How can solenoid’s coil fail open from a non-mechanical reason?

[dontknwmucboutanythng]

Hello,

Apology if this is the wrong forum for this question. 

Is it possible for a solenoid’s coil to fail OPEN from a non-mechanical cause such as over/under voltage, frequency, current?  Particularly when there is no sign of burn out to actually melt open the coil’s wire.

The coil is part of a 5v DC normally open solenoid controlling the main valve in a gas fireplace.  When activated, it is energized with about 4.5 v for 2 secs, ramp down to 2.2 v for another 2 sec, then stay at 0.6 v until deactivated at 0.0 v.

Thanks for your thought.

[floobydust]

Welcome to the forum 

A solenoid is simply copper wire wound on a bobbin, so yes they can go open circuit. It is usually due to a bad connection at the ends of the magnet wire, or damage from getting hit on the side, a break in the winding somewhere. Electrically, it would have to be a massive overload to melt open-circuit the winding yet not burn up the coil, which is highly unlikely.

Because this solenoid has a safety function, there will be extra stuff either mechanical or electrical or both associated with it.
It will only get energized if the controller thinks everything is safe. If it is intermittent pilot, it will check first for false presence of flame, dirty flame rod etc.

[james_s]

The wire can break mechanically just from temperature cycles or normal handling, especially if there is a manufacturing fault such as a thin spot in the wire or it is wrapped too tightly somewhere. As was said above, the most common problem I've seen is with the connections at the ends.

[bob91343]

All failures are mechanical, other than chemical contamination, which arguably is also mechanical.

[dontknwmucboutanythng]

Thank you for all the responds so soon.  Yes, all the conditions (pilot flame, etc) were presented for energizing the solenoid with correct (measured) voltage.  Normally, if it was a onetime failure, I would  just let the tech repair it.  But this is the fourth time same failure (open) at the same solenoid. With repair cost of $200 (part only) and weeks of wait time, this time I tried to troubleshoot to find out (root cause before repairing) if the failure could have been caused upstream electronically, hence the question earlier.

Since the same part failed 4 times in 8 years, it must be a persistent manufacturing defect.  But this valve are being used in many fire places, and I can’t imagine no one else notices this to effect a change in manufacturing.  Particular the entire (per manufacturer requirement) valve has to be replaced, each time a fireplace has to be disassembled almost completely for total cost of about $400.00.  The solenoid failed open at the coil.  Resistance was measured at the two coil’s terminals.  So the break is underneath the terminal solder joints or somewhere in the coils winding.   Reflow solder at terminals didn’t help.  So looks like I would just have to get another valve.

[Gyro]

I once had to fix the same sort of problem on a solenoid valve on a Ford Focus automatic transmission that would suddenly lose drive and flash errors. Luckily I was able to find internal photos and diagrams on the web and managed to tie it down to this one particular solenoid valve , after 70k miles the coil suddenly decided to go intermittent for no reason.

Of course the transmission was a filled for life, no drain plug, an obstruction blocking a suction pipe from getting to the bottom of the pan so I ended up covered in transmission fluid. Changing the solenoid valve was easy (apart from the fresh stream of fluid that pissed out). Just a solenoid valve with plunger and spring, connected with push-on crimps half immersed in transmission fluid. I never got around to unwinding the old one to find the break.

Sometimes solenoids just fail, maybe a nick in the wire during production, maybe a dry solder joint which fails with a bit of mechanical vibration and thermal expansion and contraction of the winding over the years. The obvious failure point would be the joints at the coil terminations but it sounds as if you've covered that.

4 times in 8 years sounds like a quality or design problem though. Over-dissipation sounds unlikely and would cause visible damage (no sign of overheating there). An inductive kickback issue would tend to cause insulation breakdown rather than an open. Maybe the winding tension was too high. It looks like as good a candidate for rewinding though (as long as it can be safely re-fitted without leakage issues!).

[CaptDon]

What controls the ramp down that you mentioned?? Is it a control circuit
powered from 120vac? Some sort of intelligent microprocessor control
package or is the ramping circuit internal to the solenoid? We used 'intelligent'
solenoids in the locomotive industry where the contactor was rated for
thousands of amps at around 1.5kv so the spring tension was huge and
the pole piece gap was big. It took lots of power to pull the contactor in
but once the gap was closed the coil current was internally ramped down
to just a bit more than what was needed to keep the contactor engaged.
Do you possibly suspect any lightning damage as a possible cause of failure?
Is this in a seriously damp location where electrolysis could be eating away
at the solenoids winding? I have seen PCB traces completely dissolved
by a single 1.5vdc AA cell when a pager fell into a bucket of cleaning
solution for the floors of operating rooms when the pagers sat wet overnight!!!
It actually happened often!!! We told them "If it falls in the bucket or toilet
rinse it off, pull the battery out, rinse it out and send it to the BioMed Lab.
We would put them in a partial vacuum at 70C for a day and they would
work fine!!
 

[james_s]

Of course the transmission was a filled for life, no drain plug, an obstruction blocking a suction pipe from getting to the bottom of the pan so I ended up covered in transmission fluid. Changing the solenoid valve was easy (apart from the fresh stream of fluid that pissed out). Just a solenoid valve with plunger and spring, connected with push-on crimps half immersed in transmission fluid. I never got around to unwinding the old one to find the break.

That's ridiculous. I think I would drill a hole to drain it and tap it for a plug.

[floobydust]

I looked at the SIT 885 Proflame and could see no reason for things to cause coils to go open circuit due to electrical issues. It's just a 7VDC controller and the two on-off gas solenoids, using peak and hold to drive the solenoids at 5V dropping to 1V. Troubleshooting guide

*There is a solenoid chassis ground connection that is dissimilar metals, I would look at that with a loupe. One leg soldered to the cast aluminum? Not going to go well. The coil could be fine but not the connections to it.

