OT Gas Oven Query

** Hi all,

anyone here familiar with modern, domestic gas ovens ?

Seems many of them have gone high tech and use AC powered igniters and gas valves.

The igniters in question run from 125 VAC ( via an auto-tranny ) and draw about 3 amps when hot - while the *really odd* thing is they have a negative tempco, starting off at about 1.5 amps and rising to 3 amps after about 60 seconds.

Google tells me the technology is called " flat surface igniter " and the conductor used is Silicon Carbide, a semiconductor - hence the negative tempco. SiC igniters are all the rage for gas ovens, driers and furnaces in the USA - explaining the 125VAC rating.

Thing is, they run continuously and sit right in the gas flame which naturally causes the SiC to deteriorate and rise in resistance, lose power and then run at a lower surface temp creating a hazard in that the gas may not ignite.

To solve this, makers have linked the current draw of the igniter to the gas valve operating current making the combination fail safe but rather critical on the igniter being in good shape.

Replacement ignites are about $100 each and real pain to fit.

You can guess how I came to know this ...

Any similar experiences ?

.... Phil

Reply to
Phil Allison
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** Pic of typical SiC gas igniter.

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.... Phil

Reply to
Phil Allison

Damn. I was hoping you were looking for suicide advice.

Reply to
I'm Fvckin' Frank

I posted a similar-ish question on Dave's EEV blog along with a youtube video.

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My 25 year old central heating system had a hot surface silicon carbide ignitor (HSI). It looked different though, it was tubular shaped and it was not in contact with the flames once lit.

There was a separate wire that was used to sense if the flame was lit.

There was also a circuit to sense the current going through the HSI. If the current was not large enough, it would not attempt to light.

I went through about 5 HSI's during the central heating units 25 year life. So not too bad I suppose. The unit died when the combustion chamber rusted out, which affected the air/gas mixture apparently, so it wouldn't light.

Unlike your oven, it was very easy to change over the HSI. I purchased two HSI's from the states (ebay) at around $50 each inc shipping. Suggest you order a couple and keep at least one spare.

By the way, my HSI was also rated at 110V but it didn't use an autotransformer. It had a simple circuit that pulsed the full 240V at about

2Hz. The lights would flicker in the house just before the heat would come through :-)

The thermal mass of the HSI was enough for it to glow quite uniformly despite the very low frequency switching.

Our system was either a Northern Air or Southern Air.,, I forget. The installer of the new system said that he had seen a model like ours that blew up after failing to ignite. He noted that the exhaust flu on this model was very small for his liking.... goes to show despite all the safety features, they still go BOOM every once in a while.

Reply to
Mr Mac

"Mr Mac"

** My error for calling it a "flat surface igniter".

** Much better idea.

** That requires the duty cycle to be 25% .

When ON the power is 4 times rated, so spending 75% of the time off does the trick.

** Was this done with an oscillating relay ??
** How very comforting to hear ...........

The "old fashioned" idea of having a continuous pilot flame seems to have gotten the flick from the safety experts ( funny how my instantaneous, gas water heater still has one) to be replaced by a variety of dodgy and unreliable alternative systems that can still result in an explosion.

Anecdote:

Some years back, a meter reader for AGL knocked on my door cos he could not find the gas meters for the block.

Being the nice guy I am, I personally escorted him to the hidden room under the stair well that contained all the meters and opened the door for him.

The room was very dark and had no light.

So the meter reader pulled a butane cigarette lighter from his pocket and used it to read the meter's dials.

.... Phil

Reply to
Phil Allison

8
Reply to
Metro

No, I think it was a triac or something. Definitely not a relay.

A friend's new-ish gas oven uses a spark ignition, which is OK but it regulates the temperature by completely turning off and turning on again many times during the cooking time. Every once in a while, the spark fails to ignite the gas and the oven just sits there and doesn't attempt to re-ignite. The result is that you come back after an hour to check on your food, and find that it's still completely raw!!!!!!!

You can imagine the fury of a hungry engineer when his meat is denied to be delivered in a timely manner.

I have no idea why the electronics don't just keep the flame going and set it to low. Maybe some bullshit efficiency star rating benefit.

Reply to
Mr Mac

"Mr Mac"

** Triacs * are * cheaper........
** Hell hath no Fury like an hungry Engineer let down by ELECTRONICS !!
** CO2 pollution.

Destroying the planet - you know .........

.... Phil

Reply to
Phil Allison

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