Quote:
Originally Posted by Stephen Kowski
ah, correct, I misunderstood their terminology. So their 20% loss is due to their internal ESR discharging it on the shelf and not referring to their internal impedance growth (your 'clogging') where the electrons remain lithiated in the anode/cathode material.
My main interest in knowing the average energy was to see if a) this battery is overkill and b) if something like an ultracapacitor stack could replace it since there is no significant capacity fade associated with a UC stack (among other benefits).
|
ESR typically means "equivalent series resistance", which hampers discharging and is what is measured for "internal impedance growth". It is not related to self discharge.
The batteries
are overkill for energy, but not power. Matches are ~1/20th of an hour (for easy math and to be conservative). This means that unless the battery is capable of a sustained 20C discharge, to get the necessary power you will have to overshoot the energy.
Since the load is rather peaky, it also has relatively severe peak power requirements. This pushes the energy surplus even higher.
Long story short, lead acid isn't the optimum choice for us but it is working pretty well. Switching to source with a higher C rating would allow us to lower the amount of excess energy we are carrying around, which would theoretically lower weight and cost. However, higher C rated energy sources are not currently economically viable for FRC (I hope this changes!).
The 36V Dewalt pack that uses A123 cells has the energy and power density necessary, and is many pounds lighter. If only...
