Re-winding solenoids.

[Jeffrey Angus]

Just a few abstract thoughts here. It makes sense to me,
but then I've been known to over look the obvious on
occasion. ;-)

I have a solenoid coil that actuates a large 3-pole
contactor. A short pulse to pull up on a lever that
will toggle it from on position to another, and back.

Making measurements of the solenoid coil, although
potted in epoxy, yields a few measurements and a
couple of guesses.

<http://www.pronine.ca/multind.htm>

Coil form 1" diameter, 1-3/8" width and 1.5" depth.
Going backwards on a solenoid coil java script, yields
a matching 125 mH inductance (as measured) and 95 ohm
DCR (as measured) for 2500 turns of #30 AWG which will
fill the bobbin.

This a 480 VAC actuator.

Am I headed in the right direction if I assume the key
factor here is ampere turns?

Not allowing for the added inductance by a movable core,
this has an impedance of roughly 100 ohms. So that works
out to 4.8 amps or 12,000 ampere turns.

Substituting 2000 turns of #28 AWG yields 80 mH, and 42
Ohms. And subsequently roughly 12,000 ampere turns at
240 VAC.

Putting 240 VAC across the 480 VAC coil yields only 6,000
ampere turns and obviously is NOT enough to actuate the
contactor transfer mechanism.

The reason I'm curious is that ASCO seems to think that
the replacement coil for this is worth $585, although
they will sell it as the "sale price" of only $421.80.

Jeff-1.0
The other other one

 

[Jamie]

Just a few abstract thoughts here. It makes sense to me,
but then I've been known to over look the obvious on
occasion. ;-)

I have a solenoid coil that actuates a large 3-pole
contactor. A short pulse to pull up on a lever that
will toggle it from on position to another, and back.

Making measurements of the solenoid coil, although
potted in epoxy, yields a few measurements and a
couple of guesses.

<http://www.pronine.ca/multind.htm>

Coil form 1" diameter, 1-3/8" width and 1.5" depth.
Going backwards on a solenoid coil java script, yields
a matching 125 mH inductance (as measured) and 95 ohm
DCR (as measured) for 2500 turns of #30 AWG which will
fill the bobbin.

This a 480 VAC actuator.

Am I headed in the right direction if I assume the key
factor here is ampere turns?

Not allowing for the added inductance by a movable core,
this has an impedance of roughly 100 ohms. So that works
out to 4.8 amps or 12,000 ampere turns.

Substituting 2000 turns of #28 AWG yields 80 mH, and 42
Ohms. And subsequently roughly 12,000 ampere turns at
240 VAC.

Putting 240 VAC across the 480 VAC coil yields only 6,000
ampere turns and obviously is NOT enough to actuate the
contactor transfer mechanism.

The reason I'm curious is that ASCO seems to think that
the replacement coil for this is worth $585, although
they will sell it as the "sale price" of only $421.80.

Jeff-1.0
The other other one

Beware that some coils are dual coils with diodes potted in them.

WHen a diode fails in one of these, they tend to generate some noise
when energized. This is because one coil is pushing both directions
against the other that isn't.

Basically what this means is, the coil is designed to operate in a
DC state.

What we have done in the past if we suspected a shorted diode in one
of these types is to put a bridge rectifier in front of it.

But I can tell you this, if the construction of core around this coil
in the device that is using it has a laminated type layers, chances are,
you have a simple coil and there is some form of shading device near the
contact point where the accouter makes contact with it.

What is this thing? A ratcheting three position device? being ASCO, it
sounds like some kind of valve.

Jamie

 

[Jeffrey Angus]

Beware that some coils are dual coils with diodes potted in them.

WHen a diode fails in one of these, they tend to generate some noise
when energized. This is because one coil is pushing both directions
against the other that isn't.

Basically what this means is, the coil is designed to operate in a
DC state.

What we have done in the past if we suspected a shorted diode in one
of these types is to put a bridge rectifier in front of it.

But I can tell you this, if the construction of core around this coil
in the device that is using it has a laminated type layers, chances are,
you have a simple coil and there is some form of shading device near the
contact point where the accouter makes contact with it.

What is this thing? A ratcheting three position device? being ASCO, it
sounds like some kind of valve.

This is a simple multi-layer solenoid.
It is fed with 480 VAC via an external bridge rectifier.

It is a pull up actuated 100 amp 3-pole contactor.

It is physically identical to this one, with the excption of
being 3-poles rather than 2.

