Relay-logic controlled printing machine, 110 vac.

A 300mfd (150v) electrolytic cap is used together with 25K (25 W) ohm
wirewound pot and a 5K ohm relay coil to control a variable time delay before
the relay opens.

The cap is shot (measures less than 1mfd). I'm having a hard time finding a
replacement locally. (Yeah, I know: Digi-Key, et al) But I need to get this
up and running today.

What other common types can I use in place of this can-type cap? (It has 2
wings that rivet to the sides of the opening in the chassis and solder terms
make the connection below the chassis.) Maybe poly-somethings, two in series
or parallel?

It's a Mallory FP119A.

Can I use a non-polar electro? (The wiring diagram shows a polarity
indicator.)

Or a motor-start cap? ::

http://tinyurl.com/y9d3ks6

Thanks,
Dave

On Tue, 06 Oct 2009 22:42:57 -0700, DaveC wrote:

Relay-logic controlled printing machine, 110 vac.

A 300mfd (150v) electrolytic cap is used together with 25K (25 W) ohm
wirewound pot and a 5K ohm relay coil to control a variable time delay
before the relay opens.

The cap is shot (measures less than 1mfd). I'm having a hard time
finding a replacement locally. (Yeah, I know: Digi-Key, et al) But I
need to get this up and running today.

What other common types can I use in place of this can-type cap? (It has
2 wings that rivet to the sides of the opening in the chassis and solder
terms make the connection below the chassis.) Maybe poly-somethings, two
in series or parallel?

It's a Mallory FP119A.

Can I use a non-polar electro? (The wiring diagram shows a polarity
indicator.)

Or a motor-start cap? ::

http://tinyurl.com/y9d3ks6

Thanks,
Dave

On the face of it anything that'll get up to 330mfd and withstand 150V
should do. That's a honking big cap, and anything that's not a 'lytic
will probably be bigger.

--
www.wescottdesign.com

DaveC wrote in
:

Relay-logic controlled printing machine, 110 vac.

A 300mfd (150v) electrolytic cap is used together with 25K (25 W) ohm
wirewound pot and a 5K ohm relay coil to control a variable time delay
before the relay opens.

The cap is shot (measures less than 1mfd). I'm having a hard time
finding a replacement locally. (Yeah, I know: Digi-Key, et al) But I
need to get this up and running today.

What other common types can I use in place of this can-type cap? (It has
2 wings that rivet to the sides of the opening in the chassis and solder
terms make the connection below the chassis.) Maybe poly-somethings, two
in series or parallel?

It's a Mallory FP119A.

Can I use a non-polar electro? (The wiring diagram shows a polarity
indicator.)

Or a motor-start cap? ::

http://tinyurl.com/y9d3ks6


A motor start cap should be ok. They're meant for intermittent use under
heavy load so they don't accept heavy ripple currents for lomg, but this one
won't have to, with a few tens of kilohms between it and the mains.

A motor start cap should be ok. They're meant for intermittent use under
heavy load so they don't accept heavy ripple currents for lomg, but this one
won't have to, with a few tens of kilohms between it and the mains.

A single rectifier in series with 50 ohms feeds the charge current to the
cap. Seems that 150v is a bit overkill, no? (The 25K pot is on the discharge
side of the circuit which is switched in at the appropriate time.)

I think I'm going to go with the 270mfd / 125v start cap. It's sourceable
locally, fits the space, and although a bit low on the capacitance it will
fit the bill better than what's there.

DaveC wrote in
:

A motor start cap should be ok. They're meant for intermittent use
under heavy load so they don't accept heavy ripple currents for lomg,
but this one won't have to, with a few tens of kilohms between it and
the mains.

A single rectifier in series with 50 ohms feeds the charge current to
the cap. Seems that 150v is a bit overkill, no? (The 25K pot is on the
discharge side of the circuit which is switched in at the appropriate
time.)

I think I'm going to go with the 270mfd / 125v start cap. It's
sourceable locally, fits the space, and although a bit low on the
capacitance it will fit the bill better than what's there.



Don't worry if the cap is specced for a higher voltage, if it's cheap, have
at it, the margin of safety is good, the wider, the better.

