Comment on Workbench tale: Resurrection of a dead Emlid Reach RS+ due to extremely low battery
troyunrau@lemmy.ca 3 weeks agoThey’re lithium iron phosphate chemistry, which typically draw down to 2.0V without problems, and tend to be a bit more forgiving. I agree 0.9V is low, but the cells were relatively new. Furthermore, no sign of damage or other typical faults associated with a failing battery, and my battery analyzer (from my drone batteries, same chemistry) approved it. According to my gantt chart, they’ve likely been charged and discharged 75 times since I brought them back to life.
Sadly, because they are a manufacturer device integrated battery pack, and the manufacturer doesn’t sell replacements, my only options would be installing a third party battery pack or buying another device at $1500 or more. I’m happy with the battery recovery process though in this case.
Thanks for sharing this.
It looks like the cutoff voltage for LiFePO4, the minimum voltage after which there should be a total power cutoff is around 2.8V. Discharging further is equal to more or less serious, but always, damage to the cell. It also looks like the effects of such over discharge might be less serious for LiFePO4 than it is for Li-Ion cells. However… doesn’t this 1500$ device have a Battery Management System, BMS, a small circuit to implement the cutoff voltage? What the hell?
Yeah, there is risk of some chemistry happening at really low voltages which cause irreversible changes to the structure of the material. Given how the battery responded to tests afterwards, I can only presume that these didn’t happen. Short of dissecting the cells and putting them through XRD. Mind you, I do know a few people in the lab…
kjo@discuss.tchncs.de 3 weeks ago
Me reading that: I wonder why they don’t sell the replacement battery.
Me: Ohhhhh 😮💨
troyunrau@lemmy.ca 3 weeks ago
Oddly enough, it’s probably one of the best and most affordable devices in this sector. You can buy 10-20x units compared to the brand leader (Trimble). So I think they assume that this is how most people will operate.