for what it's worth, I have good luck starting the 6 hp spindle motor
on my mill with a 600 uf starting cap, which is disconnected via a
potential relay once it's up to speed - the relay coil is wired from
the unenergized leg to neutral. it works very reliavbly. But if I
want to start the 2 HP motor that moves the table, I am better off
having the spindle running first.


On Sat, 7 Jan 2006 19:40:15 -0600, "Wayne S"
wrote:

It's been a few years since I've posted, but I have been lurking for
most of it. I am resuscitating a B&S 2A universal mill to which I will
mount a Bridgeport head. What I would like to do is use the 5HP mill motor
as the idler in a RPC for the Bridgeport head, while still using it to power
the table feeds and pump, and horizontal arbor when required. Yes, I could
use a separate idler motor, but don't see the point as I will never need
anywhere near 5hp on a mill. It has 32 spindle speeds and 32 feed speeds so
I really don't need a VFD. (The bridgeport head is a VS off some kind of
hydraulic driven mill)

I managed to start the mill motor using Hanrahan's self starting model,
but I needed about 12x 50 uf run capacitors to do it. According to
Hanrahan's article, it should only take 120-150 uf to start. I had to
remove the chain drive to get the motor to come up to speed. With the chain
on I could only get it up around 200 rpm (ran out of capacitors). The mills
electrical system contains all the essentials for Hanrahans RPC. I just
added the capacitors on the output of the contactor between line 1 and the
non-fed line 3.

Hanrahans RPC with the separate starting circuit using start caps calls
for around 50-100 uf per idler hp, yet the self starting version calls for
25-30 uf (per hp). Why so much more for the self starting version??

Wayne Sippola
Moose Jaw, Canada


Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com

On 2006-01-07 17:40:15 -0800, "Wayne S" said:

Hanrahans RPC with the separate starting circuit using start caps calls
for around 50-100 uf per idler hp, yet the self starting version calls for
25-30 uf (per hp). Why so much more for the self starting version?

A Hanrahan self-starter usually takes 30-35 uF/idler motor HP to self start.

A conventional ROC usually takes 100 uF/idler motor HP to start within
two seconds, which is about the limit for an electrolytic starting cap.

Since a Hanrahan converter uses run caps only, it doesn't matter if it
takes longer to start as these cannot overheat and explode, unlike
electrolytics, and you can thereby get away with less capacitance,
which improves matters, as less capacitance is probably better, from a
B-phase voltage control perspective.

On 2006-01-08 06:42:07 -0800, "Wayne S" said:

As the self starting method's line 3 voltage goes up with the
capacitance, I expect I will have to go with the separate start caps and use
my run caps to balance the RPC.

Yes, indeed so.

This is but one disadvantage of the self-starter.

With separate starting, you can employ whatever (electrolytic)
capacitance it takes to get the idler up to 90 percent of synchronous
speed in 2 seconds or under, and, separately, whatever (oil-filled)
capacitance it takes to have the idler produce a B-phase (what you are
calling line 3) which is within ± 10 percent (± 5 percent is usually
possible, too) of the single-phase line voltage.

Ideally, you want the fully loaded B-phase voltage to be ±10 percent
(±5 percent is better, especially for "technical" loads, such as
electronic equipment) provided the unloaded B-phase voltage is also
within ±10 percent (same comment for ±5 percent).

If you can get the unloaded B-phase within +10 percent (same comment
for +5 percent) and the fully loaded B-phase within -10 percent (same
comment for - 5 percent), then you have an excellent RPC, well-matched
to load.

If you cannot get ±10 percent (same comment for ±5 percent), then your
idler is probably too small.

Don't forget the case of unidirectional vs. reversible loads.

If the load is predominately unidirectional, then you probably want
more A-B (Line 1 to B-phase) capacitance than C-B (Line 2 to B-phase)
capacitance. About 60/40 percent.

If the load is reversible, such as a machine which runs forward for
some operations, using the conventional toolpost, and also runs reverse
for other operations, using the rear toolpost, then you probably want
the A-B and C-B capacitance to be the same.

