Replacing Drill pack cells

Discussion in 'Power Electronics' started by Ljk2000, Mar 31, 2017.

  1. Ljk2000

    Thread Starter Member

    Nov 20, 2016
    30
    0
    So I was thinking of replacing the li-ion cells (18650) but how many amps usually is taken from the li-ion cells. I have the Ryobi one+ system. And want it to be able to handle all of the tools even if I don't have them. So I guess basically what would be the average amp draw from any drill pack? When used with the right tool of course. I was thinking of using these cells that have a capacity of 3350 mAh capacity, but a 4.87 max amp draw. Would that even be enough? Or would I need a cell that has a lower capacity, like 1500 mAh but can deliver 20+ amps. That would simply be the best but I would like to get more capacity if I can. This is for a compact pack. And lastly what about a bigger pack, with 10 cells instead of five (2 rows of 5, parallel), then would it be okay since there in parallel that would mean more like 10 amps draw. Do not think there is anything else to say for now.
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,414
    1,223
    The capacity is in amps per hour, so a 3350mA is 3.35 amps in 1 hour Max, or multiples of that, so 6.6amps for 30 mins, 1.6amps for 2 hours etc...

    Putting cells in Parallel will increase the current capacity,..choose a capacity that is at least 10% more than what you need.
     
  3. Ljk2000

    Thread Starter Member

    Nov 20, 2016
    30
    0
    I use these packs often and use up the whole thing every time. So I would, naturally use the highest rated capacity. But these high capacity cells do not like to be discharged at a higher rate than 5 amps (manufacturer recommended for this particular cell). And I am worried I will use a tool that will use more than 5 amps and the battery will explode or some other fun thing.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,414
    1,223
    You can get 9800mAh cell on Ebay, don't know if these will last longer, if you're looking for current capacity, i would use nimhi cells, or sla battery.
     
  5. Ljk2000

    Thread Starter Member

    Nov 20, 2016
    30
    0
    The 9800 mAh cells on ebay are fake. There has been many people who tested them and only found 750 mAh. I am getting mine from IMR batteries for about $5 a pc. NiMi batteries tend not to like such a high drain condition, plus I do not have the charger for it along with I could not fit the amount of cells in the pack, since there 1.2v I would need many more. Lead-acid would be impractical. And its not really the run time I care about, it is more about weather the Li-ion cell (since there is different chemistry) can handle the drain of a given tool without a issue. So yes I want a high capacity battery, but there are limits on how much you can drain (current). So with the high capacity battery for example yes it has 3350 mAh capacity. But a 4.87 amp draw max. And I need to know if any tool that uses these packs, like a string trimmer to a impact driver or regular drill etc, use more than 4.87 amps while running (under load). I know a lot about batteries, been doing a lot of research but I do not know the draw of a tool. So it is hard for me to choose a battery with out that information. To much load on the battery and somebody could get hurt.
     
  6. tcmtech

    Distinguished Member

    Nov 4, 2013
    2,809
    2,703
    I rebuild a lot of battery packs and most cordless tools that use more than 12 volts also have the capability to draw upwards of 30 - 40 amps at full load.

    As for NiMH cells I have had no issue with pulling that sort of current from good quality sub C size cells.

    I get mine from here, http://www.all-battery.com/index.aspx ,and usually order their 3000 - 3800 mAh sub C cells a 50 - 100 at a time 1 - 2 times a year now.
     
  7. Ljk2000

    Thread Starter Member

    Nov 20, 2016
    30
    0
    I like that website as well. I also like the selection at IMR battery. I read that ni-mh did not like that kind of current draw but guess wrong there. That is impressive. And just a little tool drawing that much, may not be the best idea to use those cells then, unless there in a set. Darn I wanted to use them...
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,414
    1,223
    Nimhi cells have a simpler charger circuit than lithium, they just need a constant current,
    whereas lithium need to be monitored and then stop charging, and have a minimum voltage level, then explode!
     
  9. tcmtech

    Distinguished Member

    Nov 4, 2013
    2,809
    2,703

    When NIMH first came out they had issues with not doing well in high current draw applications but that limitation has long since been corrected and they are very well suited to high current applications where even the best Nicd and high C rate LiPos have a difficult time surviving in. Only real downside is the good high current high capacity NiMH cells are quite heavy for their size.

    Almost all of my cordless tools are Craftsman 19.2 volt based and their stock NiCad cells are pure junk right form the factory. The way I use them few of my ~16 battery packs ever made it past their one year warranty before giving up. Plus with a dismal 1400- 1600 mAh capcity their run times sucked on top of it. That's where a lot of the Tenergy 3000 - 3800 mAH NiMH cells I buy go into. The first packs I rebuilt are going on 3 years old and well abused yet so far are indistinguishable for power and run time between them and the newest packs I have rebuilt. :cool:

    Also in real life hard use it's easy to tell even a brand new stock NiCad pack from one of the rebuilt NiMH packs just by the added power the tool it's in has. They have far less internal voltage drop. Then add the ~2x run time and so far 3+x service life behind that all for 1/2 the cost it's easy to see why I use them.

    They have proven themselves well enough for me that I have been using them to rebuild other people's cordless tool battery packs for the last year or two now. I put 3800mAh NiMH cells in my grandmas Black and Decker cordless string trimmer last summer that originally had 1100mAh 2/3 C cells. Now she runs out of battery before the trimmer does. :p
     
    #12 likes this.
  10. Ljk2000

    Thread Starter Member

    Nov 20, 2016
    30
    0
    Thats really nice. And there not to expensive. I like to use them for AA and AAA around the house. And with these drill packs I am going to want to use cells that can deliver up to 20-30 amps right? The high capacity will not work then because it only allows a 4.87 amp draw at max?
     
  11. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,172
    1,115
    For lead-acid; the Ah rate is specified over a longer discharge period (can't remember if 10 or 20h). Not sure whether the same applies to any other battery chemistry.
     
Loading...