# Bosch Cordless Drill GSR 12-2 Charger testing

#### bushtech

Sep 13, 2016
1,025
This drill stopped working and I discovered that the batteries were flat/not charging. Now either the batteries are history or the charger is not charging the batteries.

How do I check whether the charger is working? I get 17V AC coming out of the transformer and roughly the same in DC after the diodes, so I suspect up to there all is good.

Measuring voltage on the prongs that charge the battery I get around 5VDC there. The batteries are 12V 1.5Ah.

Here are 2 photos of the charger:

Please tell me how I can check this charger

Thank you

#### Bluejets

Oct 5, 2014
5,997
Normally there is some type of charge indicator LED. Then again if the battery is toast then the indicator will never light up. These chargers usually have a couple of protection devices and can get complicated to trace just exactly how they operate. If your battery is around 5 years old I'd be suspecting that. Can you get another battery to try as it may save a lot of time and effort?

#### bushtech

Sep 13, 2016
1,025
Thanks Bluejets. There is a green indicator light that comes on when charger is powered up, with or without battery. Bit difficult here in the bush and buying a new battery out of the question if the charger is suspect.

#### 73's de Edd

Aug 21, 2015
3,437
SIR bushtech . . . . .

Long see . . . . .no time !

WOW !
its incorporating an actual old school power transformer.

Looks like the charger is dependent upon taking that rectified 17VDC supply voltage and then using drive from the ST Controller IC that you see on the board to trigger the POWER device you see on the heat sink to give metered bursts of DC power to the battery FROM relevant current and voltage sensing info being fed to it from the charge circuitry.

Need the ID of the heat sinked power semiconductor , ALSO what surely appears to be a 16 pin DIP ST controller IC, also V& and V9 transistors, of which V9 is probably being your GREEN LED driver.

Also the voltage and capacitance value of the sole little blue electrolytic cap being seen on the board.

On this design of charger, a lot is dependent upon the actual battery proper , with it acting as an ersatz / quasi “super capacitor”.

Would you suspect this unit to be a July of 2015 manufacture or go way back to 2007 ?

If you have two batteries with it, does one of the two seem to have a decent charge left on it when doing a test with it being plugged into a drill . . . . . with a bit of torque loading by a hand grip of the chuck ?

If so, take the strongest one and go out to a vehicle and pop up the hood and do a trickle charge through a jury rigging up of test leads and clips, along with a series ~10 ohm ~10 watt current limiting resistor . . . . then . . . .checking on voltage charge build up on the battery about every hour.

Or, you could do a full overnighter charge with a 25 ohm series inserted resistor.

(FULLY CONSIDERING . . . . . that you have NOTHING in the way of a metered lab /or/ experimenter type of power supply on your bench. )

Try the then somewhat charged up battery in the charger to see how the charger responds .

Thasssssit . . . .

73’s de Edd

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#### bushtech

Sep 13, 2016
1,025
Hi St Edd

Heh, normally around lurking and learning.

Heatsinked regulator: TYN208
16 pin IC: 6HKB 0750.... 6K71217R
V8: 2N3906
V9: 2N3094
Purdy lil' blue cap: 33μf/50V

2007 vintage. Batteries showing 0V

My intelligent CTek battery charger wants nothing to do with these batteries.

Haven't got any 10W 10Ω resistors. Can I do something with 5 x 5W 1k5 resistors?

I have got the power supply referred to here: 10-17V: https://www.electronicspoint.com/threads/power-one-power-supply-mod.284923/

Thanks St Edd

#### 73's de Edd

Aug 21, 2015
3,437
Sir bushtech . . .

I think that I have that very same Power 1 block . . somewhere ? in storage .

