Content provided by: Flexradio Engineering
When engineering the Maestro "C", we wanted the Maestro to run on batteries for a longer time than we had before with the Maestro "A" and "B", targeting a 6-10h range. To achieve this capability, we went with the largest battery that RRC builds, the 2054-2. This battery is the largest that you can ship in the postal mail (99Wh) and it provides about 8 hours of run time on the Maestro "C".
Additionally, we want the battery to charge when the Maestro "C" is connected to the external DC supply voltage. This feature is not found on the older Maestro "A" and "B" models. We also wanted the battery to charge relatively quickly. To achieve this, the charging circuit requires quite a bit of power.
To get a one-hour charge at 99Wh, the charging circuit requires 100W of power. The battery is therefore configured to have a charge voltage of 19V.
So there are two options to achieve this design goal:
- Run the Maestro "C" off 12 VDC and put a noisy boost converter in the Maestro. In this scenario, it would draw something close to 10A on the 12 VDC supply (requiring heavy gauge wiring or encountering a lot of voltage loss due to resistance with using a reasonable gauge wire
- Run the Maestro "C" using a higher voltage. The next reasonable voltage up is 24 VDC. At 24 VDC, The power supply draws around 4A, which lowers the wiring losses.
With all engineering decisions, there are compromises. In this case, it mostly concerns battery capacity and charge rate, but there are other factors like lower current and wire gauge on the charging supply.
If we had gone with a “must use a 12VDC supply” rule we would have likely used an RRC2057 battery which would have had only a 48Wh capacity, having a Maestro "C" run-time of about 4 hours.