Bosch battery charger

[ljcox]

I have several Bosch battery tools that all use the same batteries & charger. I have 2 chargers, but one failed about 2 years ago & the other one failed yesterday. I therefore want to repair them. But a circuit diagram (schematic) would be helpful. I did an internet search but found nothing useful.
It is a 14.4 ~ 21.6 Volt, 1.5 A charger (see the photo). Underneath it has N153 Q061298. I searched using these numbers & found nothing.

Does anyone have a circuit for this charger? Any assistance will be appreciated

 

[simpleGuy]

1. I would open it up and check if one or more components are damaged/burnt or changed color then I would do some diagnostics with the ohmmeter while the device is turned off.
2. I would open it up and do some diagnostics with the voltmeter to find the interruption in the circuit while the device is turned on.

-simpleGuy (Trainee)

 

[Diver300]

How much does yours weigh? I've got one and I opened it to change the mains lead. I seem to remember that there was space inside for either a conventional transformer or a switch-mode power supply. Mine has a switch-mode supply, and weighs very little.

The voltage rating may tell you. If it's rated 240 V or 220 - 240 V or something like that, it's likely to be a conventional transformer. If it's rated 100 - 240 V or similar, it's going to be a switch mode power supply.

As other threads will tell you, switch-mode power supplies are difficult to fault find and repair. If one component fails, that often causes several to fail, so fixing the burned ones can just result in more burned ones. A switch mode power supply has to have a feedback signal to enable or disable the switching device, and that feedback signal has to be isolated. The feedback on a battery charger won't be a simple voltage limiter, but will take account of the state of charge of the battery, so it is even more complicated.

 

[debe]

You should have repaired the first one that failed while you had a working one to make comparisons. Bit late now.

 

[ljcox]

1. I would open it up and check if one or more components are damaged/burnt or changed color then I would do some diagnostics with the ohmmeter while the device is turned off.
2. I would open it up and do some diagnostics with the voltmeter to find the interruption in the circuit while the device is turned on.

-simpleGuy (Trainee)

Thanks for the comments, that's what I've been doing. I found some scratches across several PCB tracks & repaired them. The next step is to reassemble the unit & see if it charges.

 

[ljcox]

You should have repaired the first one that failed while you had a working one to make comparisons. Bit late now.

They look the same outside, but the PCBs are completely different.

 

[ljcox]

How much does yours weigh? I've got one and I opened it to change the mains lead. I seem to remember that there was space inside for either a conventional transformer or a switch-mode power supply. Mine has a switch-mode supply, and weighs very little.

The voltage rating may tell you. If it's rated 240 V or 220 - 240 V or something like that, it's likely to be a conventional transformer. If it's rated 100 - 240 V or similar, it's going to be a switch mode power supply.

As other threads will tell you, switch-mode power supplies are difficult to fault find and repair. If one component fails, that often causes several to fail, so fixing the burned ones can just result in more burned ones. A switch mode power supply has to have a feedback signal to enable or disable the switching device, and that feedback signal has to be isolated. The feedback on a battery charger won't be a simple voltage limiter, but will take account of the state of charge of the battery, so it is even more complicated.

Thanks for the comments. Mine has a transformer inside.

 

[Diver300]

Can you post photos of the PCBs? If one has a mains-frequency transformer it will be easier to fault-find.

 

[ljcox]

Can you post photos of the PCBs? If one has a mains-frequency transformer it will be easier to fault-find.

Thanks for your interest. They both have mains transformers. However, I've been having much difficulty in making a proper contact with the meter probes. I think it has been sprayed with some kind of lacquer. So I'll clean it with acetone & an old tooth brush. The transformer is not visible in the Charger 1 photo but the yellow & black wires going to it are visible.

