C Rate = Maximum charge or Discharge rate/ Battery Amp hour
I don’t see much discussion on the forum about C rate. I’ve seen posts (including Inwo) who recommends planning design for a maximum of 300 amps. I have also seen posts where amp discharge rates of Gems draw north of 220 amps. But mostly I see batteries listed with Ah or Kwh (amps x voltage) for their description.
The reason I ask is recently I bought a bad Evolution battery pack for $800 on CL. The MSRP from Evolution is $4.35K) The guy disappeared. It had impressive stats 48V 205 Ah with a C rate of 2. (400amps for 10 seconds, 205 Amps continuous). It had one bad cell. Unfortunately, it had laser welded busbar terminals. I was unable make a good permanent solder connection. Additionally, the pack you build is limited by the capacity of the weakest cell. Meaning a new battery that has a higher Ah capacity would not be fully utilized. Plus I could never get the old and new cells to top balance. So, I ended up replacing all 15 cells with cost of $2250.
I’m in it for over $3k which is way more than anticipated. I keep telling myself that I’ve got a 205Ah 9.84 Kwh, 2C (maximum discharge of 400 amps) pack. Which is a better performer than I can buy elsewhere. Am I just fooling myself?
It could deliver 1,000,000 amps vs 400, but its all the same since amps is a pull and not a push. If your moton only draws say 230 amps on the hardest of hard launches, the highest load confitions, then it doesnt need the other 900+kA that pack could provide
You shouldn’t try to put a price on first hand education. Consider yourself richer for it, though. Sometimes this stuff isn’t as easy as you’d think, and has a chance that it won’t work out.
Scroll through the archives here and see what most of the gang has been through. The back room/shelves of disappointing projects is full of examples. This whole e-car thing is is NOT really a cheap form of transportation. New guys come in and think the kits offered are expensive and they are ripping people off. Yeah → no. If anybody is making a profit, it needs to pay off a bunch of other things that didn’t work out first. Any other profit after that usually gets spent on the next fun idea.
I discovered there was a direct relationship between how much you invest in a battery and how well your car performs.
Now you can sorta snicker at those that go out and think they can get a gang of 12v Li Chin batteries off amazon and be one step ahead of the game.
One thing you might consider with your Evolution pack- What BMS does it use? and you might want to replace it. It sounds like it wasn’t doing a good enough job.
Leave it to AssyRequired to make me feel warm and cozy about shrinking my wallet on a learning experience. The BMS brand that came with the pack is unknown. It only broadcasts when it is charging. (Is this usual)? It sends out blutooth signal, but I can’t connect with Iphone or Laptop.However it does seem to keep cells balanced when I check each cell voltage individually.
I am using the standard DQ charger with an algorithm that is generic for lithium batteries and has a charge limit of 52.4 volts. ((max charge Voltage for the cell pack is 54.75 volts).
It seems that at the end of charge the BMS shuts down the pack which shuts down the DQ charger and then throws an error on the Speedometer display. I will likely change out the BMS since I am “blind” without a blutooth monitor once I put the battery tray cover back on. Thanks for your input.
