Selecting a diode for an AC solenoid...

[bob prohaska]

I\'ve got a solenoid (vibratory) water pump (Fluid-o-tech) that uses
a series diode to lower the fundamental drive frequency from 60 to
30 HZ. 120 volts, 70 watts. It\'s in an expresso machine. DC resistance
is about 30 ohms, unfortunately I don\'t know the inductance.

After some years the pump became erratic in action and I replaced
the original diode with a 1n5407G, which worked well for many years.

Eventually the erratic operation returned. I checked the diode with
a multimeter, no problem. I tried warming the diode while checking,
still no problem. Normal forward voltage, open circuit in reverse.

It\'s hard to imagine that an 800 volt 3 amp diode could be invisibly
damaged in a 70 watt 120 volt solenoid circuit; is there something
I\'m missing? The only fast transients occur when the pump is switched
on and off, but with the switch in series with the diode and solenoid
that can\'t harm the diode.....or can it?

Thanks for reading,

bob prohaska

 

[Bob Engelhardt]

On 12/1/2021 12:44 PM, bob prohaska wrote:

...
is there something
I\'m missing? ...

What you\'re missing is probably that the diode is not the problem. Even
though the symptoms are the same as when the diode was the problem.

 

[Peter W.]

a) That a diode tests OK on multimeter, capable of perhaps 9VDC at most does not mean that it will test OK under actual load. Even operating well below its rating, it is still a \'wearing part\' in this application.
b) Do make sure that the pump is free of clogging and that the moving parts are not binding. If you can remove the pump safely, try soaking it in white vinegar for 24 hours.
c) Do make sure that the switches/contacts are clean and free of corrosion.

Best of luck with it!

Peter Wieck
Melrose Park, PA

 

[bob prohaska]

Bob Engelhardt <BobEngelhardt@comcast.net> wrote:

On 12/1/2021 12:44 PM, bob prohaska wrote:
...
is there something
I\'m missing? ...

What you\'re missing is probably that the diode is not the problem. Even
though the symptoms are the same as when the diode was the problem.

Sounds like you don\'t think mysterious diode failure modes are in the
cards. I\'ve no clue what might lead to the erratic behavior seen so far,
but it\'s time to bark up a different tree..

Thanks for writing.

bob prohaska

 

[ohg...@gmail.com]

On Wednesday, December 1, 2021 at 7:32:16 PM UTC-5, bob prohaska wrote:

Bob Engelhardt <BobEng...@comcast.net> wrote:
On 12/1/2021 12:44 PM, bob prohaska wrote:
...
is there something
I\'m missing? ...

What you\'re missing is probably that the diode is not the problem. Even
though the symptoms are the same as when the diode was the problem.

Sounds like you don\'t think mysterious diode failure modes are in the
cards. I\'ve no clue what might lead to the erratic behavior seen so far,
but it\'s time to bark up a different tree..

Thanks for writing.

bob prohaska

Most silicon diodes short as their failure mode, but occasionally we\'ll see one either open or get bail under load - regardless of how they test on the diode scale of a typical DMM. Try another, nothing to lose.

 

[Rob]

ohg...@gmail.com <ohger1s@gmail.com> wrote:

On Wednesday, December 1, 2021 at 7:32:16 PM UTC-5, bob prohaska wrote:
Bob Engelhardt <BobEng...@comcast.net> wrote:
On 12/1/2021 12:44 PM, bob prohaska wrote:
...
is there something
I\'m missing? ...

What you\'re missing is probably that the diode is not the problem. Even
though the symptoms are the same as when the diode was the problem.

Sounds like you don\'t think mysterious diode failure modes are in the
cards. I\'ve no clue what might lead to the erratic behavior seen so far,
but it\'s time to bark up a different tree..

Thanks for writing.

bob prohaska

Most silicon diodes short as their failure mode, but occasionally we\'ll see one either open or get bail under load - regardless of how they test on the diode scale of a typical DMM. Try another, nothing to lose.

It may gave transformed into a 6V zehner diode. Which means it looks
like a diode on the multimeter, and like a short in the circuit.

