Overheating battery charger

[petehall347]

Re: Overheating battery charger

does it go into thermal shutdown ? if not thermal sensor circuit has a fault .
you might want to monitor current draw of the battery when charging unless transformer gets hot when not charging .if it does transformer might be bad .to check that disconnect secondary of transformer and test again to see if it heats up .

[cpt.charlie]

Re: Overheating battery charger

Does the battery actually takes any charge? what is the voltage of the transformer while charging?

[madan1]

Hi everyone.
Just got another "faulty" device for pennies .
This time it is a black & decker drill HP122
After some tests I was able to pinpoint the "fault".
Indeed the problem is that the battery charger is overheating, thus getting in protection mode and refusing to charge the battery after very short time.
The battery worked fine for 20-30 minutes non-stop after just 20 minutes of charging from flat, which leads me to believe that it is still OK.

Aaand back to the problem - the charger is this one https://www.partshopdirect.co.uk/bla...lights-t11441/
5100235-04
input 230V/240V~ 50hz 30W
output 15V = 1A, 15VA
red and black are the power leads for the battery
white and blue are for the thermo sensor

When powered without the battery it reads around 20V.
After about 20 minutes of charging and then kept at -10C for another 10 minutes, the transformer is so hot that it cannot be touched. The radiator with the A1757 was significantly cooler.
The D1-D5 big diodes are not shorted.
The transistors also do not "beep" on the multimeter.
The resistance on the high-voltage side of the transformer is 60Ohm ( measured on the end of the power cable ). On the low-voltage side - less than 1ohm ( measured on the pcb ).
No visual damage to the pcb or the components except for the heat discoloration on the bottom of the board.

So any ideas what could be causing the overheating?