XC-Sjælland

Battery

 

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.

Battery charging

Converter circuit
Power circuit of a frequency converter: L1, L2 and L3 is the normal input. U, V and W are connected to the motor terminals. The battery should be connected through PA/+ and PC/-, which are the DC-terminals.
Charge Profiles
Charge profile with and without bulk charge.

All industrial frequency converters are design for 480VAC plus 5% even though we only have 400VAC in Europe.

 

Inside the frequency converter the AC-voltage is rectified to DC-voltage. The DC-voltage will become 1.414 times the AC-voltage.

This means the battery pack should be designed to have a end-of-charge voltage of 710VDC.

 

The end-of-charge voltage of af lead acid battery is 14.2VDC.

Using 50 lead acid batteries in serial connection we get exactly 710VDC.

 

Two LED-drivers can be used to charge the battery pack. These should be connected through the rectifier, to protect the LED-drivers for reverse voltages. The first one connected to L1 and L2, the second one to L2 and L3.

 

The LED-drivers can be current controlled through two DIM-wires with a 0-10V signal which can be controlled by a PLC.

 

Two of these Meanwell XLG-240-L-AB LED-drivers are only capable of charging 48 leac acid batteries, but that is still sufficient. Other model are also avialiable, if you want more power or higher voltage (do not to go above 710VDC for longere periods).

 

Lead acid batteries are exhausting gasses, even though it is a GEL-battery. Therefore ventivation are needed: passive of active ventilation.

For 48 pcs. 12V 30Ah GEL batteries a hole of 200cm2 are required in the bottom and top of the battery enclosure according to EN50272-2 for passiv ventilation and boost charge, 25cm2 for float charge.

 

 

Safety precautions:

Working with and near high voltage installations shall only be done by professionals.

Be aware that 710VDC are very dangerous. Even though you think it is an isolated circuit, the reality can be different due to electric failures on any isolation.
To comply EN60204-1 isolation monitoring is mandatory. Read more here and here.