Cabin light conversion

LONG_KEELER

LONG_KEELER

Well-Known Member
Joined
21 Jul 2009
Messages
3,720
Location
East Coast
Visit site
I have two cheapo cabin LED lights , they both take 4AA batteries each.

They produce a great light for reading etc , much better than the existing cabin lights. They don't look bad either.

I thought it might be fun to convert them to run off the ship's 12 v DC supply. It's also a pain changing batteries.

Is there much to it ?

TIA
 
LONG_KEELER said:
Is there much to it ?
Click to expand...
In principle, no. One resistor in series between the boat's 12V and the light should do it. Which resistor is the question. If the AA batteries are arranged in series then the LED is running off 6V nominally. So the resistor needs to get rid of 6 or 7V (or more if the battery is charging ...). You need to measure the current that the LED draws from its 6V batteries. Then apply Ohm's Law to find the resistor R = V / I.
So if you measure the current at say 15mA then the resistance required is 7 / 0.015 = 467ohm which is fortuitously close to a standard value of 470ohm.
Then check the power consumption P = V . I = 7 * 0.015 = 0.1W so a ¼ or ½ W resistor, 470 ohm, would be ideal.
Note that current will probably be measured in mA but you must use A in the calculations.

Derek
 
LittleSister said:
Forget the resistors, and wire the two (presumably) 6v lamps in series? I wonder if they would cope OK with the additional voltage on charge (i.e. c7.2v each).
Click to expand...

Yep. That should work, even more simple than the resistor. The only potential problem I can see is, during charging the voltage on batteries an exceed 14 V. The lights may not be happy with that... What is also a point in case you are using the resistor solution - use 14 V as a source voltage while calculating the resistor value.
As for the voltage converters: a gross overkill for any appliance with a fixed power, like these lights. They are needed only if the load is changing, like when you feed more appliances and some of them are not being used all the time.
 
LONG_KEELER said:
I have two cheapo cabin LED lights , they both take 4AA batteries each.

They produce a great light for reading etc , much better than the existing cabin lights. They don't look bad either.

I thought it might be fun to convert them to run off the ship's 12 v DC supply. It's also a pain changing batteries.

Is there much to it ?

TIA
Click to expand...

I have done exactly that as in cupboard lights. Mine were switched on/off by pressing the light to click on/off.

I ave also converted all in previous lights to LED and in some cased made then both red and warm white with switches for either.

I had some very old single LED lights that I converted to round chip leds for a brighter warm white light.
 
Re jhiris comment above "As for the voltage converters: a gross overkill for any appliance with a fixed power, like these lights. They are needed only if the load is changing, like when you feed more appliances and some of them are not being used all the time."
Voltage converters come in 2 styles the linear regulator and the switch mode converter. The linear regulator is in effect a variable resistor (LM317) which wastes the power like a resistor but does automatically adjust to maintain correct output voltage. The switch mode converter as in Big John above actually switch the DC to high frequency AC which is then effectively converted in a lower voltage then rectified and given out as the desired voltage. The advantage being that to get half the output you should halve the input current. Not quite so due to losses but less power wasted so less heating and less input current. One disadvantage is that the high frequency switching can cause radio interference. The linear regulator will not. Both types will adjust for higher on charge voltage in. So not totally an overkill. But yes a resistor is cheap and simple.
ol'will
 
You must log in or register to reply here.

Share this page

Top