Need help fixing a charger

[cepa]

Hey there, I recently found out that my car battery lead-acid charger has died. It only outputs 6 Volts on battery clips. I decided to fix it myself. Took it apart and found relatively simple construction. Some fuses, a small circuit board, transformer, bridge rectifier and a thyristor(I believe it is one). I measured the low-voltage side of a transformer and it's 13v AC, the bridge rectifier output is 11.7 Volts, but the output of a thyristor ir only 6 volts. Is this a problem with the thyristor or the small pcb. No fuses are blown. I've attached some pictures below. The charger is Einhell BT-BC 10E, the thyristor is KP20A (it also has a 600V rating). Any help would be appreciated.

<img>http://oi44.tinypic.com/ju78cp.jpg</img>
<img>http://oi42.tinypic.com/amzeyv.jpg</img>

[PA4TIM]

Look at the 6V with a scope. It does not have to be DC or you must have a good DC+AC TRMS meter.

[youbecha]

http://www.circuitstoday.com/how-to-test-an-scr

I would test the component...

[oldway]

First, i think this is not a good design.
Losses are too high.
1.2V for the bridge rectifier
1V for the SCR
More the losses of the transformer (primary + secondary)
Some 40% losses...
The only advantage is that the SCR can be used to electronicaly protect the battery charger against wrong connection (inverted polarities).

A good design would be a triac primary control, center tapped secundary windings and schottky rectifiers.
For cost effective concern, triac primary control with simple secondary winding and bridge rectifier would still be acceptable.
I have made such modifications on low cost battery chargers, with full electronic protection against short circuits, inverted polarities, current control by primary triac drive, charging voltage limitation to protect the battery. (2 levels: 13.8V and 14.7V)

http://img4.hostingpics.net/pics/253078Prototype1.jpg
http://img4.hostingpics.net/pics/831803Prototype2.jpg
http://img4.hostingpics.net/pics/757235Prototype3.jpg
http://img4.hostingpics.net/pics/452667Prototype4.jpg
http://img4.hostingpics.net/pics/870726Prototype5.jpg
http://img4.hostingpics.net/pics/200728Prototype6.jpg

First thing i would like to ask is: are you sure your battery charger is dead?
Those battery chargers don't work without been connected with a battery.
Voltages you have measure are absolutely correct for working without battery.

What happen when you try to charge a good battery?
Have you some charging current?
What's the voltage of the battery?

SCR is for sure not faulty...

[cepa]

I don't have an o-scope to test, this would have been the first thing I tried. Tried charging a good battery(but discharged) and it didin't charge, the charge current was basically 0

[oldway]

SCR is for sure not faulty...

I have changed my mind, I am not as sure as I was...
I had a look at KP20A datasheet and it's a low end, low cost chinees brand SCR.
My experience has always be with quality brand SCR's (GE, Westinghouse, Semikron, Teccor, Ixys, AEG/Eupec, Philips, ...) and they are very reliable semiconductors.
They can be protected by ultra-fast fuses.
When they are faulty, they generally have anode/cathode short-circuited by heavy overload (fused junction by overheating).
I remember some manufacturing problems with SKT40 (too weak case) and also very rare cases of loss of sensitivity of gate of very old thyristors.

But...but....but...
This KP20A is not a known brand...
Nothing to do with my experience !
It can be a crap quality. 

Then, first short-circuits anode and cathode and see if you have a charge current.
I think it would.

Than, remove the short-circuit and measure in dc 20V range the voltage gate/cathode when the charger is working with battery.
You should measure some positive gate voltage around 2 or more volts.

If not, desconnect the gate and measure the gate/cathode resistance. You should read something between 20 and 100 ohms.
If this value is a short-circuit or open, the SCR is faulty/dead.
If the value is correct, the gate drive circuit is faulty.

If there is a positive voltage on the gate, than the SCR is faulty.

[giannishalkida]

I had the same problem with the same charger.
You transformer, rectifier and SCR is ok.
The problem is on the small pcb, the transistor which is damaged
is the one which is away from the trimmer pot (NOT the one which is next to pot...the other one). I think is 2n5551, replace it and will be ok.

it is frequent problem on these chargers, my charger has burn it 4-5 times....i dont know why.

As a solution to this i ALWAYS whenever connet OR disconnect the charger to the battery the charger is not pluged to the 220v plug.


 

[Macbeth]

I have an Einhell ELECTRONIC Batteriemaster AFEN 10, i've used for over 10 years on 3 concurrent cars.

I noticed without a load it only kicked out a low voltage, so I think that is normal. My problem was the ammeter didn't show any sign of charging. I stripped it apart and the joke of an ammeter clearly couldn't show anything because the coil was embedded in a glob of shit plastic that would catch the needle or coil if it dared to tremble. I drilled out all the burrs and shite and it now works (as in the needle moves up initially, then drops as it gets closer to full charge), however the scale is a POS and is not trusted.