[dontknwmucboutanythng]

I de-soldered the coil's wire ends, stripped insulation from new ends, re-soldered them and everything works fine.  I'm kinda embarrassed this simple problem got much attention.  By the way "floobydust", how did you figure out it's a SIT 885 Proflame?

Thanks for all help everyone.

[floobydust]

We have fun solving puzzles here, no matter how big or small they seem.
I image-searched for fireplace gas valve until things matched your pictures, and there are not that many different makes.
It's a ripoff you have to purchase the entire valve body for high price, plus labour costs to fix a fireplace. These kind of repairs are well worth it.

[jmelson]

These kind of repairs are well worth it.

$400 ??!!??  No KIDDING it is worth it.  I have so much stuff here that I've had to hack into to keep running.  Dishwashers, clothes washers, cars, etc.  And, now that the OP knows how to fix it, he will be able to do so in the future.  And, maybe his soldering job was much better than the factory's work, that it will never fail again.

Jon

[james_s]

A significant percentage of the major appliances I own were broken ones somebody gave me and I fixed them. The way most people don't even try always surprises me, even so called professionals. I had a laugh a while back when I saw a post somewhere that they had determined a relay on the control board in their furnace was bad (tapping on it made it sometimes work) but the HVAC tech was charging something like $600 to replace the board because the relay was "permanently soldered" to the board. I could have repaired that control board in about 10 minutes with less than $20 in parts. I have a hard time respecting people who call themselves technicians and just swap expensive subassemblies until the thing works. A halfway mechanically inclined 12 year old with a screwdriver could swap parts in a furnace.

[Haenk]

I'm with you - if it is repairable, it should be repaired.
However, doing this for a living (which I don't) will bring up legal issues, at least in Germany you need to be a professional to work on non-low-voltage stuff (other than stuff that could be "plugged in"). Plus costs of labour, which often make a professional repair more expensive than purchasing new. Working on heating, gas and HVAC AFAIK even need a certification. Forget about installing your own plug and play pre-filled HVAC. That's illegal.
I'm pretty sure, *nobody* (a professional) would ever think about repairing that gas valve with integrated security functions - out of liability issues. Using a factory new part moves the liability to the manufacturer.
Then you have the "lifespan" issue - most systems are designed to a lifespan, if something in that system fails and you repair it, it's very likely other parts will fail soon, too.
E.g. my longtime car repair shop will not install used parts, ever. Even if they look like brand new. Easy way to avoid trouble.

[Gyro]

You have to have a grudging admiration for any company that can so finely calibrate its soldering process that it can repeatably achieve failure of a joint after two years, thus maximising spare parts income whilst comfortably avoiding any parts warranty issue! Your 'amateur' re-soldering has probably totally ruined this careful calibration and the resulting joints will last forever! 

On a serious note, I can't quite make out whether the coil and terminations are exposed to the gas. If so, moisture in the gas might possibly cause some slow corrosion of the interface between the bare end of the copper wire and the solder. It seems unlikely. but it might be worth a spot of lacquer (nail varnish?) on the joints as a belt and braces approach. Just a though.

[floobydust]

In North America, the concern is only when the product goes unsafe. A failing-open coil is not unsafe. Only a gasket might cause trouble and even then leaks are already covered in the design with a boundary seal.
These valve bodies can get hot being near the burner, so temperature swings might be part of it. I say it's shoddy manufacturing making the ground connection to cast aluminum, should be a press-fit pin that you can solder to and in Mexico they might have bodged that part.

Germany does have tons of safety/repair standards which look fine when matched with better consumer protection laws? Can a consumer show a product defect without getting in trouble? Who then reports the lifetime issue, Mr. Honest Repair Guy who profits every time from coming out to do the repair?

A friend's Samsung refrigerator, compressor would not run. Repair guy changes out the control board $400. Well, the problem happened again and digging in, the fridge is in demo or showroom mode where it everything looks like it is working, but the compressor remains off. Household people change fridge temperature and somehow the button sequence easily activates showroom mode. Nothing is wrong with the appliance but "do we need a new fridge?"

[james_s]

Reminds me of the time I somehow got my kitchen range in "Sabbath mode", I wasn't about to call for service but I had to look up online what it was and how to get out.

The concept seems rather strange to me, as if one is a devout enough believer to go through all the trouble of creating a loophole around the requirements of their god, you'd think they might have some concern that god would not appreciate people exploiting loopholes to get around these requirements.

[Gyro]

That's surreal! 

Edit: I bet Dyson hasn't thought of that feature yet! 

[Circlotron]

Reminds me of the time I somehow got my kitchen range in "Sabbath mode", I wasn't about to call for service but I had to look up online what it was and how to get out.

The concept seems rather strange to me, as if one is a devout enough believer to go through all the trouble of creating a loophole around the requirements of their god, you'd think they might have some concern that god would not appreciate people exploiting loopholes to get around these requirements.

There was an article many years ago in I think the Wall Street Journal that told about devout Jewish people not using an elevator on the sabbath day that had regenerative braking because diverting the kinetic energy in one’s moving body into electricity to be used somewhere else was considered work. I don’t know how they get on nowadays when pretty much all electric cars have regenerative braking and so would present the same issue.

[james_s]

Seems to me that if they really believe, they ought to respect the spirit of the rule and rest on that day rather than trying to find sneaky ways of working anyway, which is probably the original intent of the rule wherever it actually came from. But whatever, I'm not Jewish and none of the Jewish people I've known are anywhere near that fundamentalist so I have no skin in that game.