Auto battery drain?***TEST COMPLETED****

[Boomyal]

A thread over in 'I/O, inboard' made me think about this. When testing a car battery for continual drain, how do you differentiate between the normal continuous draw and a problem level draw on the battery. By normal continuous draw I mean all those little do dads like clocks etc. that are always drawing.

This of course is using the positive cable to positive post with a test light method.

 

[bjcsc]

Re: Auto battery drain?

Re: Auto battery drain?

When I do it, I run my DVM inline (instead of the test light) and look for a low ma draw (the do dads). To be sure, you can pull the fuses for the do dads and it should go to zero. However, a drain will usually show up in amps and not ma.

 

[Paul Moir]

Re: Auto battery drain?

Re: Auto battery drain?

That's how I do it too. 100ma will drain a typical battery flat in about 2 weeks, so it should be somewhere under that.
Use the 10 amp DC setting to check since you don't know for sure what to expect (and their are often temporary but high loads when you first make contact which may blow the meter's fuse) . This often requires you to move the red lead to a separate plug on your meter. Consult the meter's manual if this is news to you.

Don't forget to unscrew the under-hood light if so equipped.

 

[Boomyal]

Re: Auto battery drain?

Re: Auto battery drain?

Thanks guys, I'll give it a whirl. I just had to replace a less than one year old battery on my Toyota Previa so I wan't to be sure that there is not something going on that killed it.

My Radio Shack tester has a seperate, unfused, 10 amp max plug and an mA/A position on the selector switch.

Do I use the red lead to batt cable and black lead to batt?

..and do dads only draw mA's but something like a light bulb would draw A's?

 

[Xcusme]

Re: Auto battery drain?

Re: Auto battery drain?

"Do I use the red lead to batt cable and black lead to batt?
"
NOPE!!

Remove Positive Battery cable

Place meter in Amp mode (10 amps is good to be safe)

Place Red meter lead to positive battery post

Place Black meter lead to removed Positive Battery Cable end

This places the meter in Series with the battery and load(s). All current leaving the battery has to go thru the meter...

 

[Plainsman]

Re: Auto battery drain?

Re: Auto battery drain?

Good information, thank you!

 

[Boomyal]

Re: Auto battery drain?

Re: Auto battery drain?

Good information, thank you!

Ditto to that Eric. I think I will print this and put it with my meter. It won't be the first time I've learned this but sometimes things just don't stick when you don't do them very often.

 

[Reel Poor]

Re: Auto battery drain?

Re: Auto battery drain?

My Radio Shack tester has a seperate, unfused, 10 amp max plug

Your tester is most likely fused internally, usually via a fuse mounted on the ckt board.

 

[Paul Moir]

Re: Auto battery drain?

Re: Auto battery drain?

When in current reading mode, (DC or AC amps), picture your meter as a dead short like a wire joining the red probe to the black one. In fact, inside the meter there is a little calibrated wire attaching the 10A input terminal to the negative (black) one so that's precisely what it is.

A typical 10 watt illumination bulb draws about an amp (1000mA) at 12 volts.

EDIT: The 10 amp setting typically is unfused. That means no fuse whatsover.

 

[Xcusme]

Re: Auto battery drain?

Re: Auto battery drain?

One more thing to remember....

After you're done doing the current testing, be sure you set your meter BACK to Volt-Ohms settings.

Forgetting to move the cables back on the meter can cause some grief. If left in the Amps mode and you say, go to measure the battery voltage, you'll blow the Amps fuse internally. You don't want to 'Volt your Amps" The full potiential of the battery will go across the Amps fuse.......

 

[Boomyal]

Re: Auto battery drain?

Re: Auto battery drain?

One more thing to remember....

After you're done doing the current testing, be sure you set your meter BACK to Volt-Ohms settings.

Forgetting to move the cables back on the meter can cause some grief. If left in the Amps mode and you say, go to measure the battery voltage, you'll blow the Amps fuse internally. You don't want to 'Volt your Amps" The full potiential of the battery will go across the Amps fuse.......

Gotcha Xcusme. Thanks for the heads up!

 

[Boomyal]

Re: Auto battery drain?***TEST COMPLETED****

Ok, finally got a chance to do the draw test between Christmas gifts and frying the turkey.

Using the method described above, I get a 0.017 amp draw. Not being a genetic metric guy, that sounds like quite a few mA's.

I might add the the new battery has held sufficient charge to start, after sitting for three days. (hooked up)

Any opinions here?

 

[Dunaruna]

Re: Auto battery drain?***TEST COMPLETED****

[colour=blue]0.017 amps PER HOUR, that's less than half an amp per day or 2.8 amps per week. A drop in the ocean.

 

[bjcsc]

Re: Auto battery drain?***TEST COMPLETED****

What you found means you don't have a short. 17ma is nothing, Just like Dunaruna said...

 

[Boomyal]

Re: Auto battery drain?***TEST COMPLETED****

Whew! Thanks guys. That's a relief. I have a 'seething detestation' of electrical things.

 

[bjcsc]

Re: Auto battery drain?***TEST COMPLETED****

Tracking down a short indeed can take a long time. This thread is pretty complete, but the only thing I would add is what to do if you do find one. Let's say you do this and find a draw. Your next step would be to remove/replace fuses one at a time until you find the offending circuit. Then you look within that circuit until you find it. No fun...