Submitted 4 weeks ago by foremanguy92_@lemmy.ml to askelectronics@discuss.tchncs.de
I have an UPS with two 12v 7ah lead batteries. If I want to change the batteries I would typically go with lead batteries but here’s my question, can I use some portable mobile batteries to use it?
Because I have a 20000mah inui battery that is rated for 12v at 1.5A is this a good practice to buy several of these (since they are about 20 bucks) disassemble them and use them as ups batteries?
Different chemistry and voltage levels, power banks use Li-ion which is 3.7V nominal per cell, and the UPS needs a 12V nominal battery which you can’t get with Li-ion cells since 3x = 11.1v, and 4x = 14.8v.
However in some UPS models you can replace the batteries with LiFePo4 replacements, as that chemistry does match the voltage and charge profile (at least close enough). If it works or not depends on the UPS and if it complains about the slight differences.
You need a balancing BMS anyway and the UPS will not be able to charge it to what it thinks is 100% (about 15 V at trickle current) unless you trick it with a resistor (which wastes power of course).
Yeah you need a UPS that’s OK with the BMS charge FETs opening when the battery is full.
I’m not that good in electricity but basically are lithium batteries from power banks would work the same as 12v lead car batteries?
No they’re different voltages.
The problem will be that the UPS has a charge controller built in, and that charge controller also tests the health of the batteries. It expects battery voltages to rise at specific rates as they charge, and current to match specific patterns. If the charge controller does not see the specific patterns it expects, it will report that the battery is failing.
Trying to use 12v power banks to replace UPS batteries is not a good idea.
Okay thank you
What’s an “inui battery”? Do you mean the INIU B5 powerbank?
Powerbanks can be used directly as USB UPS devices if their output is enabled while charging but most devices you would power with them already have “UPS” functionality (built-in battery). By “disassembling them” you mean using their raw cells? That gets you 3.7 Wh per dollar but I recommend going for the similarly priced raw LiFePO4 cells unless you want to lug them around, getting you great longetivity and cycle life. You need a BMS anyway if you put them in series, I recommend a 4S or 8S config to avoid dealing with large currents and lossy step-up conversion. They can save you quite a bit of money if you charge them daily with solar power. Professional solutions are available, whether they are worth it depends on how much you trust your skills.
What UPS would you put the cells in, anyway? Don’t use one with a lossy and costly mains inverter unless you’re powering something that really needs mains. You can find many that have ATX outputs, or if you’re adventurous some ATX supplies can be run from 12V DC (exact!) supplied into the 12V rail and 5V into the 5Vsb rail because they use an inverter and buck converters to create all the other voltages from 12V. These can be identified by counting the mains transformers and windings of the main transformer. You can use the internals from a cheap car USB adapter (they work from 9 to 30 volts) for 5Vsb from your 4S-8S cell configuration, but the cell-voltage-to-12V supply will have to be a beast - still smaller than the mains inverter you’d need.
aubeynarf@lemmynsfw.com 4 weeks ago
No, your UPS is tailored to the characteristics of the lead-acid charge/discharge cycle. Some LiFePO4 battery assemblies are built with charging electronics that simulate lead-acid for a drop-in replacement, but those are never cheaper than traditional lead-acid batteries.
SpikesOtherDog@ani.social 4 weeks ago
This is correct.
Additionally, you would not want to substitute a larger or smaller capacity battery as the charging cycle of the UPS is built for a specific capacity.
cmnybo@discuss.tchncs.de 4 weeks ago
A larger battery generally works fine with an older, dumb UPS. You will just have to connect an external charger if the battery gets deeply discharged. Adding a cooling fan to the UPS would be a good idea since it will be running for a longer time though.