Another DIY Battery - Makita 18V Drill Packs (Konion Cells)

Scottyf

Esteemed Pedelecer
Feb 2, 2011
1,403
-1
Wurly,
I believe Jerrysimon gets his cells from an Ebay contact that can do custom packs. They are well priced for the work and genuine cells. The A123 cells are Lifepo4 cells which tend to allow more abuse without BMS and survive unlike other chemistries using Lithium.

I personally use Lipo and don't monitor the cells other than a watt meter as a fuel gauge. But balance each charg to allow them to remain ok. It also gives me a chace to see how the cells are performing each day. I believe Jerrysimon balance charges every 10 ish charges to make sure they don't go to far out of kilter.

He also had a couple cells fail and repaired them individually within the pack. (Good work by the way) and again if it was a lipo cell it could have gone horribly wrong. But with A123 it was far more robust to charging from dead without any adverse effects.

This seems to be the Merits of Lifepo4, Good dischage, life cycles, robust format, less voltage sag, better operating tempertures.
Its con's appear to be mostly weight, size and lower voltage (3.3v nominal).

I can't say whether they need more blancing or less balancing than lipo. All cells in a pack in series should be balanced properly as they will all perform slightly differently based on resistance. But the degree of this may well be less in Lifepo4... or maybe becasue of the less voltage sag people don't notice it so much...
 

jerrysimon

Esteemed Pedelecer
Aug 27, 2009
3,292
112
Cambridge, UK
The full build thread of my small A123 pack incl links to where I purchased the cells is HERE



The thread records over two years of usage incl the two failed cells and their replacement.

I think the small 36v, 2.3Ah A123 pack has limited use which for me fits my 5.25 mile commute each day. After the inital couple of balances for over 20 months I never balanced the pack and tended to run it flat to work and back without charging. Given this abuse I think it is amazing that cells did not fail earlier.

Now I never run it below about 40% charge, topping it up after I get to work/before I return home and am balancing every couple of months. If I had done this from the start it probably would have doubled its life span. The cells are rated at 2000 cycles I think.

Thus the pack would probably only do about 10-12 miles on a flat commute with a lot of abuse or 5-6 miles flat commute if you treated it well. So this pack does have a limited application or of course could provide a spare backup pack for folks with larger main batteries.

I don't use a BMS but those who build bigger 12s4p over on Endless Sphere tend do. Then again there are lots of discussion about how failed BMS circuits can drain cells and ruin them as well defeating the object of them in the first place. At this higher cell count it gets expensive, heavy and harder to maintain if you have to start replacing cells. You would probably be better buying a pucker battery.

Being 12s1p (2 * 6s1p) my DIY pack is extremly flexable and easily repaired. If I need to go further then I take two packs.

Regards

Jerry
 
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