As a brute force overnight battery charger, it does the job.

[gveloce]

I had the same problem with the same charger.
You transformer, rectifier and SCR is ok.
The problem is on the small pcb, the transistor which is damaged
is the one which is away from the trimmer pot (NOT the one which is next to pot...the other one). I think is 2n5551, replace it and will be ok.

it is frequent problem on these chargers, my charger has burn it 4-5 times....i dont know why.

As a solution to this i ALWAYS whenever connet OR disconnect the charger to the battery the charger is not pluged to the 220v plug.

Many thanks to giannishalkida.
Following his post I brought back to live my Einhell BC 10 E at the cost of less than half a Euro (transistor).
I know this is an old post but i would like to ask if any one has the schematics and component list for the small board in this Einhell charger as I have another one (!) that due to storage conditions (humid place) the board and components are full of rust and of course not working.
All rest seems still in good shape. Any help would be very appreciated.
many thanks in advance.
Giannis G.

[jure]

Dear friend Giannishalkida,  from Greece,

almost three years after you had published the above post I found the solution to my Einhell transformer.
That was a little bit thing for you but a great one for me at the moment.
I have just registered only to send you words of  thanksgiving.

God bless you forever!!!!!!!!!!!


PS.

My little contribution for gveloce:

[Mastahh]

Hi, I have problem that after turning it on with car battery connected ampermeter needle drops to 0

Is it ok to replace S8050 by this one "BC337-25BK, Diotec"?

[Mastahh]

Changed S8050 which is on picture nothing chnaged, still not working, it looks like Thyristor is dead.

[jakill]

Hello guys,

I have the Einhell WLGN 22 E charger with the same controls and my 'automatic' regime ceased working.
The NPN switchng the SCR is cracked and so is probably the diode (probably Zener?). The resistor on the transistor's collector is burned to ashes.
I haven't done any measurement yet, but I'd like to replace all these components and rather the other transistor as well.
I thought I might replace the components for some with higher power. What do you think about that?

I thought of the resistor for 5W,
Zener diode for 5W but I don't know the voltage. (I tried to read something from the diode and thought there might be "6V ST"?)
Transistors for 8W - 'BD139-16' (just without a heatsink)

Could anyone find out what voltage that Zener diode is, please?

Mastahh: How about trying to open the SCR manually, using a potentiometer connected to a positive output from Gretz rectifier (or across the tranistor's Collector and Emittor)? (I'd just rather try it on a discharged battery, so it won't potentially put there too high voltage)... If the SCR opens at a certain point (when decreasing the potentiometer's resistance), the SCR probably works and problem will be in the controls - same as in my case. Btw, are you sure there is a voltage at the input of the SCR?

[SeanB]

6V8 zener diode, and the resistor is a 470R resistor. The circuit is an old Elektor one, SCR car battery charger.

Couldn't find the original with a quick look, but here are some close ones.

http://www.electro-tech-online.com/attachments/scan0004-gif.26928/

http://www.circuitstoday.com/battery-charger-circuit-using-scr

http://chemelec.com/Projects/Car-Battery-Charger/Car-Battery-Charger.htm

[jakill]

6V8 zener diode, and the resistor is a 470R resistor. The circuit is an old Elektor one, SCR car battery charger.

Couldn't find the original with a quick look, but here are some close ones.

http://www.electro-tech-online.com/attachments/scan0004-gif.26928/

http://www.circuitstoday.com/battery-charger-circuit-using-scr

http://chemelec.com/Projects/Car-Battery-Charger/Car-Battery-Charger.htm

Thanks for the schematics. But how sure are you concerning those values?
I unsoldered the diode and looked at it under my primitive microscope and I clearly read there "6V2". I am just not sure whether something else can be before the 6 (may be badly printed). There is something like a bottom of letter C. When I google "C6V2", I find basically only Zener Diodes and the C letter appears to be just a tolerance category.

Concerning the burnt resistor, it appears from the cepa's pictures, it is coded as Red, Red, Black, Gold, Blue which corresponds to 22Ohm at 0.25% tolerance (only?!).
I also found this webpage(I wrote there as well) where they say it is 22Ohms.
Also, I found this description of another Einhell charger model with good pictures, where the code appears to be only Red, Red, Black, Gold. That is the same resistance but already an usual tolerance of 5%.

I believe that in cepa'c charger there only was the very precise resistor, because manufacturer got some series of it for cheaper price than the usual precision.

