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Directly replacing NiMh cells with Li-Ion cells - bad idea ?

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    Directly replacing NiMh cells with Li-Ion cells - bad idea ?

    Good day folks. Let's talk about batteries because it's a huge topic which I haven't tackled as well as I would like, so let's put it into practice: my colleague worked on a portable handheld vacuum cleaner which had dead NiMh cells in it. It would charge, run for a few seconds then shut off entirely. Wanting to "upgrade" it, he replaced the NiMh cells with Li Ion ones....directly - no other mods or precautions taken. Ok, he's not as stupid as to substitute a Li Ion cell for EVERY NiMh battery in there, because the voltage wouldn't match for one, so he put in 4 Li Ions, so that would make it a 16v vacuum, which I reckon is a typical voltage for handhelds. The vacuum was functional again and after leaving it for a full charge, he returned it to the chap who brought it in. All was fine and dandy.

    Now just the other day, I saw the same vacuum just lying there in the shop again, which, not to be rude, but I kinda saw coming - I warned him but he was rather dismissive to any form of suggestion or criticism, as usual, so I dug no further. I asked Mr. Knowitall what's wrong with it and he said a couple of cells had popped...not sure if literally or otherwise, because I didn't actually see them, but the bottom line is it didn't work - at least not well enough.

    I knew it from the start that replacing a NiMh cell with a Li Ion one is not as easy as simply swapping them around directly and hoping for the best - the charge characteristics are different, which is what I believe destroyed the new cells he put in. It's probably down to each individual device and how it implements the actualy charging, but how easy or advisable is it to did what he did and just swap NiMhs or NiCads for Li Ions ?
    Wattevah...

    #2
    Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

    He was lucky that his house did not burn down.
    He needs to study about Li ion battery management, protection, etc. instead just putting them in and hoping for the best.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

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    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

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    TV Factory reset codes listing:
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    Comment


      #3
      Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

      you can use lions with protection boards to stop them being totally discharged and a "proper" charger,

      but it's not worth it, modern nimh batteries have high energy and long holding times - well over a year.
      older nicad/nimh only held the power for months.

      if you want the best 3rd gen nimh cells at the best price, go to ikea and look at Ladda white series.
      the AA holds 2400mAh and a 4pack costs beer money!
      these are re-branded Eneloop-Ultra's!!!!!

      Comment


        #4
        Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

        I have a similar problem... an old vacuum cleaner that uses three sub-C NiCds and they're shot... The vacuum cleaner draws 10+ amperes, and more than that during startup.

        What's the cheapest re-cell using any technology that can sustain that current...plus the fact that my tab welding equipment is nonexistent...

        Running 3xLi-ion in series is definitely a recipe for disaster, but fortunately three NiCd voltage is not too far off from 1-li-ion (or have them all in parallel), but getting a li-ion that can pass in excess of 10 amperes is pricey?

        Comment


          #5
          Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

          NiMh is a big improvement over NiCd for capacity, around twice. Lifetime is longest for NiMh over both Li-ion and NiCd.
          High discharge is OK for most NiMh.

          Sub-C size is a real bear to find and NiCd are low capacity around 1,300-2,200mAh so I try fit AA NiMh which have more.

          Ikea Ladda batteries I find different than Eneloop Pro's. Charging to 1.50Vpc the Ladda's roasted at 1,000mA where the Eneloop Pro's back off. You can't fast charge Ladda's, it's written right on the cells.

          Li-ion needs a BMS board and precise charging. You can't just plop them in.
          Attached Files

          Comment


            #6
            Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

            I think NiCd is the most forgiving for fast discharge, I think the vacuum cleaner is drawing at near 5C+ discharge rate for the original sub-C. If replacing with NiMH AA's I don't know if they can pass that much current repeatedly without damage.

            I tried a single 26650 li-ion cell and its protection board refused to power the vacuum. Hah. Figures...

            Comment


              #7
              Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

              Originally posted by redwire View Post
              Ikea Ladda batteries I find different than Eneloop Pro's. Charging to 1.50Vpc the Ladda's roasted at 1,000mA where the Eneloop Pro's back off. You can't fast charge Ladda's, it's written right on the cells.
              you may be comparing different generations of cells, there have been 4 generations of loops so far.
              i'll try to find the datasheets

              your over-charging them anyway - 1.5 is too high.

