Painfully boring technical question re. rear lights and rechargeable batteries

[wafter]

I think I'd just get some more rechargeable batteries from somewhere like Argos or Screwfix or get some lights that you can recharge via the USB from Halfords etc.

I'd rather get to the bottom of it and understand what's going on... I don't like devices with built-in cells due to their very finite liftime; hence why I went with this product in the first place

Yes. Just before when it would normally cut out.

Thanks - if I repeat the test to failure I'll do as you suggest; usually once they've cut out you can turn them on again for another few minutes before they die again; so this could be a good opportunity.

So you have 0.95x2.62 = 2.5Wh available from the battery, and Moon claim 43hr battery life at 25 lumen for your lamp, so that suggests it's drawing 2.5/43 = 58mW, giving 25/0.058 = 430 lm/W.

Being as "The current state of the art is 150 lm/W" and "the LED industry is aiming for 250 lm/W, with 300 or so the likely theoretical limit" something doesn't sound quit right. Nevertheless, it's not as big discrepancy as you seem to be getting.

I think you need to define what your end point is (subjectively too dim or does it just cut out?), and measure the supply current, then these might be of some help:

Nickel Metal Hydride (NiMH) Handbook and Application Manual
Alkaline Manganese Dioxide Handbook and Application Manual


My charger complained that one of the cells out of my desk phone was faulty because I forgot them and let them discharge until one went into reverse, but I managed to recover it by putting it on a power supply and nuking it with an amp or so for a few seconds.

Measuring the battery on and off load, along with the current is useful, then you can calculate the source resistance.

If you know what the lamp draws that will do as your test load, especially as you already know it's lasting 3-4 hours.

Thanks for that really informative post

Presumably the 2.62v value is that between fully-charged and cutoff voltage (at which the LED dies completely)? To be fair to Moon, their figures are for Alkalines which I think potentially have more capacity than NiMH; although I appreciate this might not account for the discrepencies you describe.

After some time spent like a lobotimised monkey trying to pilot a spacecraft, I think I've figured out the multimeter. I've run a couple of current draw tests with the meter in series between the (unconnected from each other) battery and the terminal it's supposed to connect to, with fully charged batteries:

Mode 1 / 12lm: 0.12A / 120mA / 0.34W at 2.85v
Mode 2 / 25lm: 0.25A / 250mA / 0.72W at 2.85v

Both of which appear to be 18lm/W, if I've done my sums right..


So, if we consider the mode 2 figures as that's the setting the batteries were tested on, this suggests that over the 3hrs from fully charged that the light remained illuimated, it consumed 3x0.25= 0.75Ah or around 79% of the two cell's rated value of 950mAh each..?

For the grown-ups in the room, does this seem correct and would it be fair to suggest that, given the published discharged characteristics of NiMH batteries (which seem to operate well down to 1.1-1.2v then fall off a cliff) the remaining, unaccounted-for 21% could remain in the cells after the regulator circuit in the light has already shut it off?

The anecdotal evidence (thanks @albion!) suggests that the cells might be inferior / knock-offs, however the figures above seem to suggest that they're probably behaving as they should and that the light is consuming a lot more power than it should..

So; who gets the exploding box of dog turds in the post - battery seller or light manufacturer?

 

[Jameshow]

Have you read the OP?

Simply knowing that they won't power my lights for very long has limited value.. hooking them up to a load of known value to ascertain total capacity for comparison to the quoted value is much more telling. If I had the ability to lash up such a setup..



Thanks - not sure how significant this is, but a pair of my "950mAh Eneloop Pros" come in at 21.4g; potentially suggesting they contain significantly less magic than yours; if mass can be taken as an indicator of capacity..



I'd imagine it does from my minimal knowledge of battery chemistry, however it certainly shouldn't cause the difference between what I'm seeing (3hrs) and the quoted runtime (46hrs).



Nope, always on.. the quoted runtime for this being 60-odd hours, but I'm lucky if I see four.

Tempted to go to flashing as this will extend battery life, and while this mode arguably has additional benefits, I don't much like being exposed to it myself..


So.... I have a multimeter, some batteries and assorted wires with crocodile clips courtesy of my late father, however am yet to find a way of reliably connecting it to a load of some description to do a capacity test.

In any case I bought the batteries over a year ago (although they've not seen a lot of use), so I potentially have very little sway with the seller.. although if I do end up testing them and getting suspect numbers I can threaten to report them to ebay I guess; for what that's worth...

A simple bulb of known wattage across the terminals will give a load and given the watts of the bulb know so it's not hard to find the full battery capacity???

 

[wafter]

A simple bulb of known wattage across the terminals will give a load and given the watts of the bulb know so it's not hard to find the full battery capacity???

Sadly I have neither said bulb, nor a reliable way to attach it to the power source for long enough to perform a full discharge test..