<http://www.ebay.com/itm/130520617745>

The solenoid is at the top left of the contactor with the bridge
rectifier on the side.

Jeff-1.0

 

[Jeffrey Angus]

Make, model, and photograph?

A similar model. 2-pole 120 VAC rather than 3-pole 480 VAC.
<http://www.ebay.com/itm/130520617745>

This is the coil itself from ASCO.

Is there a copper D-ring on the top end of the solenoid?
Nope.

If the coil it dead, try disolving the epoxy.
<http://www.esslinger.com/attack.aspx>
It will also make a useful coil form.

Coil works perfectly with 480 VAC applied to the bridge
recitfier. My task is to wind a new coil that will work
at 240 VAC.

If you know the core dimensions and the wire gauge, you
can estimate the number of turns.

I did that, see the initial posting. Using DC resistance,
physical size and measured inductance.

Check eBay?

They have the contactors available from $750 and up, and
complete units for $1500 and up.

No solenoids only.

Jeff-1.0

 

[Jamie]

A similar model. 2-pole 120 VAC rather than 3-pole 480 VAC.
<http://www.ebay.com/itm/130520617745>

This is the coil itself from ASCO.



Coil works perfectly with 480 VAC applied to the bridge
recitfier. My task is to wind a new coil that will work
at 240 VAC.



I did that, see the initial posting. Using DC resistance,
physical size and measured inductance.



They have the contactors available from $750 and up, and
complete units for $1500 and up.

No solenoids only.

Jeff-1.0

Why don't you use a simple step up transformer for the coil?
you won't need a large one.

JAmie

 

[Jamie]

Why don't you use a simple step up transformer for the coil?
you won't need a large one.

JAmie

To add to that, a 1:1 control transformer of a very small size can
be wired as a buck boost to operate that coil.

Jamie

 

[Jeffrey Angus]

To add to that, a 1:1 control transformer of a very small size
can be wired as a buck boost to operate that coil.

As I mentioned previously, the solenoid requires a 5.2 amp pulse
to properly actuate the contactor mechanism.

With a 240/240 control transformer wired up in boost mode that
would need at 1000 VA transformer as a bare minimum.

Jeff-1.0

 

[Jeffrey Angus]

Tell him something he DOESN'T already know.

Heh, thanks Michael. What I don't know and would like to
know is if my thinking with regards to ampere turns is
correct. Because I CAN wind a new solenoid coil with a
1/2 pound spool of wire for about $20.

Jeff-1.0

 

[Jamie]

Um, however briefly, the transformer needs to supply
5.2 amps at 480 volts to successfully energize the coil.

That's 2500 VA Even a 500 VA control transformer that I have
sags too much to properly actuate the transfer switch.

Jeff-1.0

I find it hard to believe that coil is using that much? Are you
sure it's in proper working order? We have 500 amp contactors with
120V coils that only require about 2 amps to pull in. Something just
does not sound right, but what ever.



Jamie

 

[Jeffrey Angus]

I find it hard to believe that coil is using that much? Are
you sure it's in proper working order? We have 500 amp
contactors with 120V coils that only require about 2 amps
to pull in. Something just does not sound right, but what
ever.

Yes I am sure. And yes I know what some contactors take to
actuate the coils in a steady state holding condition.

To repeat. This is a pulsed operation. The auxiliary contacts
on the transfer switch contactor interrupt the source from the
solenoid as it actuates.

The solenoid core pulls up on a link that rotates the armature
of the contactor assembly from normal to emergency position.
Each time it is pulsed, it rotates it one way, then the other
way.

The actual amount of time (I haven't measured it) this takes
is under a second roughly.

Jeff-1.0

 

[William Sommerwerck]

Tell him something he DOESN'T already know.

Heh, thanks Michael. What I don't know and would like
to know is if my thinking with regards to ampere turns is
correct. Because I CAN wind a new solenoid coil with
a 1/2 pound spool of wire for about $20.

Do you have good reason to believe that AWG 30 is the proper gauge, and that
your calculations are correct? If so, then buy the wire and do it. If it
doesn't work, you're out only $20 and the time it took to wind the coil.

I don't know enough about solenoids to properly judge your calculations. But
I don't see anything obviously wrong.

 

[Jamie]

As I mentioned previously, the solenoid requires a 5.2 amp pulse
to properly actuate the contactor mechanism.

