Battery Protection Advice - Page 1
Forum section: electronics / general

author: cosmarchy
author_rank: Contributor
timestamp: November 22, 2021, 10:55:23 pm
content: Hi,I have a few devices which run off various batteries and I'm looking for some sort of protection.The devices (environmental, machine, building monitoring devices etc) are being run from various batteries and I would like some advice on protecting the batteries from over discharge. As the batteries main purpose is to start a generator or keep alive critical electronics they will all put up with a certain amount of discharge before they become useless and require recharging (obviously dependent on the load requirements and battery technology!!)So I'm looking for something that will disconnect the load when a pre-determined battery voltage is reached and then reconnect once a higher voltage is reached (when the battery has been recharged for example).My initial thoughts were a battery management IC, but was not sure there was one which is programmable to cope with the different cut-off voltages, so wondered whether there was a microcontroller suitable? My main issue with this whether the power requirements of a microcontroller would further drain the battery considering it has to check the voltage periodically to see if the load can be reconnected...Might be useful if there was a solution which re-charged the battery and re-connected the load when the battery input voltage is high enough but this is definitely int he realms of an IC and could not find anything combined.Does anyone have any experience of this or can recommend any suitable component IC's?Thanks

author: nctnico
author_rank: Super Contributor
timestamp: November 22, 2021, 11:02:25 pm
content: Every pre-package Li-ion battery pack has this feature built in! So just buy one of those battery packs and you are ready.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 23, 2021, 12:32:20 am
content: Quote from: nctnico on November 22, 2021, 11:02:25 pmThe main exception is R/C packs - those generally do not have built in BMS. Also, the cutout points are usually just to prevent catastrophic failure and relying on them for normal use would result in very short service life. You would want a programmable BMS to allow setting more sane limits like stop discharge at 3.2V/cell and stop charge at 4.1V/cell.

author: cosmarchy
author_rank: Contributor
timestamp: November 23, 2021, 09:03:28 pm
content: I could use Li-ion battery packs but I would also require this for lead acid batteries too.In some cases, such as starting generators, it would be undesirable to go below say 10v where as in other applications I could go less hence the need for some kind of adjustment for different voltages on different battery technologies...

author: thm_w
author_rank: Super Contributor
timestamp: November 23, 2021, 10:57:44 pm
content: Going to depend on load current, battery voltage, etc.But this might give you some ideas or at least somewhere to start:https://www.aliexpress.com/item/4000439634699.htmlhttps://www.aliexpress.com/item/32959313382.html

author: cosmarchy
author_rank: Contributor
timestamp: November 24, 2021, 09:35:36 pm
content: Interestingly both these use an opamp.Thanks for this, I'll give them a look

author: nfmax
author_rank: Super Contributor
timestamp: November 25, 2021, 11:52:56 am
content: For a 12v lead-acid battery protection circuit that uses mere nanoamps when the battery is in protection mode, take a look at my design:https://www.eevblog.com/forum/projects/battery-undervoltage-lockout/msg1060148/#msg1060148The protection voltage of 10.9V in that design is appropriate for fairly heavy battery load currents. If the load is lighter, the cutoff voltage should be increased, by adjusting the resistive divider network. Check with the datasheet for the battery you are using

author: cosmarchy
author_rank: Contributor
timestamp: November 25, 2021, 09:54:07 pm
content: Many thanks for the link. I'm sure there is something I can use in there