June 23, 20224 yr On my previous Axpert type setup I ran 4x 200Ah batteries and setup was straight forward, charge at 20A and draw what the inverter can give 🙂 I've installed a Sunsynk 5.5kW inverter and running to lithium batteries in parallel, my question is; max charge and discharge current. The batteries are rated at 0.5C and being a 100Ah batteries that is 50A charge and discharge but because I'm sharing the load across two batteries I can actually draw and charge at 100A because I've doubled my capacity. I obviously don't want to charge at 100A but what I want to know is if I set the charge current to 40A does that mean I'm charging each battery at 20A or due to the BMS do the inverter know that I'm running 2 batteries and if the setting is 40A it will charge each at 40A. Now that I type it I think I answered myself 🙂 If I measured the current on one of the leads with a clamp on multimeter I'm sure I will see 40A so if that goes into the bank then it will be divided by the number of batteries (2) and that will be 20A. This brings me to my next question, even though the batteries can take a charge of 50A each being 0.5C what is a good current to charge a lithium battery at? You obviously don't want to hammer it at 0.5C the whole time but charging it at to low current can also not be good? Help will be appreciated.
June 23, 20224 yr Lithium cells are well within spec to charge at 0.5C. It is a bit like buying a porshe and then driving it 120km/h. You are not hammering it... well unless you are a grandma and you drive one at 120km/h. You could charge at 1C ( or even more, like 2-3C for short periods) if eg you have limited hours of sun till the shade hits the panels. This is what lithium does well. The higher the charge rate the more uneven the cells might become due to different internal resistance. You might need more time for balancing if you want to use the full capacity. This is why you have a BMS So stick to the recommended C ratings, unless you find that you are not getting the full mileage you paid for then you can always up it. Eg. You have sudden loadshedding sheduled and you have important work to finish. Lithium is a very forgiving technology. Your batteries will likely still work fine 15 years from now when we are all running 50KWh packs and Eskom is no more
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