Resistance of gas valve solenoid
YAPH
newish Ferroli boiler[1] (DOMIcompact F24D) which seemed to have its gas
valve packed up: went through normal start-up sequence up to point of
sparking to light the gas but gas was there none. Checked 240V on wiring
to gas valve present when it was sparking to boiler electrics OK; checked
resistance of solenoid - open circuit.
Today picked up new gas valve. Sanity check: test resistance of coil. Open
bloody circuit! Call Ferroli[2] who assure me coil resistance should be
5.9 MegOhm!! (Yes, Megs not K - I asked, tech bloke assured it was so.) My
multimeter only goes up to 2M FSD. Could have put the megger on it -
technically that resistance would have passed an insulation resistance
test! WTF: even at DC that would only pass 40 micro-amps from 230V; with
ac the inductance would make it less still. How does the damn' thing even
work? Or has it some electronics in it?
Work it did, though: gas, heating, happy customer.
[1] funnily enough one I'd been asked to commission a few years ago by the
unqualified cowboys installing it. Usual response: "I've spent
many hundreds of pounds and weeks of my time getting and maintaining my gas
qualifications, and you want me to put that on the line ticketing up this
boiler for you for HOW MUCH DID YOU SAY YOU WERE OFFERING?"
[2] 8p/minute 0871 number which they spun out with blah blah press 1 for
this etc and no proper mobile-friendly geographical number for engineers
(I asked). So think of that if you're thinking of buying a Ferroli (as I
pointed out to their phone droids!)
--
John Stumbles -- http://yaph.co.uk
I used to be indecisive but now I'm not so sure
Bob Minchin
I wonder if it uses a capacitor to drop a whole load of volts without
heat and for safety, they have a high value resistor to discharge the
cap. So when you measure DC ohms, you see a coil in series with a resistor.
Do post if you find the answer. I'm intrigued!
Bob
Skipweasel
bob.minc...@YOURHATntlworld.com says...
> That is only 10mW (VA) - not enough power to move anything.
If it's the gas solenoid, then it isn't moving anything. It's just
holding open the valve that's already been pushed open by your thumb.
Indeed, it's quite likely that the lump is already magnetised but not
quite enough to hold against the spring - the small current from the
thermocouple is just enough extra to hold open.
Like I said when this came up last month - the solenoid is miles and
miles of very fine wire.
--
Skipweasel - never knowingly understood.
geoff
<bob.minc...@YOURHATntlworld.com> writes
post mortem on it
--
geoff
John Walliker
> >I wonder if it uses a capacitor to drop a whole load of volts without
> >heat and for safety, they have a high value resistor to discharge the
> >cap. So when you measure DC ohms, you see a coil in series with a
> >resistor.
>
> >Do post if you find the answer. I'm intrigued!
>
You will probably find that it has a bridge rectifier inside. The
forward voltage drops of two diodes in series are probably greater
than the operating voltage of a multimeter, which is why the
resistance appears to be very high or open circuit.
John
geoff
<skipweas...@googlemail.com> writes
gas valve solenoids are usually in the range of a few kohms
we're talking a factor of 1000 difference here
--
geoff
YAPH
> In article <ik4159$jci$1...@news.albasani.net>,
> bob.minc...@YOURHATntlworld.com says...
>> That is only 10mW (VA) - not enough power to move anything.
>
> If it's the gas solenoid, then it isn't moving anything. It's just
> holding open the valve that's already been pushed open by your thumb.
Modern condensing boilers[1] are pretty much thumb-free zones.
> Indeed, it's quite likely that the lump is already magnetised but not
> quite enough to hold against the spring - the small current from the
> thermocouple is just enough extra to hold open.
What is this thermocouple of which you speak? When C21 gas valves like
this open it's a half-inch pipe into a 24kW burner with an ignition
electrode doing its best to make sure it all lights up or shuts off again
PDQ!
> Like I said when this came up last month - the solenoid is miles and
> miles of very fine wire.
Anyway the old thermocouple-operated hold-in solenoids were very *few*
turns of *thick* wire - tens of millivolts but loads of current.
[1] or even so-twentieth-century technology standard-efficiency boilers
with a secondary heat exchanger bolted on to get up to mid-noughties
efficiency standards, which this Ferroli is.
--
John Stumbles -- http://yaph.co.uk
Religion is like a penis. It is fine to have one. It's ok to be proud of it.
Just don't wave it around in public or try to jam it down my child's throat.
Michael Chare
news:8sldqu...@mid.individual.net...
>
> Today picked up new gas valve. Sanity check: test resistance of coil. Open
> bloody circuit! Call Ferroli[2] who assure me coil resistance should be
> 5.9 MegOhm!! (Yes, Megs not K - I asked, tech bloke assured it was so.) My
> multimeter only goes up to 2M FSD. Could have put the megger on it -
> technically that resistance would have passed an insulation resistance
> test! WTF: even at DC that would only pass 40 micro-amps from 230V; with
> ac the inductance would make it less still. How does the damn' thing even
> work? Or has it some electronics in it?
>
> Work it did, though: gas, heating, happy customer.
>
I use a flow switch to control my boiler. I was rather disappointed to find
that my new replacement flow switch still had a resistance of about 50kohms
even when there was a flow. However I was subsequently pleased to find that
the flow switch would fire the relay that starts the boiler. I think that
the reason for this is that the flow switch uses a triac.
--
Michael Chare
Skipweasel
> I think he knows that
>
Sorry - I've just driven to Kent and back and my synapses are feeling a
bit battered.
Skipweasel
> Anyway the old thermocouple-operated hold-in solenoids were very *few*
> turns of *thick* wire - tens of millivolts but loads of current.
>
Mine wasn't when I took it apart. Miles and miles of the stuff, it was.
Andy Wade
> In article<8sljru...@mid.individual.net>, use...@yaph.co.uk says...
>> Anyway the old thermocouple-operated hold-in solenoids were very *few*
>> turns of *thick* wire - tens of millivolts but loads of current.
>>
>
> Mine wasn't when I took it apart. Miles and miles of the stuff, it was.
That was the mains-voltage coil for the main gas valve, rather than the
millivolt-level coil for the pilot port. A multi-function valve of that
type will of course contain one of each.
--
Andy
Harry Bloomfield
Even miles and miles of thin copper wire will not have a resistance in
the M Ohm range. Usually solenoid resistances are measured in the low K
Ohm range. Only if there is a device in series with it, will it measure
in the M Ohm range.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Harry Bloomfield
> In article <8sljru...@mid.individual.net>, use...@yaph.co.uk says...
>> Anyway the old thermocouple-operated hold-in solenoids were very *few*
>> turns of *thick* wire - tens of millivolts but loads of current.
>>
>
> Mine wasn't when I took it apart. Miles and miles of the stuff, it was.
I checked a failed one and it was not miles, but a great deal of very
thin wire.
Harry Bloomfield
> That was the mains-voltage coil for the main gas valve, rather than the
> millivolt-level coil for the pilot port. A multi-function valve of that type
> will of course contain one of each.
Not in my case, very thin enameled copper wire on the thermocouple
solenoid.
geoff
<spamb...@maxwell.myzen.co.uk> writes
Main valves are normally 240v
Modulating valves are normally 0-24V
Lately some main gas valves have been designed to run off DC as
rectified mains
Vaillant have taken to putting a bridge rectifier in the loom between
the pcb and the gas valve
--
geoff