Solenoids and thermocouples

[JohnW2]

I tried it and noted a similar result. The current is also tiny, if you check the hold in coil, they have a massive number of turns of very fine wire. They do not possess enough energy to directly hold a gas valve open, rather they operate a mechanical latch to retain the valve open.

Quite so. That's why one has to hold the (pilot light) valve open manually, until the tiny voltage/current from the thermocouple is able to activate the latch which hold the valve 'open'.

Kind Regards, John

 

[Harry Bloomfield]

Quite so. That's why one has to hold the (pilot light) valve open manually, until the tiny voltage/current from the thermocouple is able to activate the latch which hold the valve 'open'.

The point I was making was in regards to Jackrae's mention of a few thick turns in the winding. It doesn't fit with mV and uA's of the thermocouple.

 

[JohnW2]

The point I was making was in regards to Jackrae's mention of a few thick turns in the winding. It doesn't fit with mV and uA's of the thermocouple.

I agree and, as I've said, that is why one has to keep the valve open manually until the tiny voltage/current from the thermocouple is able (via a 'many turns' mini-solenoid) to activate the latch which keeps the valve open.

Kind Regards, John

 

[Harry Bloomfield]

I agree and, as I've said, that is why one has to keep the valve open manually until the tiny voltage/current from the thermocouple is able (via a 'many turns' mini-solenoid) to activate the latch which keeps the valve open.

You seem to be still missing it - Why would such a tiny current, need just a few thick turns of thick wire on the solenoid? The solenoid I investigated, an extremely high number of turns and extremely fine enamelled copper. It had failed due to shorted turns.

 

[Jackrae]

Harry,John,
Your experiences may indeed be in seeing solenoids with many turns of thin wire. On dismantling a pair of gas valves my findings were very different. For some reason I decided to keep hold of the solenoids (maybe to test thermocouples at some future date) but no matter. I dug into my box of bits and, as you'll see from the attached photo, both (slightly different sized) solenoids comprise only a total of only 16 turns of fairly thick wire.

 

[Harry Bloomfield]

Your experiences may indeed be in seeing solenoids with many turns of thin wire. On dismantling a pair of gas valves my findings were very different. For some reason I decided to keep hold of the solenoids (maybe to test thermocouples at some future date) but no matter. I dug into my box of bits and, as you'll see from the attached photo, both (slightly different sized) solenoids comprise only a total of only 16 turns of fairly thick wire.

Thanks, but I certainly remain puzzled as to how they might work. Over to John..

 

[JohnW2]

You seem to be still missing it - Why would such a tiny current, need just a few thick turns of thick wire on the solenoid? ....

It wouldn't. Why do you think I wrote (and you quoted) "a 'many turns' mini-solenoid" ??

Kind Regards, John

 

[JohnW2]

Thanks, but I certainly remain puzzled as to how they might work. Over to John..

I suppose it depends on what one is trying to move in order to latch the (manually opened) valve . If it is (which is really all it needs to be) a tiny (light) pin, with minimal friction, then I suppose it takes very little energy.

Also, on reflection, I'm not sure that the number of turns is necessarily a crucial factor, since that cannot increase the power (mV x μA) available from the thermocouple.

... so, I don't really know

Kind Regards,
John

 

[Jackrae]

Magnetic 'power' is generally quoted as "Ampere-Turns" ie product of current in the coil times the number of turns in the coil.
I think we've created a cardinal sin by hijacking Peter's thread

 

[JohnW2]

Magnetic 'power' is generally quoted as "Ampere-Turns" ie product of current in the coil times the number of turns in the coil.

Yes, I realise that, but it's not real 'power'. A certain amount of true power (which is restricted to what the thermocouple can provide) will be needed to overcome inertia and friction (and also do work against gravity, if the movement is not horizontal), won't it?

I think we've created a cardinal sin by hijacking Peter's thread

We have - but, unfortunately, for far from the first time

Kindly mods might be prepared to split the thread - I will ask.

Kind Regards, John

 

[bernardgreen]

Yes, I realise that, but it's not real 'power'. A certain amount of true power (which is restricted to what the thermocouple can provide) will be needed to overcome inertia and friction (and also do work against gravity, if the movement is not horizontal), won't it?

The magnetic flux created by the electrical power from the thermocouple does not pull in the valve mechanism.

