Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Lead-free solder is such a PITA (rant/whinge)

On Sat, 10 Sep 2016 19:32:11 -0700, Jeff Liebermann
wrote:

On Sat, 10 Sep 2016 11:46:46 -0700 (PDT), whit3rd
wrote:

On Saturday, September 10, 2016 at 9:26:40 AM UTC-7, Jeff Liebermann wrote:

...the OP reverse engineered the oven wiring and produced a
schematic of sorts. Generally quite good but a few mistakes. One was
showing an SCR keying the solenoids instead of a Triac. If it were an
SCR, it would rectify the AC going to the solenoids.


The C106D is the device used in two places. To that extent the
schematic is correct.
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Default Lead-free solder is such a PITA (rant/whinge)

In article ,
says...

On Sat, 10 Sep 2016 10:25:09 -0400, Ralph Mowery
wrote:

WE had hundreds of that brand where I worked and some were pulsed every
30 seconds or so and some were almost always on. Hardly any problems
with the coils.


Ralph, should I presume that was with pre-ROHS vintage coils? As I
mentioned in my O/P, the original pair (which were pre-ROHS) both
lasted two decades. Subsequent ones were 15-18 months AND the oven
gets less use nowadays as the kids migrate outwards. Not a
statistically significant sampling for some, but sufficiently damning
from where I stand/sit.

Most problems were either the rubber disk wearing out or the plunger
enlarging due to all the beating they take or the spring wearing out.
The plunger is enclosed so no way for it to touch the coil form.


We haven't had the moving parts show any issues, just coils.


Most of them were from days before the lead free junk.

When you pulse them about once every 60 seconds they do take a beating
after 5 or 6 months. When they were first used in that application
there were some complaints about how fast they were wearing out.
However if you calculate the number of cycles , they lasted many more
cycles than specified for by the manufactor.

You mentioned something about lowering the voltage from about 250 to 240
volts. Have you checked to see if the voltage is still around 240 ?




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Default Lead-free solder is such a PITA (rant/whinge)

On Sun, 11 Sep 2016 14:13:19 +0800, pedro wrote:

On Sat, 10 Sep 2016 19:32:11 -0700, Jeff Liebermann
wrote:

On Sat, 10 Sep 2016 11:46:46 -0700 (PDT), whit3rd
wrote:

On Saturday, September 10, 2016 at 9:26:40 AM UTC-7, Jeff Liebermann wrote:

...the OP reverse engineered the oven wiring and produced a
schematic of sorts. Generally quite good but a few mistakes. One was
showing an SCR keying the solenoids instead of a Triac. If it were an
SCR, it would rectify the AC going to the solenoids.


The C106D is the device used in two places. To that extent the
schematic is correct.


Duh. I thought C106D was a capacitor or typo error. It's a real part
and most definitely an SCR:
http://www.onsemi.com/pub_link/Collateral/C106-D.PDF
I could calculate the amount of heating from the DC present if you
would kindly risk your life and obtain a scope waveform of what is
present across the coil while energized.

I don't see any sign of heat damage around the solenoids in your
photos. (I don't like using the gas line as an electrical ground, but
that has nothing to do with the problem). The white wires connected
to the spade lug connectors would have turned brown by now if there
had been any overheating of the terminals. Therefore, my guess(tm) is
that the solenoid terminals are NOT getting hot, which would certainly
happen if they were melting the internal solder connections.

Measuring the terminal temperatures during operation would offer a
clue. If they are anywhere near the melting point of RoHS solder of
about 220C, it might be the culprit. However, since RoHS solder melts
about 40C higher in temperature than leaded solder, I just don't see
it. If you need some entertainment, try heating the terminals of one
of the failed solenoid coils with a really hot soldering iron and see
if you can reflow the solder inside the solenoid.

In other words, I don't think it's a solder problem.

Time for yet another guess(tm). I keep going back to the SCR. Besides
the rectified AC problem, if there's any oscillation or funny
waveforms feeding the SCR, the solenoids are going to get hit with
some fast rise time pulses, which could produce some rather large
voltage spikes in the solenoid. Tiny gauge wire means thin insulation
which could be penetrated by the voltage. #34 single layer is good
for 1500V. A high voltage spike could produce an arc between turns,
followed by a shorted turn. Shorted turns really increase the current
drain of an AC solenoid, which could be sufficient to fuse the #34
wire (5A).

If my guess(tm) is correct, then the problem will persist with almost
any solenoid that uses thin #34 gauge wire. So, something must be
done to prevent arcing between windings. Since the pulses are at a
much higher frequency than 50Hz, methinks a small capacitor or snubber
across the coil will take care of that. Maybe a spark gap across the
capacitor in case the voltages are really high. Too many joules
involved for an MOV to work.

Note: This was written before taking my morning vasodilator pill and
is therefore presumed to be relatively coherent and sane.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Default Lead-free solder is such a PITA (rant/whinge)

On Sun, 11 Sep 2016 11:00:01 -0400, Ralph Mowery
wrote:

You mentioned something about lowering the voltage from about 250 to 240
volts. Have you checked to see if the voltage is still around 240 ?


It is.

historyWestern Australia's grid voltage was 254(+/-6%) as a result
of the move from 40hz to 50Hz a long time back. Actually the single
phase voltage was never *defined*, rather it was 440V phase-phase
(3-phase system).

Although it was/is not interconnected with the eastern states' grid
(which was 240V as far back as the landing or the Ark), pressure to
fall in line was brought to bear, particularly as appliances etc made
for the 240V system suffered reduced lifetime at 254V, although there
were incandescent lamps made for 250V if one hunted them down.

