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Battery Replacement on Lights with Internal Li-Ion Batteries
On 2/7/2018 2:23 PM, sms wrote:
On 2/6/2018 8:48 PM, Jeff Liebermann wrote: On Tue, 6 Feb 2018 10:52:50 -0800, sms wrote: My wife's Lezyne Deca 1500XXL stopped taking a charge, at all. Taking it apart, I saw that the batteries were made in July 2015. Not too good for it to stop working that soon. These lights don't have user-replaceable batteries, but by removing two screws I was able to open it, and the battery pack does have a connector on it so at least they didn't solder it directly to the printed circuit board. I don't see a problem.Â* If your wife used the light every day for about 2 years, that would be 730 charge cycles.Â* That's about the correct lifetime for a 60% DoD (depth of discharge).Â* See table 2: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries Not nearly every day. I'd estimate about 200 total charge/discharge cycles. Something failed in the battery pack because it wasn't like the operating time was less than when new, the pack would not charge at all. Charging the batteries in parallel with a 2A USB charger is also about right.Â* For two alleged 2800mA-hr cells in parallel, that would be about 0.35C charge which is quite safe. I've found that the cells that die quickly are usually helped along by a charge circuit that overcharges the battery.Â* 4.2v should be the absolute maximum.Â* LiIon loses about 10% of it's capacity during the initial rapid discharge from 4.2 to 4.0V.Â* While I don't like losing the 10%, the battery will last much longer if only charged to 4.0v. Charging to 3.92v yields the best compromise between two failure mechanisms (electrolyte oxidation and growing crud on the anode).Â* See "summary" section: http://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_die The charge voltage was correct. And of course the protection circuit in he pack ensures that the charge voltage doesn't exceed 4.2V, regardless of what the charging circuit voltage actually is. It's a 2 cell 18650 pack with the batteries in parallel, and a protection circuit board shared between the two cells. The cells are allegedly 2800mAH, for a total of 5600mAH. Seems rather high.Â* Note that batteries are tested at a 0.2C discharge, which yields larger numbers than the usual headlight discharge rate.Â* The Lezyne Deca 1500XXL claims 1500 lumens, which also seems a bit high.Â* Assuming 120 lumens/watt at a nominal 3.7V/battery, that's: Â*Â*Â* 1500 / 120 / 3.7 = 3.4A to run the headlight at full brightness, or 1.7A per cell. Meanwhile, the cell capacity is tested at: Â*Â*Â* 0.2 * 2800 = 0.56A This is the battery in the original pack: http://www.gebc-energy.com/Uploadfile/pdf/ICR18650/ICR18650H3.pdf I disassembled the pack. The batteries are completely discharged, 0V. To me this indicates a failure of the protection circuit which normally would not allow discharge below 2.8V. The closest I could find on-line was a 2x2600mAH parallel pack https://www.amazon.com/dp/product/B003SH4BV6. Notice that his version: https://www.amazon.com/Tenergy-Li-ion-2200mAh-Rechargeable-Battery/dp/B002Y2LJW0/ is series connected, but claims only 2200ma-hr.Â* Kinda looks like the same cells, but wired differently.Â* Looks like the one you purchased might be lying about the battery capacity.Â* You'll find out soon enough if the battery is discharged faster than expected. Do any manufacturers not lie? It's a matter of degree. Tenergy is an industrial supplier of batteries with a real building in Fremont, and not like buying no-name batteries on Aliexpress. Ready to buy a battery discharge tester http://www.westmountainradio.com/cba.php and a lux meter? https://www.ebay.com/itm/391973339920 https://www.ebay.com/itm/401324425264 I moved the connector from the old pack to the new pack, plugged it in, and closed it up. Seems to work fine now. Yeah, for how long will it work?Â* Dig out your digital volts-guesser and measure the EoC (end of charge) voltage.Â* If it's over 4.2v, that may be why it died early.Â* Also, see how long it will run.Â* You don't want it going out prematurely on the initial test run.Â* Maybe carry a 2nd headlight for the initial testing. The charge voltage from the plug that connects to the battery was 4.19V. I checked that before I ordered a new battery because I thought that the problem with the light might have been with the charging circuitry. The measured lumens by mtbr.com of the Deca Drive XXL was 1390, so they were not using chilumens https://www.urbandictionary.com/define.php?term=chilumen, and there was minimal lunmenflation https://www.urbandictionary.com/define.php?term=lumenflation. This morning I put the light on the maximum setting and it ran for just about exactly two hours before it stepped down the intensity. 5200Â*Â*Â* mAH [rated] 3.7Â*Â*Â* V [rated] 19.24Â*Â*Â* Watt-Hours [calculated] 2.0Â*Â*Â* Hours [measured] 9.62Â*Â*Â* Watts [calculated] 2.6Â*Â*Â* Amps [calculated] 1390Â*Â*Â* lumens [measured by mtbr.com] 144.5Â*Â*Â* lumens/watt [calculated] 3Â*Â*Â* LEDs 48.2Â*Â*Â* lumens/LED [calculated] Of course the reality is that the batteries were not fully discharged when it dropped the output, so the lumens per watt was likely quite a bit higher. I like the design of the Lezyne and how they use 3 LEDs to mitigate thermal issues, as well as to give a more usable beam pattern that includes sufficient side illumination. Definitely NOT StVZO https://www.urbandictionary.com/define.php?term=stvzo. Scharf's dictionary editing reminds me of this Dilbert strip: http://dilbert.com/strip/2009-05-08 What some people don't understand is that optics are very important in bicycle lights where you are dealing with a limited amount of battery or dynamo power. What I don't understand is that you say that now, yet you've spent years lobbying in favor of systems that shine half of their lumens at overhead aircraft, instead of where they're really needed. -- - Frank Krygowski |
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