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Author Topic:   How to test battery draw with multimeter?
smirkless posted 09-09-2002 12:38 PM ET (US)   Profile for smirkless   Send Email to smirkless  
I seem to have a current draw on one of my batteries. I bought a multimeter to track it down but have never used one and it had no helpful instructions.

Can anyone help?

newt posted 09-09-2002 05:06 PM ET (US)     Profile for newt  Send Email to newt     
It would make sense to me that if you disconnected the positive wire at the battery and put one test lead on the battery terminal and the other test lead on the positive wire (multimeter should be set to measure volts - greater than 14 volt range), you could tell if there was an open circuit.

If you measure no voltage, then all circuits are open (no drain), and if you measure a voltage difference, then there is the possibility that something on the boat is allowing current to flow.

If your multimeter has a current (amps) function, put the test leads in the same locations, and see if there is actually current flowing. If yes, then start disconnecting power cords for your various electronics until you have no current flowing to identify the culprit.

Alternatively, disconnect both battery leads, and set the meter to measure resistance. Put one test lead on one battery lead, and the other test lead on the other battery lead. If all circuits are open, then the meter should read infinite resistance (lack of continuity - no possibility for current draw).

Hope this helps - if not one of the electrical gurus on the board could probably do better than I have!

jimh posted 09-09-2002 10:10 PM ET (US)     Profile for jimh  Send Email to jimh     
The capabilities of "multi-meters" vary all over the map. Often they do not have extensive current measuring abilities.

If you wish to measure the current being drawn from the battery, you must connect the ampmeter in series with the battery lead. Typically you would insert the meter into the positive lead.

Set the current range to the highest setting, then decrease the range as needed to obtain a measurement.

triblet posted 09-09-2002 10:58 PM ET (US)     Profile for triblet  Send Email to triblet     
What you really need is the ampmeter
function. Hook it up that way, then start
pulling fuses and disconnecting things while
somebody watches the meter (or you keep
running back to check it).

The Boston Whaler of multimeters is the
Fluke 77.


smirkless posted 09-10-2002 07:27 AM ET (US)     Profile for smirkless  Send Email to smirkless     
Thanks electrical gurus.
I will try this this weekend.


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