Problems with industrial battery chargers and optoisolators

[wolfang]

Hi I'm a freshman in the electronic workfield. I´ve been assignes to
repair a 120 V AC to 12V DC Battery charger. It got a high current
problem. I cannot locate the comparator in charge of keep the current
level, because there's no circuitry drawing. So I think the problem is
in the optoisolators. If I'm right they're used for high current
trouble handling. Theres this burning marks on the anode input
resistance wich means there is more current than is supposed to exist.
So please someone send how to test one optoisolator and what are the
mos common causes for the high current problems in battery chargers.

 

[Homer J Simpson]

Hi I'm a freshman in the electronic workfield. I´ve been assignes to
repair a 120 V AC to 12V DC Battery charger. It got a high current
problem. I cannot locate the comparator in charge of keep the current
level, because there's no circuitry drawing. So I think the problem is
in the optoisolators.

A battery charger with optoisolators?

If I'm right they're used for high current
trouble handling. Theres this burning marks on the anode input
resistance wich means there is more current than is supposed to exist.
So please someone send how to test one optoisolator and what are the
mos common causes for the high current problems in battery chargers.

Most common - shorted leads or shorted diodes.

 

[Charles Schuler]

Hi I'm a freshman in the electronic workfield. I´ve been assignes to
repair a 120 V AC to 12V DC Battery charger. It got a high current
problem. I cannot locate the comparator in charge of keep the current
level, because there's no circuitry drawing. So I think the problem is
in the optoisolators. If I'm right they're used for high current
trouble handling. Theres this burning marks on the anode input
resistance wich means there is more current than is supposed to exist.
So please someone send how to test one optoisolator and what are the
mos common causes for the high current problems in battery chargers.

Optoisolators are commonly used in switch-mode power supplies and methinks
you are in over your head.

 

[Frithiof Andreas Jensen]

Hi I'm a freshman in the electronic workfield. I´ve been assignes to
repair a 120 V AC to 12V DC Battery charger.

Mission of Doom, I.M.O:

This sounds like a switching supply so there will be LETHAL voltages on one side
of the Optocouplers, on filter capacitors, probably on heat-sinks too 'cause it
costs USD 0.000001 to insulate them e.t.c.

Did they give you a RED shirt by any chance before assigning this mission to
you??

Battery chargers are *cheap* - dump and buy new. No more than an hour of your
wages should buy a new one, so that is how much time you have to waste on it
before it becomes stupid!

So please someone send how to test one optoisolator and what are the

Measure across the LED - there should be aaabout 1.2 V if it is On (and within
the proper current range). Less than 0.8 and higher than 1.6 is dodgy.

The voltage across the transistor should be "low" if the led is On

The current transfer ratio of optocouplers decrease over time, this may cause
the loop to fail.

The current through the LED might be too high because it comes off the output
which is way too high anyway because of some other fault, this is causing the
burning but is not the real fault.

mos common causes for the high current problems in battery chargers.

Depends on what it is - if it is a switcher, the feedback loop is probably shot.

If it is a linear regulator then the series pass regulator is likely short as
well as the chip/device driving it.

 

[Rich Grise]

Battery chargers are *cheap* - dump and buy new. No more than an hour of
your wages should buy a new one...

Where the heck do you get a battery charger for fifteen bucks? ;-)

Thanks,
Rich

 

[Al]

Where the heck do you get a battery charger for fifteen bucks? ;-)

Thanks,
Rich

I got mine for free at the town's recycling center. Then again, I'm
retired ;-)

Al

 

[Homer J Simpson]

Where the heck do you get a battery charger for fifteen bucks? ;-)

http://freecycle.org/

or

http://www.craigslist.org/

--

 

[Frithiof Andreas Jensen]

Where the heck do you get a battery charger for fifteen bucks? ;-)

I collect bottles ;-)