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bulbs to LEDs



 
 
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  #11  
Old August 13th 13, 07:25 AM posted to aus.bicycle
James[_8_]
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Posts: 6,153
Default bulbs to LEDs

On 13/08/13 15:04, TimC wrote:
On 2013-08-13, James (aka Bruce)
was almost, but not quite, entirely unlike tea:
On 12/08/13 16:43, Trent W. Buck wrote:
James writes:

On 06/08/13 18:41, Trent W. Buck wrote:
I suspect the responses are all gonna be "I hate dynamos! Batteries are
not that hard, just HTFU" so I haven't bothered to dig up hub specs &c,
but I'll do so if there's interest. The bulb claims to be a Philips
HPR60, 3.6V 2.4W.

Interesting that the bulb is rated for such low voltage.

What is the rating of the hub dynamo you have?

Most dynamos and the required bulb are rated something like 6V, 3W.

Now you've got me freaked out, because I tried a "HPR53 4V0.85A JAPAN"
in it, and it didn't light up *at all*. (A replacement bulb finally
arrived from LBS, and that's working, hooray.)


Ah, well that's good. Perhaps the light housing has a voltage limiting
zener diode or similar, to protect the 3.6V bulb from the full 6V. Or
perhaps the original lighting circuit had the front and rear bulbs wired
in series, so that the 6V was shared across two bulbs. I can't tell
from here.


Dynamos are current sources (not voltage sources). LEDs are current
sinks (not voltage sinks).


That's one way to look at it. Dynamos have sort of regulated current
output due to the inductive impedance increasing proportionally with
speed (X = wL).

And yes, the I-V curve of LEDs has a fairly flat voltage independent of
current, once a threshold of current is reached.

Your 3W LED will typically have about 3 or less volts across it, and
if you wired it up to a non-current limited 12v power supply, it would
blow.


Absolutely. However I have 4 LEDs, each with about 3.5V across at up to
1A, configured as a full bridge rectifier and connected directly across
my 6V 3W dynamo. (Two LEDs in series, in parallel with two LEDs in
series but connected to conduct in the opposite direction. And yes the
reverse polarity breakdown threshold of each is about 5V, well above 3.5V.)

If you hooked up an appropriate resistor in series with your 3W
LED, and then the un-current-limited 12V power supply, then you'd end
up with a voltage divider and the appropriate current flowing through
the LED that caused it to have a ~3V voltage drop (with 9V and most of
the power being dissipated by the resistor). But in the ideal case of
having a current source, then the LED will just sink as much current
as the source supplies. Both will match their voltage if you've got
no resistor or anything else in the circuit. But of course, you don't
presumably know the actual current limit of the dynamo - at least I've
never seen it documented before.


I measured the output voltage and current from my dynamo at home at
various speeds with a fixed resistor load, and recorded and graphed the
result. It gave me a good understanding of the output characteristics.
There is also a set of test results for various dynamos he
http://www.myra-simon.com/bike/dynotest.html. It's also instructive
to consider the electrical model as an AC voltage source proportional to
speed, and a resistive and inductive element. Note that the inductive
reactance increases linearly with speed like the internally generated
voltage. This is what limits the current.

But given they are ~3W, it should be
more or less right. The LED won't work perfectly at 2.9W and blow
catastrophically at 3.1W.

LEDs of different types *have* to be wired in series (the current
source will just double its voltage output in order to maintain the
same current going to 2 equal LEDs in series).


Only if the LEDs can both handle the same current.

You can get away with
very similar lights being in parallel, until they age. Then one will
start taking more current, until the power supply starts overpowering
it, and there'll be thermal runaway and that LED will completely short
out, rendering you with a Dark Emitting Diode.


Well, my home made headlight has been in regular use (3 times a week)
for the past year. I've descended some pretty big hills as well. Zero
defects thus far.

--
JS
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  #12  
Old August 13th 13, 08:00 AM posted to aus.bicycle
Trent W. Buck
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Posts: 21
Default bulbs to LEDs

TimC writes:

On 2013-08-13, James (aka Bruce)
was almost, but not quite, entirely unlike tea:
Ah, well that's good. Perhaps the light housing has a voltage
limiting zener diode or similar, to protect the 3.6V bulb from the
full 6V. Or perhaps the original lighting circuit had the front and
rear bulbs wired in series, so that the 6V was shared across two
bulbs. I can't tell from here.


