So I bought a 3DR Solo “Smart Drone” and some spare batteries. To charge them all faster I thought I’d make my own charger. I’ve also made a little adaptor so I can charge them in my car. (run another cable off the car battery or turn the current down when using a car)
First of all you must use a voltage and current limited power supply. If you don’t you’ll damage the battery or worse, start a fire. These may be “smart batteries” but they will happily accept more voltage and current than what’s good for them.
I’ve made lots of assumptions in this build log/tutorial. if you can’t do some of the stuff it assumes then this project probably isn’t for you.
Before starting you should be comfortable with:
- Using a multimeter for measuring voltage and current
- Soldering
- Reading basic circuit diagrams
- Having a power supply of 12v at ~7A per charger
Parts:
Boost Converter ~$7 (link)
I used one of these boost converters off eBay. They’re cheap and can be used for many things as you can set the exact output voltage and apply a current limit. I ordered a couple to keep on hand.
Input Connector – XT60 (you can use anything)
I love the yellow XT60 connectors, they come on most LiPo batteries I buy and can handle 60 amps. They are easy to solder and plug/unplug. Anything I have that uses/supplies around 12v has an XT60 on it making lots of things interchangeable. (like my glue gun that can be used on batteries, desk power supply and car) You can get these online or from HobbyKing.
Output Connectors – Copper Clad Board (link for Australia)
The output connectors are a bit tricky. They don’t use a readily available connector. I just found some copper clad board that fit snugly and cut out the correct size. My calipers broke so I can’t measure it properly but I’d guess it’s the standard 1.5mm thick stuff. I’m currently working on a 3D printed connector, at the moment you have to manually plug the +/- connectors in. If you get the polarity wrong, you will blow up your boost converter and probably the battery controller.
Hint: shorten one side so it’s harder to short.
Optional Case/Fan
I also bought a plastic case for about $3 and used a random 12v fan I had lying around. This makes for a clean setup that stays cool.
How to assemble
1) The Case/Fan
If you’re putting the boost converter inside a case like I did you need some form of active cooling. I drilled a bunch of holes in the tops roughly the shape of where air blows from the fan. I drilled about 1/3 of the holes on the side to force the air into the case then out the side. I then use a rubber band to hold the fan in place. I only put it over half so more of the blades were over the holes and so I can attach another charger.
2) Wiring
The wiring is pretty straight forward. I’ve attached a diagram to help out. Make sure you use cables capable of carrying 16.8v @ 5A on the output and 12v @ 7A on the input.
3) Setting Voltage/Current
If you got the same boost converter I did (or one that looks similar) you can probably use the diagram below for reference. Turn the current limit all the way down to the minimum. (you should hear clicking when the trim pot hits the min) Next, get your multimeter and check the voltage. Keep twisting the voltage trim pot until it gets to exactly 16.8v. If you go any higher you risk damaging the battery.
Now set up your multimeter to measure the amps going into the battery from the charger. Hook it all up, start charging the battery and measure the current. Adjust the current up to a maximum of 5 amps. Any more than 5 amps will damage the battery and be a fire/explosion risk as it can’t safely charge that fast. I recommend doing this on a half charged battery for optimal results.
4) Fin.
Congratulations, you just made a $10-$15 solo battery charger. Also at 5A, this charges approximately 50% faster than the original charger.