MacAllister 36v 2.6ah / 4ah b&q batteries

[whereswally606]

I am starting this thread to pull together some knowledge about these little packs that I have gathered for myself and learnt from others.

I've been trying to make suitable mounts for these for a while and recently my friend kev came good on printing my latest design in abs 6 times for the 6 batteries I have bought.

My initial idea was to reverse engineer the mount on the charger to get a secure way of slotting them onto a bike mount, without needing to add or remove anything from the batteries so that I could just use the charger it comes with and not void any warranty.

Now I have 4 working batteries and 2 not so working ones. I tried tonight to charge some of the dead cells with a dumb cccv charger and then my intelligent cb86 charger. I managed out of the 10s cells to get 9s charged to 4.10v , the penultimate cell seems like it can't be revived and the second cell had discharged almost to zero after I double checked a few hours later.

I am wondering whether the cells 2a and 2b are really broke other whether the bms which has Nickel strip taps permanently soldered to it is causing the fast discharge or preventing the charge on the penultimate cell.

The cells probably are dead however I will check in 24 hours all the voltages again and then I will take off the bms and have another go at charging and look again at the volts after another 24hrs to see if the self discharge is as bad as with the bms attached.

My hope is that the bms is causing this as it isn't going to be easy to swap out the 4 most likely toasted cells.

As mentioned earlier I have 2 packs which have gone faulty left too long between charges and murdered by their own bms. I may try and use good cells from one to rescue the other and buy 20 single cells from nkon.nl to replenish the remaining case. Need to build my spot welding kit too.

Anyway updates to follow. Will post some pictures of my setup too.

 

[whereswally606]

Ok didn't get to do too much more with these last night. I checked the voltages, the 2nd cell was 0v and the penultimate cell was about 1.4v .

I did however iron out the issue I was having with my 3d printer inductive sensor so last night did my first 3d print of a test cube with the marlin skynet3d firmware with auto bed levelling before each print. still need to refine the z offset to get a really good first layer but it did a pretty good first print. not bad for £125 anet a8 from bang good.

 

[TwoHorsePower]

Dear All - I have a query on the macallister fast charger & hoping someone can advise.

I have a bunch of the 2.6ah 36v macallisters which i have wired in parallel via schottky diodes - This works great on my cheapo ebike conversion with only a 0.5v voltage drop across the diodes. However I am charging the batts separately/individually using the standard macallister fast charger, a charger i understand is common to both the 2.6ah and the 4ah batts.

Noticed some of the batts get quite warm when charging - The charger has the usual + & - cables from its pcb and also has a temperature sensing cable. I was trying to understand the behaviour of the charger with different batt temps & did the following wee bit of testing:

the battery uses a ntc10k thermistor - as determined by measuring resistance between the ntc and 'c-' contacts of the battery (i.e., the middle and neg contacts on the fast charger) at different ambient temps. on this basis, i expected that when the resistance dropped across the thermistor terminals, i.e., batt temp rising, the charger would be clever and reduce the charging current or voltage. Alas not, and instead some rather strange behaviour (at least to myself as a battery novice), which has me scratching my head.

when initially connecting the charger to a batt & powering it up, the charger does indeed test that the thermistor resistance is in an acceptable range and will error if it finds either a short or open circuit across the battery thermistor.

however, once it has started charging, amazingly i can short across the ntc and c- terminals, i.e., if the charger sees a zero resistance from the thermistor, it still continues to charge in fast charging mode (e.g., >2A) without reducing current or voltage. now that worried me as this suggests the charger, once charging, ignores a high temp reading from the batt. even more strangely, again once charging is already underway, if i disconnect the ntc from the charger, i.e. create an open circuit (high resistance) on the thermistor terminals, only then does the charger throw an error - quite the opposite of what i had expected.

one possible rationale for this behaviour might be that the charger is just poorly designed, & may only be intended to prevent one from charging a battery which is already hot from delivering a recent load, but once it has decided to start charging, it pays no attention to the thermistor other than to error if it detects the ntc in open circuit (the most common thermistor failure mode). another possibility is that this batch of chargers have dodgy firmware which was cooking the batts and shortening their life - might explain why B&Q sold them all off very cheaply? or maybe the bms inside the batt protects the cells and dumps the excess power when the temp is high (there is a big lump of metal bolted across 2 mosfets on the battery's bms), and perhaps the charger does not need to be so clever, but then this begs the question as to why the charger even gets to see the ntc.

thinking perhaps i'd be better 'showing' the charger a dummy 10k resistor, i.e., not the real battery thermistor, and instead having the latter sensed by a thermostat device which in turn cuts the power to the batt if the temperature goes out of acceptable range.

Any advice or comments on this gratefully received!

2HP

 

[whereswally606]

underslung Macallister B&Q battery 36v mount
View attachment 1
extreme close up

I love cable ties

 

[whereswally606]

with battery insitu

full bike in all its Heath Robinsonesque glory

My wife, husky, son and i took this bike and a Scott ransom (with the same battery mount on) out for a 5 mile test ride the other day, no complaints so far which from her indoors is a kind of compliment.

no pics taken of that unfortunately