pwd
10 kW
Great, thanks for the information Pajda!
Pajda said:If we talk about a specific cells. 40T and 30Q definitelly belongs to the 2. category. They lose their capacity almost regardless on load. Both are designed for continuous operation at 1.3C charge and 5C discharge and so the are best suited for powertools. 30Q has shitty cycle life (only ca 400cycles no matter when discharged at 1C or 3C continuous, there is also no benefit when the 30Q is charged to 4.1V, the capacity loss is the same as for 4.2V charging) 40T is significntly better than 30Q and can do 1000cycles with 63% of initial capacity at 100% DoD.
But for the comparison 50E will do 1000cycles with 85% of its initial capacity and so it totally outperform 40T at 100% DoD in the cycle life if your average load is lower than 1C and you do not need faster charging that 0.5C. So I can only repeat that 50E is actually the best cell for traction application in 21700 size. LG cells excells in 18650 size, but in 21700 their actual production has poor cycle life and I still did not find reason why.
Allex said:Did you have the chance to test Sanyo NCR2070C 20700 3500mAh - 30A?
I have a 6p 30q pack that sees 90A currents and start to get unbalanced. I need a new set of cells and looking at sanyos or 40Ts. I am after the most light weight pack so I do not want to add a lot of cells in P. 18Ah is plenty fine for my needs.
3.16 Operating Temperature(*2) Charge: 0 to 45°C
(Cell Surface Temperature) Discharge : -20 to 60°C
dukestar said:Ok, so after going back and forth between 40T and 50E I built my battery with the 50E because of the cycle life rating of >80% after 500 cycles. The 40T had same rating as 30Q which is what my current pack used.
dukestar said:Did a test run and here are my observations.
Did a 20 mile run with some pretty steep hills. In 50.5 minutes used 11.4A so that averages 13.54Ah - approx .4C. Max A reached was 48.89 - approx 1.4C. Used 847.75wh - 41.1 wh/mi. Battery voltage at end of ride was 74.8V. Min voltage reached was 68.9V.
Pack temp started at 20.3°C and ended at 34.4°C. Half hour later pack temp decreased to 33.9°C so it does not cool off quickly. I imagine it is a heat sink and with no active cooling takes a lot of time to cool.
dukestar said:Not sure what to make of the pack temperature. Problem with my setup is I have no easy way to cool the pack and am wondering if that is going to be a problem. I don't doubt if I continued riding that the pack would have continually increased in temp.
The 50E data sheet has temperature rating of:
3.16 Operating Temperature(*2) Charge: 0 to 45°C
(Cell Surface Temperature) Discharge : -20 to 60°C
Does this mean I can get close to 60°C and not be concerned? At what temp will the pack start to be damaged?
Note that when charging at 2.4A the pack temp reached 35°C so if I took the battery off charge and immediately started riding the temps would start at 35°C. Not sure if that is an issue or not. My last pack did not have an embedded thermistor so I'm wondering if I had heat issues with my old pack and that helped it degrade.
Could please you specify them?Pajda said:40T has signifiantly lower DCIR than 30Q. ("LG" 10sec 0.5C load DCIR test method at 50% DoD): New 40T has ca 16 mOhms, new 30Q has ca 25 mOhm, new 50E has ca 34 mOhms at 27°C. But as I mentioned many times before, almost all modern cells with low DCIR does not have good cycle life! In fact there only few cells on the market with low DCIR and great cycle life.
john61ct said:So really the only "quality" factors left are Ah capacity and cycle count longevity
Thanks, discharge and fast charge might approach 0.6C occasionally, but usually both kept under 0.3Cdukestar said:john61ct, based on your quote the 50E may be a good option for you but note the datasheet has a recommended charge current of 2.45A for pack longevity, max 4.9A (not for cycle life). If you need a fast charge it may not be the cell for you.john61ct said:So really the only "quality" factors left are Ah capacity and cycle count longevity
Waynemarlow said:My 50E 14S3P pack which is now about 18 months old and circa 100 charges has not shown any real change from new. In some ways it took about 10 charges before it settled down at better than manufacturer specs. Max is 20A but I do fully charge it and run it down to below 2.9V at times, everything you shouldn't do.
For the cost, if I get 500 charges or even less I don't care as by then there will be superior cells available probably lighter and with more capacity, everything an EBiker would want..
As long as they actually respond to the sensor, yes. See Methods' failure analysis thread on a Daly BMS about what happens when they don't.Waynemarlow said:Sorry the battery is located in a compartment so there’s no real way of looking at the temp. I thought of fitting a BT BMS and should have in some ways, but the cheapo simple types with a temp sensor on seem to be OK as a backup in case of a high core temp.