The mechanism is "pulled in" mechanically by the person pressing the button which opens the gas valve and also closes the magnetic path by bringing the magnetic faces into contact with each other .

When the magnetic path is closed it requires very little magnetic flux to keep the magnetic faces in contact with each other.,

EDIT the word mechanically added

 

[ericmark]

The magnetic flux created by the electrical power from the thermocouple does not pull in the valve mechanism.

The mechanism is "pulled in" mechanically by the person pressing the button which opens the gas valve and also closes the magnetic path by bringing the magnetic faces into contact with each other .

When the magnetic path is closed it requires very little magnetic flux to keep the magnetic faces in contact with each other.,

EDIT the word mechanically added

Agreed, but why would this need an earth connection?

John - Thought about an earth rod but not sure how that affects the MCB and RCD trip.

This seems to be a continuation, and I seem to remember the post was about using non mains power, but the title seems to have changed to "Solenoids and Thermocouples" not sure what has happened here? The relay is more than a simple solenoid

and the same basic device is found on boilers and space heaters, and has some time function as well as sensing flame.

It caused a problem with my own boiler, as an intermittent fault was causing the boiler to fail, it seems there were many scenarios, including fuel gases getting into the fresh air supply, and the oil guy used a process of elimination temperature swapping parts etc, until the fault was found, turned out to be fuel cut off solenoid over heating.

But even a worn jet can cause the flame colour to alter and for the photo cell not to register the oil is burning. But the oil guy had test gear I don't have, to test the burn is complete etc. I know on the Falklands I would use smaller jets to recommended so the space heaters produced less smoke, watching the oil guy seems there is an adjustment I simply did not know about, but in the land of the blind the one eyed man is king, and in the Falklands non of us really knew how to repair space heaters, but it was a case of do your best or get cold.

 

[Harry Bloomfield]

The magnetic flux created by the electrical power from the thermocouple does not pull in the valve mechanism.

The mechanism is "pulled in" mechanically by the person pressing the button which opens the gas valve and also closes the magnetic path by bringing the magnetic faces into contact with each other .

When the magnetic path is closed it requires very little magnetic flux to keep the magnetic faces in contact with each other.,

Yep, I pointed that out long ago.

 

[JohnW2]

*** Thanks to mods for splitting this thread in response to my request ***

The magnetic flux created by the electrical power from the thermocouple does not pull in the valve mechanism.

Quite - that's what virtually all of us have said. Power from the thermocouple obviously would not be enough to actually operate the valve mechanism

The mechanism is "pulled in" mechanically by the person pressing the button which opens the gas valve and also closes the magnetic path by bringing the magnetic faces into contact with each other . .... When the magnetic path is closed it requires very little magnetic flux to keep the magnetic faces in contact with each other.,

Interesting. That's a little different from what I envisaged. I was thinking that current from the thermocouple was used to move a small 'pin' or suchlike which 'jammed' the mechanism so that the valve remained open when one removed one's finger from one button.

If what you suggest is correct, then I see one weakness (potential problem) with the approach. In order to 'fail safe', and to ensure reliable/safe closing of the valve when no current was coming from the thermocouple, there presumably has to be a reasonably strong spring to close the valve when it is not be held (manually/mechanically or electromagnetically) open - and I would not have thought that the thermocouple would be able to generate enough magnetic flux to 'win' in a fight against that spring.

What I've just written could be consistent with the fact that it usually takes quite a bit of manually pressure on the button - although that could be due to a fairly strong spring in the button mechanism, not the valve mechanism.

Kind Regards, John

 

[JohnW2]

Agreed, but why would this need an earth connection?

It presumably doesn't. As I said, my thermocouple-using boiler works fine from a floating generator - although, as I've said it's actually all-but-impossible, with copper plumbing, to have a boiler which is not connected to earth, even if the 'generator supply' doesn't provide an earth. Even if all the 'water plumbing' is plastic, gas pipework can't be,and that will usually be main-bonded to the MEWTT (aka 'earth').

One of the connections from the thermocouple to the mechanism it operates is in electrical continuity with the metalwork of the earth, but I see absolutely no reason why it could/should need to be connected to 'true earth' - and the same is true of the igniter in my boiler.

I have no idea of the details of how the new-fangled ionisation-based flame detectors work but I would again suspect that a connection to 'true earth' is not required.

Kind Regards, John