Trouble with reading light

[eddystone]

Electrics is not my strong point (what is!)
I replaced an LED reading light assuming the unit was defective but doesn’t work. I’m not sure if this is right but I placed the probes of a multi meter on the connections and got 0.6v so does this suggest a problem with the feed rather than the light unit itself?

 

[Concerto]

Check for corrosion on the cable joints. That can cause a voltage drop. Alternatively you may have a fractured cable that is still passing a little current.

 

[doug748]

Electrics is not my strong point (what is!)
I replaced an LED reading light assuming the unit was defective but doesn’t work. I’m not sure if this is right but I placed the probes of a multi meter on the connections and got 0.6v so does this suggest a problem with the feed rather than the light unit itself?

Have a good scratch with the probes of the meter, you may find you are not getting down to the metal and surface corrosion is giving a false reading. If not, the wires connected to the light fitting often corrode, disconnect them (often a small screw) clean and replace. If you don't have 12v at the wires you problem is down the line - see if you have full blast at the other end.

Make sure the contacts are clean on the led and fitting. Most inexpensive festoon bulbs will only work one way around so don't let this trip you up when you get 12v.

 

[thinwater]

Just because it's 12V vs. 240V at home, don't assume this is easy stuff. Read up a lot and don't be afraid to get an electrician if electrics are not a strong suit for you. You don't want to get it wrong by guessing. I had a small fire on my boat because the PO (he was an electrical engineer but without practical knowledge of doing it right) connected a reading light poorly. Not funny when you are offshore.

 

[Cerebus]

Your initial actions seem sensible.

A new, replacement device if like for like should obviously work, so your conclusions are probably correct too.

A bit more info needed really. Is there a label stating wattage? And voltage?

Of the supply and receiving light?

Can you plug the light into a different supply.

Don’t almost almost all LEDs require 3.3V at least (if white especially)? As far as I have learned.

Can you supply photos of the LED? COB or single LED?

 

[William_H]

Your initial actions seem sensible.

A new, replacement device if like for like should obviously work, so your conclusions are probably correct too.

A bit more info needed really. Is there a label stating wattage? And voltage?

Of the supply and receiving light?

Can you plug the light into a different supply.

Don’t almost almost all LEDs require 3.3V at least (if white especially)? As far as I have learned.

Can you supply photos of the LED? COB or single LED?

A bit confusing here and OP post. Yes an LED actual diode needs has a bout 3 volts across it when operating. Almost always however 3 diodes are wired in series Often so you can't identify individual diodes. Three in series can conveniently run on 12v with a series current limiting resistor. Often again built in so you can't see it. or sometimes it will have an electronic current control circuit. (identified by it's rating of 10 to 30 v supply)
So typically an LED light will be setup for 12v supply. Replacing an incandescent bulb. Or intentionally LED.
Now using a digital multimeter to check for supply voltage can have traps. The meter is very high resistance. That means it will detect voltage without drawing any current. (it can small voltage) However in a boat situation this means that it can indicate voltage that can creep through corrosion but a voltage that is not present with any current drain. I would suggest OP 3v measurement is just that a smidgeon getting through a corroded connection. He should measure 12v at supply to lamp and even then that is not always good. Check the wiring for joins bad fuse holder or switch. ol''will

 

[Refueler]

If the + / - are flipped - then LED often will not work ... swap the connection round 180 deg.

 

[Shaz77]

If the + / - are flipped - then LED often will not work ... swap the connection round 180 deg.

Light emitting diode is a one way only circuit. You have to get it right where as a normal bulb filament will work with electricity flow in either direction in the bulb.

 

[Refueler]

0.6v is about right for reverse connected LED !!