Oil Fired Boiler Oil Valve Solenoid

John.G

I'll keep this brief as I've posted similar in Plumbing.

The above has two windings, one is 1400 ohms, the other 1.4 ohms, on start up 30VDC is supplied to the 1400 winding and 3VDC to the 1.4 ohm winding to hold it in. The boiler control also also supplies 54VAC for other control purposes. With the boiler/burner running normally if I probe the (black) wire supplying this 3VDC I get 54VAC and no reading on any of the DC scales, I can't figure this out as 54VAC would surely blow the 1.4 ohm winding in a second or two? even though it is, apparently AC?. I didn't check the voltage on the 1400 ohm winding on start up as I would have needed another pair of hands.

John.G

Also checked the brown (1400 ohm) wire and get 4.74VDC so this coil power is 0.016 watts or 16milliwatts, not a lot!! and I still get 54VAC on the black (1.4 ohm) wire at the same time. Just doesn't make sense.

Bruthal.

Is the system working properly? If you have a probe on the black wire reading 54v ac but expect 3v dc, where is the other probe connected to? Any wiring diagrams?

John.G

Yes, my system was/is worked perfectly with not one combustion failure trip in over 18 years. The other M.meter probe gives the same reading whether just earthed or connected to the main neutrlal, I cant connect it to the neutral in the control terminal box. On these Riello burners the main motor is 230v but this then generates 54VAC which powers the control box. Some of the newer controllers have just a two wire coil with switcing via the controller from 30VDC to 3VDC, if my thinkins ic correct, power is proportional to V squared so the holding power is only 1.0% of the closing power? seems very low even though its only a very small coil, I though hoding power for any coil might be more like 10% of the closing power. these oil solenoid valves actually close when energized, they fail open.

Here are my musings/ramblings from another (UK) site with the problem unit.

With boiler/ running, as well as the apparent 54VAC on the black wire (1.4 ohm),I also measured (today) 4.74VDC on the brown (1450 ohms) ,wire this means that IF this is the holding voltage then the coil power is 4.74*4.74/1450, 0.0155 watts, if one ignores the apparent 54VDC on the black wire then it means that the closing power, at ignition conditions is 30^30/1.4, 642.9 watts. Doesn't make much sense to me.

If 4.74VDC was feeding the black (1.4 ohms) (closing wire) at ignition conditions then the closing power is, 4.74*4.74/1.4, 16 watts

and if 30VDC was feeding the brown (holding wire) wire then the holding power is, 30^30/1450, 0.62 watts. This makes far more sense but not what I am measuring.

The manufacturers figures are 30VDC & 3.0VDC and 1470ohms (brown) & 1.4ohms. (black) which is more or less what I measured, (resistance readings)

I am told that the replacement burner for the Riello G2SX is the Riello G5X. (like mine)

My 530SE Control Box Bottomside.jpg

My 530SE Terminal wiring.jpg

Bruthal.

What method is used to produce the 3v dc?

Bruthal.

For example, and not necesarilly related to your setup, but to show how different voltages can be seen, if you put a 1k resister in series with a 100k resistor and connect 230v across it with phase to the 1k resistor end, you will have 2 or 3 volts across the 1k resistor but will get a reading of about 227v if you measure between N and the point where the 2 resistors are joined to each other. To get the voltage, the 2 probes have to be connected to the 3 volt source at both positions (each end of the 1k resistor in this example)

John.G

I don't know how the DC voltages are generated but as stated below as part of the fault finding, the holding coil (brown wire) is 1470 ohms and I am getting 4.74VDC, so the power is 4.74x4.74/1470, 0.015watts, seems tiny and if the voltage was the nominal 3VDC then the holding power would only be 0.006watts, practically zero?. I am definitely reading 54VAC (nothing on the DC scales) on the black closing wire which shouldnt have anything on it when the burner is running, if 30VDC is the closing voltage then the coil closing power is 30x30/1.4, 643watts, which is huge?, I did measure those resistances on the brown and black and they are as stated.

But that "54VAC" I am measuring is probably someting like what you explained above otherwise the coil would burn out straight away.

The only thing thats not correct below is that the solenoid valve closes, not opens when energized but that shouldn't change the facts?.

John.G

The plot thickens.

I ran 3 flying wires out of the terminal box bottom from 1, (brown wire), 2, common blue from the coil and 3 from 8 (black wire)

On start up I get 25VDC from the black wire (8) immediately on start up and this voltage remains there throughout the firing cycle. 12 secs after start up, pre purge. I get 5VDC on the brown (holding wire), 0 VDC up to this 12 sec which is correct. If I probe from the coil common (2) I get a continuous 25VDC from start up to finish.

