Just wondering if anyone has any experience with the 12VDC fluorescent light fixtures manufactured by Thin-Lite Corp. In my seemingly never-ending quest for a suitable 8-watt instant start fixture, I wonder if one of these might fit the bill. It appears the ballasts incorporate two wires per lamp socket, but I wonder if they can still run lamps with broken cathodes?

Thanks.

It depend why the cathode is broken. If the cathode was broken due to mechanical reason (shock,...) or if it break after the emission coat was consumed and the starter overheated it.
Better to say, if there is the emission coat intact or completely consumed.

If the cathode broke mechanically, it may work. Even when the ballast have to heat up the filament, one filament working would be sufficient for start, if it is ever necessary at all. The second filament you may have to bypass by a small incandescent, about 12V/5..10W would be OK.

If the coat is consumed, the ballast would be greatly stressed by the excessive lamp arc voltage, so either shut down (if it have an electronic protection), blow it's fuse (if the fuse is supposed to protect it from EOL lamps), or blow itself up (if there is no protection whatsoever).

What I want to find out is whether or not the ballast is designed in a way that will allow running a lamp with broken cathodes (assume a still-functional lamp). All I know is two wires go to each lampholder, and there is only one transformer on the ballast. So either the cathodes are fed straight from the 12V supply (which I can't imagine, because I once tried such a trick with 12V , and it caused an uncontrolled arc to strike across the cathodes once the lamp was running), or the cathodes are powered from the HV until the lamp strikes, like a CFL ballast, or the extra wires serve as EOL protection, or no purpose at all. Hopefully there may be someone here who owns one that can investigate for me.

With the DC ballasts the filament is usually driven from separate winding from the transformer, so when it goes open circuit, it have no influence on the main ballast functionality.
On some ballasts, one filament is connected in the feedback path, so the ballast shut down, when the lamp is removed. With these, just try to insert the lamp in both ways, at least one will light.

A bit different ale ballasts with two large transformer like cores (one is really a transformer, the second is just an inductor). Only these (two transformer-like components of about the same size) are the types, which work in the same way as mains ballasts (CFL,...) and need both cathodes to be intact. These always use either two or four power transistor and at least one control IC.
With this style is the only one containing the real lamp-fault detection/shut down circuit (the "intelligence" of the control IC allows it), but it is not 100% sure.

If there is only one large transformer, two power transistor and one small inductor (beside few capacitors), it is most likely the Royer oscillator type. These normally instant start, or at least one filament should be enough as a RS-style starting aid. If the filaments are heated, their supply comne from extra winding, so if left open, nothing happen (only the lamp is not heated). This ballast style quite well tolerate the missing lamp, so frequently the "missing lamp lockout" (checking the filament presence) is not used. But when the lamp have higher drop than designed for, the input stage is overloaded by high current and so can overheat. But when the lamp cathode coats are OK, there is no danger: Either the lamp does not ignite at all (so equal to missing lamp), or the lamp ignite, so then run up normally.

If there is only one power transistor and only one transformer, it would be the blocking oscillator type and these do instant start. However with the blocking oscillator type, the filament connection is sometimes used in the feedback path, as this type likes to fail with missing lamp. The second filament is then fed from an auxiliary winding and so when it is not conductive, it does not influence the main operation either.
This ballast style usually does not run the lamp at 100%, but it is so simple, you can quite easily build one, e.g. this one, the transformer work quite well even on a plain ferrite rod (just recently tried that in the scope of a "simplest F4T5 from 6VDC" experiment; maybe some photos will come...)

And if you like something from the mains, this style work quite safely (for the ballast, not as much for the lamp) with lamp in virtually any state...
The ballast will be either the 0.17A PL-S or F4..8T5 choke, or a 40W incandescent (on 230V mains; on 120V it should be 20W incandescent) But it feed the lamp by DC. But II remember operating a F40T12 on such ballast for at least five years (before the light was converted to PL-S 11W) without any visible degradation, only each year the tube polarity was swapped (during cleaning)

I heard Iota.makes good ballast, and they can run up to 4 foot 32 watts on some of those ballast for 12 volts

get a fulham workhorse 1 that's going to work perfectly

I just may do that, or perhaps, a Workhorse 2 since those can run longer lamps in addition to the small T5 lamps. But don't Fulham ballasts have EOL protection?

Only some do such as the pony but the workhorse ballasts I have including the 2 have no EOL cut

Ah, nice. That may be just what I get then. I've been looking at ballasts I could use to finish off longer lamps, but if I get a Workhorse 2 I can do those in addition to the T5s and kill two birds with one stone.

Would you trust one as a lamp-killer, though? Opinions on here seem to be mixed regarding their durability. Perhaps it won't hurt to try, regardless. I'll get a new one so I have a warranty to back me up.

thinlite ballasts can indeed run a lamp with 1 broken cathode.
if it does not start just swap ends.i have done this several times in my motorhome and solar system.

I heard Iota.makes good ballast, and they can run up to 4 foot 32 watts on some of those ballast for 12 volts

Yes, The IOTA 12V DC ballast works great and you have to look label to see which size fluorescent will work with. Those T12's fluorescent are more energy saver (less current amp draws) than T8's fluorescent.

I have one no longer in production the Falcon 12V DC ballast would run fine with F96T12 8 ft slimline but draws near 5 amp.               

Yes, low voltage ballasts have to draw a ton of current (which in your ballast's case, still isn't quite ideal, with 5A equating to only 60 watts). I'm guessing that's why they don't handle EOL lamps as well as mains-powered ballasts; they're already running on the edge in terms of the amount of heat they have to handle.

Anyway, I have a WorkHorse 2 coming for Christmas. 

The high current is the reason, why you nearly can not find any higher wattage (~20W and above) ballast for 12VDC supply.
It simply become too impractical. Second reason is, such power is not needed for small vehicles (either cars, trailers, boats, aircrafts,...). The larger vehicles, where you could use the higher power level (buses, trains, larger boats,...) use either 24V or even (mainly trains,...) higher voltage batteries, simply to keep the currents in the installation reasonable. And the really large vehicles use generated AC power (large aircrafts 120V 400Hz, vessels 50/60Hz "house-like" installations).