the rpc, and at the Fadal. I'm a little
surprised cnc makers don't put voltmeters somewhere on the machine.
You can use a multimeter for your testing.
fyi, for people curious as to why caps have to be rated at 350+ V, that's
because AC voltage is rms, and the zero-to-peak voltage of a 120 V sine
curve is 177, iirc.
If the 120 V is 180 deg out of phase (which gives 240 V--which means the 3
ph from 240 V svc is right away slightly hobbled, phase angle-wise), you
have momentary voltages of 354 V.
120 V (to ground) legs that are true 120 deg out of phase gives slightly
less peak to peak, and is what gives 208 V rms. And is true-blue 3 ph.
Have you thought of switchable banks of caps, for ranges of loads? Good
idea?
For caps in parallel, you just add the cap values, right?
Should the run caps be disconnected at start up?
You start your Baldor from something that is already running right?
If so, then you can leave the caps.
If you want to make a new phase converter, it is a different story.
i
The start caps disconnected on run? Many designs disconnect the
start caps, maybe because the start caps are what give that really
high generated leg?
I'm also thinking of experimenting with a very light resistive load
(few amp draw), connected to all three legs in delta and/or wye
fashion. May help initial regulation?
Have you noticed that the generated leg is very high wrt ground? I guess
that makes sense, since there is not really a complete circuit between the
two.
It's an inneresting trig problem to show the resultant sine curve and rms
voltages of two out-of-phase sine waves. May want to put his on your
algebra site as a real practical problem.
And from this show the intuitively obvious, that if two 120 V legs generate
240 between them, they MUST be 180 deg out of phase.
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