Wierd makita battery

[SentinelAeon]

I got a bunch of non original makita batteries. Some of them have correct sense wires to all batteries to prevent overcharge. But some of them wierdly only have 1 sense wire. It's a wierd place to save money since most of the cost are the batteries themselves and this seem to make them really dangerous.

I am mostly wondering if anyone knows if this is intentional or just a bad batch. And why a single sense wire is put to the battery near the negative terminal ? If anything, i would put it near the positive terminal.

 

[Externet]

I play very often with tool battery packs, but not yet with a non-original Makita. Seems they just reference one cell for charging.
if other packs have more sensing nodes, well, it is the factory choice. Compare the packs with multiple sensing nodes if the control board is different or not.
If you have difficulty charging, suggest you safely apply 21.000 V to the + and - main terminals of the pack. Monitor its pictured single sense wire until reaches 4.2V respect to minus.

 

[SentinelAeon]

I play very often with tool battery packs, but not yet with a non-original Makita. Seems they just reference one cell for charging.
if other packs have more sensing nodes, well, it is the factory choice. Compare the packs with multiple sensing nodes if the control board is different or not.
If you have difficulty charging, suggest you safely apply 21.000 V to the + and - main terminals of the pack. Monitor its pictured single sense wire until reaches 4.2V respect to minus.

My interest is more in the way of, why include sense wires anyway if ur only gonna include one. You can just measure total voltage and divide by number of cells in series. In the meanwhile i managed to get some data and apperantly the logic is being driven by the cell near negative pole. Its still wierd, but apperantly early packs only included 1 sense wire and i couldnt find any data of lots of packs exploding. Still, if cells get unbalanced, u can get some serious over voltage to 1 or more cells. I did read about someone putting apart lots of said packs and said he never noticed any serious unbalance even after years of usage.

 

[Galgso]

My interest is more in the way of, why include sense wires anyway if ur only gonna include one. You can just measure total voltage and divide by number of cells in series. In the meanwhile i managed to get some data and apperantly the logic is being driven by the cell near negative pole. Its still wierd, but apperantly early packs only included 1 sense wire and i couldnt find any data of lots of packs exploding. Still, if cells get unbalanced, u can get some serious over voltage to 1 or more cells. I did read about someone putting apart lots of said packs and said he never noticed any serious unbalance even after years of usage.

Sounds like the tap is to get 3.7v which can go through a low dropout regulator to power 3.3v control circuitry (or power the control circuitry directly perhaps depending on the rated supply voltage of the ICs) rather than to monitor the voltage of the first cell.

 

[rjenkinsgb]

A single tap on the battery is definitely a bad design, as there is nothing to keep the cells in balance.

It will degrade and fail faster, possibly catastrophically!

 

[Diver300]

On another forum I heard that Makita packs do run some electronics from just one cell, and it does lead to discharging of that cell.

Worse, repeated attempts to charge a battery pack that has one cell low will cause the electronics to decide to brick itself.

A battery that is in that state need to have that cell charged on it's own, which need dismantling the battery.

It's a terrible design

 

[Externet]

Sounds like the tap is to get 3.7v which can go through a low dropout regulator to power 3.3v control circuitry (or power the control circuitry directly perhaps depending on the rated supply voltage of the ICs) rather than to monitor the voltage of the first cell.

I like that. We need to explore the IC datasheet on the 'single wire' pack. But what is the management board supposed to protect/balance/perform ? Just turn off the mosfet - 21V supply when level is reached/sensed where ?
Please tell us the chips for the single and for the several wire packs.