Personal & toysCommon
Cordless vacuum
Also called stick vacuum, robot vacuum battery.
A lithium pack and a motor. The pack is why it was scrapped: one weak group, or a BMS that will not wake. The motor is usually fine.
A donor is the dead machine. The parts below are what is still worth removing from it. “Leave it” is a part that is physically in there and should stay in there: too dangerous, too worn, or only useful as part of a repair you are not doing.
The flat end is negative, the button end is positive. Nominal voltage is about 3.6 to 3.7 volts. Full, for an ordinary cell, is 4.20 volts. Below about 2.5 volts for a long time, or any swelling, means it is for recycling, not for a project. Tape the ends so a bunch of them cannot short in a drawer.
Why it is in the trash while the parts are not
It no longer holds a charge. That is the cells. A robot vacuum is the same pack story plus cliff sensors.
Before you open it
Do this while it is still unplugged, cool, and not leaking. The pack may be hot or swollen. If it is swollen, stop and recycle it. Do not puncture it to 'let the gas out'.
Where the dead machine usually is
- Home office — In the house
- Repair-shop scrap — Commercial
- Bulk trash day — Curb
Repair counters have a bin of these packs.
How it comes apart
Battery off first. Packs are often a separate cartridge.
Tools: Torx or Phillips, Meter, Tape.
Words on this page
- BMS
- Battery management board. The small circuit that cuts a lithium pack off if it is too full, too empty, or drawing too much current. It has to match the number of cells.
What to take
The table is the short version. The notes under it describe that part inside this machine, not only the general description.
| Part | Call | How many | How often | Where to look |
|---|---|---|---|---|
| Cylindrical lithium-ion cell | Prize | a pack | usually | The cartridge. |
| Battery management board | Worth pulling | 1 | usually | Inside the pack. |
| Brushless DC motor | Worth pulling | 1 | usually | The suction motor. |
| BLDC controller | Worth pulling | 1 | usually | With the motor. |
| Microswitch | Bonus | 1 | usually | Trigger. |
| Charger module | Worth pulling | 1 | usually | The dock. |
Prize
18650 or 21700, series-parallel. One group is weak.
The cartridge.
Test each group. Tape the ends as you separate them.
Mixed. Do not keep the weak group.
Worth pulling
Matched to that series count.
Inside the pack.
Only reuse it on the same count.
May be the actual fault.
High speed, on the pack voltage.
The suction motor.
Keep the controller.
Good.
Battery voltage in.
With the motor.
Keep the pair.
Good.
Matched to the pack.
The dock.
Read the label.
Good.
Bonus
Logic level into the controller.
Trigger.
Map it.
Good.