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I got a fair amount of old lithium ion batteries from smart phones and a laptop/tablet and I thought it would be nice to use them for a large power bank. Since they are all different capacities, I was planning on putting them all in parallel. Will each cell need it's own BMS or can all the batteries be put in parallel and then have one BMS (the TP4056 in my case) charge them as if they were one battery? Thanks.
How to make a battery bank using old phone batteries
- Thread starter uraniumhexoflorite
- Start date
Its more elegant to use only all identical cells - the main issue is paralleling loads of cells with random amounts of charge. join them all up with current limiting resistors first, leave them to equalise before hard linking them all in parallel.
So a circuit similar to this one would equalize the cells charges?
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The smart phone batteries are each a single cell so they should be the same voltages. I will double check tomorrow to be sure.
If the the same brand and model, OK. Otherwise, better you check.
I've done some of this ... just check the voltage of each cell first before you solder it into the pack , if the voltage is within about 1 V of that of the pack you can just connect it ... the fairly high internal resistance of old cells prevents a high current adjustment ... I don't use a BMS just have a small $1 led voltmeter permanently connected ... it reads to 1/100 of a volt .... meter stops working below 2.25V ( the pack should never get that low )
you can shrink wrap it into a nice package with the voltmeter inside ,the light can be seen through the shrink wrap , the voltmeter doesn't drain the pack appreciably.
you can shrink wrap it into a nice package with the voltmeter inside ,the light can be seen through the shrink wrap , the voltmeter doesn't drain the pack appreciably.
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I checked the battery voltages and they differ slightly. The batteries from samsung are 4.4 volts fully charged and there are apple batteries at 4.35 and 4.2 volts fully charged. I assume that the voltages can't be mixed.
No ...you can mix them all (as long as they're one cell) ...
The voltage you charge too has a great effect on the number of cycles you get from Li cells ...
I wouldn't charge any cell above about 4.1V
The industry standard is 4.2 V which gives a life of about 400 cycles (before capacity drops to 80% new)...
But you can charge the same cell to 4,35 which will give you 15% more energy storage but only 100 cycles ... that's 100 charges /discharges before it only holds 80% what it did when new ... I don't think many phones charge that high...
To get the most life cycles 4,000 !!! only charge to 3.93V ,batteries in satellites usually charge to this voltage because they want maximum life ... but each cycle only gives 65% of 4,2V capacity .....
Old phone batteries are usually thrown when they still have most of their life still left ... And billions are junked each year these could be salvaged on an industrial scale and used for grid storage etc...
18650 cells are most popular for re using ...usually 6 of these in a laptop battery , they come in a convenient standard package , it's the same type of cell that's in phones , just rolled up and put in a metal can.
The voltage you charge too has a great effect on the number of cycles you get from Li cells ...
I wouldn't charge any cell above about 4.1V
The industry standard is 4.2 V which gives a life of about 400 cycles (before capacity drops to 80% new)...
But you can charge the same cell to 4,35 which will give you 15% more energy storage but only 100 cycles ... that's 100 charges /discharges before it only holds 80% what it did when new ... I don't think many phones charge that high...
To get the most life cycles 4,000 !!! only charge to 3.93V ,batteries in satellites usually charge to this voltage because they want maximum life ... but each cycle only gives 65% of 4,2V capacity .....
Old phone batteries are usually thrown when they still have most of their life still left ... And billions are junked each year these could be salvaged on an industrial scale and used for grid storage etc...
18650 cells are most popular for re using ...usually 6 of these in a laptop battery , they come in a convenient standard package , it's the same type of cell that's in phones , just rolled up and put in a metal can.
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Apologies for the slight thread hijack....
I too have thought about paralleling large numbers of 18650 cells to create a 15kWh 96V battery pack for an electric vehicle application. This would require 25 cells in parallel. There is lots of information available about balancing the series connected cells but not much is said about the implications of connecting multiple cells in parallel. Is it really just as simple as balancing the cells before hand then connecting them solidly in parallel?
I think you mean 25 in series ..25 x 3.6v = 90 V you would need around 2000 cells 95Kg .... 80 cells in parallel in each 3.6v pack ...
With this sort of number of cells there 's no real need for balancing (I found) ... I run a powerwall of 100p 7s (24V) , I have a small voltmeter monitoring each 100 cell 3,6 V pac , and they all stay very close together ,voltage wise .... the purpose of balancing is only to prevent one pac becoming so high so too low that it reduces the life of the cells in that pac ... it's not important that they all have the same voltage ...
If you're looking to buy cells this thread might interest you ... https://secondlifestorage.com/t-Battery-offer-received-Any-opinion-is-welcome ..$1 per cell 2600mAhr and the manufacture has made them into the pac size you want 80p !!!
So if I get the batteries (1 cell each) to the same voltage and then connect them all in parallel they should be fine?
Yes ....once in parallel all will be at the same voltage , and the whole pack can be treated like it's one big 3.6V cell.