With a 240/240 control transformer wired up in boost mode that
would need at 1000 VA transformer as a bare minimum.

Jeff-1.0

Then it must be pushing a large load a long distance.

at that current, you looks like you have ~ 100 ohm coil.

which means the wire in the coil is rather a large gauge since
this is DC going to it.

I would start around 20awg and see what the DCR 1M is on the
chart. Then see if that will physically fit on the form.


Jamie.

 

[Jeffrey Angus]

Then it must be pushing a large load a long distance.

at that current, you looks like you have ~ 100 ohm coil

Did you read the details from my original posting? (Se below)

which means the wire in the coil is rather a large gauge since
this is DC going to it.

I would start around 20awg and see what the DCR 1M is on the
chart. Then see if that will physically fit on the form.

Coil form 1" diameter, 1-3/8" width and 1.5" depth.
Going backwards on a solenoid coil java script, yields
a matching 125 mH inductance (as measured) and 95 ohm
DCR (as measured) for 2500 turns of #30 AWG which will
fill the bobbin.

This a 480 VAC actuator.

roughly 100 ohms, yes.

This is NOT a constant pull and hold solenoid. This is a
pulsed operation.

So that works out to 4.8 amps or 12,000 ampere turns.

Substituting 2000 turns of #28 AWG yields 80 mH, and 42
Ohms. And subsequently roughly 12,000 ampere turns at
240 VAC.

Based on: Ampere turns =
(Applied voltage * number of turns)/(coil resistance)

Both estimations of the needed number of turns and wire size
seem correct.

Putting 240 VAC across the 480 VAC coil yields only 6,000
ampere turns and obviously is NOT enough to actuate the
contactor transfer mechanism.

This tends to indicate that ampere turns is indeed the magic
number as 6000 is not enough to actuate a mechanism that
appears to require 12,000.

Jeff-1.0

 

[Jeffrey Angus]

Do you have good reason to believe that AWG 30 is the proper
gauge, and that your calculations are correct?

<http://www.pronine.ca/multind.htm>

Yields both the correct inductance and DC resistance with #30
AWG for the assumptions I've made for the physical size of the
coil bobbin.

If so, then buy the wire and do it. If it doesn't work, you're
out only $20 and the time it took to wind the coil.

I don't know enough about solenoids to properly judge your
calculations. But I don't see anything obviously wrong.

And that's why I thought I'd ask here. I was hoping to find
someone that _is_ familiar enough to at least tell me, "Yeah,
you seem to be heading in the right direction."

Jeff-1.0

 

[Jeffrey Angus]

You didn't say this solenoid was part of a transfer switch. This
raises the stakes substantially. Transfer switches are used to switch
the mains supply to a generator when mains power is interrupted. They
serve two main purposes: to keep critical equipment functioning when
mains power is interrupted, and to deenergize the power line so that
workers can assume it is deenergized when they work on it.

Now, the transfer switch was tested to meet specifications with the
designed solenoid installed. Knowing nothing of the design or
construction of the component, you propose to roll your own and stick
it in.

Which would be fine, if no one's life depended on its working. And if
the vendor would stand behind your handicraft.

I don't think Asco could reasonably foresee that someone would use a
program that gives the number of turns for an air-core inductor to
design a part for a life-safety application.

Thank you for your information.

It changes nothing. The original solenoid develops about 12,000
ampere turns at 480 Volts. The replacement needs to develop 12,000
ampere turns at 240 volts.

If this were a customer, such as a extended care center where I
originally bought the used generator from and replaced their
original automatic transfer switch with a new compatible one I
would have (and did) take proper steps to insure everything worked
within the confines of a life-safety application.

This is a manual transfer switch with some control logic to determine
if all the power is present prior to switching. What in essence it
does is not allowing you to switch to a non-existent source.

I asked for an opinion that ampere turns was the right direction I
was headed in to change an operating solenoid from 480 to 240 volts.

I did not ask form someone such as yourself to presume that I totally
lack the ethics to endanger life with a crap modification.

Ya know, the way this transfer switch operates, I can just as easily
add the optional "manual handle" on the side of the box to switch from
normal to emergency power and throw away all the complicated stuff
inside.

As far as life safety is concerned, this is to handle a loss of power
at the shop I operate. Simple. "The power failed." Go outside, start
the generator and once it's running go back and flip the transfer
switch. When the utility power returns and stays on, flip the siwtch
aback and then go outside and turn the generator off.

This really isn't rocket science.