This is not correct, to prevent oil dribbling out of the nozzle as the fan/oil pump motor is running up, the NO oil valve restricts the the pressure to below 5 bar and returns this recirculated oil to the tank, 12 secs after the prepurge is complete 25/30VDC should be supplied from the black wire, probably at the same time (by my stopwatch ) 5V is also spplied to the brown wire (this allows the oil pressure to rise to 8bar to 10bar running pressure) BUT the 25/20VDC to the black wire should then be switched out to the coil. Also if 25VDC is supplied to a 1.4omh coil then the power, theoretically is 446watts, probabl OK for a few seconds but not continuously.

I also get 54VAC as well as the 25VDC on the black wire and 24VAC as well as 5VDC on the brown wire while energised.

Query: With the coil energized shouldn't I get O volts between the common (2) and neutral?.

Wearb

John, seeing as the current would be low, measuring the current in those wires using your meter in series (I'm not sure if clamp is as accurate. Maybe sparks can answer). It would -seeing as you already have the resistance- give another view of power.

Wagos are great for the mm probes and wires, so that conductors aren't exposed.

I'll try it myself in the spring, but at the moment I'm sort of too sick of working on them to be experimenting with them in the evenings.

John.G

Very strange, I removed the burner from the boiler and ran it for 4 consecutive 9 sec periods, stopping it before each 12 sec prepurge elapsing/ignition, 36 sec in all, I couldn't see any sign whatsoever of a oil dribble from the burner which one would think should happen if the solenoid valve is energized from the very start.

Wearb

Difficult to understand what's going on. There's the making of a few good YouTube videos on your testing John 😄

whizbang

Those control boxes were a genius invention in the 60s when electronic components were expensive and unreliable. I dont think many people in the world have figured out the complexities of the circuitry.

I think the solenoid itself is acting as a transformer, and so does the timer heating element.

Riello have a video diagram of it working, might be usefull.

Be aware the dc component has very little capacitance on it, so its mostly half rectified ac voltage you are trying to measure.

John.G

Yes, seems pretty clever, one other thing I didn't mention is that if I probe (with M.meter set to 200VDC) between 8 &2 or 1&2 then the RCD trips, this is with the boiler running normally and with 24VDC from 8 and 5VDC from 2, also one would think that 2 would connect with neutral, I should then get 0V between 2 and neutral but I never do, I get 25VDC (and 54VAC).

Wearb

Big Clive (YouTube) had a great video on a similar control box. Worth a look fo anybody interested in this sort of thing.

So weird that you can trip an RCD with a mm set to voltage.

John.G

Can you post the link to that please.

Wearb

https://youtu.be/TYhv6fgP_u4?si=DZ4Cjxxb--t31gnU

Link to control box video.

John.G

Amazing how these controllers can run for well over 25 years without any trouble.

Wearb

I don't know if these are pertinent. They are files/notes that I saved when I was starting out on the game. I no longer remember the context in which I saved them.

John.G

A friend of mine tells me he has the same 530 SE control box on a 35 year old Firebird, so they must have been in production for years.

I wouldn't be recommendating this as a cost saving measure but he also only changed the fuel nozzle (a 0.5 80H) after well ove 30 years!, he gave me the old one and its absolutely spotless with no sign of carbon build up anywhere, I'd love to return it to Danfoss to take a few tests off it, I wonder how much do these nozzles actually wear, but still prudent to change at every service as relatively quite cheap.

Tom, Riello 40 G3B.jpg

Wearb

They wear and clog in roughly equal terms as far as I can see. So the output remains roughly the same. I know that the above is very anecdotal, but I rarely see an increase in soot as a result of nozzle age on a boiler with clean oil tank.

I see the opposite more often, especially when customer in habit of tilting the tank.

I've read reams of pages on Danfoss and Delevan nozzles and never came across a wear chart.

John.G

This is the +30 year old nozzle, exactly as removed from the burner, around 30,000 L of kero has passed through it, the newer nozzles have just the sintered filter holding the bits in place.

Fuel Nozzle +30 years.jpg

John.G

https://www.boards.ie/discussion/comment/121386891#Comment_121386891

One last bit of info, if I remove either the black wire or the brown wire then the fan motor will just run and run and run with no burner lock out,

Wearb

Yes. Creating the same conditions as a faulty coil.

10-10-20

For what it's worth John, the description of what's above had me wondering if you have a broken wire or a grounding fault as the voltages on the positive lead of the DVM are of course relative to the voltages on the negative.