How do I build my own Camera Battery Charger using USB?

I'd like to build a Charger for my 8.4v Sony Camera Batteries. I have a few of them but decided it might be interesting to learn how to make one that will utilize USB.

From what I understand the Battery is a 8.4v Lithium Ion (i.e.. 2cell 4.2v Battery Pack). The chargers I have state an output of 8.4v and 400mA. I figured it might be possible to utilize the 5v that USB provides and I guess step up the voltage.

I found plenty of charging controllers that seem to be good for 1cell (4.2v) batteries, but not seen any way to charge a 2cell battery pack. 

I guess I am hoping for some guidance on what I will need to:
1) Step up USB 5v to 8.4v
2) Control a Charge to a Lithium Ion 2 Cell Battery Pack

cheers,
Jon

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ketan7s2 years ago

Hi, did you find a solution? The charger is rated 8.4v and 0.28A if it is sony. So USB miliamps will be sufficient. But if you use a power bank, you will get higher amps. I have been experimenting the same lately.

-max-2 years ago

Here is a good video discussing how to charge LiPo packs https://www.youtube.com/watch?v=A6mKd5_-abk

Essentially you will need a suitable step-up lithium charging chip, but all the ones I've found are in SMD packages, so you will need to create a circuit board for it. I am not sure if they make them step up on their own, they may be configured to take, say 9V in and step in down to 2S (8.4V max) In that case, you will need a boost converter.

Some charging chips come in super simple 3 pin transistor-like packages, while others will have more pins and more functionality (like the ability to choose charging voltage, charging current, LED status lights, digital control, etc.)

You will need to charge the cells slowly with USB, as many of them are still limited to 500mA (I am beginning to see this change with modern electronics, as devices draw more and more power)

Would it be fairer to say you want a multi-channel charger with a single power cord ?

The battery needs 8.4V for charging. You won't get that from USB. Stepping up the voltage is an idea but to do so you sacrifice amperage. The base line for most USB (i.e. the usb port on your PC or laptop) is 400mA. So to setup up USB to 8.4V you will have well less than 400mA available so charging will be slow at best but likely it won't charge at all.

JonathanR10 (author)  mpilchfamily2 years ago

Yeah sorry, I was hoping to use USB wall adapters or hubs, that would provide at least 1Amp per port. I should have mentioned that.

If in theory I could get a 5v 1A power supply (from a USB wall plug / hub) I'm curious if its possible and how I would go about Stepping it up for 8.4v and Controlling a Charge for 2 cells in series (this is what appears to be inside the Sony Camera Batteries)...

http://randybuildsthings.wordpress.com/2013/02/25/sony-infolithium-m-teardown/

Get a boost converter rated for 5V input and that will provide at least 8.4V output. The you'll need a charge controller for the battery. You can salvage one from an existing charger.

You may struggle to get 400mA at 8.4 V from a standard USB, without complex effort to persuade the computer to allow you to pull 600mA from it. USB is usually limited to 500mA, unless you're on USB 3, which can give you 1A

JonathanR10 (author)  steveastrouk2 years ago
Hey Steve,
thanks for the response. I guess I should have clarified that I'm intending to use it with a powered USB hub, the point being multiple batteries charging.

My frustration is that I have to use 6 Wall plugs to charge 6 batteries, and they are bulky as hell and don't play well with powerstrips (awkwardly shaped). So figured it'd be cool to make individual USB-like units that coudl charge the battery from a (high) powered hub.... If I can get around 8 ports with upto 1A per port then I could theortically charge 8 batteries at once.

I figured that putting the logic into the unit that attaches to the battery and keeping it separate from the hub would be useful (as I could use my iphone or android USB charger to charge a battery if needed).