typical battery life?
 

Fellers,

We replaced the battery on our '92 SVX LSL soon after we bought it about 18 months ago and yesterday the battery was dead again with the car sitting in the garage at about 40 degrees F. Is there a potential drainage source that i'm not aware of? Could this be alternator related? any info appreciated.

thanks and Merry Christmas!

Tdog

The quick, down and dirty way to check for a parasitic draw is to remove a battery cable while the engine is OFF (never remove it while the engine is running, no matter what the idjit at the parts store says - it'll fry the alternator) and all accessories, ignition, lights, etc. are also OFF (don't forget that big amp for your thumpers in the trunk.) Gently touch the cable to the battery and watch for any small sparks - that will indicate a load. Beyond that, doing the same but with a voltmeter between the battery and the cable ( one lead to the battery, the other to the cable) will indicate how much voltage is being drawn. The absolute correct way to check for parasitic draw is to use an inductive low-amp clamp around a battery cable in order to see exactly how many amps (or portions of an ampere) are being drawn - should be less than .02a . Some modern cars will draw a bit more until all systems 'go to sleep', typically a few minutes, some up to 45 minutes - but that draw will be low, typically less than 1amp.

If you don't see any spark and you don't have access to a meter, check the battery with a hydrometer. One bad/weak cell will draw down the other cells. You can usually buy a hydrometer at any parts store, K-Mart, WalMart, etc. for a buck or two. Downside - if you have a sealed battery...

Don't you mean an ammeter?

Nope, a voltmeter. It will indicate how many volts are required to fulfill the load's requirement. Just don't try to start the car (or operate any other high-load devices - blower, cig lighter, etc.)while doing this, unless you want to let the smoke out of the meter...

Most parasitic draws are less than an amp or two and most ammeters would be useless at indicating that low of a current draw. I was just trying to offer up a reasonable method that would more likely be available to lightly equipped DIYers.

As a qualified electrical engineer, electronics engineer and electronics service engineer, I am trying to get my head around this one.

Voltage cannot be drawn, it is purely a potential difference. I guess you are trying to measure the voltage on a closed circuit as opposed to an open circuit, which would not give a reading.

Operating high load devices would not cause a voltmeter to smoke. It will only display the voltage, whether through components or straight across the battery.

But if you try to draw a high current load through a voltmeter would it be able to handle the load? The leads and the meter itself aren't exactly built for that. I could be wrong, I never tried it.

If there is a parasitic draw it couldn't be an open circuit, therefore there would be a differential. No draw, no differential, no reading.

How can you draw current through a voltmeter?

As para 2

If your SVX sits in the garage alot, remove the battery.

I'm assuming (and I know that's how I get into a lot of trouble...) that the voltmeter works by inductance. A small coil attached to some test leads probably isn't stout enough to carry much current.

I should have finished up with ".... no reading, no problem." 'No problem' would then equal a battery problem. Mechanics have been using the voltmeter method for years. A light bulb could also be used but if the draw is small the bulb may not illuminate. With a voltmeter a low voltage draw, such as a module not going to sleep or an analog clock with burnished contact points, would still be indicated. Watching the meter as you remove one fuse at a time would indicate the troubled circuit when the needle falls to zero. Not an absolute method with today's electronics but a handy substitute for those without access to a low amp measuring device.

I totally disagree with Larry, what if you ever have to get it out in a hurry (i.e. fire etc). Totally recommend a Battery tender if it sits. You can even have them wired in a circuit and charge all your toys at once. Only works when the battery hits 12volts and keeps it charged to 13.2. It'll even tell ya if you have a bad battery.

A voltmeter works by resistance. A very high resistor is in series, thereby allowing only a fraction of a mA to pass through the meter. This is a greatly simplified description as a modern digital meter uses electronics to achieve this effect. This idea could work on an old car with no electronics, and using an analogue voltmeter. I would not trust the results if any electronics are involved.

As current cannot flow through a voltmeter, an electronic fault is unlikely to show itself, conversely a good circuit could appear to be faulty.

The only way to be sure on a modern car is to use a low current ammeter. These tend to be rather pricey.

the extent of my practical knowledge about electricity could be written on the head of a pin - using a crayon - nonetheless, I will press ahead.

I remember a high school science lab wherein we employed a galvanometer (low current ammeter) to build both a voltmeter and an ammeter - only difference had to do with parallel vice series placement (respectively) and the use of resistors.

So, I assume Beav's use of the voltmeter in series effectively makes it an ammeter - or did I stray down the wrong road yet again?

Slightly, A low current ammeter with a F@#*ing big resistor, in parallel act like a voltmeter ;)

Ya see, that's the problem with assumptions. They're usually made with just enough information to make one dangerous. ;)With the advent of electronics in vehicles the old methods were abandoned without reasons given. This is another one of those times I wish the person(s) involved in deciding what we needed to know would have been a bit more generous.

thanks Andy, please note I did not specify the size of the pinhead encompassing my knowledge:eek: