LEDs don't respond simply to voltage they are driven by current. LEDs
should consequently be all in series so that they get the same current
through them. The difficulty comes in generating that current with a simple
yet efficient circuit. A battery of sufficient voltage connected to a
series resistor in series with the string of LEDs will need to be
approximately 2 volts per LED depending on the type of LED and the
temperature of the LED (this typically varies during operation further
complicating matters.) It won't be very efficient but it will work.
Paralleling batteries doesn't produce a useful result; don't bother. Get
batteries of sufficient capacity to produce approximately 2V per LED, add
another cell(s) to give 2 volts of drop across the series resistor and
provide the 20mA necessary.
Here's a typical set of numbers: 4 LEDs (two wingtips, nose, tail) means
~8-9volts needed. This means an 8 NiCD or NiMH cell battery with each cell
rated at ~100mAH so that it can actually drive 20mA. You might get by with
50mAH cells. Add another two cells to drive the drop across the resistor.
That makes a 10cell pack. Use a 100ohm resistor to give about 20mA. If you
didn't care about recharging you could probably use a 9v alkaline battery
with a 100ohm resistor if you only used three LEDs.
You could do this a heck of a lot more efficiently by using niteops or by
using a single cell with a voltage converter like the LT1932 and a few
parts.
have fun
jtm
----- Original Message -----
From: "Perry Hudson" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, August 21, 2001 11:25 AM
Subject: [RCSE] LED's
Um. I'm hooking up some LED's on my night slope ship and was wondering if I
need to go in parallel or series??
The LED's are rated at 2V and 20 mha. They don't seem very bright at 2V.
Any
guess on how much they can take??
I have two 2.4v 500 mha packs wired in parallel. Any guess on duration with
18 led's pulling 20 mha's. A battery guy once told me you won't realize the
batteries full capacity by wiring the cells that way. All the ohms law
stuff
went right over my head. Oh yeah! I was surfing that day Mr. Ohms was
presented.
Comments.
Regards,Perry
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and
"unsubscribe" requests to [EMAIL PROTECTED]
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and
"unsubscribe" requests to [EMAIL PROTECTED]