 

[Mike Ayling]

"cough" , buy a small pack of alkalines and place in your light, if they also discharge rapidly your light is cactus, if not your charger or rechargeables are cactus.

 

[Bazzer]

I'd be inclined to take the suggestion up thread and get some batteries from a reliable source.
IIRC I paid less than a tenner for 4 AAA rechargeables the other week at Tesco. They work perfectly in their non bike device. My ASDA rechargeables are still good despite being at least 3 years old and get used both on my bike and in a waterproof torch.
If the light works only for a short period, it's the light and you have some spare decent batteries. If the light stays on for longer, it was the batteries.

 

[wafter]

As per my previous posts I run rechargeables because I don't like the waste of disposibles. I'm not about to burn through a load to test a light if there are alternatives..

 

[Ming the Merciless]

I have a couple of rear LEDs both running off two Eneloop AAA. They last about 90 hours of use. Haven’t needed to charge for a wee while.

 

[Mike_P]

As per my previous posts I run rechargeables because I don't like the waste of disposibles.

Sent for recycling alkalines are mechanically separated to recover the zinc, manganese, steel etc.

Lithium batteries are the problem ones as it is not cost effective to recover the lithium and cobalt.

 

[ColinJ]

"cough" , buy a small pack of alkalines and place in your light, if they also discharge rapidly your light is cactus, if not your charger or rechargeables are cactus.

Hmm... not necessarily so!

My search for batteries was needed because one of my NiMH cells died suddenly. I have long since stopped carrying spare AAs for my Garmin Etrex. I always recharge the cells before a long ride and they usually last 25+ hours on a charge. Only this time, they didn't! One of them died after just 3 or 4 hours of riding.

Here is some free advice, folks: Batteries can and do fail!

Second item of free advice: If your smart battery charger suggests that there might be a problem with a battery, believe it - don't just switch it off and try again later! (It charged the battery on my second attempt, but was obviously telling me the truth initially.)

I managed to get replacement batteries from Morrisons in Malton. They only had packs of 8, which was a pain because I rarely use standard batteries (NiMH rechargeables make far more sense). What was worse was being charged £8 for the pack - way over double the going rate! I'll carry 2 of them with me for backup on rides in future, though this the first rechargeable failure that I have had in years.

Battery update...

I am WELL peed off!!! I went to use 2 of those bloody Duracells in my wireless mouse yesterday and they were dead. I tried 2 more - dead. In fact, all of the bloody things are dead. Their use-by date is 2028 and I had never used the 6 that I hadn't used on this ride, and the 2 that I did use were only used to get me home!

 

[wafter]

Sent for recycling alkalines are mechanically separated to recover the zinc, manganese, steel etc.

Lithium batteries are the problem ones as it is not cost effective to recover the lithium and cobalt.

That's as may be, however they're still single use, recycling still requires energy and resources (providing those charged with doing so don't just dump them in landfill).. so NiMH batteries remain far superior in terms of lifetime energy cost / waste / financial outlay..

 

[albion]

That size problem occurs with a lot of rechargeables. I've put them in a device and had a real fight to get them out so much so I tend now to use Aldi or Lidl alkalines and recycle them when dead. Having a good battery tester is useful. Often it's only one battery that has gone dead. Given how long the alkalines last in comparison I'm not convinced rechargeables are that green given the amount of charging needed.

Eneloops are accurately rated up to 2100 charges. They are then only batteries that I have yet to have any sign of failure.

 

[Mike Ayling]

That's as may be, however they're still single use, recycling still requires energy and resources (providing those charged with doing so don't just dump them in landfill).. so NiMH batteries remain far superior in terms of lifetime energy cost / waste / financial outlay..

Looks like scope for many more PHD these!

 

[fossyant]

That's as may be, however they're still single use, recycling still requires energy and resources (providing those charged with doing so don't just dump them in landfill).. so NiMH batteries remain far superior in terms of lifetime energy cost / waste / financial outlay..

But, if you did a burn test, you wouldn't be wasting a huge amount of time on here and fiddling with multi-metres. I'll bet a decent set of alkaline batteries way outlast rechargeable NiMH.

I stopped using rechargeable AA/AAA in lights many years ago as the burn time wasn't great - charging every day, or every other day. I still charge my built in Lipo's daily, or once every two days for the 'removeable lipo' front light.

 

[Dadam]

Occam's razor: batteries are knockoffs.
A large helping of that plus maybe a dash of highly optimistic claimed runtime for the lights.

 

[albion]

Looks like scope for many more PHD these!

The 'higher voltage' of alkalines is weird. Whilst Eneloops stay near 1.2V for most of their drain, Alkalines have near 50% of their usage time below 1.2V, assuming the power item does not stop working far too early. And for high drain devices it can be far worse.

So if you get a brighter light with Alkalines, likely it is short lived.