 

[Jeff Liebermann]

On Wed, 1 Dec 2021 17:44:36 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

After some years the pump became erratic in action and I replaced
the original diode with a 1n5407G, which worked well for many years.

Was the original diode a 1N5407 or something else?

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[bob prohaska]

Jeff Liebermann <jeffl@cruzio.com> wrote:

On Wed, 1 Dec 2021 17:44:36 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

After some years the pump became erratic in action and I replaced
the original diode with a 1n5407G, which worked well for many years.

Was the original diode a 1N5407 or something else?

This was back in the late 1990\'s and I don\'t remember. It\'s
possible the diode was physically damaged to the point the
markings weren\'t readable. I do remember the pump coil potting
cracked and I replaced the pump at some point, though maybe
not at the same time.

What got me suspecting the diode was a strong but not perfect
correlation between how long the espresso machine had been heating
and the onset of low pump output. First cup in the morning was
fast, subsequent (~20 min later) much slower. Next morning the
cycle repeated.

Occasionally the first cup from a cold start was slow also, but
that was relatively infrequent, maybe once a week.

Right now the machine is set up with three parallel 1n4007\'s of
unknown quality plus two connected as crowbars. The crowbars do
seem to make a difference in slowing down the water flow, which
is undesirable. That they do make some difference is slightly
encouraging, as crowbarring the coil would slow field decay.
And, so far the pump behavior has remained consistent.

I probably should pull the pump apart and look inside, but I really
can\'t imagine a mechanical explanation on something so simple.

Thanks for reading and replying!

bob prohaska

 

[Jeff Liebermann]

On Thu, 2 Dec 2021 18:47:47 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote:
On Wed, 1 Dec 2021 17:44:36 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

After some years the pump became erratic in action and I replaced
the original diode with a 1n5407G, which worked well for many years.

Was the original diode a 1N5407 or something else?

This was back in the late 1990\'s and I don\'t remember.

I thought that I was the only one who tears something apart, let\'s it
age for 10 to 20 years, and only then tries to fix it.

It\'s
possible the diode was physically damaged to the point the
markings weren\'t readable. I do remember the pump coil potting
cracked and I replaced the pump at some point, though maybe
not at the same time.

Sigh. That\'s not very helpful. For all I know, the original \"diode\"
could have been a thermal fuse that somewhat resembles a diode.

Do you have the manufacturer and model number so I can do some
Googling for info? Taking a shot in the dark, I found this hint
suggesting that the diode might be a zener.
<https://www.fixya.com/support/t782403-breville_800e5xl_didoe>
Here\'s the service manual and schematic:
<https://siber-sonic.com/appliance/breville800sm.html>
Hmmm... See schematic on printed Page 19. Looks like the motor has a
1N4007 diode across the winding and an SCR for power switching. That
suggests that it\'s running on DC, not AC.

What got me suspecting the diode was a strong but not perfect
correlation between how long the espresso machine had been heating
and the onset of low pump output. First cup in the morning was
fast, subsequent (~20 min later) much slower. Next morning the
cycle repeated.

Yep. Something is getting hot. The cracked epoxy(?) potting compound
suggests an overheated pump coil. The zener for the Breville depresso
machine drops the peak line voltage 24V. An ordinary diode in place
of the zener drops it only 0.6V. Kinda sounds like it might be a hot
pump coil. Got a gun type Infrared thermometer? Measure how hot the
pump coil gets.

Occasionally the first cup from a cold start was slow also, but
that was relatively infrequent, maybe once a week.

Overheating the pump coil might make the pump parts move around. My
guess(tm) is you\'ll find some correlation between the number of
minutes (or hours) you ran the expresso machine the previous night.
The longer it ran, the greater the likely hood that something in the
pump became mis-aligned or moved out of place. Just a guess(tm).

Right now the machine is set up with three parallel 1n4007\'s of
unknown quality plus two connected as crowbars. The crowbars do
seem to make a difference in slowing down the water flow, which
is undesirable. That they do make some difference is slightly
encouraging, as crowbarring the coil would slow field decay.
And, so far the pump behavior has remained consistent.

