Thought I would post here as there a lot of topics on this in the Gen 2 forum with a better engagement it seems. I've read through most of them and understand the theory/procedures however never having used an 'RC charger' and the information I am getting from Google/elsewhere gives me mixed opinions. Specifically in regards to charging the modules up, I am using a Hota F6 Ultra charger, settings wise: NiMH battery type, Delta Peak detection of 3mV, 6 cells and a charge of 3.0A. I initially started with 5mv and a charge of 2.0A but the behaviour which is confusing me is the same regardless, Google advised to use a lower Delta of 3mV and up the charge. There is no end voltage parameter on this charger, it relies on the Delta Peak detection/safety timer. The modules are bolted down and compressed in their original bar enclosure, using a digital temperature probe in-between the packs and occasionally measure other areas of the pack with an infrared temperature gun. Have small fan at moderate speed blowing air on the pack, room temperature is around ~28 degrees Celsius. The pack has sat for a few days, the resting voltage before charging was 7.8V. I began charging and let it go to 8.6V before manually terminating it. The pack temperature never rose above 29 degrees Celsius, I can't see any swelling. It allegedly put in 2.18Ah. The Delta Peak hasn't triggered. I am seeing advice that you should never charge the pack beyond 8.4V? Or that nearing the end the pack will get warm/hot i.e. 40 degrees Celsius - 45 degrees Celsius? What is the absolute maximum the pack can actively charge up to (safely) before having to manually terminate it? I am assuming the pack hasn't reached the max? Again online it says it can reach up to 8.7V - 8.9V, just monitor the temperature and then once it hits the higher temps it should trigger the Delta Peak?
Delta is an unreliable parameter for a multi-cell module. You can trigger the delta early in the charge if you have insufficient cooling while dealing with a well used pack that has higher resistance. You need very good cooling even at 2a charge. Otherwise you will need to do 20 or more cycles per module. When rebuilding a well used pack I use a process that terminates at 38*C or 5000mah. First step is to measure remaining capacity of all modules by discharging down to 6v. This will tell you the overall health of the pack and it looks something like this. Besides a handful of modules this is a weak pack that performed poorly in the car. Up next is charge to 5ah, terminate at 38*C or 5000mah. Very few modules reached 5ah. This is what you're likely running into and why the charge terminates @ 2ah using delta. You are dealing with weak, high resistance modules and will require lots of charge and discharge cycles to overcome this. First discharge after a full charge looked like this: This particular pack required 14 charge/discharge cycles (I normally run 7). In the end it looked like this, here is the charging curve: Here is the discharge curve: Focus on battery efficiency, after 4 or 5 reconditioning cycles most of your modules should be able to absorb the full 5ah, how much are you getting back on the discharge? Really good modules will be in the 95-99% range, you can get away with as low as 75% as long as the whole pack is like this. This particular battery achieved 84-85% after reconditioning (50-65 before), with one strong outlier being 88%. I replaced the 1 underperforming module in this pack as it was only reaching 75%. Visualizing the charge and discharge curves helps a lot, if you could run some sort of graphing multimeter it will improve your chances of success tremendously. I used to use VC8145s many years ago for graphing but there's probably something better these days.
Just as an update ever since my post, I just let the charger do its thing in the meantime, all detected the end charge cycle (Delta Peak - allegedly) all being identically at the ~8.70V or so mark. I also ran a basic load test on these modules after letting them rest for several hours to reach resting voltage (5+ hours). Resting voltages were between 7.90-8.00V with the exception of one module being 6.50V (this one was always the problem one as per Dr. Prius App confirmation as well). Used a 12V 55W H7 headlight bulb for 5 minutes and end voltages for all were in the 7.50V region with the exception of that single module 6.00V. I know the load test isn't conclusive and I need to now test the real capacity, but it gives an indication. As per your comments, aware that the Delta Peak can be triggered too early and not enough charge (false drop) but I'm more worried about overcharging and damaging the battery than undercharging (slightly). I could set the tolerance of it higher whilst monitoring pack temperatures if necessary as you state for the 38 degree Celsius mark? How are you monitoring the packs temperature? I'm using an infrared gun and finding that the "front" of the packs closer to the fan are cooler by about 1-2 degrees Celsius as opposed to the back of the packs - hottest near vent tube region. I know what overcharging does and looks like, as stupidly done that on the first pack, with it not being compressed (bolted down), wrong settings, pack bloated a bit, was pretty hot about 42 degrees Celsius, could hear hissing from the vent tubes...that's how NOT to do it. In regards to discharging I'm facing an issue here at this stage as the 'RC charger' I purchased specification wise is meant to support a 4-channel max of 1.7A discharge per channel. However it is bottle necked at 0.5A per channel doesn't live up to its spec...that is just way too slow time wise for my needs, with 1A that would be doable with 4-channels. So as of now, I have no clue about the discharge and am trying to figure out the best/most accurate way which is affordable to test. I have been advised and came across, a dedicated capacity tester such as the "Treedix Mini Electronic Load Tester 120W Battery Load Tester" this would allow discharging, monitoring voltage cut-off, mAh and pretty flexible discharge current settings. This unit is pretty expensive though given it can only do 1 battery at a time. As in order to get an accurate capacity mAh reading apparently the lower the rate the better so around 0.2C (1A in this case) is ideal, this then means for a 6500mAh battery can take up to 6 hours. Alternatively was looking to just utilise a 12V 21W car bulb this would mimic a ~1A draw, hooked up to a wattage meter, can then again measure voltage and mAh, this would be the cheaper alternative doing around 3 at once, however manually. Charging isn't an issue, just the discharging in my case. Yeah I'm not sure if I can get some sort of graphing like you have there, would be impossible to do so manually. However judging by the majority of my modules, given they all started on a similar mark i.e. 7.90V-8.00V and by 5 minute mark drained to 7.50V mark. It is a very short test but would most likely be a steady drop like your graphs? All the drops were steady no sudden drops, as done them 1 by 1 alternating between different bulb to let it cool down in between, so was monitoring all 28 modules for the whole period!
