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[SOLVED] LTC4020 chip - troubleshooting

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mathar

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Hello, I am currently doing a Hardware Coop and I have been assigned to troubleshoot a battery backup board that should work for a 12V lead acid battery. Initially when I started working on the board I was getting output of around 8V. I figured out that it was configured for Li-ion batteries. So I changed the ratio of the resistors connected to the Vfb and Vfb max pin from 2.36 to 4.73. After replacing the resistors the board started to work as I wanted and was charging 12V battery. However, I notice one of the output capacitor getting really hot. After testing it for 4 hours it stopped working and now the output voltage dropped from 13.8 V to 0.8 V. I am really confused as this is my first time working with LTC4020 battery charging circuit. I would appreciate some help in troubleshooting.
 

Hi,

We can not guess how your schematic or your PCB looks like...
We don't se the parts, we can't measure voltage or current.

If you don't tell/show us these things ... it will be hard to help.

Klaus
 

This is the schematic of the board I changed the resistance R 10-R13 to configure for Lead Acid battery. The capacitor marked below is the one that is heating up.
1595282296899.png
 

Hi,

Impossible to read the texts in the schematic.

When a capacitor is getting hot then maybe because of
* wrong polarity, or
* high ripple current

Maybe due to the higher voltage the inductor gets saturated...

Klaus
 
As Klaus said, it's nearly impossible to read the component values.
Is it only the last capacitor (circled in red) that got hot? I think it's C26 with a value of 56uF, 25V. Are C24 and C25 the same value?
If it's only C26 that got hot, there's a good chance that it was defective. Have you tried replacing it?
 
Sorry, I didn't realized that it was that hard to read my bad. Yes C24 and C25 are also 56uF, 25 V. C26 was the only capacitor getting hot and I realized while doing some tests I shorted it. I removed it from the board and it's working fine now. Thanks for the help.
 

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