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I have this small palm sized toy drone. It uses a 'charger' which houses 8 AA alkaline batteries. The charger plugs into the drone and the charger is activated by a toggle switch.

I want to replace the charger with a USB cable that plugs into my PC monitor or even wall socket.

Can I hack this existing charger into using a USB power source instead of 8 1.5v alkaline batteries?

Charging device and toy drone.

A little bit of 'f it, I'm gonna try it' resulted in this. enter image description here

gh0st
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    Plugging USB 5V directly into the drone would be a bad idea, likely. I would guess that the contacts on the drone are connected directly to the lithium battery. The charge controller for Lithium is probably in the battery box (and not in the airframe; to save weight). – Nick Alexeev Apr 26 '16 at 02:38
  • If you read my comment to the answer below you'll see I tried it anyway. The USB cable I used was very small, the two wires in the USB cable had to be 64 gauge or something. They're insanely tiny. – gh0st Apr 26 '16 at 02:39
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    It's good that you got away with it. But please don't do it again. If you abuse a Lithium battery it becomes a delayed action incendiary device. We've just had a [discussion about safety of Lithium batteries](http://electronics.stackexchange.com/q/230155/7036). – Nick Alexeev Apr 26 '16 at 02:43
  • Very interesting. So how could I make sure that the output power of this charger is not going to make my little toy UAV into an IED? – gh0st Apr 26 '16 at 02:45
  • Open it up and look for a battery. I suspect that you will find a capacitor instead. – Mark Apr 26 '16 at 02:49
  • @gh0st A proper charging circuit takes care of this. It generated the appropriate voltage and current that are safe for the Lithium battery ([details here](http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries)). – Nick Alexeev Apr 26 '16 at 02:49

3 Answers3

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Edit: Hold on, wait.

Normally 8 AA batteries equals 12 volts DC. But looking at the parts involved, it's possible the batteries are in series-parallel. I would reassemble it as-supplied, put the 8 batteries in, and measure what's coming off the end of the batteries.

If it's 12 volts (all batteries in series) nothing easier. Dive into your shoebox of old wall-wart power supplies. One of them is bound to be 12 volts DC, since that is the most common voltage. Hack off the wires... or if you want to retain it for its original use, visit Radio Shack for a socket compatible with the plug (the 12V DC ones are fairly standard). These can also be bought new if you never save them, or ask your friends or neighbors if they have any.

enter image description here

If it's 6 volts (2 parallel strings of 4 each), you can use a common wall-wart that is 6 volts instead of 12. These are far less common, but you can buy new ones. But try this: test the product again, only use NiCd or NiMH AA batteries. These cells are 1.2 to 1.25 volts per cell, or in a stack, 4.8 to 5 volts. Exactly the voltage of USB! So if the charger and drone work normally and to spec on NiMH/NiCD batteries, they should adopt straightaway to USB charging. I would use a 2A supply like an iPad charger, and not a computer port.

The general concept here is to supply power in a way which emulates and replaces the AA batteries, and do not tamper in any way with the factory as-designed circuitry which is responsible for safely charging a lithium battery.

Harper - Reinstate Monica
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Are you able to measure the output voltage of the charger or check how many battery cells are in the drone? If the drone has a single 3.something volt Li-Ion battery, the charger can probably be persuaded to work on 5V (if the AA's are arranged to give 6V, you might not even need to mod the charger at all). Otherwise a cheap boost regulator should do the job, nothing fancy as the voltage from a AA varies from over 1.6V down to less than 1V per cell as you drain it, so you've got some margin to play with.

Sam
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  • Well I kind of went crazy and hacked away at a cheap USB cable and tried it anyway. There are two LEDs on the other side of that green board. One red, and one green. When the board has power, both LEDs are on but the red is significantly brighter than the green. And to be honest, under normal charging circumstances, I don't think the green is supposed to come on until the toy is fully charged. – gh0st Apr 26 '16 at 02:37
  • Yes, a cheap boost regulator should do the job. I would not assume there are any batteries in the drone itself - that is why there are batteries in the charger. I suspect that the charger is simply filling a capacitor inside the drone, which is much lighter that a battery. I had a toy helicopter that worked that way (although not for very long on each charge). – Mark Apr 26 '16 at 02:45
  • Good one, that's probably what I'd have done as well, if it lights up that's a good sign, the minimum current to light a led is bugger all and the circuit looks so erm... sophisticated (!), I reckon the faint glow from the green one is probably normal, let it run for a while and see what happens I guess. – Sam Apr 26 '16 at 02:55
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USB nominally outputs 5V. Even a near flat 12V battery could easily damage your USB port. So only plug into chargers that you can afford to destroy. Definitely do not plug into a computer unless you want to destroy the USB port or worse still the computer.

CyberFonic
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