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Do Makita Power Tool batteries have built in over discharge?
#1

Ok so just a quick question to anybody that knows a thing or two about makita packs from disassembling them in the past to salvage cells.

Do makita battery packs have an over discharge circuit built into the battery? I know that the battery it self has BMS of some kind however i dont know what it controls in deatail. When plugged into the charger the battery charging turns off one full charge is reached to protect the cells inside from over charge. I also know that the tools stop when the batteries reach the over discharge voltage (there are also over temperature and current draw protections) however my question is for the batteries themselves.

If i where to discharge a makita battery outside one of the tools will the battery it self shut of before it kills itself or will it continue to feed power till it drops down below recovery voltage.

Im asking as i would like to use these packs to power a future project due to their conveninace and the fact i have tons of them laying around as i use them for my everyday job.


Thanks in advance.
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#2
Most drill packs have OD protection, yes. That's why you can use the drill and all of a sudden it just stops. Drop the battery in the charger even for a few minutes, and you can use the battery again for a short while.
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#3
(12-26-2018, 05:09 PM)WoodWorkStudios Wrote: I also know that the tools stop when the batteries reach the over discharge voltage (there are also over temperature and current draw protections) however my question is for the batteries themselves.

If i where to discharge a makita battery outside one of the tools will the battery it self shut of before it kills itself or will it continue to feed power till it drops down below recovery voltage.

"Bold" is the main question, isnt it ?
The answer is: Most probably yes.

( to do it electronic needs contact to all cells. But the battery has a strange connector...many contacts, so it COULD be in the machine.)
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#4
I doubt the BMS is in the tool. The pack itself probably has bms of it's own, even if dumb (basically just resistors, fets, etc to trigger at set voltages).

A lot of times, the extra pins on the battery pack is not for the "tool", but for the "charger". The charger talks to the bms on the pack and they work together to keep the pack balanced. And just because the tool may have contact pins as well, doesn't mean they are actually doing anything inside the tool.

Maybe they are grounded internally and that's what tells the bms on the pack that this is an authorized tool and turns the power on. Or, maybe there's a certain resistance between 2 pins to tell the bms it's authorized. (theories, of course)
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#5
From personal experience, tearing down tool packs:

Dewalt and Makita have the BMS/LV cut off in the tool.

Ryobi, Ridgid, Milwaukee all have a basic BMS in the battery.

The difference here is that when Dewalt and Makita switched from NIMH/NICD to Li ion they introduced a whole new line of tools tailored for the li ion batteries. The others wanted the new batteries to be reverse compatible with their old tools, so the electronics needed to be in the batteries.
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#6
Today's power tools are very complex. Aside from the BMS they actually have data pins that communicate between charger-battery and battery-tool. If the data pins don't connect, the tool does not work, even if the battery is 100% new and charged. Also, the battery won't charge if data connection is not present (so you won't be able to manually charge them unless you directly connect to a cell pair internally).

As for the power tool BMSs, in many cases, they only balance the charge, not the discharge. In the case of Makita, there is good charge balance and you can replace very easy a bad pair. Many power tools do not limit/balance the discharge because that will reduce the performance of the tool.

If you try to manually charge a Makita battery, the load balance will still work, which is good (for us). I have not tested the latest (*) models to see if data pins are needed for the charge, but on the older batteries from a few years back manual charging from any good DC source did work.

From an over-discharge p.o.v. I consider Makita batteries a bad design. Let me explain.

Inside a Makita battery there are 8 (14.4V) or 10 (18V) 18650's, and the BMS.
Here is there the  design flaw: the BMS draws power only from the first pair of cells. If you leave it sitting for a while, the BMS  will deep discharge that first cell to zero, while the others remain charged.  Result: dead battery.
If you put it in the charger, the charger will mark the battery as bad (the data pins I was mentioning) and it's unusable forever.

As a direct answer to the main issue: the batteries marked with a * (star) or yellow marking have over-heating and over-discharge protection. The non-star ones do not.

@Lucan Makitas have BMS inside the battery... since a long time ago.
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#7
All should have over-discharge protection.

The only problem with BMSs is that they can drain the battery pack flat.

While a lithium ion cell at 3,2V could stay years without self-discharging and losing capacity, one with a BMS will get drained down to 2,5V and below, which is harmful to capacity.
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