SpeedEBikes wrote:Can you explain the reasoning behind the cutoff threshholds of 3.0V LVC and 4.29V HVC?
3.0V to 4.2V is the commonly accepted range for Lipo. Setting cell level LVC to 3.5V would = fail because you would be bouncing off of LVC under load all the time. I understand the practice of discharging to only 3.5V but that can be done by the user watching voltages. Would not make sense to set hardware limits here. If you really want a limit that high use the CA pack level LVC Limit... no need for cell level protection when so far from cell limts.
The 4.29V comes from the fact that these are 18650 production parts - they were accounting for high internal resistance and the dynamic charge current verses the resting voltage. The reality is that if you were to cut charge at 4.2V under load it would settle to way below 4.2V - so cutting at 4.29V will usually result in a resting voltage of 4.2V. Again this is a situation where the user may choose to under-utilize the capacity of their batteries in order to gain a perceived increase in cycle life... but this can be done by simply setting the charger to a lower voltage. It would never make sense to actually set the hardware limit lower.
These boards are first and foremost developed for the motorcycle racing scene... and you better believe that those guys are getting as many wh into their packs as they can. I have seen many a rider pushing bikes across the finish line. The hesitancy to do deep cycles wears off quick in that community.
I'm guessing the device is intended as a last resort fail safe to prevent destruction of the pack rather than the regular means for terminating either charge or discharge,
The proper method for terminating charge is by setting the charger to the correct voltage for a balanced pack. I dont like the idea of relying on a BMS to terminate charge on a regular basis... this is how fires start. The Battery must be able to be hooked to the charger with no BMS for safe operation at all times.
For LVC -> I never recommend that people empty their packs - so the proper way to do this is to set Pack Level LVC in the CA -> that can cut one off early... but one still has the choice of getting more if they have a few miles to go.
Are the cutoffs modifiable? I'd expect a tighter range, say 3.5V LVC to 4.2 HVC would be fine for many like myself who try to keep their batteries in a 3.7 to 4.1 volt operating range and don't want their occaisional screw ups to go too far out of bounds.
These values are not out of bounds. I think folks have taken this idea WAY too far... Lipo is meant to be run from 3.0V to 4.2V. I have thousands of cycles on RC packs where I run cells down to 2.5V and up to 4.3V over and over and over. I dont buy any of this hype about extended cycles -> the reality is that prices are dropping so quickly that by time one actually gets 3,000 cycles out of a pack... that pack is now totally irrelevant in terms of C rating and power density.
I paid $150 each for the 6S 4.15Ah packs I built my first bike with. They were 15C. Now I can get 20C packs for $40 that are 5Ah. I beat the hell out of those original packs and they are *still running* on another guys bike who I just gave them to.