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EEVblog 1449 - What Causes Excess Battery Drain? (BM235)

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EEVblog:
A BM235 customer has a BM235 that drains the batteries in OFF switch mode, lets look at the PCB to find out the possible culprits. Potentially applicable to any battery powered product.

Old Fart Analog Engineer:
Most likely that "giant plastic water pipe" overflowed with some liquid (probably sugary) and deposited and dried on those capacitors causing the excess leakage current.  Even more likely the dried conductive residue is on the function switch.  Take it Apart, Clean it off, Dry it and Robert is one of your parents sibling!  😉

ormaaj:
Any way the diodes could become forward biased? You've got diodes, inductors, caps, and a switch - the ingredients for a momentary impulse current.

I don't actually know whether a diode can quickly degrade from a momentary surge through a mechanism other than junction overheating. Unlikely for a diode that size. The MLCCs are certainly very suspect.

rob77:
actually i had a similar issue with high current draw of a different brymen meter here...

https://www.eevblog.com/forum/testgear/brymen-bm869s-rejecting-fresh-9v-batteries/msg959057/#msg959057

G7PSK:
I had a digital tyre inflator /pressure gauge that used a coin cell, right out of the box it drained the battery over night and did several new batteries the same so I contacted PCL who made or sold them and they just sent me a new one. Having been told I could bin or do whatever I wanted with the first one I took it apart and had a look at the board , first thing that caught my eye was a big fat ceramic capacitor right across the battery so I removed it and not having a replacement I put the board back in and the gauge worked perfectly and the coin cell is still working the unit two years later. Not sure why the designers thought the cell needed a bypass cap. when the microchip had several of its own. Excessive battery drain is often down to leaky by pass capacitors and always worth a look if you have that type of trouble. 

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