In article ,
David writes:
On Sat, 27 Dec 2014 13:39:46 +0000, David wrote:

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.

http://i817.photobucket.com/albums/z...ttleGreyCatUK/
Hymer/20141227_140052.jpg

A bit blurry but hopefully shows enough.

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.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]