"DaveC" wrote in message
...
Relay-logic controlled printing machine, 110 vac.

A 300mfd (150v) electrolytic cap is used together with 25K (25 W) ohm
wirewound pot and a 5K ohm relay coil to control a variable time delay
before
the relay opens.

The cap is shot (measures less than 1mfd). I'm having a hard time finding
a
replacement locally. (Yeah, I know: Digi-Key, et al) But I need to get
this
up and running today.

What other common types can I use in place of this can-type cap? (It has 2
wings that rivet to the sides of the opening in the chassis and solder
terms
make the connection below the chassis.) Maybe poly-somethings, two in
series
or parallel?

It's a Mallory FP119A.

Can I use a non-polar electro? (The wiring diagram shows a polarity
indicator.)

Or a motor-start cap? ::

http://tinyurl.com/y9d3ks6


You can potentially vary the values of the resistor and capacitor greatly
depending on how much drive is needed. As long as the time constant R*C is
the approximately the same it should approximately work. Obviously if it's
driving a relay then it needs enough current to turn it on. So your probably
not going to be able to vary R much unless it wasn't chosen well in the
first place.

The electrolytic caps were used because of the high voltage and high
capacitance. I doubt you can find anything but an electrolytic to replace it
with. Remember you can put them in parallel to increase the capacitance.
Just get you two, three, or how ever many you need to get approximately
300uF at 150V. I woudln't get any lower voltage and try to use them in
series because it is usually more trouble than it's worth.

Note, you can replace this simple delay circuit a mosfet who's gate is
charged up by a lot smaller capacitor and larger resistor.

Basically the gate is turned on in a similar time frame as the original but
requires virtually no current to do so. The mosfet then turns on which turns
on the relay.

All you need is a resistor(actually two), a cap, a suitable mosfet that can
handle the current and voltage(relatively easy to find for a few dollars),
and a diode for a snubber.

Since your input is 150V or so you'll have to reduce it for the mosfet's
gate voltage. I'll want to use a P ch but could probably put an Nch on the
low side of the coil.

R1
|
+-----+---mosfet Gate
| |
| C
R2 gnd
|
gnd

(use a fixed width font to view)

The R1 and R2 form a voltage divider. You'll want something about 12 to 1 so
that the mosfets gate only sees at most about 15V. A large voltage spike
could ruin the mosfet gate so technically it would be best to proect it. You
can do this by adding a 15-20V zener from the gate to ground.

Add the diode across the mosfet drain to source(look up diode snubber). Most
power mosfets actually have a diode built in to do this though.

In any case if you want to go this route then I'm sure someone can whip you
up a circuit. It's relatively simple and should do the trick better than the
large cap(And probably cheaper). Theres just a few small issues such as
getting hte polarity right and getting the voltage divider right(pch on the
high side would reverse the resistors and the cap would be to vcc rather
than to ground).

All you need is a resistor(actually two), a cap, a suitable mosfet that
can
handle the current and voltage(relatively easy to find for a few dollars),
and a diode for a snubber.

BTW, if ac is on the cap and not rectified you'll either want to add
rectification or go with a triac/scr version instead. Mosfets only work well
one way. I'm assuming the relay is DC since you mentioned an electrolytic
cap.

DaveC wrote in
:

Relay-logic controlled printing machine, 110 vac.

A 300mfd (150v) electrolytic cap is used together with 25K (25 W) ohm
wirewound pot and a 5K ohm relay coil to control a variable time delay
before the relay opens.

The cap is shot (measures less than 1mfd).

What was the existing cap? Any clear indications as to why or how it failed?

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?

DaveC wrote in
:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated loss
of electrolyte. Did the cap look like it had burst from inside earlier than
any final appearance of internal gubbins? Another possibility is the voltage
it saw. When you say 110 volts, you mean the mains, right? If so it will be
rectified and that cap will be seeing the peak value, not the RMS, so around
125V when under no load, so you really do need it to have a higher voltage
rating than that.

Lostgallifreyan wrote in
:

DaveC wrote in
:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated
loss of electrolyte. Did the cap look like it had burst from inside
earlier than any final appearance of internal gubbins? Another
possibility is the voltage it saw. When you say 110 volts, you mean the
mains, right? If so it will be rectified and that cap will be seeing the
peak value, not the RMS, so around 125V when under no load, so you
really do need it to have a higher voltage rating than that.

