I was fixing a consumer electronics RF doorbell type transmitter for a friend and got a weird fault.
When it was activated the voltages went haywire and nothing seemed to make sense.
The first thing I tested was the 9v battery, this measured 8.94v which I assumed was "good enough".
When I pulled the product apart and separately powered the internal modules from my bench supply everything worked. The total device drew 12mA at 9v DC. Then when reassembled and running from the 9v battery it was all haywire again.
After an embarassingly long time checking all the voltages and trying to diagnose what was wrong I finally checked the voltage on the 9v battery when it operated! The 9v battery dropped to less than 5v!
I subsequently tested the battery with a resistor load etc and with a resistor to cause 12mA at 9v the battery voltage dropped to 5v! The battery itself was only capable of providing about 5mA of current into any load. Wow.
It was a "Battery World" brand 9v battery and my friend said it was expensive, supposed to last "5 years". I'm not sure if it was alkaline etc but it lasted less than one year and then developed this weird fault.
I've seen lots of high internal resistance faults with lead acid batteries but never before with a 9v battery. They are normally good, or flat. I wonder if the special "5 year" type of battery has some weird internal chemical makeup? There was no sign of corrosion, leakage or bulging and it measured 8.94v on the multimeter.
When it was activated the voltages went haywire and nothing seemed to make sense.
The first thing I tested was the 9v battery, this measured 8.94v which I assumed was "good enough".
When I pulled the product apart and separately powered the internal modules from my bench supply everything worked. The total device drew 12mA at 9v DC. Then when reassembled and running from the 9v battery it was all haywire again.
After an embarassingly long time checking all the voltages and trying to diagnose what was wrong I finally checked the voltage on the 9v battery when it operated! The 9v battery dropped to less than 5v!
I subsequently tested the battery with a resistor load etc and with a resistor to cause 12mA at 9v the battery voltage dropped to 5v! The battery itself was only capable of providing about 5mA of current into any load. Wow.
It was a "Battery World" brand 9v battery and my friend said it was expensive, supposed to last "5 years". I'm not sure if it was alkaline etc but it lasted less than one year and then developed this weird fault.
I've seen lots of high internal resistance faults with lead acid batteries but never before with a 9v battery. They are normally good, or flat. I wonder if the special "5 year" type of battery has some weird internal chemical makeup? There was no sign of corrosion, leakage or bulging and it measured 8.94v on the multimeter.