Hi
I have some camping 'round style' LED arrays that consist of 20 LEDs in parallel and no external resistors in circuit. These operate from 4 AA batteries and have fantastic light output. I want to connect two of these lamp arrays together and run from a deep cycle 12v (14v) battery in my van. To experiment, I pulled two LEDs out of the lamp array and series connected to the 12v battery and this resulted in their early demise. Prior though I ran each from the 4 AA 6v supply with no problem!
Rather than setting up a regulated 6v from the 12v deep cycle and wasting precious power from regulation, can I series connect the 2 lamp arrays together and perhaps use a zener to control voltage to each and not waste any power in the process? My design knowledge is limited but I thought the wasted power that is generally accepted from voltage regulation could be used for the second lamp array. If this is possible will the zener waste some voltage resulting in too low a voltage? Essentially I want to split a 12v supply into two 6v supplies without drilling into the battery (expensive AGM) or by using DC-DC convertors. I fear connecting the two lamp arrays in series further destroying the remaining LEDs.
Appreciate any knowledge on this.

 

A strange arrangement, those 20 LEDs in parallel. If there's no other circuitry and they run off 6 V then I can only assume the LEDs have their own internal resistor, or linear current source circuit. Either way, they're not going to be very efficient.

I think you've hit on the problem of voltage balancing - it wouldn't work well with 2 x 6 V incandescent light bulbs in series either, as upon power-up one bulb hogs more current than the other (all things being unequal, which is generally the case), and the same could happen for LED arrays. It's difficult to tell without knowing the LED spec and internal circuit.

You might get away with 2 sets of 6 V LED arrays in series if you limit the voltage with a chunky zener across each of the two LED sets. You'll need a bit of a safety margin with the zener voltage as you don't want the zeners trying to shunt a constant current from a lead-acid battery - try a 7V5. Include a fuse, as if one zener fails short-circuit (as they do) then the other will be destroyed, probably also in a shorted condition; this will crowbar the battery, which will then blow open one of the zeners, and then 50% of the LEDs will be destroyed.

 

Another thought occurs, use a high wattage light bulb that is rated around 3V to limit their current as part of their series arrangment.

If you get a chance you might measure the current used with a DVM.

 

A strange arrangement, those 20 LEDs in parallel. If there's no other circuitry and they run off 6 V then I can only assume the LEDs have their own internal resistor, or linear current source circuit. Either way, they're not going to be very efficient.

I think you've hit on the problem of voltage balancing - it wouldn't work well with 2 x 6 V incandescent light bulbs in series either, as upon power-up one bulb hogs more current than the other (all things being unequal, which is generally the case), and the same could happen for LED arrays. It's difficult to tell without knowing the LED spec and internal circuit.

You might get away with 2 sets of 6 V LED arrays in series if you limit the voltage with a chunky zener across each of the two LED sets. You'll need a bit of a safety margin with the zener voltage as you don't want the zeners trying to shunt a constant current from a lead-acid battery - try a 7V5. Include a fuse, as if one zener fails short-circuit (as they do) then the other will be destroyed, probably also in a shorted condition; this will crowbar the battery, which will then blow open one of the zeners, and then 50% of the LEDs will be destroyed.

Thanks Darren
I am not great with circuits but I thought of trying this but the comments re unbalanced current draw are of concern! I really don't want to destroy the lamps (which have great light output). You indicate using 2 zeners but not sure how to do this.

Just measured the current draw of one of these lamps at 1.5A. Rather high!