              Comment


                #8
                Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                The problem now days is that it is very hard to get Panasonic or Sanyo which are the only ones that worth a shit

                I have bought China batteries and they just do not last

                Either one of two things happen

                One when you charge the batteries and let them sit not being used 3 or 4 week the run time is either very short or not at all

                Two when you charge them and use that day and come back a few days then they have no power
                9 PC LCD Monitor
                6 LCD Flat Screen TV
                30 Desk Top Switching Power Supply
                10 Battery Charger Switching Power Supply for Power Tool
                6 18v Lithium Battery Power Boards for Tool Battery Packs
                1 XBox 360 Switching Power Supply and M Board
                25 Servo Drives 220/460 3 Phase
                6 De-soldering Station Switching Power Supply 1 Power Supply
                1 Dell Mother Board
                15 Computer Power Supply
                1 HP Printer Supply & Control Board * lighting finished it *


                These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                2 Hem Saw Computer Stack Board

                All of these had CAPs POOF
                All of the mosfet that are taken out by bad caps

                Comment


                  #9
                  Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                  Originally posted by stj View Post
                  you may be comparing different generations of cells, there have been 4 generations of loops so far.
                  i'll try to find the datasheets

                  your over-charging them anyway - 1.5 is too high.
                  I replaced NiCd AA pack with Energizer, Eneloop, Eneloop Pro, Ladda AA NiMh batteries.

                  The problem is the NiMh pack loses capacity after a month ~20 cycles. It seems to be the charger's voltage is a bit low, the NiMh never get a "top off" charge and it does something to the batteries. Voltage depression happens and I constantly get low battery alerts.

                  If I manually charge to 1.50Vpc things are good for a few months; CC 500-1,000mA at most, and 100mA when it's at 1.50Vpc for 1/2 an hour to top up. I got that from the charging curves. The battery pack behaves for a few months.

                  But Ikea Ladda whites are not liking it at all. They get hot at 1.5Vpc while the previous Eneloops never did. Ladda 2450 says "standard charge 245mA for 16 hrs. Made in Japan".
                  Attached Files

                  Comment


                    #10
                    Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                    i think i'm charging them at 500mA,
                    i'll need to check the default current on my small charger.
                    this one:
                    https://lygte-info.dk/review/Review%...-202%20UK.html

                    Comment


                      #11
                      Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                      The Lii-202 tests show going above 1.55Vpc and "With NiMH the charger turns off current to measure the voltage and will terminate on voltage without doing a top-off charge. This means the batteries will not be fully charged, but they are fairly close."
                      It's even more confusing.

                      Comment


                        #12
                        Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                        well it's filling them up, i use them in all my test gear after some fucking alk's tried to kill a 2 week old meter!

                        Comment


                          #13
                          Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                          Meanwhile in DIY land, my colleague thinks the cells blew because of the charger....which is not entirely incorrect (the charger is what killed them with no BMS in place), though it's not a defect of the charger - just a mismatch more like...
                          Wattevah...

                          Comment


                            #14
                            Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                            your lucky he didnt swap in some lipo packs!!

                            Comment


                              #15
                              Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                              Regarding the question in the title:
                              Directly replacing NiMh cells with Li-Ion cells - bad idea ?
                              YES, very BAD idea!

                              You should smack your colleague on the head He's going to set someone's house on fire with that kind of repair "work". Li-Ion batteries are not to be messed around with like that.
                              Last edited by momaka; 02-01-2019, 11:04 PM.

                              Comment


                                #16
                                Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                                Funny thing is he did this to ANOTHER vacuum a while back but that one apparently still works or the owner gave up on it so maybe he got lucky Not to sound like an ass, but I love these "I told you so" situations, and yes, he does deserve a smack every now and then, even though he's roughly 40 years older...don't know if that's relevant - a 24 y/o going head to head with a 60+ y/o
                                Wattevah...

                                Comment


                                  #17
                                  Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                                  he needs 2 smacks then, 1 for doing stupid shit, and 1 for being old enough to know better by now!!
                                  btw, isnt what he's doing overvolting the motor by about 3.5 times?

                                  Comment


                                    #18
                                    Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                                    Not sure about overvolting it - I probably don't remember the details exactly, but I'm sure he worked out the voltage of the whole pack to be roughly identical to the original, which is the only sensible thing about this project of his
                                    Wattevah...

                                    Comment


                                      #19
                                      Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                                      Also if he just bought random li-ion cells that aren't rated for high current (which are notably more expensive) it also doesn't work...

                                      Technically if he replaced 3 NiMH cells to one Li-ion cell, he would get quite close. Even better if he used all "protected" cells. But typical individually "protected" cells don't have high discharge rates as there's significant loss, better to be group protected to minimize losses.

                                      Comment


                                        #20
                                        Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

                                        There were more like 9-10 NiMhs in there from what I remember. What I know for sure is that he used 4 LiIons in series because I went to fetch them for him. I think they are 2000mAh capacity cells, but I could be horribly wrong on this also
                                        Wattevah...

                                        Comment

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