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Posted by Robert Swinney on July 14, 2008, 12:25 pm
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Sorry Karl. I shouldn't have personalized my reply. My mistake and I apologise.
But you will note,
I did say "probably lost sight of the need to properly balance . . ." having
not read previous
threads, as Bruce pointed out, I assumed you were talking about a 3-phase
installation. (think
definition of assume here ! ) So, please accept my apology, and disregard my
comments as
personalized. Certainly, if your 3-phase units were balanced, ala Fitch, there
is nothing more to
be done there.
What I was addressing was the posting in RCM of some individuals that have made
rotary phase
converters. They throw a few components together, more often than not without
regard to good
electrical practice; then set out to brag about how they built a rotary phase
converter.
Bob Swinney
...
> Karl, like so many who build RPCs, probably lost sight of the need to
> properly balance the
> idler-motor / load network. They throw in a few random-valued capacitors
> and step back to admire
> their work, giving no thought to completing the job in anything resembling
> good electrical design.
> They seem totally thrilled their RPC will start and run and assume that is
> good enough.
I don't know what i did to get on your bad side. FWIW, you're right I know
nothing of balancing. So, I had Fitch tune my units(three) I sent him loaded
and unloaded voltages. He told me what to install.
BTW, anybody heard from Fitch lately?
Karl
** Posted from http://www.teranews.com **
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Posted by Rick on July 21, 2008, 12:28 am
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> Sorry Karl. I shouldn't have personalized my reply. My mistake and I
apologise. But
you will note,
> I did say "probably lost sight of the need to properly balance . . ." having
not read
previous
> threads, as Bruce pointed out, I assumed you were talking about a 3-phase
installation.
(think
> definition of assume here ! ) So, please accept my apology, and disregard my
comments
as
> personalized. Certainly, if your 3-phase units were balanced, ala Fitch,
there is
nothing more to
> be done there.
>
> What I was addressing was the posting in RCM of some individuals that have
made rotary
phase
> converters. They throw a few components together, more often than not without
regard to
good
> electrical practice; then set out to brag about how they built a rotary phase
converter.
>
> Bob Swinney
And a few of them brag about a hell of a lot less than that...
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Posted by Bruce L. Bergman on July 13, 2008, 3:12 pm
Please log in for more thread options On Sat, 12 Jul 2008 18:28:53 -0500, "Karl Townsend"
>You may remember I asked about the pressure switch wire for my pump last
>week...
>
>The group convinced me to replace all the wires and put in conduit. More
>investigation shows I should move the pump control box to near the pressure
>switch at the same time, in the basement.
>
>Anyway, I now will have a 380 foot run from the basement to the well with 2"
>conduit installed. The pump uses three wires with loads as follows: red
>wire - 27.5 amps, black wire - 19.1 amps, yellow wire 10.8 amps. I learned I
>need THWN wire last week. What wire sizes should I order?
>
>Karl
Oops - well, I have the book in front of me now...
For a two wire single phase circuit:
Vd = (2K x L x I) / Cm *or* Cm = (2K x L x I) / Vd
Vd - Voltage drop
I - current in amps
L - one-way length of circuit
K - resistance in ohms of one circular mil foot of conductor
K = 12.9 for Copper 21.2 for Aluminum at 75C
Cm - cross section of wire in circular mils
#10 10380
#8 16510
#6 26240
#4 41740
#2 66360
#1 83690
#1/0 105600
#2/0 133100
#3/0 167800
#4/0 211600
5 horse 1Ph well pump might be 28 A Full Load, but it should have a
200% breaker or fuse to hold on the start surges. 60A would be a
conservative sizing. So we do the math for 60A and get...
42.4 x 380 X 60 / 5 volts = 193344 cm = 4/0 Aluminum
25.8 x 380 x 60 /5 volts = 117648 cm = 2/0 Copper
5 volts drop during the start surge is being rather conservative, but
now you have the numbers - and you can decide how conservative you
want to be.
Remember you also have that 180' of pump lead going down the well to
the motor that is NOT figured in, and unless you pull the whole pump
and stack out of the hole you can't change it.
2" Rigid PVC Sched 40 max fill is three 300MCM THHN/THWN or four #4/0.
Myself, I would go for a 70A or 100A sub-panel out at the wellhead.
If the majority of the load is 240V you can undersize the neutral one
gauge from the hots, but not under the normal minimum. 4/0 4/0 2/0 4
makes it easy to ID the neutral and ground.
That way WHEN (not if) the load grows out in that direction (*) for
lights or a battery charger and block heater for the tractor, or a
chlorine dosing pump because some bugs get into the well, you don't
have to rework it again. And wire prices aren't going to go down
much, if at all.
* - We do work for a few ranches and camps, it always does.
Oh, and if you want to move the pressure switch to the wellhead (I
would, save on running those control leads and eliminate several
points of failure) you need to either move one of the stored-pressure
tanks to the wellhead or add a surge chamber with a needle valve in
front of the pressure switch. That should smooth the pressure surges
in the line enough to stop any short-cycling.
--<< Bruce >>--
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> properly balance the
> idler-motor / load network. They throw in a few random-valued capacitors
> and step back to admire
> their work, giving no thought to completing the job in anything resembling
> good electrical design.
> They seem totally thrilled their RPC will start and run and assume that is
> good enough.