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LI Ion charging question — Parallax Forums

LI Ion charging question

jdoleckijdolecki Posts: 705
edited 2021-01-04 16:44 in General Discussion
If I have Multiple Li Ion pack connected to the same power buss will the higher charged one's try to charge the lower ones?

Can stop this buy using a diode on each pack to prevent reverse flow into the battery pack?

Also can the multi cell pack be reconfigured so the batteries are connected by wires instead of metal jumpers? I want to change the packs physical dimensions to fit the spaces in my robot.

Does all this make sense?

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,930
    edited 2021-01-04 18:25
    jdoleki wrote:
    Also can the multi cell pack be reconfigured so the batteries are connected by wires instead of metal jumpers? I want to change the packs physical dimensions to fit the spaces in my robot.
    The metal jumpers are spot-welded on. It's a process that releases very little heat. You do not want to solder a wire to a li-ion cell. The cell will overheat with possibly hazardous consequences.

    -Phil
  • sam_sam_samsam_sam_sam Posts: 2,239
    edited 2021-01-05 07:15
    [img][/img]
    jdolecki wrote: »
    If I have Multiple Li Ion pack connected to the same power buss will the higher charged one's try to charge the lower ones?

    Can stop this buy using a diode on each pack to prevent reverse flow into the battery pack?

    Also can the multi cell pack be reconfigured so the batteries are connected by wires instead of metal jumpers? I want to change the packs physical dimensions to fit the spaces in my robot.

    Does all this make sense?

    What type of battery cells are you using 18650 or a different battery type

    ****Disclaimer Warning ****** doing this at your own risk

    If they are 18650 cells you can change the configuration of the pack if done correctly ( you must use some type of battery protection circuit board for theses type of battery use the correct one for the type of cell voltage and the number of cells being used ) <— very important to follow

    Are these cells glued together and a possibility of plastic sleeves torn by trying to to separate them apart if this is the case

    You can separate them but you have to very careful doing this process because you do not want to short the cells together ( use plastic tools when possibles something like a plastic knife the good quality ones not cheap quality plastic knife will not work for this )

    The first thing that I would highly recommend that you buy the 18650 sleeves to replace the ones that tear when separating them apart this is very important ( you can buy them on eBay )

    When you have them separate them apart if you cut the tabbing in the middle of the two cells then you would have a place to solder your wires to the cells positive and negative side of the battery ( this can be done correctly with a cutoff wheel from a dermal tool or use a small wire cutter but this dull the tool very quickly if you do a lot of them )

    ***************** Disclaimers Warning doing this at your own risk ************

    You can solder them directly to the cells them self HOWEVER unless you have the right type soldering equipment with the right temperature controller so that you can make the solder ( with a flux core ) to flow and then get off the cell quickly I would highly recommend that you do not do it this way

    I have personally done this but I have the right equipment to do it this way but very rarely do this on 18650 cells ( I have a battery welding machine and when I use very narrow tabbing I will sometimes solder the tabs after welding them because sometimes they do not welded correctly to the cells but use a lot of CAUTION when doing this )

    ***********************

    Now if you are using a different type of cells and you post a picture of them I try to help you with how you might be able to use them

    I hope this helps you ( but be very careful when working with these type of battery work carefully and take your time and do not be in a hurry when working with batteries )

    This type of battery can be soldered to the battery terminals but you do have to have the right soldering equipment to do this as you can see in the picture below ( one note this type of battery is a little bit more forgiving than the 18650 batteries but you still have known how much heat you are applying to each cell to be done safely )

    **********************
    This can not be done safely or correctly

    “ If I have Multiple Li Ion pack connected to the same power buss will the higher charged one's try to charge the lower ones? ”

    You do not want to charge battery with different milliamperes hour capacity on the same battery charger controller even if the battery packs has battery protection circuit boards this not a good practice I would not recommend this at all

    *********************

    Now if this is not a battery charging controller and you are using a power supply that you can control the voltage and limit current going to the battery packs and you use a diode on each battery pack module and they are the same exact voltage maybe you can do this however you need to check the current going to each battery pack to make sure that it is not over the recommended charging current for that type of battery use caution when do this test to find out if it can be done correctly and safely ( I have not done this myself personally so I can not answer this question for you )

  • I'm aware of the dangers of working with Li Ion batteries.

    I will be using this chip for a charger/controller. Analog Devices LTC4162-L Specifically for its I2C data telemetry.

    The reason I want to separate the battery pack and use wires is to fit them to the available space on the robot which may be
    only room for 1 cell.

    The pic explains the idea.







    882 x 459 - 16K
  • sam_sam_samsam_sam_sam Posts: 2,239
    edited 2021-01-06 03:43
    I only skimmed the data sheet but if it’s like most things my guess is that it might not be a good practice to use different milliamperes hour batteries on any battery management device because it senses battery voltage and when ever any battery cell reaches the battery voltage cutoff it stops the battery charging sequence now it might be possible to use a single battery management ic chip for each individual cell then probably could be done but you would have to test this idea

    I look at the data sheet again and what is not clear to me is if each cell is independent of each other and it also not clear if there are ic chip that are set up to independently work correctly by them self and just managed by the main charging controller ( I have used multiple cell battery management circuits before and I was not impressed with the results ) because if your cells are not correctly matched the results are very poor

    Or get in touch with the chip manufacturer and ask them this question and see what they tell you if can be done

    One note you have not mentioned what type of cell size you are using just curious what cell format you are using
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