Re: Rechargeable v. throwaway batteries

On 22 Oct, 22:38, Frank Krygowski <frkry...@xxxxxxxxx> wrote:

Well, one of my new acquaintances is vice-president of research for a
company that specializes in LED products.  He's done tons of
experiments with high powered LEDs, so I asked him.  He assures me
everything should be fine.

Well I've said some of this in response to Clive.
So then it's good to connect 24, 5mm LEDs in parallel to a bike dynamo
without further circuitry If the LEDs are matched (forward voltage and
current draw)? Because that is what my new lamps are. And if I
wanted double the power I just connect the lamps in series? Like
Clive says, I'll need to dig around in the shed for the dynamo, but if
it works then it looks like I'll be fixed for lights for ten years.
[[It's not worth looking any further now, for if my calulations are
correct we will face the beginings of the apocalypse around
2018-2023]] Perhaps in ten years I'll be thinking more strongly about
carbide lamps. You should probably ignore my double bracketed
comments, totally out of place here..


As an example of what I'm talking about:  I previously tested the
output current of the Soubitez generators I use.  Here are the results
at a road speed of 26 mph, for various resistive loads:
6 Ohms, 0.63 Amp ; 12 Ohm, 0.58A; 18 Ohms, 0.54A; 24 Ohms, 0.50 Amp.
And at just 6 mph, this one put out over half an amp into the 6 ohm
load.

looking good. but diode junctions are not exactly resistive, that's
why we refer to the conductance of the junction. Ok, some may use the
term forward resistance and switch on voltage.

So you see, load resistance has an effect, but not nearly the
approximately inverse-proportionality effect it has with a battery.
With zero resistance, even this relatively high output dynamo won't
put out much more than 0.63 Amp.

so 24 LEDs if they share the current equally will be individual draw
of 27mA, sounds good.


Diodes usually require something less than a volt to conduct in their
forward direction, but then they display very little resistance.

LED forward conductance is at a higher voltage than typical Si
diodes.  There seemed to be a wide variation, of forward voltage,
available in the original 5mm format when I was looking for devices
about three years ago. IIRC you take the forward voltage from the
supply and the excess voltage is used to determine the current
limiting resistor, not forgetting with a battery power source, the
battery internal resistance will have to be factored into that
calculation. But a bicycle dynamo does not external current limiting
if it is current limiting itself. or does it???

A
battery with no resistance in series can dump very excessive current
into them and pop them, so batteries need current limiters of one type
or another to drive LEDs.  (The exception is a coin cell, which
apparently comes with enough internal resistance to let the LED
live.)  Bike generators give LEDs exactly what they want.

A 3V coin cell typically drives a 2.5V LED. the 0.5V aint worth doing
the sums because of the internal resistance of the cell.

If the LED handles that 0.63 Amp (which most high powered ones do)
there should be no problem.  I hope!  We'll see how it does long term..

But are you powering a single junction without any other components in
the circuit?

The headlamp I installed is this one:http://www.velo-orange.com/spluledhewst.html
and although I took it apart far enough to re-design the mount for my
purposes, I resisted the temptation to dig deep enough to see its
circuitry, but the internal wiring made it clear that it was
originally designed for either generators or batteries.

That hasn't answered my question.
.

Relevant Pages

  • Re: LEDs in parallel
    ... qualitative "higher currents". ... which is running LEDs from a voltage source. ... resistance of the LED in each case - yields for the first case: ... It would be more efficient (uniform brightness vs battery voltage, ...
    (sci.electronics.design)
  • Re: LED voltage drop
    ... If you connect a 9v battery across a red LED it blows. ... The voltage drop across an LED is fixed at about 1.4V so what happens ... So the 7.6 volts didn't disappear. ... If you have any old 9V batteries that you are tempted to connect LEDs ...
    (sci.electronics.basics)
  • Re: Driving LEDs with a battery pack
    ... battery holder with 3 AAAs in it). ... I can calculate the right resistor for any give voltage, no problem, ... How delicate are LEDs? ... It sounds like you just need a simple boost converter to boost your battery ...
    (sci.electronics.basics)
  • Re: LED impedance
    ... It won't bother the voice stuff, but it might affect the ring voltage, ... Phone DC resistance: 33 ohms ... Some red and/or reddish orange LEDs ... A resistance of mostly about 10-20 ohms ...
    (sci.electronics.design)
  • Re: Cant get enough current for 1W Luexon LED even without resistor
    ... Then I tried without the resistor but ... the LED I have to raise the voltage to about 11V and of course I ... Seems like my battery has too much internal resistance. ... voltage with LEDs, although your calculations are of course all correct. ...
    (sci.electronics.repair)