LEDs of different types *have* to be wired in series (the current
source will just double its voltage output in order to maintain the
same current going to 2 equal LEDs in series). You can get away with
very similar lights being in parallel, until they age. Then one will
start taking more current, until the power supply starts overpowering
it, and there'll be thermal runaway and that LED will completely short
out, rendering you with a Dark Emitting Diode.


FWIW, when the front halogen bulb was absent, the rear LED still worked
fine -- and it would even activate a bit (maybe blinking, I don't
remember, it's normally constant-on) when backing up, which it doesn't
do with the working bulb in the front.

Based on my high school electronics, I took that to mean they're wired
in parallel.
  #13  
Old August 13th 13, 11:46 PM posted to aus.bicycle
James[_8_]
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Posts: 6,153
Default bulbs to LEDs

On 13/08/13 17:00, Trent W. Buck wrote:
TimC writes:

On 2013-08-13, James (aka Bruce)
was almost, but not quite, entirely unlike tea:
Ah, well that's good. Perhaps the light housing has a voltage
limiting zener diode or similar, to protect the 3.6V bulb from the
full 6V. Or perhaps the original lighting circuit had the front and
rear bulbs wired in series, so that the 6V was shared across two
bulbs. I can't tell from here.


LEDs of different types *have* to be wired in series (the current
source will just double its voltage output in order to maintain the
same current going to 2 equal LEDs in series). You can get away with
very similar lights being in parallel, until they age. Then one will
start taking more current, until the power supply starts overpowering
it, and there'll be thermal runaway and that LED will completely short
out, rendering you with a Dark Emitting Diode.


FWIW, when the front halogen bulb was absent, the rear LED still worked
fine -- and it would even activate a bit (maybe blinking, I don't
remember, it's normally constant-on) when backing up, which it doesn't
do with the working bulb in the front.

Based on my high school electronics, I took that to mean they're wired
in parallel.


Yup. I don't know what's in the rear light, but it could just use a
resistor to limit the current to something safe for the LED inside with
6V supplied.

Along similar lines, I've been thinking about adding a small low power
LED to my headlight circuit, on a bendable lead so I can have a light
over my bike computer at night.

--
JS
  #14  
Old November 13th 13, 03:04 PM posted to aus.bicycle
Trent W. Buck
external usenet poster
 
Posts: 21
Default bulbs to LEDs

Zebee Johnstone writes:

In aus.bicycle on Wed, 07 Aug 2013 11:10:14 +1000
Trent W. Buck wrote:
Zebee Johnstone writes:
The dollar's just dived so it ain't as easy as it was, but look at
bike24.de and see if there's anything you can come at.


A couple of weeks ago my OEM bulb headlamp decided to get stuck on "dim"
instead of the more useful on/auto/off settings it started with.

So I finally got around to buying an LED-based replacement from bike24.
IIRC it worked out at AUD70, of which about a third was shipping. Meh;
I tend to view capital expenses as an investment.

Arrived Tue, installed it Wed. Brief panic because until I hooked up
the ground, the rear light was lighting up, but the front one wasn't.

Used it the last two nights and it's *definitely* nicer than the bulb
one, thanks for putting me onto bike24.

It's not *super* bright, but I'm OK with that. Assuming both spec sheets
are honest, I went from 17lux to 25lux. Most of my commute is under
street lighting anyway.

The light output is much whiter than the bulb, and the output is mostly
in two rectangles, with the upper-middle bit brightest:

+---+-------+---+
| | | |
| +-------+ |
| |
+---------------+

But it does some funky optics so there's also dimmer light spilling
around the edges (inc. straight down) as well. And it has a capacitor,
so when stopped or going up a steep hill, it stays on. That always
annoyed me with the previous one.

One thing I didn't expect, is that it flickers a bit even at speed,
whereas with a bulb that was only noticable when the bulb was only just
getting enough juice to light up.

