[time-nuts] Li-ion Batteries
ziggy9+time-nuts at pumpkinbrook.com
ziggy9+time-nuts at pumpkinbrook.com
Mon Jan 23 10:35:22 EST 2017
Balancing series packs is indeed important. This is why laptop batteries have all those pins on their connectors, and why hobby type batteries have balance charge connectors. Although they are different chemistries (laptop and 16450/18650 batteries are typically Li-Ion while hobby type batteries are typically Li-Poly) they both have this requirement. And each chemistry has it’s own charge/discharge requirements. Note that within Li-Ion there are still different chemistries that again have their own requirements, which are different from LiFE which are different from A123. Be careful making blanket statements.
At the risk of violating my own comment above, if you are discharging to 2.5V *under load*, then that could be OK depending on the specific battery. If you are measuring 2.5V with *no load*, then that is over discharged for pretty much any chemistry. And there is really nothing to be gained by discharging to this level. 3V is considered to be a safe low level cutoff for most cases, and below about 3.2V there is little capacity remaining anyway.
Over discharge and over charge both wind up plating metallic Lithium on the electrodes. Doing both is asking for trouble. Trickle charging a Li battery is also bad news as it over charges and again starts to plate out Lithium.
Yes, you can use a power supply to charge Li batteries. But you must be using a current limited supply, and voltage regulated. 4.2V at say .5 to 1C should be fine as long as you are there to babysit. But if you forget and leave it go then you will be trickle charging. Do that for too long it may become a problem. You simply cannot treat Li batteries/cells as you did anything else.
Proper multi-chemistry Li chargers are not hard to find, nor are they horribly expensive. Please use one. (And not the cheapest one you can get from Hobby-King or eBay.)
References? Please see:
NFPA: <http://www.prba.org/wp-content/uploads/Exponent_Report_for_NFPA_-_20111.pdf <http://www.prba.org/wp-content/uploads/Exponent_Report_for_NFPA_-_20111.pdf>>
Sony: <https://cdn.sparkfun.com/datasheets/Prototyping/Lithium%20Ion%20Battery%20MSDS.pdf <https://cdn.sparkfun.com/datasheets/Prototyping/Lithium%20Ion%20Battery%20MSDS.pdf>>
Panasonic: <http://actec.dk/media/wysiwyg/Actec/PDF/Li-Ion_handbook.pdf <http://actec.dk/media/wysiwyg/Actec/PDF/Li-Ion_handbook.pdf>>
Li/SOCl2: <http://www.varta-microbattery.com/applications/mb_data/documents/sales_literature_varta/handbook_primary_lithium_cylindrical_series_er_en.pdf <http://www.varta-microbattery.com/applications/mb_data/documents/sales_literature_varta/handbook_primary_lithium_cylindrical_series_er_en.pdf>>
Li-MnO2: <http://www.varta-microbattery.com/fileadmin/user_upload/downloads/products/lithium-rundzellen/HANDBOOK_Primary_Lithium_Cells_en.pdf <http://www.varta-microbattery.com/fileadmin/user_upload/downloads/products/lithium-rundzellen/HANDBOOK_Primary_Lithium_Cells_en.pdf>>
> On Jan 23, 2017, at 6:47 AM, Bert Kehren via time-nuts <time-nuts at febo.com> wrote:
> The biggest mistake you can make if you plan to use them in series not to
> equalize them before use. They come in different state of charge. Maybe
> close if from the same lot but not close enough and I do not count on the
> equalizer. I start with a discharge to 2.5 V and charge two at a time in
> Parallel with a holder that I modified. Set a power supply to 4.2 V precisely and
> charge all batteries for that particular application with that setting.
> Bert Kehren
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