Battery voltage vs capacity

[yes8s]

I'm curious, has anyone measured what voltage their batteries charge and discharge to? (Please post for reference)

Mine charges to about 65.6V and cuts out when the voltage gets down to 55.5V This means that the average single lithium cell voltage range is about 4.1V - 3.45V. I suspect that under load the voltage will sag a little but surely there is more range to be gained here... Are these limits too conservative?

I presume the battery pack has a BMS that controls charging and cell-balancing so couldn't the cells be pushed a little further on both the charge voltage and discharge level?

Thoughts?

Edited February 3, 2015 by yes8s

[Gimlet]

I believe that most wheels, with a few exceptions are about the same to within a volt or so and with cheap voltmeters not being very accurate it will be very difficult to get any meaningful results.

 

If you do a little searching you will find some wheelers who have problems with over charging when they start off down hill with a full battery so you don't really want that little bit extra that might be possible.

[yes8s]

I didn't think about the re-gen being an issue.

 

I guess in this application you can't afford to get too close to the limits because it would cause a real safety concern especially at the lower limit. In comparison, where a consumer electronics device would just turn off when battery is depleted close to it's lower limit, this is more safety critical than that.

 

According to this info http://www.powerstream.com/lithium-ion-charge-voltage.htm, I suppose you would only be loosing about 10% of rated capacity when using the battery between this charge levels.

 

Running the cells down below 3.5V, there is not much capacity to be gained there anyway but there could of been at the upper voltage if it we're not for the re-gen thing.

[Rywokast]

On 2/3/2015 at 1:40 AM, yes8s said:

I'm curious, has anyone measured what voltage their batteries charge and discharge to? (Please post for reference)

 

Mine charges to about 65.6V and cuts out when the voltage gets down to 55.5V This means that the average single lithium cell voltage range is about 4.1V - 3.45V. I suspect that under load the voltage will sag a little but surely there is more range to be gained here... Are these limits too conservative?

 

I presume the battery pack has a BMS that controls charging and cell-balancing so couldn't the cells be pushed a little further on both the charge voltage and discharge level?

 

Thoughts?

no need to measure, it's known already.. gotway wheels cut off at 3.3V per cell, depending on the voltage 67,84,100.. they would cut off at 52.8V, 66V, 79.2V respectively.. they are 16S/20S/24S in that order according to the voltage of the wheel... you can figure this out for any wheel, some KS are 3.15 and some 3.0 (18XL and 16X), and I believe inmotion wheels are 3.15 so for say example an 84V gotway wheel you just do 20x3.3=66V is how low you can go