Help making a safe system for charging/discharging liion batteries, questions about overcharging.

Discussion in 'General Electronics Chat' started by -live wire-, Feb 11, 2019.

  1. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    I do know a fair bit about liion batteries and their chaging (CC/CV charging, C ratings, over-charge/discharge) and got this charger and these batteries. So first of all, charging-wise. I will make sure to set it to 4.2V, as that is the voltage of my batteries, and .75C (600mA) doesn't seem too unreasonable for charging. But are there any possible concerns with overcharging, where boards are unsafely designed?

    Also, for overcurrent protection I think I'll just use a fuse soldered in series with the wires (I don't plan on have shorts, but while a blown fuse is ok, explosions are not). However, the one thing I will need that I'm not sure about is some sort of overdischarge protection. I've got an assortment of standard BJT transistors, some power mosfets (IRFZ44Ns), comparators, some other standard stuff, including a wide range of your typical passives. Can someone recommend a circuit I could make with those components that is fairly simple, uses <1uA when off, and is 90% or more efficient under normal use? It could be turned back on by a push-button.
     
  2. dendad

    Well-Known Member

    Feb 20, 2016
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  3. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    Any suggestions for DIY circuits? I don't want to have to wait a month.
     
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
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    And you don't think that buying parts, designing a circuit, prototyping it, testing it, building it...etc will not take a month?
     
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  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Ask how his fire starter is coming along. Seems like he thinks things can be designed and built for less time and money.
     
  6. iONic

    AAC Fanatic!

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    The 4 Commandments of Project Design(or are there more?)
    ...always more time
    ...always a design change
    ...always another part
    ...always more $$$
     
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  7. BobTPH

    Senior Member

    Jun 5, 2013
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    I use those same batteries. They have protection built in. And, by the way, they can produce an amazing amount of current.

    You might want to get the little charger that charges 5 of them at the same time from a USB port.

    Bob
     
  8. Audioguru

    Expert

    Dec 20, 2007
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    Since Amazon knows nothing about Li-PO batteries, I looked for detailed spec's for the Tattu batteries sold on Amazon. The Tattu/Gens Ace company does not sell that battery so it must be old, a cheap copy or fake. Maybe they are made only for the Amazon seller.

    I buy good American Li-PO batteries and chargers for them from my local hobby store, not from "a seller" somewhere.
     
  9. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    Are you sure they have protections built in? It seems unlikely. Especially overdischarge. Anyways, I already have the batteries and a charger. And all those parts. So are there any suggestions?
     
  10. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    But there are 22AWG wire, meaning the wires can only handle a few amps max.
     
  11. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    [​IMG]
    This is my charging solution. The indicator light is so bright for some reason! I made sure it was set to 4.2V and 600mA. The voltage seems to change a lot when it's unloaded, but it is very stable when loaded. If there are any issues, it is in a glass so the fire will be contained (if the charger is really bad). And it has... wait for it... a 2A USB port that never goes below 5V at full load! So it seems like a real product.

    I could put in an hour or two to design it and solder it together. I mean, I do have some free time, and would rather spend it doing this. Also, it's pretty much free if I have parts lying around that I actually need to use for something.
     
  12. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    Also, separate thing. Can I turn my 6x 1S 600mA lipo charger into a 1x 1-6S lipo 600mA balance charger? It should charge all to about the same voltage, right? Then, the only issue would be protection that cuts it off at 3V for one cell, right? Or is this not safe, and would there be too much variation?
     
  13. dendad

    Well-Known Member

    Feb 20, 2016
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    Building your own LiPo charger is a good way to make a bomb if you do not know what you are doing.
    Just stick a professionally made one. That seems to be the going advice.
     
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  14. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    I AM NOT TRYING TO MAKE A CHARGER! I am just trying to make a discharge protection circuit out of components I have. And also maybe re-wire an existing one that has well implemented CC/CV. Please read through carefully before commenting!
     
  15. Audioguru

    Expert

    Dec 20, 2007
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    The 6x 1S 600mA charger might be extremely simple and feed each battery through a current-limiting resistor. Then one or more becomes fully charged first and becomes over-charged until all of them are fully charged, which might never happen.

    A 6S balanced charger is much more complicated and is safer, because each cell is charger separately and properly.
     
  16. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Can you actually overcharge a LiPo if it's charge voltage is fixed at 4.20V? Over-discharge is another story and does not include the charger. Over-discharge is circuitry that could be incorporated as part of the battery or added to the device. See link below:

    Battery Protection PCBs

    EDIT:
    Perhaps I was off. The charger is also the source supply voltage, from what I am reading. It also mentions that it turns off so that the battery does not get too discharged.

    Are there and IC's/components on the underside of this charger? From the top view it doesn't look like it can control anything...nothing but two-pin components aside for two selector switch with each battery section.
     
    Last edited: Feb 12, 2019
  17. dendad

    Well-Known Member

    Feb 20, 2016
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    Hmmm. Heading =


    "Help making a safe system for charging/discharging liion batteries, questions about overcharging"
     
  18. -live wire-

    Thread Starter Active Member

    Dec 22, 2017
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    The system can include boards I purchased. I just mean getting all the parts together and maybe making a circuit for overdischarge protection.
     
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