[jakill]

So I've replaced both the NPNs, the burnt resistor and the Zener diode, but the charger doesn't charge anyway. I am basically in the same situation as Mastahh is.
Output voltage is only 4.8V. I tried what I proposed to Mastahh (shorted the transistor over its Collector and Emittor) and the Ammeter showed a reasonable charging current, so I thought the SCR should be working well and the problem would still be on the controller board. I also though that setting of the trimmer might be incorrect as I changed the transistors and might have influenced the whole feedback sensitivity. So I tried to change its value in both directions (I didn't want to get rid of the paint locking its position for now, so I tried to connect some resistors in series and in parallel) but without any progress

I started testing the SCR as oldway proposed:

...measure in dc 20V range the voltage gate/cathode when the charger is working with battery.
You should measure some positive gate voltage around 2 or more volts.

If not, desconnect the gate and measure the gate/cathode resistance. You should read something between 20 and 100 ohms.
If this value is a short-circuit or open, the SCR is faulty/dead.
If the value is correct, the gate drive circuit is faulty.

If there is a positive voltage on the gate, than the SCR is faulty.

With following results:

C-G voltage with battery: 0.09V 
C-G (diconnected gate): 76.5 Ohm BUT in both directions!
C-G (diconnected gate): 1.21V

So I disconnected the SCR completely and measured it by the youbecha's process:

A multimeter can be used to test SCRs quite effectively. The first procedure is to check the diode action between the gate and cathode terminals of the SCR. This test is just like what you have done in the case of testing a silicon diode (see testing a silicon diode).

Now put the multimeter selector switch in a high resistance position. Connect the positive lead of multimeter to the anode of SCR and negative lead to the cathode. The multimeter will show an open circuit. Now reverse the connections and the multimeter will again show an open circuit.

Then connect the anode and gate terminals of the SCR to the positive lead of multimeter and cathode to the negative lead. The multimeter will show a low resistance indicating the switch ON of SCR. Now carefully remove the gate terminal from the anode and again the multimeter will show a low resistance reading indicating the latching condition. Here the multimeter battery supplies the holding current for the triac. If all of the above tests are positive we can assume the SCR to be working fine.

With following results:

C-G as diode: 76.5 Ohm BUT in both directions! Same results when measured in multimeter's Diode mode
A-C: open circuit in both directions 
A-C+G: 76.5 Ohm BUT not latching when I disconnected the gate.  Although I am not sure whether the current from multimeter is enough for it. I tried to connect my primitive analog multimeter and it didn't even move the needle at the range of 0.5mA!

I decided that I'll buy a new BT152 SCR for testing and if the test shows that really the SCR was wrong, I will buy a more powerful one.
I found SKT24/12 for 'only' 5.1USD.

Does anyone have any thoughts meanwhile?
Do you think that 40TPS16 SCR might be satisfactory? I found it in a local store for only 4USD...

[jakill]

So I bought the BT152 mentioned previously. Before I installed it, I did the same measurement as with the original SCR, but it behaved completely the same way.
After installation, the charger still doesn't work

I've already even checked resistances of the resistors by their color stripe codes and all are corresponding. The only things that might be wrong, are those two ceramic capacitors. I have no idea how possibly could have they get broken as I assume them to be rated for at least 50V and no connection to any inductive load...

[Mastahh]

Checked all resistors with colors marks all are ok, checked Tyristor KP20A also ok

[jakill]

I got the capacitors measured, were OK, so I asked for some time with a scope and we found a total rookie mistake 
I had incorrectly read the transistor pinout and flipped Base with Emmitor 
After I fixed the flipped connections, everything started working 
Now I'll just need to tune the feedback trimmer.

[dariocdj]

Hi everybody. I have a couple of AFEN10 charger, and thanks to your post i've fixed one changing S8050 transistor.

Now the other one doesn't charge anymore and i've changed the transistor and tested the circuit conductivity. resistor seems to be good and zener too.

Can be the scr ? I've tried to test with conductivity between G and K and between A and K and seems to be faulty !!! i'm not sure because i'm a newbie

Exit Voltage is about 1,7v ! (not 6v like the other that i've fixed).

Ah... V out from transformator is 11,7v....

Do you have any experience of scr faulty on this charger ?

Thanks
Dario

[skarmoutsosv]

Einhell AFEN10 Pb charger (produced at 2007)
Reversed engineering schemetic and some PCB photos.

[Pluribus]

I have an Einhell AFEN-10 battery charger. Its output (charging) voltage has been about 14,0 V, so a battery being connected to it for a longer time would not harm the battery.

Some time ago I noticed that the (charging) output was about 14,6 V, so it seems that the output had increased without a cause. There is a trimmer to set the output. It was locked into the middle position, so I broke the (paint) locking and turned the trimmer clockwise. The idle voltage decreased. It can be changed between 10,3 – 10,9 V. It was earlier about 10 V (trimmer in middle position).

When I connected the charger to the battery, the charging voltage seemed to be increased even more and was about 14,5 V. This is the minimum value. Turning the trimmer counterclockwise the output goes over 15 V. The voltage over the zener is 5,3 V.

What is wrong with the charger?