I probably should pull the pump apart and look inside, but I really
can\'t imagine a mechanical explanation on something so simple.

After 26 years, I would expect some corrosion and lime deposits.

>Thanks for reading and replying!

Y\'er welcome. Good luck.

bob prohaska

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Michael Terrell]

On Wednesday, December 1, 2021 at 12:44:40 PM UTC-5, bob prohaska wrote:

I\'ve got a solenoid (vibratory) water pump (Fluid-o-tech) that uses
a series diode to lower the fundamental drive frequency from 60 to
30 HZ. 120 volts, 70 watts.

A diode alone, can not change 60Hz to 30Hz.

 

[philo]

On 12/2/21 9:13 AM, ohg...@gmail.com wrote:

On Wednesday, December 1, 2021 at 7:32:16 PM UTC-5, bob prohaska wrote:
Bob Engelhardt <BobEng...@comcast.net> wrote:
On 12/1/2021 12:44 PM, bob prohaska wrote:
...
is there something
I\'m missing? ...

What you\'re missing is probably that the diode is not the problem. Even
though the symptoms are the same as when the diode was the problem.

Sounds like you don\'t think mysterious diode failure modes are in the
cards. I\'ve no clue what might lead to the erratic behavior seen so far,
but it\'s time to bark up a different tree..

Thanks for writing.

bob prohaska

Most silicon diodes short as their failure mode, but occasionally we\'ll see one either open or get bail under load - regardless of how they test on the diode scale of a typical DMM. Try another, nothing to lose.

I repaired industrial equipment for almost 40 years and it is very rare
to have an intermittent diode, but it can happen.

Considering how cheap they are, I\'d just replace it.


Is the solenoid DC perhaps?

Are you sure the diode isn\'t there just to provide DC?

I never heard of an AC solenoid that required 30hz

 

[bob prohaska]

Michael Terrell <terrell.michael.a@gmail.com> wrote:

On Wednesday, December 1, 2021 at 12:44:40 PM UTC-5, bob prohaska wrote:
I\'ve got a solenoid (vibratory) water pump (Fluid-o-tech) that uses
a series diode to lower the fundamental drive frequency from 60 to
30 HZ. 120 volts, 70 watts.

A diode alone, can not change 60Hz to 30Hz.

You\'re right, my error. The diode prevents doubling the 60
Hz of the line to 120 Hz in the plunger motion.

In any event, I think Bob Englehardt\'s analysis might be close
to the truth; the problem is not be what I suspect.

After reading Bob E.\'s remarks, I had another look at the machine
and found what looks like a check valve that was open both ways.
It\'s far from obvious how that could change from one cup of coffee
to the next, but I took it apart, turned over an o-ring and it sealed
in reverse. This valve is in series with at least two other check
valves in the pump, so it isn\'t obvious how it might matter.....
Over the next few days I\'ll learn if it makes any difference.

Just for completeness, here\'s a link to some information on the pump:
https://www.fluidotech.it/site/assets/files/1331/solenoid-pumps-accessories-1.pdf

Item 6 is a 3 amp diode, with no hint why, how or when it\'s used.
In my pump it\'s in series with the coil.

It should be noted that the GAS in the parts callout must refer to the
fitting types, this is most definitely a water pump. Also, the outlet
fitting used is item 10, so there\'s no relief valve nor flow regulator.
The check valve I fixed isn\'t part of the diagram and I\'m not sure why
it\'s present at all.

Thanks to everyone for reading and replying!

bob prohaska

 

[Bob Engelhardt]

On 12/3/2021 2:58 PM, Michael Terrell wrote:

On Wednesday, December 1, 2021 at 12:44:40 PM UTC-5, bob prohaska wrote:
I\'ve got a solenoid (vibratory) water pump (Fluid-o-tech) that uses
a series diode to lower the fundamental drive frequency from 60 to
30 HZ. 120 volts, 70 watts.

A diode alone, can not change 60Hz to 30Hz.

If you have a solenoid connected to 60 Hz AC, it will be activated 120
times a second (positive and negative going voltage). A diode will cut
that in half. So from 120 Hz to 60 Hz. Not 60 to 30, but still by 1/2.