Remaing Charging Cycles on Rechargable NiMH AA 1.2V Batteries - Page 1
Forum section: electronics / projects

author: carloszoom3000
author_rank: Newbie
timestamp: October 14, 2015, 03:48:44 pm
content: Hi,I'm trying to find out the remaining charging cyles on NiMH AA 1.2V rechargable batteries.I'm placing a battery in series with a the parallel of 3 resistors of 2.2 ohms which are 5, 10 and 20 watts respectively.To log the discharge and using an Arduino UNO and with some visual basic code i can see on every second, the voltage values measured (it also shows a graph).When checking a functional battery it takes 15327 seconds before the curve shows it's discharge and it takes 9000 seconds on the non functional.I would like to know what parameters i should take into account to know the remaining charging cycles.Regards,

author: DanielS
author_rank: Frequent Contributor
timestamp: October 14, 2015, 04:08:36 pm
content: How many cycles you can get out of a battery depends on how quickly you are charging and discharging it, how hot the battery gets, how deep the charge/discharge cycles are, random manufacturing process variations and a number of other factors.The only way to know with reasonable certainty would be to repeat your test following your application's charge/discharge profile and see how many cycles you get out of a given cell model over a sample of however many cells as you need to improve your confidence interval.

author: IanB
author_rank: Super Contributor
timestamp: October 14, 2015, 04:26:26 pm
content: A (NiMH) battery doesn't have a fixed or countable number number of charging cycles. Instead, there will be a gradually decreasing level of performance over time. The loss of performance will include decreased capacity, increased internal resistance and increased rate of self-discharge. When the measured performance is less than you need for the application you will discard the battery and replace it with a new one. A battery might be considered end of life, for example, when the measured capacity has dropped to 80% of the capacity when new.

author: Pjotr
author_rank: Frequent Contributor
timestamp: October 14, 2015, 05:11:53 pm
content: Quote from: DanielS on October 14, 2015, 04:08:36 pmBy itself this is correct but the total amount of AH over the life time, say up to 80%of initial capacity, does not depend that much on the charge-discharge regime, provided it is within the limits of the battery.One pitfall with NiMH is charging at a too low rate. Most chargers based on the dV/dt method for end of charge do not properly detect when the battery is full then, overcharging the battery and reducing useful life. A problem with many cordless phones.

author: mikerj
author_rank: Super Contributor
timestamp: October 14, 2015, 05:44:29 pm
content: Quote from: Pjotr on October 14, 2015, 05:11:53 pmNiMh/Cd chargers in products like cordless phones don't have any kind of charge termination detection, they just trickle charge the cells to death.

author: IanB
author_rank: Super Contributor
timestamp: October 14, 2015, 06:11:41 pm
content: Quote from: mikerj on October 14, 2015, 05:44:29 pmOn my Panasonic phones the handsets get charged until the battery is full and then charging is stopped. There is a charge indicator light that goes out when charging is complete.

author: Pjotr
author_rank: Frequent Contributor
timestamp: October 14, 2015, 09:08:30 pm
content: Some (maybe most cheaper ones) indeed only trickle charge, but mine terminates charging when full.

author: carloszoom3000
author_rank: Newbie
timestamp: October 19, 2015, 03:00:59 pm
content: Thanks for replying.As mentioned, the life of a battery depends on many factors like how often is used, the load that is connected to and even the charger (dumb or smart) that is used.One thing that i wanted to test, was to connect the battery to an specific circuit in which i could analyse its performance and determine if the battery should continue operating or just needs to be replaced.A dumb charger that i have has a blinking LED when the battery is "no longer taking charges", but that leads to an inmediate corrective action.If let's say you are checking devices (like 200 of them spread nationwide) and you only get to check them twice a year, you would like to prevent when to change the batteries (for not to carry lots of batteries on backpack all the time).Any help will appreciated.Regards,

author: Ian.M
author_rank: Super Contributor
timestamp: October 19, 2015, 03:25:27 pm
content: There is no quick test, though obviously a load test lets you reject failed and nearly failed batteries fairly easily. If your application doesn't have smart Coulomb counting and data logging to allow you to do predictive failure analysis you are S.O.L.The best you can do for a dumb battery system is to maintain a pool of batteries so that on each maintenance visit, you swap one set out and test it over a full charge/discharge cycle at a comparable charging and load current to the application, which is *NOT* a quick process, then either condemn it or put it back in the pool.

author: IanB
author_rank: Super Contributor
timestamp: October 19, 2015, 04:20:29 pm
content: Quote from: carloszoom3000 on October 19, 2015, 03:00:59 pmTwo major failure modes in NiMH cells are increased internal resistance and loss of capacity.Chargers tend to reject cells when the internal resistance exceeds some threshold. They measure this by applying a known charge current and testing the rise in voltage across the cell.Loss of capacity cannot be measured with an instant test. The only way to measure this is to perform a measured discharge after applying a full charge to the cell (or battery). This is much more readily done on a test bench than in the field. As noted above batteries are usually replaced when the capacity drops to 80% of the original capacity.

author: all_repair
author_rank: Frequent Contributor
timestamp: October 19, 2015, 04:43:58 pm
content: Before that you may want to recondition your cell first by doing a slow discharge at 0.1c or lower till 0.1 or 0.2V and then slow charge at also 0.1c. Repeat 3 cycle. Each cycle shall take about 20 hour.If the cell is not dried up, the capacity shall be increased after the reconditioning.

author: carloszoom3000
author_rank: Newbie
timestamp: October 19, 2015, 10:05:58 pm
content: Restoring the battery by completely discharging and recharging the battery for around 3 to 4 times should bring them back to work.I also tested 4 eneloop AA NiMH rechargeable batteries using a 10W 2.2 homs resistor, in order to test the different internal resistances, these are the values that got:Type Resistor No Load Voltage Voltage Accross Resistor Battery Internal ResistanceDischarged non functional 2.6 ohms 1.09V 0.14V 17.64 ohmsPartially charged non functional 2.6 ohms 1.29V 0.82V 1.49 ohmsPartially charged functional 2.6 ohms 1.33V 0.79V 1.77 ohmsCompletely charged functional 2.6 ohms 1.46V 0.88V 1.71 ohmsRegards,

author: MikeW
author_rank: Regular Contributor
timestamp: October 19, 2015, 10:28:15 pm
content: Working on long term emergency lighting batteries returned from site after failures I've seen a Ni-Mh battery come back to life after just one deep discharge-recharge cycle beyond what the emergency control module will 'let happen'.It's all about crystalline formations and shithttp://batteryuniversity.com/learn/article/how_to_restore_nickel_based_batteries

author: carloszoom3000
author_rank: Newbie
timestamp: October 20, 2015, 07:38:00 pm
content: I plugged a six pack of batteries to a circuit and tested 2 types of batteries (non functional partially charged and functional partially charged).I Tested the voltages on each battery, all of them together, in the input of the circuit.This circuit displays a message indicating that there's 20% of charge left.To reach simulate that state, a potenciometer was connected to the circuit and both voltages (with and without the potenciometer) were measured.Here are the results.Type Voltage on Each Battery All Batteries Circuit Input Voltage Circuit Input Voltage (Minimum)Non Functional Partially Charged 1.25 1.27 1.26 1.28 1.26 1.24 7.6 6.63 6.33Functional Partially Charged 1.38 1.31 1.38 1.31 1.31 1.30 7.94 7.88 7.01Regards,