running 3 emitters from 14.5v NiCad?

I'm looking to run three Seoul P4 emitters at 1000 mA, powered by a 14.5v NiCad battery pack (from a cordless drill).

My question is... if I use a buck converter, is there a danger of damaging the battery pack by draining it too low? Should I be taking a different approach (More emitters? Direct drive?)? Am I just being paranoid?


Thanks!

12 cells?

You could simply direct-drive four of them, and then you would know when to charge the batteries, as they would dim - all of a sudden. To me, that would be the perfect solution.

if you direct-drive LED's do you need any resistor at all or is it simply as the name implies a direct connection? would a fuse be a good idea?

The LEDs would blow first, thereby protecting the fuse. I'd say a small value resistor would be a good idea. Your LED operating voltages may be lower than nominal and the battery voltage when freshly charged may be quite a bit higher than 14.5 V, both of which would cause the LEDs to draw more current than wanted.

TorchBoy said:

The LEDs would blow first, thereby protecting the fuse. I'd say a small value resistor would be a good idea. Your LED operating voltages may be lower than nominal and the battery voltage when freshly charged may be quite a bit higher than 14.5 V, both of which would cause the LEDs to draw more current than wanted.

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I completely agree. I would imagine that fully charged your looking right around 16.0V (my 18V is 20.1V off the charger). At 16V I'd say you should go with 5 emitters (3.2V-2.9V) or 4 emitters (4V-3.63V).

You could do 4 with a resistor to pull some voltage.

With this setup, you'll never see more than 1A, but 2A will blow the LEDs. You can't get a 2A fuse or 1.5A fuse, so doing a fuse would be pointless.

sorry to hijack this thread but now I'm learning!
how would I figure out what value and type of resistor to use?

LED series resistor calculator:
http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm

If you get 1.35W then make sure you round up, not down. Also use the highest voltage that you will see, such as around 16V for the 14.5V pack.

Drewfus2101 said:

You can't get a 2A fuse or 1.5A fuse, so doing a fuse would be pointless.

Click to expand...

You can, but even fast-blow fuses blow much slower than LEDs do.

As another idea, there has been talk about the new Kennan driver board coming with components that shut it down when voltage drops under a certain level. I'll dig up a link to the thread where that was discussed if you're interested. The component values would have to be changed for it to cut off at 12 or 13 volts.

vtunderground said:

I'm looking to run three Seoul P4 emitters at 1000 mA, powered by a 14.5v NiCad battery pack (from a cordless drill).

My question is... if I use a buck converter, is there a danger of damaging the battery pack by draining it too low? Should I be taking a different approach (More emitters? Direct drive?)? Am I just being paranoid?

Click to expand...

The key to remember is that although general precautions apply - each modding case is unique, and you can tailor your design to just your needs...

Start by doing some actual real-life measurements: Use a mulitmeter and find out what exactly your battery-pack outputs are (charged and 'tired') when loaded down with (say) a 10W car lightbulb (designed to run at 13.5v), which will approximate a 1-amp load.

LEDs too, even from the same bin/batch, exhibit variations in tolerances, they also 'mature' after being used for a day or so. Measure the voltage (Vf) you need to run each at your desired amperage - a quick trick is to put the LED in series with your 10W car bulb and measure the amperage, then measure the voltage across the LED.

Then you can decide if you need a resistor and the value.