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9v battery draw

Scott Collins

Sep 6, 2017
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Sep 6, 2017
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I have a guitar that has 2 9v batteries powering an 18v pre amp. The circuit should only be active when the cord is plugged into the input jack. The batteries keep draining even when the guitar is not in use and the cord is unplugged. How can I use a multi meter to tell if power is being drawn from the batteries even though the circuit should be open?
 

Tha fios agaibh

Aug 11, 2014
2,240
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Aug 11, 2014
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2,240
Select milliamp setting on dial and making sure lead is plugged into proper milliamp jack insert test leads into circuit between battery and the terminal that it normally contacts. In other words the meter will complete the circuit. Red lead to battery positive and black to where it normally connects (load)

You may want to check the output jack of your guitar has a normally open switch that closes when its plugged in. Metal prong may need to be bent to suit.
 

Scott Collins

Sep 6, 2017
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Sep 6, 2017
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Yes I do unplug it. Thank you for the information. I had tried it since that's what I would normally do with a car battery but my amp gauge did not register. I am now guessing I need one that has milliamp setting
 

Awesome Academy

Sep 6, 2017
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Hi Scott,

The latter half of this video shows exactly how to measure current flowing from a battery. Basically you need to splice the multimeter in series with the load you are powering (in this case the preamp). Current measurement starts at 3:31

 

Robert_fay

Jun 15, 2017
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Jun 15, 2017
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You may be able to ohm out the switch as well. If the input switch is closed while your cord is plug in and remains closed when unplugged this may tell you if that is the issue as well. Though probably not the switch you have the diagram below in the lower left shows an example schematic.
upload_2017-9-7_8-44-15.png
upload_2017-9-7_8-44-15.png
 
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