 

[Les Jones]

The second board is a switch mode power supply design. the transformer is not used at mains frequency. (50 / 60 hz) It is working at several tens or hundreds of Khz.
The first board I think probably uses a normal mains transformer but if that is so I don't see the need for the 4 pin device which I assume is an opto isolator. Can you confirm that the black wires go to the transformer primary and the yellow wires go to the secondary ? What is the part number of the 4 diodes that look like they form a bridge rectifier ? Can you try to read the part numbers of all the ICs on both boards. (I can't read them on the pictures.) A picture of the transformer connected to the first board would be helpful. It would also be a great help if you trace out the schematics for the two boards so we can suggest a faultfinding approach.

Les.

 

[rjenkinsgb]

I'm guessing the transformer primary supply is controlled by a small triac and the opto provides feedback to control that, shutting down the transformer when the output load is low and the reservoir caps have adequate voltage.

 

[Diver300]

The one that I have is the same as the second one. The label starting "F-TC.." on the inductor is even at the same slight angle. The transformer in the middle runs at high frequency.

The plastic mouldings have spaces to hold what looks like a conventional transformer. The model is an AL2215CV and the instructions (here) show that there is a lower rated, but heavier, charger, the AL2204CV, that is the same size. I guess that is what charger 1 is, and that the transformer that's not shown is a conventional one.

The MOSFET on the primary side is a F3NK80Z. There is a 2n3904 transistor on the primary side in the corner of the board.

The IC in the middle is an LM324. V12 and V15 are BC546 and N2 is a TL1431

The IC in the corner seems to be a special one. It's got the ST logo, manufacturing code and country code, the same as the LM324, but the part number just seems to be 07502221

There are no components on the bottom. For a 2010 build, that's a surprise.

I don't know how much help this will all be. The're not going to be easy to fault find. The one with the conventional transformer will be easier.

There a several second hand ones on Ebay in the UK

 

[ljcox]

The second board is a switch mode power supply design. the transformer is not used at mains frequency. (50 / 60 hz) It is working at several tens or hundreds of Khz.
The first board I think probably uses a normal mains transformer but if that is so I don't see the need for the 4 pin device which I assume is an opto isolator. Can you confirm that the black wires go to the transformer primary and the yellow wires go to the secondary ? What is the part number of the 4 diodes that look like they form a bridge rectifier ? Can you try to read the part numbers of all the ICs on both boards. (I can't read them on the pictures.) A picture of the transformer connected to the first board would be helpful. It would also be a great help if you trace out the schematics for the two boards so we can suggest a faultfinding approach.

Les.

Thanks Les. Yes, you're right about the transformer in Charger 2. It is too small to be a 50 Hz. Yes, the transformer on the Charger 1 is a mains T/F. The black wires go to the primary. The diodes are 1N4007. The 8 pin IC is a dual Op Amp LM158. The 16 pin one is labelled 07502046 G402107W. I could not find any info on it by searching using either of these numbers. So it must be proprietary. I have not studied Charger 2 in any detail as I'm concentrating on Charger 1. The 4 pin IC is an opto isolator. I have been tracing the circuit & hope to finish it today. It is time consuming. I had to clean the PCB with acetone & an old toothbrush in order to be able to read the numbers on the ICs & TO-92 devices & because it was very difficult to make measurements. I think they sprayed the board with some type of lacquer. It appears to me that the control is done on the high voltage side where the current is lower - hence the opto coupler.

 

[ljcox]

I'm guessing the transformer primary supply is controlled by a small triac and the opto provides feedback to control that, shutting down the transformer when the output load is low and the reservoir caps have adequate voltage.

Thanks for the comment. Yes that is my assumption since the current is smaller on the high voltage side. I'm still tracing the circuit, so I should be able to confirm that later today.

 

[ljcox]

The one that I have is the same as the second one. The label starting "F-TC.." on the inductor is even at the same slight angle. The transformer in the middle runs at high frequency.

The plastic mouldings have spaces to hold what looks like a conventional transformer. The model is an AL2215CV and the instructions (here) show that there is a lower rated, but heavier, charger, the AL2204CV, that is the same size. I guess that is what charger 1 is, and that the transformer that's not shown is a conventional one.

