Blog: Build your own Hangglider and Paraglider Winch
Design of battery
A winch is a quite tough task for a battery, as you can extract up to 20-30kW in peak from the battery.
That means the power requirement is quite tough compared to the energy requirement.
“C-rate” is a way to describe how fast you charge and discharge a battery. 2C means that you charge or discharge that battery with 2 times its capacity per hour, which means it will only last for 30 minutes.
So if the battery has a capacity of 17.6kWh, you draw 35.2kW of power from the battery. And if the battery has 30.6Ah you draw 61,2A from the battery.
UPS-systems is probably that industry application that utilize lithiums in the hardest way in terms of power, as they discharge the battery with 6C. Which means less than 10 minutes of use.
But these systems are not design to last for more than full 30 cycles.
An electrical typically car discharge with up to 2.5-3C, as it have to last for many more cycles.
Energy storage systems that have to live for very many cycles to be economic attractive only has a C-rate of ~1.
We have chosen to use lead acid batteries instead for lithium for most of the winches, as they does not have any problems with high discharge currents and less complex (no need for BMS).
However the prototype still runs with lithium batteries.