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Thread: USB charging a saber

  1. #1

    Default USB charging a saber

    I'm starting to gather some pieces and build various portions of a saber and would like to make it as modern, from an electronics perspective, as possible. I've got one set of electronics built and various portions of MHS hilt that I'm playing with. One thing I'd really like to do is add USB charging to it.

    I've done quite a bit of electronics work and I've fiddled with Adafruit's Li-Po/Li-Ion charging circuits. I'm using one right now to charge a double 3.7v 18650 cell battery. At this point, I should be able to get 500mA charging without an issue, but I'd like to get at least 1A if I can with the newer USB-C version (if it can handle it).

    Has anyone else gotten something like this to work with a saber here? I'm always overly cautious when it comes to batteries and charging, because I know it's not as simple as it seems, so I wanted to check first. Especially when I want to charge an $80 CFX.

  2. #2

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    Not that I'm aware of, most of us just use the standard 2.1mm recharge jacks. In theory you probably could do this, but not through the USB connection on the CFX board. It would have to be it's own circuit.

  3. #3
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    I bought the Adafruit charging circuits to do something like this as well, but have yet to set it up haha, so you are a step ahead of me!

  4. #4

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    You want your battery disconnected from everything else when you are charging, that is why many use a charge port. There are USB chargers that have built in load pads, but those are usually limited to 3A with a protection circuit.

  5. #5

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    Quote Originally Posted by RavenXp View Post
    Not that I'm aware of, most of us just use the standard 2.1mm recharge jacks. In theory you probably could do this, but not through the USB connection on the CFX board. It would have to be it's own circuit.
    Agreed, it would simply be a more universal charging port. IE, I don't want to have to find a special lightsaber charger, would be nice to just plug it into a USB port somewhere. Those are ubiquitous. I'm thinking it would go inline with the battery just as the charging port currently does. I just don't want to get any wires crossed. I know the boards I have now have their own charging solution, so don't like being given 3.7v on the power lines, unless I cut the built in charging circuit.

    I'll see what I can figure out and keep people posted. If anyone else knows, share the knowledge!

  6. #6

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    Quote Originally Posted by jbkuma View Post
    You want your battery disconnected from everything else when you are charging, that is why many use a charge port. There are USB chargers that have built in load pads, but those are usually limited to 3A with a protection circuit.
    Hmm. Okay, this is the kind of thing I need to know. Thanks a bunch. I'll need to figure out how this is handled.

    Any idea what a typical amperage for the LED loads are? I know some are around 3A for in-hilt illumination, but I have no idea on a Neopixel blade.

  7. #7

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    An in-hilt will draw anywhere from 1-5A and a pixel blade will be about 3-8A for a 120x2 pixel blade typically. Longer pixel blades and different configurations will provide different results.

    I wouldn't rely on these boards to be able to handle 3A loads for extended periods.

  8. #8

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    Quote Originally Posted by jbkuma View Post
    An in-hilt will draw anywhere from 1-5A and a pixel blade will be about 3-8A for a 120x2 pixel blade typically. Longer pixel blades and different configurations will provide different results.

    I wouldn't rely on these boards to be able to handle 3A loads for extended periods.
    Well, I've dug through the datasheets on the part used, and I can't find any mention of a max throughput current for the part. The functional block diagram of the part has a couple resistors in the path from Vbat to Vss, so there has to be some sort of thermal limit.

    However, I know they have projects on the Adafruit site driving over a hundred Neopixels off this circuit, so it can't be too terrible. Also, they don't disconnect power while charging, as it can charge and run all those neopixels at the same time. My current setup is only running 7 pixels, but I have a string of 144 I can put on it, and I've seen other people do it without a problem. No idea how long it lasts, though. The charger does have thermal shutdown protection, but I'm not positive it works in non-charge mode as well.

    Edit: Also, they do have a USB-C one that exposes the USB data lines as well, so in theory it could be wired into the data lines on the sound board so you could charge and program at once. That's getting a little more risky, though.
    Last edited by AmpCat; 02-03-2020 at 05:41 PM.

  9. #9

  10. #10

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    Quote Originally Posted by jbkuma View Post
    Which charger are you looking at?
    Their new USB-C one. 4410 I think is the product ID. It has the advantage that the VBat is in parallel with the charging circuit, so you should be able to pull the max current of the battery without affecting other components. However, at that point you're starting to get into the realm of whether or not the traces will handle 8A of current.

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