Bosch PBM 7,2 VE Cordless Drill of 1990, Restoration & Electrical details

[Kiriakos GR]

I am getting lots of electrically dead gifts from friends these days.

Bosch PBM 7,2 VE this must be from the oldest BOSCH Cordless Drill,  this is 95% a Drill and 5% screwdriver for carpenters.
The incoming gift came with rusted drill bits head, heavily dirty, with a dead battery and no charger.

I did invest my entire Saturday evening, at restoring it and make it shine again. 
By performing electrical tests / functionality tests, I did discover several VERY interesting details about it electronics.

I am starting this presentation by demonstrating some stock pictures and in the upcoming post I will present my own gift and all details that I did discover in my lab. 

[Kiriakos GR]

Round No 2 

Lets see pictures of the real thing and details from it battery.

[Kiriakos GR]

Bosch PBM 7,2 VE: Electrical specifications

1) The yellow trigger it does offer speed control due unseen electronics.
2) The actual trigger switch this is a small factory regarding functions.
Functions
There is input voltage protection and a 9.6V battery this can not be used instead.
The circuit will block a 9V battery and the motor will simply spin as to were damaged.

There is also Voltage polarity protection.

Ni-CD Battery
The Bosch PBM 7,2 VE when this is offered in the economy carton box version, this is advertised as three hours charging ability to Full.
Single SANYO Cell this is 1200mAh and the supplied charger will deliver the 1/3 of 1200mA that is approximately 400 (353mA charger).
 
The basic charger an simple transformer, this can not use the temperature sensor for overheating protection within the battery.
 
Most users does not READ the instructions, which them inform to not leave the battery pack  continually plugged to the basic charger.
It is obvious in the specific battery pack allot of misuse    liquids inside the cell had evaporate and formed crystals in all cells.

Even so it is hard to believe but one of the six cells this looking still alive after all  these years, and a second one this is also partially alive.
A number of four of the other cells they are shorted, they are not storing any energy but they do work as wire bridge and the battery it does deliver 2.5V as is. 

I am not going to restore (rebuild) this power pack right away, but just for fun I am going to discover how much usable capacity there is left in to this HERO an 30 Years old SANYO Cell. 

Accessories
1) Drill bit head Key
2) Single end FLAT bit for flat head screws.

[giavra]

The question mark point at the photo is the left right rotation of the drill,for sure the drill deserve any try to restore it,So keep walking

[Kiriakos GR]

The question mark point at the photo is the left right rotation of the drill,for sure the drill deserve any try to restore it,So keep walking

The Bosch PBM 7,2 V this is restored, cleaned in depth and with new grease. 
But still I do hesitate about restoring the battery 7.2V, I have another two Bosch tools at 9.6V system, they are a good team.

 

[giavra]

I'm still waiting for the restoring

[Kiriakos GR]

I'm still waiting for the restoring

Spesific battery pack will be restored if there is any cell collapsing, from my greater  9.6V packs.
7.2V tools they have less rotation strengths than 9.6V.
I am no carpenter in need for such electric screwdriver