I am trying to fault find a fluorescent light on the 12V circuit in our motor home.
Opinion seems mixed, but there are several postings which claim that these are actually 240v AC lights with a built in inverter so that they can run off 12V.
There is certainly a lot of circuitry inside.
Firstly, do camper/caravan/boat 12V fluorescents usually run at 240V with a built in inverter (or sometimes)?
Secondly if so is there usually clear marking of the 12V and 240V parts?
I don't particularly want to probe a 240V AC circuit with the 50V DC part of my little multi-meter.
There are probably lots of ways of doing it but the most simple is basically just an oscillator and transformer to produced approx 240v AC. Plus a way of producing a higher voltage pulse for starting.
If it is fluorescent then it will have high voltage on it, a tube of this type will not run at 12V. Could it be a filament tube, a long light bulb? If so it would likely be 12V, but if there is "a lot of circuitry" then it is almost certainly an inverter, providing it does have 12V feeding it I would first suspect the tube, very cheap from any lighting shop. If the tube is old and the temperature cold then it would not be unusual for it to have failed.
A thought about replacement, with a bit of mechanical ingenuity, an emergency light unit would provide the parts to make a good replacement. Probably a darn site cheaper than a new fitting from a motor home shop.
I would look for LED lighting. In particular, LED retrofits for 12V electronic transformers will just work without needing anything else.
That seems unlikely to me. It would make the unit unnecessarily expensive and reduce efficiency.
No, they ure just electronic ballasts (which use an inverter to drive the tube directly.) They are usually nowhere near as good as mains electronic ballasts though.
A 12V electronic ballast may well produce in excess of 240V (particularly cheaper circuit designs) to start the fluorescent tube.
AIUI they're 120V fluorescents with an inverter circuit. Amazon sell them for about £20 and are not worth repairing. Google "Lumo lights" or whatever the manufacture's name is on yours.
If it is a fluoro., then yes it has an inverter and a current limiter: basically whizzes up to about 200v ac, then the tube fires, then the voltage drops to IIRC about 90v peak.
there shouldn't be much on the HV side..half a ferrite transformer and some sort of ferrite cored choke/current limiter.
the usual suspects here are switching transistors and electrolytics and bad joints.
if replacing those doesn't work - chuck it. You can buy a new one fr less than the cost of fixing the old.:-(
One thing doing my head in is that the wiring is blue and brown, (which should mean 12V negative earth, I think) but to the light the blue seems
+ve and the brown -ve. If you look at the pictures you can see a blue wire going to the switch and a red wire coming back from the switch to the circuit board. I've put a multi-meter on it twice and both times confirmed that blue is +ve and brown -ve. The positive is switched.
The fitting has been in the van and working since we bought the van in
2008 and only recently became progressively more difficult to get started, and often ran at half brightness at least for a while.
It failed completely a couple of months ago and it proved not to be the tube as a new tube didn't make any difference.
I assume the circuit board has failed but there are no obvious brown and smoky bits.
Oh, and just found
formatting link
"Fluorescent lamps can run directly from a direct current (DC) supply of sufficient voltage to strike an arc. The ballast must be resistive, and would consume about as much power as the lamp. When operated from DC, the starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube. Fluorescent lamps are (almost) never operated directly from DC for those reasons. Instead, an inverter converts the DC into AC and provides the current-limiting function as described below for electronic ballasts."
So presumably it is likely (but not certain) that the circuit board in the photo includes an inverter.
The electronic ballast runs from the battery voltage.
Maintained ones (i.e. can also run light off mains) either have a completely separate ballast for mains operation (most common case in my experience), or the low voltage charger circuit has enough spare capacity to run the lamp and charge the battery at the same time.
A common design for the two ballast types uses a 50Hz ballast for mains running, and a high frequency ballast for battery running. An advantage with this scheme is both are permenently connected to the tube and no relay is required. When operating off mains, the
50Hz can't get back through high frequency capacitor ballast into the high frequency ballast, and when operating on the high frequency ballast, that can't get back through the 50Hz ballast as the impedance is far too high at 20kHz+.
Emergency lights are in any case horribly inefficient (at least, the minature fluorescent tube type with integral battery). They charge the batteries at high current (has to fully recharge in 14 hours), but they don't have any smarts inside to stop doing that when the battery is charged, so it just goes on to waste several watts after that. They use high temperature batteries so the resulting excess heat doesn't destroy the batteries.
Most of the circuit is going to be 12V. The big transformer at the right hand end of the circuit board is where this is transformed up to a higher voltage for starting and driving the tube, and you'll find this higher voltage on the white wires and the tube itself.
These short tubes actually don't run at particularly high voltage when running at full output, but the starting voltage might be several hundred volts, depending on how the control gear tries to start the tube. If the tube dies or is removed, that higher voltage might remain continuously at the transformer output and white lamp wires. (It often knackers the transformer winding insulation if left switched on with a dead or missing tube.)
These short tubes are not as efficient as longer tubes (probably not much different to a 5W 12V filament bulb), and I would suggest looking at LED options as I described before.
Some of the modern LED lights have quite decent light temperature and are are a good replacement for fluorescents. I changed all mine in the motorhome last year and I'm pleased I did. A 5W LED is very nearly as bright as a 20W fluo.
Presumably you are talking about striplights? I think they usually have an inverter of some sort in the mount.
Maybe going off topic, you can buy CFLs with standard bayonet or ES caps which run straight off 12 volt DC. The electronics is all built into the cap and they are pretty efficient. (I use these off 12 batteries in a stables and get much better battery life than I did from a 240 volt setup with an inverter). You do have to get the polarity right but they don't "blow" if fitted the wrong way.
LED is going to be better all round, 12V LED tape will live happily up to around 15V and there is a variety of driver modules and star mounted and COB LED packages around to retrofit existing fittings. You`ll get more light for less battery drain.
Normally these are little blocks that are unserviceable. In answer to your question yes they use the same tubes as are used on the mains, but instead of the starter, choke and capacitor used in the mains version to heat the heaters, and give a higher voltage to strike the tube, the job is done by an electronic circuit. There seem to be two types, Cheap cold cathode ones and ones that emulate the heater use. If the circuit is duff, the cahances are its pretty terminal as mostly its the inductor that dies, usually gets damp in it and pops its clogs taking the semiconductor with it. I'm sure new units are available from source on the web. If you have checked the tube of course. Normally they are the same fittings as ordinary ones so find one and test it. Personally, I often found them annoying in motor caravans with their radio interference issues and ability to self destruct. Brian
Yes back in theday, I had a unit that had obviously been retro fitted in our old commer, and when it went on the blink, at first I had no idea of how it worked. In the end I sussed that it basically had three main bits. A Unijunction transistor as a high frequency oscillator f driving two power transistors with the high voltage generated by a centre tapped transformer, then the output rectified. The third part appeared to be some kind of current sensor that operated a regulator for the heaters for a second or so until the tube started to take current. I rmremember this one as it was one of the few where the transformer was not to blame, it was one of the two output transistors that had gone open circuit internally. I suspect these days its all done in one chip and therefore nobody can fix them. Get a decent meter though, as cheapo ones have poor protection. Brian
A lot of vehicle wiring uses black and brown as the ground return. Your lights were probably wired that way to avoid confusion with the vans original wiring
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