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.