Btw, I know that that cap ought not to be unloaded to the point where the
voltage gets to full height in that system, but best assume it will, so if
the load fails the cap remains safe and you get no bad future comeback. I've
seen an amplifier that had an internal fire resulting from a cap failure. It
shocked me. Very very messy scene. I wasn't given to me for repair, I didn't
even get much salvage out of it.

On Wed, 07 Oct 2009 22:27:31 -0500, Lostgallifreyan
wrote:

DaveC wrote in
al-september.org:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated loss
of electrolyte. Did the cap look like it had burst from inside earlier than
any final appearance of internal gubbins? Another possibility is the voltage
it saw. When you say 110 volts, you mean the mains, right? If so it will be
rectified and that cap will be seeing the peak value, not the RMS, so around
125V when under no load, so you really do need it to have a higher voltage
rating than that.

---

peak = RMS * sqrt(2) = 110 * 1.414 ~ 155V

JF

John Fields wrote in
:

On Wed, 07 Oct 2009 22:27:31 -0500, Lostgallifreyan
wrote:

DaveC wrote in
l-september.org:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated
loss of electrolyte. Did the cap look like it had burst from inside
earlier than any final appearance of internal gubbins? Another
possibility is the voltage it saw. When you say 110 volts, you mean the
mains, right? If so it will be rectified and that cap will be seeing the
peak value, not the RMS, so around 125V when under no load, so you
really do need it to have a higher voltage rating than that.

---

peak = RMS * sqrt(2) = 110 * 1.414 ~ 155V

JF


Agreed. I even knew the formula and entered exactly 1.414, no less, so I'm
still wondering what the hell else I wrote into the Windows calculator this
morning to get an answer of fractionally over 125V. I'll put this down as yet
another reason to aim for safe margins if the cost doesn't prevent it.

(Actually I found it. I typoed as 1.141...)

peak = RMS * sqrt(2) = 110 * 1.414 ~ 155V

JF

This is for half-wave rect.?

Thanks.

peak = RMS * sqrt(2) = 110 * 1.414 ~ 155V

My line voltage runs well above 110.

PG&E says they target for a min of 114 and a max of 126.
That's at the handoff point. I think the idea is that
you get a min of 110 if you allocate a few volts for
drop on the wiring within your house.


Here is PG&E's blurb:
http://www.pge.com/tariffs/tm2/pdf/ELEC_RULES_2.pdf


--
These are my opinions, not necessarily my employer's. I hate spam.

Old age isn't a mechanism, but is a cause for caps to go bad old age =
drying, drying = dieing
Frank

"Lostgallifreyan" wrote in message
. ..
DaveC wrote in
:

What was the existing cap?

DaveC wrote in
:
It's a Mallory FP119A.

Any clear indications as to why or how it failed?

No. Guesses: Old age? Heat?



Old age isn't a mechanism. Heat could well be right. Also accelerated
loss
of electrolyte. Did the cap look like it had burst from inside earlier
than
any final appearance of internal gubbins? Another possibility is the
voltage
it saw. When you say 110 volts, you mean the mains, right? If so it will
be
rectified and that cap will be seeing the peak value, not the RMS, so
around
125V when under no load, so you really do need it to have a higher voltage
rating than that.

"Frank S" wrote in
:

Old age isn't a mechanism, but is a cause for caps to go bad old age =
drying, drying = dieing


I agree. Was just saying that length of time is like the length of a piece of
string. Like someone else here said, some electrolytic caps work fine in gear
tens of years old. Valve/tube gear even, where you have enough heat to
accerate drying. It sort of suggests that looking at lengths of time is
missing plenty, there's a lot of difference between electrolytics, they're
not at all consistent.

DaveC wrote in
:

Or a motor-start cap? ::

http://tinyurl.com/y9d3ks6


Another thought, if you ever need a high quality cap with high voltage and a
few hundred µF at short notice and can't buy one, look for disposable or
otherwise surplus camera flashes. they're usually good for electrolytics
at 350V at 200µF or more.