How Bad it is to overdrive using 6V(zinc carbon)?

[ViReN]

Hello All,

I have a simple question, How Bad will it be ... if i drive about 16 LED's in Parallal with 4 AA Ordinary Zinc Carbon (Zn-Cl) Battries ? ... I want to overdrive without using any resistance.

I want to modify an Old Lantern.. which currently uses a 4.6 V .5A PR Bulb... there is no scope for putting up Step-up at the moment (limited space) ... Later on I might just add up an Step Up... (currently held up .. for recieving Zetex Components)... hopefully will come to my rescue.. space savings /ubbthreads/images/graemlins/smile.gif

Thanks in Advance,
ViReN

 

[LED_ASAP]

I believe ZnC is rated for low current use and has quite high internal resistance. It shouldn't be too bad---just my GUESSTIMATE, though.

 

[ViReN]

I was wondering similar thing too....

But not sure....

May be The "Guru's" will probably throw some light on it...

I checked by shorting the fresh battery terminals to DMM's Current shunt @ 10 A ... the meter reading was about 750 mA .... When i did with 2 A shunt.... it was about 950 mA ....

I dont want to blow / degrade LED's by trying to measure current directly throu a 2 A shunt....

Thanks & Regards,
ViReN

 

[Burnt_Retinas]

Not such a good thing.

The Zinc Carbon batteries do have limited current capability thereby perhaps avoiding blowing the LED's IF, and I mean IF, each LED conducts it's equal share of current, or a single high current LED such as a Luxeon is used.

Putting them in parallel without a resistor for each is the bad thing. You may find that each has a different Vf and this means the one with the lowest ***edit - Vf*** will steal the king's share of the current, possibly causing it to blow. LED's often don't fail by going open cct, unless real high current is used therefore it'll probably just fry and as it heats take any current from the rest - no light. If it goes open circuit, then the next lowest Vf LED will do the same and so on.

Use resistors to each LED and you'll survive the experiment. Ensuring a very close match of Vf's of LED's may also do the job. Throw a few SMT resistors on your next Digikey order is my recommendation.

Chris

 

[ViReN]

I have finally done it....

I used about 16 LED's in SERIES... with a Transistor based switching circuit ... and it works very well too.... for any type of battery chemistry...
just modified the inductance value to 100 uH... and there was the amount of voltage that i was requiring /ubbthreads/images/graemlins/smile.gif

Here is a picture...

Thanks & Regards,
ViReN