So the supply authority relented and cranked the grid back to 240V
where it has been ever since as a statutory requirement./history


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Default Lead-free solder is such a PITA (rant/whinge)

In article ,
says...

On Sun, 11 Sep 2016 11:00:01 -0400, Ralph Mowery
wrote:

You mentioned something about lowering the voltage from about 250 to 240
volts. Have you checked to see if the voltage is still around 240 ?


It is.

historyWestern Australia's grid voltage was 254(+/-6%) as a result
of the move from 40hz to 50Hz a long time back. Actually the single
phase voltage was never *defined*, rather it was 440V phase-phase
(3-phase system).

Although it was/is not interconnected with the eastern states' grid
(which was 240V as far back as the landing or the Ark), pressure to
fall in line was brought to bear, particularly as appliances etc made
for the 240V system suffered reduced lifetime at 254V, although there
were incandescent lamps made for 250V if one hunted them down.

So the supply authority relented and cranked the grid back to 240V
where it has been ever since as a statutory requirement./history



Fine on the history of Australia's grid. Too bad all the coutries of
the world did not set one standard to go by. Most of the US seems to be
around a split system for the homes of 120 and 240 volts at 60 Hz.
There are some places that may have other odd values.

I worked in a large plant and most of the larger equipment was 480 volts
3 phase. The smaller equipment and offices were set for 120 or 240
volts.

Then we built a building of about 6 floors and while another and I were
calibrating some 3 phase heaters we could only get about 380 volts out
of the controler. Checked the incomming voltage and that was what we
had. Seems that the engineer had bought some equipment from a country
that required 380 volts. We were not told of this to start with and
found out about it when we were checking out the equipment.

Years ago in the US it seems that the standard was 110 and 220 volts,
then 115 and 230, now it is 120 and 240 volts. I hae a digital voltmeter
on my ham radio desk that stays on all the time. It is usually around
122 volts, but I have seen it between 118 and 124 volts depending on the
time of the year and day. I know it is accurate as I checked it against
some meters at work that were calibrated by a lab to the government
standrds.

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Default Lead-free solder is such a PITA (rant/whinge)

On Sun, 11 Sep 2016 10:19:06 -0700, Jeff Liebermann
wrote:

Duh. I thought C106D was a capacitor or typo error. It's a real part
and most definitely an SCR:
http://www.onsemi.com/pub_link/Collateral/C106-D.PDF


Certainly is. Been around a while too.

I could calculate the amount of heating from the DC present if you
would kindly risk your life and obtain a scope waveform of what is
present across the coil while energized.


Unlikely. Solenoids are cheap, I only have one life to give and it
isn't going to be for this cause, however noble from the scientific
research pov.

I don't see any sign of heat damage around the solenoids in your
photos.


The original pair were showing darkened areas on the brown stuff, but
that was two decades worth of higher utilisation.

(I don't like using the gas line as an electrical ground, but
that has nothing to do with the problem).


There is quite a bit of earth bonding in there, excessive in my view,
but I guess paranoia never killed anyone.

The white wires connected
to the spade lug connectors would have turned brown by now if there
had been any overheating of the terminals. Therefore, my guess(tm) is
that the solenoid terminals are NOT getting hot, which would certainly
happen if they were melting the internal solder connections.


Typical oven operating temp is 200C. Some occasions are 220/230 for
30 minutes. Coils have limited prospects for ventilating airflow, and
self-heating to boot, so they would reach ???

Measuring the terminal temperatures during operation would offer a
clue. If they are anywhere near the melting point of RoHS solder of
about 220C, it might be the culprit. However, since RoHS solder melts
about 40C higher in temperature than leaded solder, I just don't see
it. If you need some entertainment, try heating the terminals of one
of the failed solenoid coils with a really hot soldering iron and see
if you can reflow the solder inside the solenoid.

In other words, I don't think it's a solder problem.

(snip)

A high voltage spike could produce an arc between turns,
followed by a shorted turn. Shorted turns really increase the current
drain of an AC solenoid, which could be sufficient to fuse the #34
wire (5A).


When I have one of these failures, need to remember the
characteristics. They go O/C when hot, with normal program resuming
as they cool (at say 125C oven as a WAG). What I then do, after the
mandatory outburst of expletives, is grab my diagnostic lead which I
recall referring to earlier. This interposes a small naked 6V
incandescent lamp in series with each coil. Then I fire the oven up
again and wait for one or the other lamp to extinguish as the coil
reaches the failure temp again. I do NOT recall the current spec of
the lamps but suspect it is 50mA. They glow with decidedly equal
brightness until one is interrupted, so any inter-layer etc shorts
must also be transient.

If my guess(tm) is correct, then the problem will persist with almost
any solenoid that uses thin #34 gauge wire. So, something must be
done to prevent arcing between windings.


If it *is* arcing, it reoccurs with regularity on these post-failure
test runs - or not at all - as it would possibly take out the lamp or
at least show substantially increased illumination prior to the return
of O/C mode.

Since the pulses are at a much higher frequency than 50Hz,

(snip)

I'm not supporting that hypothesis at this stage.

Note: This was written before taking my morning vasodilator pill and
is therefore presumed to be relatively coherent and sane.

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tiny wire is inherently unreliable

adding a transformer and using 24V valves is a good idea.

or use 120V valves and wire the 2 in series instead of parallel?

m
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