Choices, choices, choices.

you can wire 220 with or without a neutral. To save you some time, I
use Leviton 2711 plugs (and matching receptacle) - this is a 4 wire, 2
hot, ground, neutral arrangement. There is another 4 wire plug that
has 3 hots, don't use that one. These are available from a nice
seller on e-bay for about half of retail, by the way.

Having neutral at the machine is advantageous for me because then I
can have an outlet there for a lamp or other accessory that wants 110
and not have extension cords on the floor to trip on.

If you would rather not have neutral, you can use a circuit with a
second relay.
this link provides a sensible and clear approach
http://www.homemetalshopclub.org/pro...nv/phconv.html

there are other sites with some rather "ad hoc" and somewhat
nonsensical approaches.

if you would like the schematic for the two relay approach, contact me
off line and I'll scan it and send it to you. You can also make a
solid state affair with a triac instead of a relay and a op
amp/zener/etc circuit to activate the relay - I figured that since I
wanted a neutral anyway, I'd use the approach with the single relay. I
had built the two relay one first (and it worked also, but the one
relay one seems to work a little better). The second relay, if you
use it, should pull in around 70 to 80 V and drop out below 30 to 50 V
- you can use a DC relay with a diode and cap, or an AC relay.

On Sun, 8 Jan 2006 08:30:07 -0600, "Wayne S"
wrote:


"William B Noble (don't reply to this address)" wrote
in message ...
for what it's worth, I have good luck starting the 6 hp spindle motor
on my mill with a 600 uf starting cap, which is disconnected via a
potential relay once it's up to speed - the relay coil is wired from
the unenergized leg to neutral. it works very reliavbly. But if I
want to start the 2 HP motor that moves the table, I am better off
having the spindle running first.


I suspect I will go this route. Have to go and buy some start caps.
I've been collecting run caps over the years knowing I would eventually
build a phase converter, but don't have much for start caps.
You said the potential relay is wired from the unenergized leg to
neutral. Does 3 phase wiring have a neutral? I was expecting to use the
4th wire as ground. The 220 line is just 2 hots and gnd.
Wayne

Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com

It's been a few years since I've posted, but I have been lurking for
most of it. I am resuscitating a B&S 2A universal mill to which I will
mount a Bridgeport head. What I would like to do is use the 5HP mill motor
as the idler in a RPC for the Bridgeport head, while still using it to power
the table feeds and pump, and horizontal arbor when required. Yes, I could
use a separate idler motor, but don't see the point as I will never need
anywhere near 5hp on a mill. It has 32 spindle speeds and 32 feed speeds so
I really don't need a VFD. (The bridgeport head is a VS off some kind of
hydraulic driven mill)

I managed to start the mill motor using Hanrahan's self starting model,
but I needed about 12x 50 uf run capacitors to do it. According to
Hanrahan's article, it should only take 120-150 uf to start. I had to
remove the chain drive to get the motor to come up to speed. With the chain
on I could only get it up around 200 rpm (ran out of capacitors). The mills
electrical system contains all the essentials for Hanrahans RPC. I just
added the capacitors on the output of the contactor between line 1 and the
non-fed line 3.

Hanrahans RPC with the separate starting circuit using start caps calls
for around 50-100 uf per idler hp, yet the self starting version calls for
25-30 uf (per hp). Why so much more for the self starting version??

Wayne Sippola
Moose Jaw, Canada

----- Original Message -----
From: "Ignoramus20351"
Newsgroups: rec.crafts.metalworking
Sent: Friday, January 06, 2006 9:21 PM
Subject: RPC Question

Capacitance needed to start a motor (even without considering
mechanically connected load), varies wildly between motors.

I have two motors. 10 HP and 7.5 HP. They are both inside my RPC here

http://igor.chudov.com/projects/17.5-Phase-Converter/

Very nice looking RPC!

