Voltage sag graph & "ArduWattmeter"

Hello guys,
I was not sure where to write this topic because it's not only referred to battery, but also DIY and E-Scooter..
Recently I did my first project using Arduino, and I was surprised by the fact it was so easy to implement that solution.

I made a sort of cycle analist where I can see by using a LCD: Voltage, Temperature, Battery Temperature, Ampere, Ampere Hour, but this is only the start :wink:

The image below show the LCD


Here you can find a video with Arduino in action !!
http://www.youtube.com/watch?v=zzJGZ5NogDs

Coming back to "Voltage sag graph" after checking the instantaneous value I wired my laptop to Arduino in order to log the value and I found the incredible sag during acceleration. Please note my scooter is 18 40AH TS cells bought 6 months ago.

Below you will find a full throttle accelleration sample of 26 sec


What is you feeling respect this value, I know Thundersky Cells are just 3C max continuous, but I was expecting something better, what are your feeling or real experiences?

ha, congrats.. you've made a turnigy watt meter / cycle analyst

At 55-60v nominal, a 10v sag is fairly bad. I notice that you are pushing them to 2C occasionally.
It's my belief that the best performance out of lifepo4 is around 1C..

And here to whom are interested attached the excel file containing the complete log (it last just 6min) coming out from Arduino and related graph
View attachment 3-12_giro intorno a quartiere.xls
The complete graph of my test is also below

What wire gauge are you using(bat-controller)? Do this TS have full capacity as stated by manufacturer? Where are you measuring Voltage (bat side or controller side)?

I'm not sure, but as far as I remeber it's a 8 or 9 AWG (I will check)
This TS stil have 40AH capacity
Voltage come from controller side

Please note the temp is around 10° here and when I get this graph the battery were near 70%SOC

Hello,

your ~10v of sag is not that bad really, during the summer with my old 36v LI-MN battery i used to get ~3V of sag @ 2C but in the winter that voltage sag was going up to 4-5v @2C. I would immagine what you are seeing is about normal for a TS pack that is run @~2C discharge. Unfortunately they have a reputation for being a saggy battery, hence the nickname "ThunderSag". But all in all, they are a reasonable battery as long as they are able to put out the rated cycle life.

Thank you for your info

The sag of 10V is related to a near 3C discharge (2.75C to be precise -> 110A on a 40AH battery) at 10° temp, so we can say it's a normal sag for "Thundesag"?
I decided to buy Thundersky because the expected cycle life is 3000, but I hope it is true. I search real life experiences on the WEB, but none has still reached that number

Hey,

@ 2.75c discharge 10v of sag i would say is very normal. As for the cycle life. they are reated for 3000 cycles at 0.5c discharge.. or 20amps discharge. You are discharging 5x that fast at peak.. i would immagine therefore that your predicted cycle life would be somewhere in the 500-800 region, maybe a little more if your average discharge falls more into the 1-1.5C area. I'm no battery scientist but i would be highly surprised if your TS cells reach 1000 cycles at those discharge rates.

They don't call them ThunderSags for nothin'...