Hello everyone, I have a question about these two ignitors: does the SX72 work for a 18W SOX lamp or it could damage the lamp or the ballast? I ask this because SX26 is very expensive and rare, so if the SX72 is equivalent I will use it permanently.

Thank you!

Leonardo.

 

The SX72 should be ok, I'm not aware of any problems with them on 18W lamps. I've never understood why the SX26 is so hard to get, it took me ages to find one at a reasonable price. Same with anything to do with SOX lamps now, I suppose, since they're not being made any more   

Thank you, yes the SX26 is very very expensive. Also the prices of ingitors and ballasts for 18w Sox lamp, continue to rise over time!

Generally I would not think a mismatched ignitor could damqge any lamp.
What I would expect to happen:
The ignitor wont fire at the givenballast OCV (as it would "think" the lamp has already ignited; like ignitor designed for 90 or 180W with a 18W lamp). Consequence would be just the lamp not starting.
Or the ignitor will continue firing when the lamp has been already ignited (when the lamp has so high voltage drop so the ignitor "thinks" the lamp is still off; like a 18W ignitor in a 90W circuit). That could wear off the ignitor, but most likely it will just trigger its EOL protection (usually a PTC "fuse") first.
But none of that could damage the lamp, according to me.

The starting pulse voltage of sx26 trigger is about 380-430v, which can match 18W, 26W and 35W

The starting pulse voltage of sx72 trigger is about 420-460v, which can match 26W, 35W, 36W and 55W

When the bulb fails, the bulb tube pressure remains at about 75V, the bulb tube pressure does not drop, and it is not under the normal working voltage and current, the sx26 trigger will automatically cut off the power for protection

When the bulb fails and the bulb tube pressure is maintained at about 85V, the bulb tube pressure will not drop. When not under normal working voltage and current, sx72 trigger will automatically cut off power for protection

18W can work under sx72 trigger, but it will slightly affect the service life, but the problem is not big. The main problem is that when the service life of 18W is about to end, it may not be able to accurately detect the bulb and power off the protection circuit, affecting the service life of the trigger.
If you are not afraid of trouble, you can often observe the use of the bulb before starting the 18W lamp and judge whether you can replace the bulb in advance

Thank you! Maybe I will buy SX26. What about the capacitor? Which one is correct for a 18w circuit?

The capacitor is only for power factor correction, and don't affects lamp performance. high power factor is recommended in large installation of fixtures to prevent overloading the electrical infrastructure.

Ok many thanks!

Nevertheless, a power factor capacitor is always worth adding, I never run my lamps without them. It may not be strictly electrically necessary, but I like to have one for the sake of completeness.

For an 18W lamp (on the correct ballast) on a 230-240V supply, use a 4µF capacitor.