10 HP is reliably started by 184 uF capacitance.

The 7.5 HP requires about 500-600 uF of capacitance. Otherwise is hums
and barely turns, and does not come up to speed.

Okay, so perhaps this particular motor I'm using needs a lot of capacitance
to start. Seems odd to me that they would vary much. The motor is a GE.
probably a late 1940's. Very large for 5hp.

So, I start my 10 HP first and after it spins up, the 7.5 HP starts
quite easily on already generated 3 phase. It merely enhances quality
of the generated 3rd leg by adding capacity.

Hanrahans RPC with the separate starting circuit using start caps
calls
for around 50-100 uf per idler hp, yet the self starting version calls
for
25-30 uf (per hp). Why so much more for the self starting version??

I am confused, the number that you cited for the self starting version
is lower, not higher.

My mistake - the main question I had and I phrased it wrong. The Self
Starting version in Hanrahans article uses much less capacitance than the
one using the separate start circuit. I don't understand why. I will
probably go this route, as that much capacitance is more easily done with
start caps. I expect I will need around 800 uf to start with the drive
chain on the motor.

If you leave the starting caps plugged in during actual 3 phase
generation, that makes voltage in the 3rd leg to one of the utility
powered legs, somewhat higher than single phase line voltage. The more
caps, the higher. That could damage sensitive equipment.

So, the starting caps that would be disconnected after startup, do not
have this effect since they get disconnected. But the starting caps
that stay connected, do have this effect.

When I was messing with my first RPC, more starting caps did make my
10 HP idler start faster, but the quality of third leg was worse.

i

"William B Noble (don't reply to this address)" wrote
in message ...
for what it's worth, I have good luck starting the 6 hp spindle motor
on my mill with a 600 uf starting cap, which is disconnected via a
potential relay once it's up to speed - the relay coil is wired from
the unenergized leg to neutral. it works very reliavbly. But if I
want to start the 2 HP motor that moves the table, I am better off
having the spindle running first.


I suspect I will go this route. Have to go and buy some start caps.
I've been collecting run caps over the years knowing I would eventually
build a phase converter, but don't have much for start caps.
You said the potential relay is wired from the unenergized leg to
neutral. Does 3 phase wiring have a neutral? I was expecting to use the
4th wire as ground. The 220 line is just 2 hots and gnd.
Wayne

"Peter Haas" wrote in message
news:2006010623510050073-peterh5322@aolcom...
On 2006-01-07 17:40:15 -0800, "Wayne S" said:

Hanrahans RPC with the separate starting circuit using start caps calls
for around 50-100 uf per idler hp, yet the self starting version calls
for
25-30 uf (per hp). Why so much more for the self starting version?

A Hanrahan self-starter usually takes 30-35 uF/idler motor HP to self
start.

A conventional ROC usually takes 100 uF/idler motor HP to start within
two seconds, which is about the limit for an electrolytic starting cap.

Since a Hanrahan converter uses run caps only, it doesn't matter if it
takes longer to start as these cannot overheat and explode, unlike
electrolytics, and you can thereby get away with less capacitance,
which improves matters, as less capacitance is probably better, from a
B-phase voltage control perspective.

I don't think this is it. Hanrahans article gives time to start with
the self starting method from 1 sec using 150 uf to 2.6 seconds using 120 uf
of run caps (5hp idler). So if we go with a 1 sec start time using 150 uf
of run caps, why 250-500 uf of start caps to start the same motor. Maybe it
just starts faster yet.
My problem is I need approx 600 uf of run caps using the self starting
method, with no load on the idler. I need to start it with a minimal load
so will need something more than this to use the mill motor as the RPC
idler. As the self starting method's line 3 voltage goes up with the
capacitance, I expect I will have to go with the separate start caps and use
my run caps to balance the RPC.
Wayne

On 2006-01-09 16:58:00 -0800, "Wayne S" said:

How much resistance do I need to add to bleed down the caps after they
are disconected??

