0
\$\begingroup\$

My gas fireplace has an electric spark ignition that isn't sparking. I'd like to 'test' it, but I'm not sure what a working one would be doing.

The spark contact has 120VAC with 4A current when I hook up my multimeter from the 'high voltage' to the 'burner return'. I would have thought it'd be enough to cause an arc of sorts, but even when I use probes that are very close together and attached to the terminals, no sparks.

How, generally, do these things work and where might I start in debugging it? Should I expect sparking with that kind of current?

enter image description here

I'm especially curious if the black circular part in the bottom left can be identified (there are no markings on it and I don't even know what kind of thing it might be).

This control module is RAM-1MC1-06, if that makes a difference.

\$\endgroup\$
  • \$\begingroup\$ how are you measuring the voltage? ... how are you measuring the current? .... how do you know that there is a problem with the ignitor? \$\endgroup\$ – jsotola Dec 15 '19 at 1:42
  • 1
    \$\begingroup\$ The circular black thing is likely an insulator designed to keep you or anyone else from sticking anything near that tab -- especially between it and anything nearby it. That "high voltage" is supposed to have a few thousand volts on it. 120 isn't enough to cross an igniter spark gap. Could you take a very close look at CR5 on that board, especially on the board itself near where the silk screened CR5 itself is located? It looks a bit "artificially darkened" to me. But it could be the lighting for your photo. \$\endgroup\$ – jonk Dec 15 '19 at 2:08
  • \$\begingroup\$ The pinout of the black module may give some clues. How many pins connect to the PCB? \$\endgroup\$ – sstobbe Dec 15 '19 at 3:31
  • \$\begingroup\$ Unfortunately, that is just the poor lighting in the photo. It looks fine in person (I can't find any evidence of burning or damaged components, visually). The black thing has 3 pins on the bottom. One connects to the big blue thing next to it, another connects to CR5, and the third connects to the white thing next to it (which connects to the pin I tested with in the red line coming from it). \$\endgroup\$ – Sydius Dec 15 '19 at 3:33
3
\$\begingroup\$

The voltage at the igniter is probably high enough to damage your multimeter, if you succeed in getting it to operate.

The high voltage transformer output (the tab on the black cylinder) goes to the electrode not to the mains.

You should not be fooling with this safety-critical subsystem, please cease before you electrocute yourself or blow up your house.


As to how it works, the incoming mains is stepped down by the transformer T1 and rectified and filtered, then likely regulated down to 5V to power the microcontroller U1 which controls the ignition sequence and gas valve actuation via the Omron relay, including flame detection, limited restart attempts and safety lockout. The safety redundant components near the connector are likely a flame rod type detection scheme. It’s very important that the gas not flow for more than a very brief time without a flame, lest the gas fill your house and eventually find a spark with unfortunate consequences.

The spark itself is typically generated by triggering an SCR to discharge a capacitor into the primary of transformer T2, creating a high voltage spark at double mains frequency, and not isolated from mains (so an electrocution hazard).

The board has redundant parts for safety, the micro has safety-critical approved hardware and firmware and the circuit is conformally coated.

It is designed to fail only in a safe manner (to sufficiently high probability to satisfy UL and CSA that it won’t kill too many people), which it apparently has.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ While I appreciate the safety advice, I'd still like an understanding of how the thing works and what might be causing it to fail. \$\endgroup\$ – Sydius Dec 15 '19 at 8:49
  • \$\begingroup\$ Thanks for the updated answer. Do you happen to have a guess as to what the black cylinder might be? It has three pins on the bottom. \$\endgroup\$ – Sydius Dec 15 '19 at 16:45
  • 1
    \$\begingroup\$ The 'black cylinder' is T2, the high-voltage output transformer. If you actually managed to get 4A to flow through the secondary, it should be well fried. T1 is the split-bobbin power transformer (with the yellow polyester tape on the windings and steel E-I core). \$\endgroup\$ – Spehro Pefhany Dec 15 '19 at 16:47
  • \$\begingroup\$ Ah. I surely made it worse by trying to measure the current, right? \$\endgroup\$ – Sydius Dec 15 '19 at 17:12
  • 2
    \$\begingroup\$ I think you made the decision to get a new board easier. \$\endgroup\$ – Spehro Pefhany Dec 15 '19 at 17:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.