sUAS Charging Systems

Manual charging systems must be operated with great care to reduce the risk of explosion or fire. The automatic systems such as those found on the DJI Phantom and Inspire are safer because it is less likely to charge them improperly.

The DJI system also estimates the amount the battery has degraded and shows its current maximum storage capacity. Each battery has its own memory of number of charges and various other values.

• The optimum charging rate of a LiPo battery of any size takes about an hour. This translates to charging at one time its capacity or 1C. Charging slower is OK, but charging faster will decrease the life of the battery. Charging at 2-3C is fine and sometimes it is necessary.
• Field charging today is problematic. Flight batteries are generally quite large and thus require a lot of current to charge them. Batteries found on the Gryphon 1400 for instance are 22,000mAh 6S. Four batteries are used at once. After a 15-minute flight all four batteries need to be charged. Charging the batteries at 2C or 45 amps (1,100 watts) is necessary to get them charged quickly. This is a ton of current which requires a large portable gas generator capable of about 6,000 watts to operate the four chargers. Multiple generators are required if multiple sets of batteries are available. For 100Wh batteries a large inverter connected directly to a car battery can charge one battery at a time which will not allow continuous flight. Be sure to keep the car running when charging. A 6,500watt generator, is a good-sized generator for this. The biggest problem with this sized generator is that it cannot be used when driving from place to place until it is mounted into a trailer or truck bed, so it can run continuously.
• For continuous operation of the sUAS typically 4-6 sets of batteries are required. Three or more are charging while one is being used. This can get expensive and cumbersome. Typically, you should keep 6-8 sets to be on the safe side.
• Even charging the 100Wh batteries in the field takes planning. For example, you would need a truck with two deep cycle marine batteries, an alternator which is upgraded to 200 amps from the stock 90 amps and 6-gauge wire run into the engine compartment to supply enough current. The truck engine must idle continuously at 1,000 rpm instead of the stock 600 rpm to put out adequate current.
• Charging at night at home or in a hotel room requires special equipment. Checking into a hotel at 11pm and leaving by 7am doesn’t make one want to wake up every hour to take one battery off of the charger and put another one on the charger. There are multiple output chargers available or simple purchasing of several single output chargers is an option.