Help

[tibd]

Having problem with a Matti automatic car battery charger. (Matti automatic 12V, 7A)
The charger is not working. Here is the PCB and schematic view for the device.
Already checked the BT152, BC557 and TL431 and they are fine. D1,2,3 are fine too. The first VDR checked ok. As for the R11 which according to schematics is also a varistor/ thermistor (why its named R11 is a bit confusing) I'm getting very low resistance, around 57 ohms.

I attached two pic for R11 and need help identifying its properties, values and whether is really a varistor or a resistor. As you see it has two colors, brown at bottom and orange at top. There is also a small ( grayish / green ) dot as of the sec pic.

Thanks a head for help and any further ideas of further troubleshooting would be appreciated.

[tibd]

Re: Help

With some further testing R11 seems to be a NTC thermistor. But is the value of 66ohms right????.

I can see its responding to temp change but drop of resistance as temp rise (getting closer to bench light bulb).

Ant help appreciated.

[stj]

Re: Help

what exactly is wrong?
from that diagram, if you push the button in, you should get 12v at the output.
if you dont, i'd start by testing your transformer.

[tibd]

Re: Help

what exactly is wrong?
from that diagram, if you push the button in, you should get 12v at the output.
if you dont, i'd start by testing your transformer.

Well the only button is for the manual/ automatic, the on/off button here is not present.

I'm getting no reaction when bat attached for charging, no led lit. Usually the red lit first until its fully charged then green led lit.

As for the transformer, it's providing 12 and 24 v at secondaries according to attached pic. I also get 12VAC at terminal according to pic but 0v at terminal tested against each other.

What's wrong?

[stj]

Re: Help

if the red button is missing, add one - then see if pressing it in make the output turn on.
if not, your scr's are suspect.
if it does then you need to look at the transistors.

[tibd]

Re: Help

Transistor BC557c (PNP) both checked ok.
Thyristor BT152 600r , how do you test it?
TL431 is fine.

As you see the original schematic isn't mine, I downloaded it from some finish site. I think the on off button (as of its drawn in red) wasn't there from the beginning, may be its a work around as the word by the button mean "force to download" ( google ). Will try using the auto/man button and see if it works. Thanks for support.

[stj]

Re: Help

fastest way to test the scr's is to just short the colector and emiter on t2 to turn them on.

[tibd]

Re: Help

as for the BT152,
I shorted the gate with anode which turned on connection between Anode and Cathode, Is it so you mean. Here's a bit of the datasheet.

[budm]

Re: Help

This charger will not put out any Voltage unless it hooked up to the a working that still have enough Voltage to start the circuit, it is made so that if the battery Voltage is too low (bad batteries) the charger will not try to charge the batteries.
It is also pulse charging circuit, not clean DC output.
The Voltage from the good battery is used for running the circuit (T, T2, IC, etc.) to to turn on the SCR.

[stj]

Re: Help

or you jump-start it with the (missing) button.

[Agent24]

Re: Help

With some further testing R11 seems to be a NTC thermistor. But is the value of 66ohms right????.

I can see its responding to temp change but drop of resistance as temp rise (getting closer to bench light bulb).

Ant help appreciated.

It's impossible to say if the resistance is correct without checking against another, known working unit or seeing the datasheet. But it's more likely for a thermistor to fail open circuit than drift in value.

The fact that it changes at all suggests it's probably OK, and you don't know what the characteristics of it are anyway, so even if it was faulty it's not like you could do anything about it...

[stj]

Re: Help

it has nothing to do with the missing output anyway, it will just change the current and phasing slightly.

[CapLeaker]

Re: Help

Or the problem is something real simple and the wire inside the battery clamp broke off. That red jumpstart button in the diagram is not there inside the charger. It is something you can put in in order to test it. I've dug out "expensive" chargers out of the recycling that only this was the case. In any case, this charger won't do squat, unless you add that red marked button or a jumper wire like it is in the schematic, or you add a half decent battery that has more than 10.5V.

[tibd]

Re: Help

This charger will not put out any Voltage unless it hooked up to the a working that still have enough Voltage to start the circuit, it is made so that if the battery Voltage is too low (bad batteries) the charger will not try to charge the batteries.
It is also pulse charging circuit, not clean DC output.
The Voltage from the good battery is used for running the circuit (T, T2, IC, etc.) to to turn on the SCR.

Thanks everyone.

As simple as stated above the charger seems working with a bat that at least supply 11v. Turns out the battery I tested upon was almost dead.

The device working fine, no part was changed (p.s nothing was defective).

Thanks again for all help.

[budm]

Re: Help

Thanks for feedback, sometime it is good to understand how the circuit works before trying to troubleshoot the problems that are not there to begin with.