Jeff-1.0

 

[Jeffrey Angus]

Ok, that's not going to work. Most of the impedance is coming from
the DC resistance of the wire. Decreasing the gauge decreases this
resistance, but also decreases the number of turns that will fit on a
the spool to a maximum OD of 1.5". This isn't working. I give up for
tonite.

Well as long as your bitching at me for leaving something out....

The original coil is being fed through a bridge rectifier (mentioned
elsewhere in the thread). So the AC impedance is less of an issue.

Using the proline scripting, I came up with 80 mH using #28 AWG wire,
1988 turns and 1.54" outside diameter with 42.63 ohms.

I come up with 11192 ampere turns. I've got some wiggle room to
increase the bobbin size a bit. So rest well good sir, we are at
a point that is "close enough" to wind up a prototype and see if
works properly.

If it does, then it gets potted in Epoxy to match the original
physical dimensions and we call it a success.

Jeff-1.0

 

[Jeffrey Angus]

I always find something to complain about. It's part of my standard
usenet protocol. Nothing personal.

Well of course, I've known you long enough now to fully understand
the protocol. ;-)

You cheated by going over the OD by 0.04". Assuming you can pack the
windings in as tight as the original, that shouldn't be a problem. I'm
not all that confident you can do it. Use a mandrel and a slow
turning lathe.

The physical demisions after the epoxy potting are 1.55, instead of
my guess of 1.375), and 1.66 rather than my also guess of of 1.50.

It will probably work. I just hate to say that as I'm sure you'll
blame me when it explodes and sprays coil bobbin parts all over the
shop.

Isn't that also standard Usenet protocol?

Right. Hide the evidence. Be sure to embalm the windings in yellow
Kapton (Polyimide) high temp tape before potting.

I still have several rolls here at the shop from when I'd rewind
surplus wall warts for laughs.

Jeff-1.0
the other other one.

Having a vacuum pot and temperature chamber helps make stuff
"right" when you do it. I kind of prefer a polyurethane for
potting myself.

 

[Jeffrey Angus]

You said in an earlier post that the current in the coil needs to be
around 5 amps, and you propose to use 28 AWG wire to wind it.
AWG 28 wire has a rated ampacity for chassis wiring (inside a bundle,
similar to your solenoid coil), is only 1.4 amps. I doubt that your
coil would last very long with that amount of current.
More investigation is necessary. Might be less painful to spring for
the proper solenoid from the manufacturer.

OOps.. I got that wrong.. That figure was the capacity in free air... The
capacity of AWG28 wire in an enclosed space is 0.83 amps.

I'm sure that it is. The original coil at 480 volts draws 5.2 amps
and is wounnd with #30 AWG.

Guess I need to repeat this. It is PULSED not STEADY operation.

Jeff-1.0

 

[Jamie]

Well as long as your bitching at me for leaving something out....

The original coil is being fed through a bridge rectifier (mentioned
elsewhere in the thread). So the AC impedance is less of an issue.

Using the proline scripting, I came up with 80 mH using #28 AWG wire,
1988 turns and 1.54" outside diameter with 42.63 ohms.

I come up with 11192 ampere turns. I've got some wiggle room to
increase the bobbin size a bit. So rest well good sir, we are at
a point that is "close enough" to wind up a prototype and see if
works properly.

If it does, then it gets potted in Epoxy to match the original
physical dimensions and we call it a success.

Jeff-1.0

You know, at this point, you pretty much don't care I would assume how
ever, have you thought about constructing a voltage double rectifier
instead of that bridge rectifier to drive that coil?





+-------+-------++
| | |
+ | |
D1 - | |
^ | |
| | +
C1 + + C|
240 AC in | --- C| 480 Solenoid
|| | ---C2 C|
+---+-||+------+ + |
|| + | +
| | |
- | |
D2 ^ | |
240 AC in + | |
| + |
+-------------+-------++-------+
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


I suppose if you had to motor caps around you could use those, the
large ones of course.

What ever.
Jamie

 

[Jeffrey Angus]

At 60Hz, that's 276 uF. 330uf 600VDC caps should work. I'm not very
confident with my crude approximations. Therefore, I would feed the
model to LTSpice and see what it's really going to do.

You're charging to the peak values, not RMS, so it's going to be 680
volts at a minimum, and probably more like 750 for some margin of
safety.

Caps of that size and rating will end up costing as much as the coil
itself.

Jeff