Place it at full 17 VDC output and insert a current limiting ~5 watt 47/50 Ω resistor in series with its + output lead and connect to the battery using clip leads and check on it initially to see if the charged voltage is slowly rising by millivolts. If so, and after about 12 hours of charging, if you are lucky the charged voltage wil have risen to ~ 13VDC.
If not you must have marginal cell(s) inside and need to disassemble the case for access to test individual cells voltages.
No Bosch schematics seem to be floating around on the net, but I can read the board as using a variable pulse width driven series SCR, with voltage and current sampling feedback.
Totally useless numbering is being assigned to the 16 pin dip inline I.C.

Haven't got any 10W 10Ω resistors. Can I do something with 5 x 5W 1k5 resistors?
That feeble of a charge presented hardly overcomes batteries internal leakage loss , see what resistance Mamas electric Iron or blowdrier or some other current hog ohms out as being, in order to then utilize it as a POWER resistor.

Pee Ess . . .I got's this gut feeling of 99 86/100th's per centum . . . . .that there is being NO fault with your charger.

BOARDS BLOWUPS:

73's de Edd

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#### kellys_eye

Jun 25, 2010
5,149
Given the charger/batteries are probably ni-cad based I'd go for dud cells in the battery pack, especially if the battery was more than 2-3 years old.

If the battery pack internals are accessible via screws (and not sonic-welded) then making quick tests of each cell will quickly reveal the dud one(s).

I usually obtain three working batteries when purchasing portable tool appliances so that I always have one pack I can cannibalise to repair dud cells in the event - inevitable event - that one or more goes mammaries skywards.

PS - try measuring the battery open-circuit voltage. Unless the battery is utterly dead there is usually a voltage indication that can show whether the pack has dud cells in or not. If the battery pack is rated at 12V you should see - if only briefly - a measured 12V at the terminals.

If it is 'wrong' by any multiple of 1.2V (as each cell is such rated) then you have some duff internals.

i.e. if it's supposed to be 12V and you might only measure 10.8V (one dud cell) or 9.6V (two dud cells) etc

#### bushtech

Sep 13, 2016
1,025
Thanks Edd.

I'll have a dig around and see what I can find. Your thinking that the charger is OK carries a lot more weight than my opinion, so I'm hopeful.

Some googling turned up these guys: http://www.batteryexperts.co.za/battery-repacking/
The repacking carries a one year guarantee and I'll be in their neck of the woods in about a month, so I'll drop 2 battery packs in their grubby paws and we'll see.

#### bushtech

Sep 13, 2016
1,025
Thanks kellys_eye. These blighters are sonically welded. Heh, these are totally dead, I briefly see 0.2V

"mammaries skywards"

#### Bluejets

Oct 5, 2014
5,997
Don't know what it's like over your way but here it is hardly worth the effort.

New drill with charger and usually 2 batteries in a case (Makita or similar) can be bought for near the price of 2 replacement batteries alone.

Repacks are generally rubbish.

My Dad used to salvage my older drills and run a bit of twin cable up the end and run the old drills off a car battery. ( 7.2 volt ones used to get mobile ...9.6 volt lasted ok)

#### bushtech

Sep 13, 2016
1,025
Thanks for the heads up Bluejets. Hmmm, maybe I'll just have one repacked and see. Drill still in very good cond. so would hate to dump it.

Is it possible to break the sonic welding with a soldering iron? I have never been successful. Small blowtorch maybe? Or give it a brief 220V heat up? @davenn: please don't lock the thread because of this. I know my way around mains voltage and I'm not a hold my beer and check this move jockey.

#### kellys_eye

Jun 25, 2010
5,149
A sharp crack with a hammer on the welded joints may break it open enough to start the dismantling process. This is a 'nothing to lose' situation so go for it!

#### bushtech

Sep 13, 2016
1,025
Thanks kellys_eye. Just looking forward a bit. This is now strong current stuff, not like a torch battery. I'm sure I can get this disassembled,(my dremel or small sharp chisel) but if I get new batteries, will some good soldering be as good as the welds?