The code gives you a time to 48 volts or less (48 volts being the limit
voltage for low-voltage circuits), which means that each value of
capacitance would require a separate calculation and perhaps a separate
value.

For practical purposes, a 1.5 kilohm 5 watt wire wound resistor is fine.

Caps which are permanently shunted by the idler or load motor are going
to be bled down, anyway, so you really only have to provide bleeders
across caps which are switched, which would certainly include the
electrolytic starting caps.

Most caps have at least two places per terminal for the connection of
1/4" "Fast-on" connectors, and oil-filled caps usually have four such
places.

For my own convenience and safety, I usually place a 1.5 kilohm 5 watt
wire wound resistor on each capacitor bank: A-B, C-B, A-C (if used for
power factor correction), and A-PR-B (PR = Potential Relay, for
starting, assuming an intermittent, potential relay starter is
employed).

This way, when I am moving around caps during "tuning" each bank will
have its own resistor.

An especially careful person might solder a 1.5 kilohm 2 watt carbon
composition resistor across each individual capacitor.

If this was done at the base of the "Fast-on", a terminal position
wouldn't be lost.

"William B Noble (don't reply to this address)" wrote
in message ...
you can wire 220 with or without a neutral. To save you some time, I
use Leviton 2711 plugs (and matching receptacle) - this is a 4 wire, 2
hot, ground, neutral arrangement. There is another 4 wire plug that
has 3 hots, don't use that one. These are available from a nice
seller on e-bay for about half of retail, by the way.

Having neutral at the machine is advantageous for me because then I
can have an outlet there for a lamp or other accessory that wants 110
and not have extension cords on the floor to trip on.

If you would rather not have neutral, you can use a circuit with a
second relay.

Thanks, I had a surplus contactor that only had one pole left, so using a
second start switch, I use this contactor to engage the capacitors. Push
both start switches until the mill comes up to speed and let go. Seems to
work alright. I have it starting now under the minimal load of the drive
chain. Just have to find a box to mount it all nicely in and add on the
receptacle for the vertical head. Also need to get the main contactor to
stop buzzing. From a thread on RCM a couple of weeks ago, I expect the
shade pole thingy is broken. Learn lots of stuff here!
Wayne

"Peter Haas" wrote in message
news:2006010707424316807-peterh5322@aolcom...
On 2006-01-08 06:42:07 -0800, "Wayne S" said:

As the self starting method's line 3 voltage goes up with the
capacitance, I expect I will have to go with the separate start caps and
use
my run caps to balance the RPC.

Yes, indeed so.

This is but one disadvantage of the self-starter.

With separate starting, you can employ whatever (electrolytic)
capacitance it takes to get the idler up to 90 percent of synchronous
speed in 2 seconds or under, and, separately, whatever (oil-filled)
capacitance it takes to have the idler produce a B-phase (what you are
calling line 3) which is within ± 10 percent (± 5 percent is usually
possible, too) of the single-phase line voltage.

I checked the B phase voltage with the 600 uf of run caps still in the
circuit. About 320 volts! I've redone it to use the oil filled caps in a
separate start circuit. (yeah, I could use electrolytic caps, but I didn't
have any handy) I am using a separate push button which engages a separate
contactor.
How much resistance do I need to add to bleed down the caps after they
are disconected??
Wayne

On 2006-01-07 17:40:15 -0800, "Wayne S" said:

Hanrahans RPC with the separate starting circuit using start caps calls
for around 50-100 uf per idler hp, yet the self starting version calls for
25-30 uf (per hp). Why so much more for the self starting version?

The self-starter uses oil-filled caps, which have no time limit, and it
does not matter if the motor takes a tenth of a second or ten seconds
(or ten hours) to start up.

With electrolytic caps, there is a time limit (and a number of starts
limit, too), thereby forcing you to use enough capacitance s the
startup occurs in less than two seconds (better yet, less than one
second).

The issue is the high equivalent series resistance (which causes high
self-heating) in the electrolytics.

The oil-filled caps don't have this property, or this restriction.