max input voltage for LED lamps
02GF74 - 26/2/14 at 11:02 AM
I think I know the answer but will throw the question out here anyway.
I have a set of 3x CREE LED lamps, like those below. They have a 4x 18650 rechargeable battery pack to givre 4.2 V; so are two pairs wired in
parallel.
Can I connect the lamp to a pack with 4 cells wired in series, i.e. 8.4 V? (there are CREE LED lamps with such packs).
I do not know what is inside the lamps and I don't think it will be easy to dismantle them - but I have made my own LED lamps using a LED driver
which takes a variable voltage (up to 18V or so) to provide the correct current.
In theory these should have drivers so should take a variable input voltage but how high can it go before they go pop, if indeed they do go pop?
MikeRJ - 26/2/14 at 09:50 PM
quote:
Originally posted by 02GF74
I think I know the answer but will throw the question out here anyway.
I have a set of 3x CREE LED lamps, like those below. They have a 4x 18650 rechargeable battery pack to givre 4.2 V; so are two pairs wired in
parallel.
A single lithium ion cell has a terminal voltage of 4.2v when fully charged, so if you have four cells and the terminal voltage is only 4.2v, then
they must all be connected in parallel. Four cells wired in series would be 16.8v fully charged.
The limiting factor for voltage will probably be the design of the LED driver rather than the LED's themselves. Doubling the voltage is unlikely
to be safe.
FWIW I have a single LED Cree bike lamp similar to that one in design with four 18650's in a pack and they are wired as you suggest, two sets of
paralleled cells in series to give 8.4v. Why do you think yours is only 4.2v, have you measured the output of the pack it with a voltmeter?
omega 24 v6 - 26/2/14 at 10:40 PM
Don't know if this will help but most of the industry std automotive led's come in 3 forms that I've sen so far. 12V, 24v and the
mutivoltage units that are stamped at 9 to 32 volts. Obviously there will be higher tolerances on the 12 and 24 volt units.
coyoteboy - 27/2/14 at 09:52 PM
If They Are raw leds, don't. You are aware that led devices are current controlled, if you just apply a voltage without limiting current (quite
precisely) they'll go into thermal runaway. As they heat up they draw more current, heating themselves further etc. They *need* a driver or you
will find expensive results. As for overvolting, no. Not unless you can pulse them to allow time for cooling.