battery pack protection - NTC half stack V?

Thread Starter

racmaster

Joined Feb 13, 2018
29
hello, could somebody assist pls?

im experimenting with battery pack for my cordless chainsaw blackanddecker 36v gkc3630l20 h1 36v.

i created 36v battery pack from lifepo4 batteries instead of liion. it should be able to provide much more moment and continuous current then original battery, 250% of capacity, 1000% cycle life... nice enough for motivation...

i allready tested the batteries using revolectrix gt1200 charger, capacity test video could be found at
if you want. so far evrything looks optimistic. getting to first problem...

after i tried to connect the new battery pack, chainsaw doesnt start. seems like kind of protection.

there are 2 thick wires red/black, which seems for me to be positive/negative, standard...

there are also another 2 thin cables, which i considered to be ntc temperature control, which could result in: chainsaw doesnt start problem. misleading is, they are also red and black, pointing to be positive/negative, but that should not be in case of NTC, isnt it?

so i connected standard ntc 10k probe to them, measuring about 11000ohm so probably working... unfortunatly, still cannot start the chainsaw, engine doesnt move... i checked the switch, also no problem, working fine. so these 2 thin red/black cables seems to be something else.

disasembled quickmade video for better imagination, not so quality, but may help

description on board, where these cables are connected say its: **NTC half stack V**

half stack - maybe it tries to read the half stack voltage as some kind of very basic balancing protection? not sure...

anyone has an idea?
 

oz93666

Joined Sep 7, 2010
737
The reason LifePo4 are not used in portable devices is because of their weight , about 75% heavier for same capacity ....

Failure to start may mean you haven't got the right voltage ... black and decker "36V" could mean many things , perhaps it's a 10s li-ion ... but could be 8s ... look in the pack to see how many cells in series ...

LiFePo4 has lower voltage ... so if Black and decker original battery is 10s , you may need 11s or 12s LiFePo4
 
Last edited:

Thread Starter

racmaster

Joined Feb 13, 2018
29
LiFePo4 has lower voltage ... so if Black and decker original battery is 10s , you may need 11s or 12s LiFePo4
thats not the reason, liion 18650 bats works between discharge limit 3.0v-4.2v charge limit... 10s means 30v-42v.

my lifepo pack is 12s. limits for lifepo is 2.5-3.6v/cell, thanks to so called hockey stick lifepo discharging curve 80% of capacity is between 3.0-3.5v/cell. 12x cell is 36v-43.2v max lower limit 30v. resting voltage is about 41-42v, which means both are completly inside the original liion interval....
 
Top