#### kellys_eye

Jun 25, 2010
5,149
It IS possible to solder directly to the replacement cells but I like to try to cut the old cells out but leave a decent amount of spot-welded tab on the one that remains in place to get at least one good soldering point! Use a HOT iron, ensure the surface to be soldered is well roughened, add some decent external flux, and do it quickly!

#### davenn

Moderator
Sep 5, 2009
14,085
New drill with charger and usually 2 batteries in a case (Makita or similar) can be bought for near the price of 2 replacement batteries alone.

Repacks are generally rubbish.

Hmmm, maybe I'll just have one repacked and see. Drill still in very good cond. so would hate to dump it.

I rebatteried my Makita battery pack ... worked an absolute treat and so much cheaper than buying at complete mew unit

As with you Bushtech, the drill itself was in excellent condition considering its 7 yr age and there was no way I was going to toss it out

re-batterying the battery pack was a no-brainer solution

Dave

#### davenn

Moderator
Sep 5, 2009
14,085
Is it possible to break the sonic welding with a soldering iron? I have never been successful. Small blowtorch maybe? Or give it a brief 220V heat up? @davenn: please don't lock the thread because of this

why do you want to nicely break the welding between batteries ?

just tear them apart .... BUT AFTER you have made good drawing of how they are connected and laid out in the pack

DO NOT just replace a single cell or two .... total waste of time

#### kellys_eye

Jun 25, 2010
5,149
The sonic welding relates to the plastic container housing the batteries (cells).

Replacing individual cells is only advised if you have an old battery to salvage the required replacements from. Purchasing a complete set of replacement cells is simply not cost-effective.

Short story - I won a battery drill in a competition some years ago and, along with a hammer (also won in a competition) and half a dozen throw-away saws, I rebuilt my house over a couple of years.

The battery drill was dropped one day and the case cracked - it soldiered on using a SS clip to hold it together but I was distraught at the damage and searched high and low for an identical one to use the casing to replace the bust one. You get 'attached' to some tools and mourn their loss unless you do something about it.

The replacement case (complete drill found on eBay) cost more than buying a new (albeit cheap) replacement drill but it was a love affair kind of thing! I STILL have the drill - it's now 6 years old and I've salvaged cells from one of the three battery packs I have to keep two batteries going strong.

One day I will eventually have to give up on it but I'm almost paranoid about keeping this one going!

#### davenn

Moderator
Sep 5, 2009
14,085
Replacing individual cells is only advised if you have an old battery to salvage the required replacements from

sorry, I cant even make sense of that comment ???

Purchasing a complete set of replacement cells is simply not cost-effective.

as I said earlier it was a very good way to go, specially from a cost perspective for my Makita ... they are a very good and reasonably pricy drill

an el-cheapo drill may be a different story

#### Bluejets

Oct 5, 2014
5,997
As I said, depends where you are I guess.
Here is a 12v Makita, charger, battery and case for $99.00 with a 3 year warranty. Battery is$40 alone.
Guess it's an individual thing to determine what is good value and what is not.
To be fair though, it is an el-cheapo Makita from China.
Ok for domestic duties. Gear we use is 6 or 7 times that.
Then again I did see the Op drill is "made in China".

https://sydneytools.com.au/makita-d...MIopiG56jE1QIVhCy9Ch0UjgxHEAQYASABEgItKfD_BwE

#### davenn

Moderator
Sep 5, 2009
14,085
As I said, depends where you are I guess.
Here is a 12v Makita, charger, battery and case for $99.00 with a 3 year warranty. Battery is$40 alone.

that's quite different to my Makita ... Guess I don't have the el-cheapo china one LOL

this is the closest I can find to my one ( the right hand one) ...

but with the charger, case and batteries of the one below

my last company bought 6 of these and when it went down the gurgler, I made sure I bought one of them out of the sale off for a cheap price

Yeah, there are drills and then there are good drills

@bushtech just needs to decide if the one he has is worth repairing/replacing the battery pack or just buy another drill

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