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Current meter

bugmenot

Mar 5, 2013
5
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Mar 5, 2013
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I'm trying to diagnose which component on my car is draining the battery. I have a Kill-a-Watt which works great for 120VAC, but this is of course 10-15VDC. Is there some sort of similar device I can buy and wire it in series with the load that will track current usage in the same way? My multimeter works fine, but I'm looking for something that I can leave plugged in for a few days rather than just doing spot checks.
 

Bluejets

Oct 5, 2014
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If you require it to log activity it could end up anexpensive piece of equipment for an off-the -shelf item. If you or anyone you know are familiar with Arduino or similar, a logging ammeter could be set up for maybe $50.
 

dorke

Jun 20, 2015
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Since an element that drains the battery is usually "constant current". you don't need a "current logger".
An Amper-meter is what you need.

Connect it in series with the battery.
important !!! don't start the engine!!! it will blow the DMM internal fuse.

Now check the current with the car switch at off,
there should be no current(actually ,very little depending on what car and equipment you have ,like alarm etc.).
If there is "meaningful" current disconnect a single fuse in the fuse-box,each time another one,
till you find the faulty circuit.

Another thing you should check is the charging of the battery.
 

kellys_eye

Jun 25, 2010
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Whatever is draining your battery is doing it 'all the time' - connect your current meter (or a clamp ammeter if you can get hold of one) and do a straightforward test.

Report back on the drain current reading (if any) as it is sometimes possible to tell (approximately) what it is that's causing it.

BTW, what make/model is your vehicle - some have known current drain issues.

Lastly, if your battery is over 5 years old then it could be the battery itself that's simply self-discharging.
 

bugmenot

Mar 5, 2013
5
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Battery is an Optima gel cell, less than 2 years old. The main suspect is a two-way radio, which I believe is pulling power when switched off, but who knows why it needs the power. Data logger would be great.
 

dorke

Jun 20, 2015
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Battery is an Optima gel cell, less than 2 years old. The main suspect is a two-way radio, which I believe is pulling power when switched off, but who knows why it needs the power. Data logger would be great.

In this case the simplest thing to do is to measure the current that the radio draws when off.
There should be none.

You can also physically disconnect the radio,and see if the battery is still drained.
 

kellys_eye

Jun 25, 2010
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Some devices have memory retention and require permanent connection to the battery. Indeed even modern factory-fitted radios will do so and require re-coding if the battery is disconnected. Our car rescue services (AA, RAC etc) now carry plug-in power packs - they fit the cigarette lighter/accessory socket - to supply power if they have to disconnect the main battery for any reason.

After-market fitted equipment....?? Who knows - although the installation manual should offer some clues.

But, as mentioned, some makes of vehicle have known and reported battery drain issues - visiting a forum dedicated to the make/model will quickly reveal such issues after a search therein.
 

Cannonball

May 6, 2017
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All the advice that you have received is good. What you really need to know is how long does it take to drain the battery. Overnight or several days. If it does it over night. Kellys-eye #5 and dorke #3 will do the trick. One other thing to check is, with one cable off. Take your volt meter and place the + lead close to the + terminal without touching it. Do the same with the - lead. If you get a voltage reading, you may need to replace the battery.
 
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