Can I use unprotected 18650 batteries in handheld devices? - Page 1
Forum section: electronics / beginners

author: Twiggy
author_rank: Contributor
timestamp: October 06, 2024, 10:32:29 pm
content: Hello,I start to get into handheld equipment powered by 18650 batteries (let's say owon hds272 or radiomaster tx12 for example ). I intend to charge the batteries within the devices with the supplied charging port, or with a commercial battery charger.I have a hard time figuring if I should get (pcb) protected or unprotected cells for such devices.I have read the devices user manual but it does not explicitely mention which kind of cell to get or if there is any low voltage protection.My google-fu led me tohttps://oscarliang.com/best-18650-li-ion-battery/in which it is said:QuoteI have then read the datasheets:https://www.dnkpower.com/wp-content/uploads/2022/08/SANYO-NCR18650GA-Datasheet.pdfandhttps://www.molicel.com/wp-content/uploads/INR18650M35A-V2-80096.pdfbut I cannot find if the cells include or not a protection pcb.As far as I understand all that I risk with unprotected batteries is the battery venting and destroying itself. Did I miss something?Many thanks

author: Infraviolet
author_rank: Super Contributor
timestamp: October 07, 2024, 12:12:36 am
content: Do you NEED 18650 LiPos for the projects you plan on building? If it's something that flies, yes you need LiPo for its energy density, if it is something that drives around quickly LiPo may be very helpful, but you mention handheld, so while keeping weight down might be desirable, it isn't essential the way it is for drones/planes. The simplest solution might be to use NiMH cells (available in common AA form factors among others), unlike LiPo these don't have a huge fire risk associated with them, they're easy to charge with commerically available chargers (some of which can cope with a whole bunch of them in series inside a device and charge them all together without individual cell removal), they can supply plenty of power. They have a bit more internal resistance than LiPo, which means they aren't great for HUGE currents, but they'll supply currents in the range of 1 to 5 amps (at higher currents they discharge faster, not only in time but in terms of acting at high currents like they have less mAh worth of energy stored in them) happily. You'll need more weight worth of NiMH to provide a given current, given voltage (they're 1.2V each not the 3.7V of LiPo/LiIon), or given amount of WattHours of stored energy, than you would with LiPo, but beyond this they're good to work with. And unlike LiPo, where putting cells together, even simply in series, needs delicate balancing to ensure that one cell doesn't get discharged first, then over-discharged, and then potentially catch fire when next recharged, NiMH can self-balance to an extent. The only protection features NiMh needs is a voltage monitor ( just one for the entire set of cells if you want) with a relatively conservatively set cut-off voltage (for the whole pack, you can calculate this by various fromulae, one of them asks what the pack voltage is when all cells get down to their individually empty voltages, the other is the full pack voltage minux the 1.2V voltage of one cell) to turn it off when low. For recharging you can find ICs which will handle it all for you, in device, or you take the cells out to put indivdually in a wall wart charging unit. Also, NiMH can stand, so long as given the right type of recharging now and then, more charge-discharge cycles (thousands) than LiPo typically* (a few hundred cycles) will.*if the cut-off voltage on these is set quite high, optimising for overall system longevity rather than the amount of time of device use before a recharhe is needed then sometimes LiPo can get up closer to NiMH's number of charge-dischrage cycles before ageing sets in

author: K5_489
author_rank: Regular Contributor
timestamp: October 07, 2024, 12:31:31 am
content: Quote from: Twiggy on October 06, 2024, 10:32:29 pmFor stuff like that, when there is charging circuitry built in, typically unprotected cells will be called for as the charging circuity will also have voltage cutoffs built in. You'll also likely often find that protected cells physically won't even fit due to being several millimeters longer than unprotected cells. That said, if the protected cells do fit, without forcing them in, there's no harm in using them outside of a higher cost to purchase them.