I read on a youtube post of all places where someone was explaining that an FS2 starter ad FS85 starter were very similar electrically due to the arc voltage these lamps run at.

I've got some F90T17's NOS that I acquired and will likely be building a T17 fixture using an appropriate T17 ballast, and mogul bi-pin sockets acquired on ebay.

But, starter sockets, that's another challenge so I got to thinking that maybe I can build a fixture and use common small form starters in FS2's?

Otherwise I need to source T17 starter sockets.

Thanks!

Voltage : if the starter is appropriate, it will work. If not appropriate, it and the lamp will keep flashing forever and not start after a few flashes

Current : the higher current of F90T17 ballst means, that the expected short circuit current is higher. This likely won't have immediate effect on the starter or on the lamp starting, but can greatly shorten the starter's life, making the starter fail sooner either as stuck starter (contacts welded together from the high current) or in nasty ways (the bimetal breaking in the glowlamp and it glowing continuously, melting the starter case, possibly setting it on fire, possibly damaging the starter socket, and so on)



Are there some modular automatics (time relays for Y/Delta motor starting, power relays, ...) available to you ? If yes, you might be able to build a starting circuit with those, that would work comparable to the 4 pin starter, using automatic relays instead of thermal system. The downside is, it would be more complicated to build in a way that retries if the lamp didnt start from the 1s attempt

If you're just testing, you could always wire it up in a manual preheat (like antique desk lamps). Then when you get a proper starter and socket, it will be easy to wire it up into the circuit in the starter loop and in the ballast loop for the heating part (assuming the starter will be 4 pin).

As Sol mantioned Manual Preheat, thinking of what i proposed with the automatic time relay is by far more equivalent to Manual Preheat than to the 4 pin starter

I'm assuming you're in North America.

As far as using the wrong type of starter, usually it won't harm much. If the ballast OCV is too high for the starter (FS-2 on a 40W autotransformer setup), it will not extinguish when the lamp strikes and will give a result similar to a strobing EOL lamp. If the OCV is too low (FS-4 on a 20 watt choke), the starter will not heat enough to close the bimetal switch and the lamp will not start.

Occasionally, you will have a catastrophic failure like Ash mentioned so it's best to use the proper starter.

There is the ballast OCV, and there is the lamp arc voltage, to which the voltage drops after the lamp started

The starter sees the same voltage as the lamp (as it and the arc in the lamp are in parallel). The starter's own attribute is its firing voltage. We wamt the starter to fire on OCV, but not fire when the lamp is allready on

1. If the starter firing voltage is higher than OCV, it won't light up or start at all. It'll stay dark and cold. It may occasionally flash as result of spikes in the line voltage though, when the ballast OCV momentarily reaches a level at which the starter lights up

2. If the starter firing voltage is lower than OCV but higher then the lamp arc voltage, it'll start when power is applied, light up the lamp, then stay off after the lamp is working

3. If the starter firing voltage is lower than the lamp arc voltage, it'll start the lamp, but not extinguish after the lamp is allready working - so it'll keep flashing forever

As FS-2 are the starters with the lowest firing voltage of the lot, we can rule out possibility 1. Then the starter is either appropriate, or too low firing voltage

Exactly and number 2 is the desirable scenario.

Thanks guys for the explanations. Sounds like the advise I saw about an FS2 may indeed be accurate. This will be for a fixture that will be lighting a specific bench with a pull switch to activate it when I need it and want to see it lit. So if a starter fails, I can shut it down and remedy.

I got 12 bulbs, so as long as I have one fixture that's a supply for a long time for me.

Still planning on what to use to build a fixture.

I will be trying this in a couple weeks when I get the ballast.

The more I think about it I can just build some starters using the glow bottles from FS85's in an FS2 can, I heard that the glow bottles are about the same size internally in the can.

I'll get some FS85's and take them apart and compare them to an FS2 glow bottle and post the results here.

Thanks!

John