Compass light bulb replacement

W

waterboy

Well-Known Member
Joined
9 Oct 2003
Messages
313
Location
Hampshire
Visit site
The bulb has blown in my Plastimo steering compass. It is the sort with no visible bulb holder, 2 visible mounting screws and presumably, 2 further screws hidden under 2 plastic lugs with lettering on. Has any forumite any idea how to reach the bulb to replace it , hopefully without having to disturb the mounting and adjustment magnets?
 
I had to lift compass off housing by undoing screws. Needed an electric drill to put a hole through mounting to drain the water - suprised it had worked for as long as it had.
 
Compass has 1 small bulb on the inside top, inserted into a rubber sleeve. On the outside another bulb is set into a sort of epoxy fillet inside the plastic bit that sticks up into the bottom centre outside the glass.

..well, if we're talking about the same compass that is..
 
Mu Bulkhead Contest had ..... HAD ..... an led in a rubber piece held on the top centre section of the compass bowl. It was an interference fit onto a small spigot on the mount ring. Pulling / wriggling got it off and turning it over exposed the led buried into a channel in the rubber. I haven't replaced mine yet - but would only mean buying a similar size / red coloured and inserting into channel after twiddling the wires together respectively with the supply leads .....

But of course original post does not actually state which compass it is exactly for correct ID for an answer ...
 
Been there, done that thing, got the T shirt

aboard a friend's boat, mind-cruise.

Only thing I can clearly remember is (a) it's a swine of a job and (b) at risk of teaching grandma, do it over the cabin table, with fiddles, in daylight!
 
A LED does not run on 12 v unless you buy one with a built in current limiting resistor. An LED usually drops about 2.5 volts and has a rated current for correct light output. Any less and it is not so bright and more is death.
LEDs vary from 15 milliamps for a small low brightness one to 50 or more ma for a high intensity LED. The resistance value is calculated from the formular R= voltage divided by current. The voltage is that dropped across the resistor ie 12 volts minus 2.5, the current is that required for the LED. If you use 2 LED in series then the voltage is 12 volts minus 2.5x2 or 7 volts.
if you put 4 LEDs in series you get 4 times the brightness for the same current from the battery however 4 LEDs means 2 volts dropped across the resistor. If you put the battery on charge however and it goes to 14 volts then you end up with twicw as much current through the LED.
(with only one LED the voltage wasted in the resistor is 9.5 volts which goes up to 11.5 volts with 14 volt battery the current rise then is only about 20%.)
So choose a resistor based on 14 volt battery or perhaps 13 volt in practice and accept a lower light on 12 volt especially with multiple LEDs

Often you will find LEDs in old radio tape players etc pull them out and fiddle if you have a multimeter. Just remember that one lead is + and one is - and it won't glow or conduct current if it is reversed. Most old LEDs can be assumed to be 20 ma type. a typical resistor will be 47 or 50 ohms and it can be of the smallest type low wattage. regards olewill
 
Interesting - I had a feeling it was complicated! I'm sure I've seen somewhere a sort of made-up LED set that is the same size as the 10w bulbs that go in the average cabin light (the sort of lozenge shaped ones, or zeppelin shaped..) and I keep meaning to give them a try. I guess they come complete with the right amount of resistance. Not sure who markets them though, but expect Maplins would. Are they sold as Led Zeppelin I wonder??
 
You must log in or register to reply here.

Share this page

Top