Author Topic: Advice needed for DIY spot welding of 18650 cells  (Read 339 times)

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Online emece67

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Advice needed for DIY spot welding of 18650 cells
« on: January 20, 2022, 11:49:37 pm »
Tired of the n-th home appliance whose batteries fail —this time a vacuum cleaner—, I decided to fix it not replacing the way-overpriced whole battery pack, but just its six 18650 cells.

Thus I bought one of these cheap, small spot welders from Aliexpress. Although I was able to easily weld with it some nickel strips to cells, I'm not at all sure about the correct way to get such welds, so I ask here for some advice from more experienced DIYers.

My main concerns are:
  • What «gear» to use? They call gears to the different «power levels» of the device. Mine has from 1 to 8. All can weld 0.1 mm nickel strips, from an easily removable weld al level 1, to causing a nasty hole in the cell at level 8. Around level 4 the nickel strips start to break, instead of un-weld, when trying to remove them.
  • What distance between electrodes to use? In my first attempts I placed the electrodes quite close (around 1 mm), but I have seen some guy in YT claiming that greater separations help the current to go deeper into the cell metal, thus producing better welds.
  • What thickness for the nickel strips? The battery pack I want to fix has 0.1~0.12 mm strips, so I bought strips of the same thickness. What is the maximum thickness these cheap devices can weld? Any benefit (on top of the higher current capacity) or caveat when using thicker strips?
  • Same on width. I have 8 mm strips (again, as those in the battery pack).
  • How many spots per cell?
  • As a summary of the 3 above, is there any rule of thumb about what {strip dimensions, # of welds} to use for a given cell/current-capacity combination? My rule now is: «mimic that of the device you want to fix», but, what to do if building a battery pack for some random application?

That's all, thanks a lot & regards.

Note: it is NOT a Dyson, removing the BMS (that has a pair of connectors to totally disconnect it from the cells and power source) does not cause any harm.
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Offline abdulbadii

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Re: Advice needed for DIY spot welding of 18650 cells
« Reply #1 on: January 21, 2022, 12:17:11 am »
Have a work inspecting, reviewing the pack situation is worth it

meant if there's possibility an extra space in all dimension
we'd try transform it to 'normal way' ie. replace them with the bumped (+) pole ones, give them the on-market-available houses and charging them with their special quality charger
by this all drawbacks of resistance-welded pack get avoided, mainly dissimilarity temperature surrounding batteries
the ones in the inner position always get hotter hence degraded more quickly .
temperatures above 60°C gives Li-ion battery loses capacity linearly, in turn its performance
it's must be within 10°C to +55°C.temperature range, but when charging take place must be ~ +5° - +41°C.

preventing from going down to nominal V is not hard to do manually as the using tool performance should be a telltale
whenever it shows noticeable down performance quickly pull out and put into charger one by one,
could google better than me ones:

IMHO this'd give the Li-ion battery far longer lifetime as they get rolled over position and evened in high temp. impact

might benefit read
« Last Edit: January 22, 2022, 05:38:43 am by abdulbadii »
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Online emece67

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Re: Advice needed for DIY spot welding of 18650 cells
« Reply #2 on: January 21, 2022, 11:15:44 pm »
This battery is never partially charged. We simply charge it fully when the device ceases to work.

Of the 6 cells inside, five are almost perfectly matched, but the 6th is ~300 mV lower. I'll change the 6. I do also have a Liitokala charger/discharger.

Thanks & regards.
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