DIY backup battery
A few of you have asked about the backup battery I made for my plane. Its purpose is to provide power to my screen, instruments and electronic ignition during the engine start. Without a backup power source there is a chance of the G3X screen going black (rebooting) as well as my electronic ignition not working.
The picture shows a schematic of my main power & batteries. The backup battery is the blue box and consists of 3 LiPo 18650 batteries, a protection circuit board and a relay.
The unit is able to provide 1.5 AH of power with a maximum current of 9A.
-That is 1.5A for an hour / 3.0A for 30 minutes / 5A for 18 minutes / 9A for 10 minutes.
When fully charged it PCB tops & balances the 3 batteries at 12.15 volts (4.05 x 3), which is sufficient to keep any 12V circuit powered.
-The batteries are 1500 mAh and are rated for a 15A draw.
-The PCB completely takes care of the batteries. It is rated up to a 9A draw. I would suggest keeping it under 7 amps if you want to use use it as a continuous power source.
The PDF file lists the components that I used and gives tips for the construction of the unit. I used Tenergy brand batteries and PCB. Don't buy cheap parts. I bought the batteries, PCB and relay for about $45.
Undoubtedly this unit could be adapted for other backup or emergency uses as long as you keep within its limits. You could also make two units to double the current or the time.
I have been using it for over a year and it has worked perfectly. At my condition inspection I isolated the P+, turned it on, checked the voltage and it was right at 12.15 volts. I am very happy with the unit.
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