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Battery Replacement on Lights with Internal Li-Ion Batteries

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Old February 12th 18, 06:33 PM posted to rec.bicycles.tech
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Default Battery Replacement on Lights with Internal Li-Ion Batteries

On 2/12/2018 9:23 AM, Joerg wrote:
On 2018-02-12 08:51, sms wrote:
On 2/12/2018 8:03 AM, Joerg wrote:


Simple: When clicking the light on you must stand over it or near it.
It could, for example, issue three short flashes after turn-on for
batt-ok, two flashes for "enough but not for more than a few hours"
and on flash for "it'll be empty very soon".

That's reasonable for a USB powered light with Li-Ion batteries. For a
device running on AA or AAA batteries, not really, because different
chemistry AA batteries have very different voltages and discharge curves.

Battery voltage for primary D, C, AA, AAA, AAAA cells:
***** Alkaline-manganese dioxide: 1.5V. Linear voltage degradation
***** NiMH: 1.2V with almost do voltage degradation until fully
***** Primary Lithium (LiFeS2): up to 1.83V, typically 1.7V, discharged
if 1.6V or less. Decreasing voltage during discharge, not quite linear.

I have seen a device where there was a switch to flip for NiMH versus
Alkaline to account for the different voltages in order to provide a
more accurate low battery warning, though no option for LiFeS2.

You could provide a zero-cost alkaline-NiMH function swap by, for
example, pressing the on-off button for 3sec. Not necessary though
because more rear lights are a bit dim with 1.2V NiMH and I bet 99% of
riders use AAA cells. So just provide a lo-bat warning for alkaline and
that goes a long way.

Of course, for that to work the IC designers must be competent enough to
include a decent bandgap reference. You wouldn't believe how many aren't.

It doesn't have to be accurate, just ballpark. Mainly because almost
nobody remembers how many hours the recent set of batteries has been used.

Another near-zero cost method would be to provide a coarse timer.
5h-10-15h-20h-25h. Simple RC or relaxation oscillator, one through five
flashes for status, done. Or just count the number of blinks. Serious
riders know how long batteries of their choice will last so they can
then decide at 15h or 20h to change them out.

Product design can be quite simple and cheap if we just think outside
the box and most of all try the designed products ourselves. A bike
accessory manufacturer should preferably hire ... riders.

Yes, but they need to hire riders that aren't geeks if they want to
design something usable.

To do low-battery right on a light where you don't know what type of
batteries will be used, you can't do correlation, you need an optical
solution, like an opto-isolator inside that tracks the light output of
the LEDs and indicates when intensity is falling, independent of battery
type. For internal rechargeable Li-Ion batteries it's easy to roughly
correlate voltage with remaining capacity.

And seriously, while geeks may count blinks and program the battery type
via button presses, not everyone that bicycles is an engineer. It's hard
enough to explain how to cycle through the different modes.

The battery indicator on my Lezyne is simple and perfect. Green 50%.
Yellow =11-50%. Red 10% or less. I don't need a bar graph LCD or a
digital readout.

I saw "the perfect light" at one Interbike because you could program the
modes including intensity and flash rate via button presses. Since many
lights keep the DRL flasher at full intensity, which is unnecessary, I
thought that this was a good idea. But it was way too complex for the
normal rider. A software person would get frustrated and dump their
herbal tea onto the light.

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