The model I got was a B+M Classic (IIRC the "CSNDI" flavour).
  #15  
Old November 13th 13, 07:49 PM posted to aus.bicycle
Zebee Johnstone
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Posts: 1,960
Default bulbs to LEDs

In aus.bicycle on Thu, 14 Nov 2013 01:04:50 +1100
Trent W. Buck wrote:
Zebee Johnstone writes:

In aus.bicycle on Wed, 07 Aug 2013 11:10:14 +1000
Trent W. Buck wrote:
Zebee Johnstone writes:
The dollar's just dived so it ain't as easy as it was, but look at
bike24.de and see if there's anything you can come at.


A couple of weeks ago my OEM bulb headlamp decided to get stuck on "dim"
instead of the more useful on/auto/off settings it started with.

So I finally got around to buying an LED-based replacement from bike24.
IIRC it worked out at AUD70, of which about a third was shipping. Meh;
I tend to view capital expenses as an investment.


There might be cheaper places, but I haven't found anything much
cheaper as it seems to be more expensive EUR-AU than US-AU.

Arrived Tue, installed it Wed. Brief panic because until I hooked up
the ground, the rear light was lighting up, but the front one wasn't.

Used it the last two nights and it's *definitely* nicer than the bulb
one, thanks for putting me onto bike24.


Yeah, I found that going from halogen on my 'bent to the LED IQ Fly.


One thing I didn't expect, is that it flickers a bit even at speed,
whereas with a bulb that was only noticable when the bulb was only just
getting enough juice to light up.


HAven't seen that on mine, wonder if it's an effect of the low power?
OR maybe just a bad connection somewhere?

Zebee
  #16  
Old November 14th 13, 12:20 AM posted to aus.bicycle
Trent W. Buck
external usenet poster
 
Posts: 21
Default bulbs to LEDs

Zebee Johnstone writes:

One thing I didn't expect, is that it flickers a bit even at speed,
whereas with a bulb that was only noticable when the bulb was only
just getting enough juice to light up.


Haven't seen that on mine, wonder if it's an effect of the low power?
OR maybe just a bad connection somewhere?


I might still have a short in the wiring somewhere...
  #17  
Old November 18th 13, 10:03 PM posted to aus.bicycle
James[_8_]
external usenet poster
 
Posts: 6,153
Default bulbs to LEDs

On 14/11/13 01:04, Trent W. Buck wrote:
Zebee Johnstone writes:

In aus.bicycle on Wed, 07 Aug 2013 11:10:14 +1000
Trent W. Buck wrote:
Zebee Johnstone writes:
The dollar's just dived so it ain't as easy as it was, but look at
bike24.de and see if there's anything you can come at.


A couple of weeks ago my OEM bulb headlamp decided to get stuck on "dim"
instead of the more useful on/auto/off settings it started with.

So I finally got around to buying an LED-based replacement from bike24.
IIRC it worked out at AUD70, of which about a third was shipping. Meh;
I tend to view capital expenses as an investment.

Arrived Tue, installed it Wed. Brief panic because until I hooked up
the ground, the rear light was lighting up, but the front one wasn't.

Used it the last two nights and it's *definitely* nicer than the bulb
one, thanks for putting me onto bike24.

It's not *super* bright, but I'm OK with that. Assuming both spec sheets
are honest, I went from 17lux to 25lux. Most of my commute is under
street lighting anyway.

The light output is much whiter than the bulb, and the output is mostly
in two rectangles, with the upper-middle bit brightest:

+---+-------+---+
| | | |
| +-------+ |
| |
+---------------+

But it does some funky optics so there's also dimmer light spilling
around the edges (inc. straight down) as well. And it has a capacitor,
so when stopped or going up a steep hill, it stays on. That always
annoyed me with the previous one.

One thing I didn't expect, is that it flickers a bit even at speed,
whereas with a bulb that was only noticable when the bulb was only just
getting enough juice to light up.

The model I got was a B+M Classic (IIRC the "CSNDI" flavour).


I'm waiting for this one...

http://www.xxcycle.com/busch-and-mul...ndi-04,,en.php

--
JS
 




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