Running 3 LED lights on one battery

Most 3 cell led lamps make use of the internal resistance of the batteries to somewhat limit the current. They also run them way over current to make them brighter and hence more salable at the cost of an extremely short life.

One way to proceed would be to use an LM317 in each lantern configured as an appropriate current limiter. The efficiency this way is not fabulous but you can use the lamps independently and reliability is not reduced as it would be with the lamps in series. I assume battery capacity is not an issue - leds use very little current compared to almost anything else.

Measure the voltage of one led using original circuit. If they are pulsed, might need scope. How many LEDs does I actually use ?

Greg

** There must be a resistor of about 39ohms in series with each LED. ** What sort of battery, SLA ( gell cell ) or other ?

** Three in series is fine, then a resistor of about 82 to 100 ohms as well.

The white LEDs take about 3.4V each to run at 30mA.

... Phil

"David Eather"

** No they don't.

The resistance of a good AA alkaline is only 0.1 ohms.

Even a carbon zinc AA cell has only 0.5 ohms.

... Phil

Connect the lanterns in series, and drive them with the Joule Thief circuit powered by whatever source you want (one 1.25V NiCd cell to ...).

Some of them do after a fashion, but they use an incredibly weird discrete step up circuit from two AA cells in parallel to charge them from the cheapest possible solar cell configuration and then a flyback transformer. The circuit fails to oscillate with only one battery in!

The solar cell doubles as both charger and sensor. I traced the circuit of one once to adjust them so that they coped with the UKs long summer twilight. Otherwise the battery would run out just after it got dark!

The OPs best bet would be something like a simple one chip and an LC buck converter to convert 12v down to something appropriate for an LED or one of the devices intended to do constant current LED driving but I can't think of any of those in a DIY amateur friendly packaging.

Amateur astronomers here had a habit of replacing the lamp in those cheap ticktack box torches with a red LED and using spent batteries in them and under those brutal conditions the LED does seem to survive. If they ever forget and put fresh cells in the LED will surely die though!

These days you can buy cycle lamps which are LED based (and *much* more cheaply than the ones they still try to sell to amateur astronomers).

--
Regards, 
Martin Brown

** Get your hand off it - wanker.

On Jun 18, 12:04 am, snipped-for-privacy@toyotamail.com wrote:  I want to connect them to a 12V

Look on Ebay for LED replacements for lamps in cars. They work on 12 volts and are cheap.

Dan

You asked for the -> easiest

Assuming that you are using a proper solar charge controller, just add a

11 to 15 V input to 5 V output SMPS module. Then you can make the existing lantern LED drivers happy as well.

?-)

Yes they do - at least in some cases. It has not just been my experience.

These guys also pulled part torches and found no resistors used and wrote it up in a project

Click on item 12 in the side bar. The link won't get you to the exact page they give there experience (it is actually the next page where their results are).