Tricolor/Anchor light 2 wire system ?

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ddlon47

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My newly aquired moody 27 combined tricolor/anchor light (not sure of make but looks quite new from the deck) is not working ... 3 pin deck socket with only 2 wires connected which reverses 12volt supply when tricolor/anchor centre off toggle switch is switched... does this sound right for some version of combined tricolor/anchor light ... many thanks for any light (scuse the pun) you could shed.
 
One would normally have a supply for each light and a single return, thuse using all three contacts in your deck plug. It sounds like an 'owners' special where he has rigged some diodes in the lamp unit to make one polarity light the triclolour and the other light the anchor. I suspect this may be where your problems lie. I suspect most would recomend rewiring to the morenormal solution though the diode system is perhaps as good in theory at least.

Looks like a trip to the top of the mast.
 
It is possible to drive the tricolour and anchor light with two wires but the light unit itself needs a couple of diodes.
The centre position of the toggle switch provides is off whilst the two on positions of the toggle switch change the flow to light unit. i.e. + & - to drive one bulb and - & + to drive other bulb.

Another option is to have the two wires drive the positives to the two bulbs and have the negative of the bulbs earthed to the mast which inturn has it's own negative to the battery.
 
I should have said I have 3 core cable already there ... the third wire just wasn't connected and doesn't seem to do anything.. the reversing polarity is what confuses me .. I wondered if there were old combined tricolor/anchor lights that work that way .. can't think why .. but this is my first boat so thought I would ask the question.
 
From memory, Orca Marine who do LED nav lights offer such a system with their lights. If you go to their website I think they describe it in more detail. However if you have three wires then I would wire it in the conventional way.
 
If the third wire is there is it deliberately disconected or just fallen off. The reversing polarity does made one think that the diode solution is the one in play here.
 
While on the topic, does anyone have any recommendations as to diode type if one is going to use a reversing polarity system? I seem to recall that some types lose less voltage, or something like that.

We have only two wires up the mast (for an all-round white), but I would prefer to have a tri-colour as well. I know a replacement mast cable with three wires is the ideal, and haven't tried on this boat yet, but know from bitter previous experience what a palaver replacing a mast cable can sometimes be.
 
All silicon diodes drop around 0.7v, so your lights will see 11.3v instead of 12v, and will therefore be 5% dimmer. You need to bear in mind that the diode will be disipating that 5% as heat, so if the bulb is rated at 24W 12V then the diode will need to be rated at 1.4W. If you use LED lights then there will be no such loss...

That 0.7V drop is why simple diode based split battery chargers(for charging Engine and Domestic batteries separately) don't tend to work too well, as the batteries never see enough voltage to get fully charged.
 
Schottky diodes have a smaller voltage drop but it may still be significant.

BTW diodes are normally rated by Peak inverse volts (PIV) and forward current (IF) not by watts

Maplins list some at 30volts and 3 amps
 
MAPLIN do the 1N5820 3A schottky diode part number N91CA for 35p each

or

1N5400 silicon 3A diode part number QL81c for 21p each.. not much difference in voltage drop but probably worth the extra 10p or so for the schottky.....
 
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