I have an old battery (6 x D cells) torch which has a fluorescent tube, a spotlight and a flashing light behind a red (plastic) glass.
The torch also has a DC power input of unspecified voltage which then runs into some circuitry.
1) The battery compartment has got corrosion, half of a spring has gone (there are two springs at the bottom, one for each set of 3 batteries), but there is continuity between the spring connections. I plan to take a spring off a defunct 6v lantern battery to replace the damaged spring. What would be the best way to fix it?
2) The fluorescent tube is a Sylvania White F6W/W which has probably been superseded. 210mm x 16mm. Grey/black at one end. Is there anyway to test if this works outside of the torch?
3) I've put a 9v supply into the torch and at least the spotlight functions though nothing else. All the connections appear to be accessible. What should I be measuring for the fluorescent tube?
Whilst this is one of numerous "Covid" projects I have on the go are modern LED torches a better bet? Though I don't like the light from my head torch or even any that I've put into lamps
Tubes work best with sine wave (AC) drive. In this example web page, the "working" voltage listed for the tube is 70V.
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"After start, the voltage collapses from several hundred volts to the operating voltage, which is ca 70V for an 8W rod."
It's highly likely there is an inverter of some sort, inside the plastic housing. And with any luck, glued plastic pieces to keep you out.
"Pure flyback single-transistor inverter, makes voltage spikes in the kilovolt range in idling condition, so that the lamp will start. Disadvantage: One filament evaporates and blackens the lamp, makes it electrically unsymmetric and shortens the lifetime."
So THAT'S where it went. If you ever come round maybe you could bring it back :)
same as the battery, 9v. Polarity matters for the fl tube, and probably for the flasher. You haven't just given it the wrong polarity?
Usually it's easiest to replace the whole piece of spring wire rather than splice partial bits. So however it's fixed on now. IME battery holder springs don't solder well. Some battery holders rivet the springs, and the rivets do solder.
close to 99% of fl tube failures are filament burnout. Check continuity between the 2 pins at each end. If either end is o/c it's a deadun - though there are ballasts that can get such tubes going.
Oh yes, much more efficient, longer lived, better efficacy, more reliable. But those old things are still cool. Before you shuffle this mortal coil they'll be collectible retro.
As Paul pointed out, cheapskate ballasts blacken & kill one end of the tube, so put it back in the other way round to increase its life.
snipped-for-privacy@gmail.com has brought this to us :
The end filaments are not used as heaters when an invertor is involved, instead they rely upon creating a high voltage / high impedance between the ends, which is enough to get them to strike.
At this stage I don't know, I've assume centre = +ve but there is no indication on the socket. As also I'm assuming 9v because that is 6 x "D" at 1.5v ea.
I guess I'll lose nothing if the fluorescent tube isn't in by rigging up a reverse polarity connection or clip a PP3 in where the 'D' cells go and see which way round things are at a bulb.
A filament bulb won't care at all which way round the battery is but the inverter for the fluoro tube will probably emit its magic smoke if you connect the battery the wrong way around.
Usually you can work out the polarity in the end with the conical coiled spring is negative and the end with the small rigid centre is positive.
These days it might be altogether simpler to buy a modern power LED torch and throw the old thing away. It might even be cheaper than buying a replacement mini fluoro tube. It will almost certainly be brighter.
Are you going to make the measurement with a load, or with no load ?
First of all, this web page is *not* about a Johnlite 6W fluorescent lantern. What it does show though, is the "ignite/burn" curve. If the tube runs at 70V, it ignites at 200V.
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If the tube did not ignite, the voltage could rise above 200V.
My objective here, is to prevent two things from happening.
1) Avoid having AnthonyL zapped by the voltage across the tube socket pair. And thrown across the room. Now, it's not going to do that, as long as the frequency remains high. At 20KHz, you might not feel it, but it might cause a flesh burn if you don't rapidly remove your hand. At 100KHz, it would definitely be a "skin effect" thing, rather than hitting a nerve. If the frequency were to drop (due to loading caused by human dead short across socket), then that aggravates the shock hazard.
2) Prevent multimeter AC 1000V range from blowing out, taking out measurement chip. I've only seen one meter blown out that way, a Fluke with about >2kV across it. That was in a physics lab, a Xenon flash tube driver, which a masters student destroyed by being not clever. When I saw him reach for the meter, I thought to myself "he's not that stupid, he's a genius". Oh, well, never assume anything.
I don't want you to get hurt fooling with this stuff.
If the filaments are not hooked up (circuit uses two pins of the four pins total on the tube), then it's not using the filaments to heat the mercury, and it's relying on a little extra voltage to establish the initial plasma. You could place a resistor in place of the tube, using the two pins that are connected.
What value should you use ? Is it a 820 ohms 6 watt power resistor ? Is it a 1 megohm resistor ? The circuit has a high Q, and the trick is intuitively picking the right load to prevent runaway behavior. 70V 6W would be 820 ohms (V^2/R = P = 6W = 70v*70v/820 ohms.
That's a rather obscure value for the parts cabinet, and by the time you were done, you could likely purchase a replacement tube instead :-) And measure with that present. Or, don't even bother to measure and just use it. I have power resistors, but they're in the 1 ohm to 10 ohm range or so.
I have one of these Johnlite lamps, but I don't know where it's got to. It's not on my junkroom list, which means I have no hints to work with. It's one of the black plastic ones.
TBH refurbishing battery connections is a PITA, and my experience of such lights is that the inverters are not very good. A modern LED torch will certainly give you more lumens per battery.
I know which polarity the batteries would go in but I don't have 6 x "D". However I do have a 9v power supply but which fits but I don't know whether it is centre +ve or -ve as there is no marking on the torch. I thought if I put a PP3 onto where the "D" cells terminate I'd be able to reverse check the polarity of the power supply socket.
you can pick the bones out of it by hand, and translate the various html escape codes, but I tend to click the link, that follows google's redirection, then in firefox's download list, right click and copy location, which gives e.g.
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