The MOSFET on the primary side is a F3NK80Z. There is a 2n3904 transistor on the primary side in the corner of the board.

The IC in the middle is an LM324. V12 and V15 are BC546 and N2 is a TL1431

The IC in the corner seems to be a special one. It's got the ST logo, manufacturing code and country code, the same as the LM324, but the part number just seems to be 07502221

There are no components on the bottom. For a 2010 build, that's a surprise.

I don't know how much help this will all be. The're not going to be easy to fault find. The one with the conventional transformer will be easier.

There a several second hand ones on Ebay in the UK

Thanks for the comments. Yes, my Charger 2 is the same one, so I've saved your comments for future reference. At the moment, I'm concentrating on Charger 1 as it is smaller & simpler. It has a 50 Hz transformer rather than a switching mode power supply. I'm currently tracing the circuit & hope to be finished today. I'll then post it here.

 

[ljcox]

After much effort, I have drawn the circuit diagram.

I presume U1 is a microprocessor but I cannot find a data sheet for it. So it must be proprietary.

I found the high voltage section difficult to understand. My best guess is that on positive half cycles (where A is more positive than N) the current into C1 is set by the Opto transistor which is proportional to the current through the LED in the opto. The DIAC (E8) conducts when the C1 voltage reaches its trigger point thus triggering the TRIAC. A current therefore flows though R3, V4 & the primary of the transformer. On negative half cycles, C1 charges via D2 & C3. Again, the DIAC triggers when its trigger voltage is reached & this triggers V4. The current through R3 causes V5 to turn on which discharges C3. I don't know what the purpose of C2 is. The voltage applied to the battery is therefore adjusted by the above mentioned feedback mechanism. Any assistance will be appreciated.

 

[rjenkinsgb]

The first thing to check is, are you getting a DC supply at the rectifier output, the points you marked + and 0V?
If not, something has died in the primary control side, quite possibly the triac.

As an educated guess to the operation:
If the opto is off, C1 will charge via D2 and then do nothing.

C2, R1 and the diac / triac setup form a phase trigger like light dimmer. That will normally fire continuously, so the transformer has maximum primary supply.

If the opto starts to turn on, that will discharge C1 to some amount each cycle, which in turn will partly bypass C2, delaying or preventing C2 from charging to the diac trigger threshold before the end of the half cycle.

 

[rjenkinsgb]

After a bit more research, I suspect the MCU is probably an ST6200 series one - 16 pin types with power on pin 1 are very scarce; that fits plus the RC osc is pin 3 and pins 7/8/9/10 have analog input capability, which also matches your sketch.
(Though I think the connections around pins 5 & 6 may be messed up?)

Data:

https://www.farnell.com/datasheets/1690425.pdf

 

[Les Jones]

I have not yet worked out exactly how it works but it MAY need to see at least 5 volts from the battery to be charged before starting to work.

Les.

 

[ljcox]

The first thing to check is, are you getting a DC supply at the rectifier output, the points you marked + and 0V?
If not, something has died in the primary control side, quite possibly the triac.

As an educated guess to the operation:
If the opto is off, C1 will charge via D2 and then do nothing.

C2, R1 and the diac / triac setup form a phase trigger like light dimmer. That will normally fire continuously, so the transformer has maximum primary supply.

If the opto starts to turn on, that will discharge C1 to some amount each cycle, which in turn will partly bypass C2, delaying or preventing C2 from charging to the diac trigger threshold before the end of the half cycle.

Thanks for the replies. I measured the voltages some 3 days ago. The voltage on the + spring was 10.5 V wrt to the - or 0V spring - too low to charge an 18V battery. There was 5.1V on U1/1 & U2/8 as expected. I also checked the resistors, looked for dry joints & measured the ESR of the electrolytics. All was well. I did not check the TRIAC. I'll do that next.
If its OK, I'll check the feedback path, i.e. the Opto & the U2 operation.

Re your next post: I'll check the U1/5 & 6 connections.