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Thread: USB charging a saber

  1. #11

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    Quote Originally Posted by AmpCat View Post
    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.
    This is only meant as a charger, not to support a load of any kind. To use this you would disconnect the battery from your project and connect it to this charger.

  2. #12

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    I mean, you could in theory set up a system that could cut power to the board when a charging current is applied, but being able to cramfu that into a hilt with everything else.... not something I plan on attempting.

  3. #13

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    Quote Originally Posted by jbkuma View Post
    This is only meant as a charger, not to support a load of any kind. To use this you would disconnect the battery from your project and connect it to this charger.
    Well, I talked to the folks at Adafruit and they said it shouldn't be a problem, unless you run into the issue of too much current through the traces, or pull more current than the battery + charging circuit (if plugged in) can source. But if your load is in parallel with the battery as well, as it should be, the current should flow through the larger conductor wires anyway. Might have to bypass the circuit board's battery and load terminals with a wire harness to skip those traces, though.

    Also, the batteries have protection circuits that should prevent you from over-drawing the battery and the charging circuit is designed to drive a load while charging (it has intelligent constant current and constant voltage modes and drivers). I'm not sure if that's also the case with the wall chargers. To be honest, I'm not sure why you need to disconnect the load while charging to begin with. Since my engineering background is mostly with digital circuits, I did some digging and the consensus seems to be 'Yeah, if you designed your circuits right, you should not need to disconnect the load.'

    I could be missing something and wrong, but so far, I'm not sure why disconnecting the load is required.

  4. #14

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    I think it's a best practice ' just in case' preventative measure to protect the board electronics. Considering how small the boards and traces/components on the board are I prefer not to chance it. It could also be just a side effect of the standard 2.1mm charge port that we use, it's designed to kill power to the board when a charger or kill key is inserted.

  5. #15

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    I know it was best practice a while ago, because most circuits on the load side weren't designed to handle a wide range of inputs, so couldn't tolerate the charging voltage delivered by a charger. But these days most boards, like the CFX, are designed to handle higher voltages. Though I don't know the limit. I'll have to see if I can figure out the max voltage input on the boards, as well as the max the charging IC puts out.

    But, as I mentioned, this part was designed to charge and power in parallel with other 3.3-4v devices.. (like Neopixels), I think it'll be fine.

  6. #16

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    The load needs to be disconnected so the charger can detect the state of the battery. If you have a load drawing off the circuit while it's charging you risk damaging the battery by either over charging it or applying too high a current for the state of the battery. If you are intent on using a charger in this way you should select a charger that is designed to have a load connected to it and wire it appropriately. Charge circuits that are designed to work this way either have a method of disconnecting the load, or they power the load directly from the charge source.

    Before asking more questions I urge you to read up on lithium batteries, charging, and related topics.

  7. #17

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    As I mentioned, this battery charging circuit and IC was designed to charge batteries while under load. It has constant current and constant voltage modes that ensure the battery is handled properly. I spoke with the designer, and they confirmed there should be no problems pulling a load and charging at once, aside from trace and wire size concerns.

  8. #18

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    Guess it'll be an experiment. Let us know how it works or if it doesn't.

  9. #19

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    You do not understand what you are talking about. I am very aware of all of these things. You will likely not see a problem right away, and take this as confirmation that you were right, since you are intent on maintaining you poorly formed idea, and you hopefully you won't experience a catastrophic failure, but if you will damage your battery and shorten its life. That is not my opinion, it is a statement of fact.

    As I said before, read about charger cycles, why they have different stages, and why you should disconnect your load.

  10. #20

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    Quote Originally Posted by jbkuma View Post
    You do not understand what you are talking about. I am very aware of all of these things. You will likely not see a problem right away, and take this as confirmation that you were right, since you are intent on maintaining you poorly formed idea, and you hopefully you won't experience a catastrophic failure, but if you will damage your battery and shorten its life. That is not my opinion, it is a statement of fact.

    As I said before, read about charger cycles, why they have different stages, and why you should disconnect your load.
    Okay, while I'm quite proficient in micro-electronics, I'll agree this is a very sensitive subject both from a safety perspective, as well as apparently, a technical capability perspective. I've received some confirmation that this should be fine from the group that made the charging board and I have read about charger cycles, but for everyone else's sake, and to make sure what I'm doing is safe, I'll ask them to confirm that this indeed will not damage the battery in anyway. After all, they designed it to charge these exact batteries, in this fashion. Likewise, I'll reach out to Microchip about this charging chip (the MCP73831) and discuss this with them.

    Also, think about this from a purely logical perspective: People do this all the time, with these same batteries, in electronics sold literally by the billions. Every laptop, phone and almost everything else these days will run while being charged, most of them using Li-Ion, or the even more dangerous Li-Po batteries. Obviously, there exists a safe and effective way to do this.

    While I realize you've done this for a while, I would recommend that before telling people they don't know what they're talking about, you provide some evidence other than 'I know what I'm talking about.' New things come out all the time that you may not be aware of, and you may have gotten your information from incorrect or out of date resources. Not only is it not very polite, it doesn't help people push the boundaries of common techniques and develop better designs in the community. And on top of that, you might just be wrong.

    Edit: Just as a note, I am fully aware that there's a good chance I am wrong too. Either way, I'll post what I learn here.
    Last edited by AmpCat; 02-11-2020 at 07:02 PM.

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