What would happen to your battery if the electrical components were drawing too much current?

[BigToque]

My car battery keeps dying, and I'm getting the battery fully charged and having it tested for parasitic drain.

The next thing I wanted to check was the stereo system.

I've done some rough calculations and around 1/2 load, the amplifiers in my car are pulling 50A, and under max load 110A.

The thing is that I never see things like dimming lights when the system is on and running full load, so I've always thought I was alright.

Could not having a high-output alternator cause the battery to slowly drain if I'm pulling just slightly more than the alternator can keep up with?

Just by looking online it seems like the alternator is 90A.

How can you tell how much the car uses under normal driving conditions?

I'm sure my stereo is pulling roughly 50-75A under normal conditions so that leaves me 15-40A for everything else.

 

[Jeff7181]

What would happen to your battery if the electrical components were drawing too much current?

Ummm... it gets drained and dies.

 

[dpert1]

ur amps wont drain a car battery if your alternator is working properly, you need a hell of a lot of amp-age to do that (unless ur running like redic amounts of woofers). Either ur battery is on its last leg, or your alternator is bad, or you have a short somewhere. If you'd like piece of mind, grab a deep cycle battery.

 

[LTC8K6]

If your alternator can't keep up with the load, your dash light should come on to let you know.

 

[mooseracing]

If you are drawing too much of a load with the car running the Alternator will burn up first as it will constantly max itself out and get to hot trying to keep the battery full/keep up with demand.

If its happening when its off teh batt goes dead.


Take your voltmeter, set it on amps (should have at least a 20amp fuse, an dif you are drawing this much you have other issues, very unlikely.)

Take off one battery terminal, doesn't matter whether is ground or pos, i go for ground. Put one lead from voltmeter to the batt term that you unhooked, and the other to the battery lead that is unhooked. See what the draw is.

If you have ideas on what is drawing, unhook them and see how much draw change there is. I wouldn't want more than .5 amp draw on most vehicles.

 

[natto fire]

Originally posted by: mooseracing
...Take your voltmeter, set it on amps (should have at least a 20amp fuse, an dif you are drawing this much you have other issues, very unlikely.)...

I am not sure what cars you are working on, but pretty much every modern car will draw more than 20 amps very easily. Hell, just having a seat warmer on and the blower on full tilt will draw more than 20 amps, not to mention the electronics of the engine.

OP: Calculations are good and all, but you should get an inductive ammeter to determine your actual current draw. It is very hard on conventional batteries to be fully drained and then recharged. Also, keeping your alternator at full load will overheat the rectifier bridge and possibly windings as well. Just because you are not seeing voltage loss via dimming headlights and such does not mean that you are not pulling too much current from the alternator.

 

[Zenmervolt]

Originally posted by: Captain Howdy

Originally posted by: mooseracing
...Take your voltmeter, set it on amps (should have at least a 20amp fuse, an dif you are drawing this much you have other issues, very unlikely.)...

I am not sure what cars you are working on, but pretty much every modern car will draw more than 20 amps very easily. Hell, just having a seat warmer on and the blower on full tilt will draw more than 20 amps, not to mention the electronics of the engine.

Not when the engine's off.

He's talking about measuring the parasitic draw, which is measured with the car switched off completely. That should be well under 0.5 amps. On most cars, the parasitic draw should be between 10 and 50 milliamps.

ZV

 

[jtvang125]

Also unless you have some super expensive voltmeter most of the common ones can only measure up to 10 amps which a car can easily exceed.

I read awhile back in a car audio magazine that whenever your sound system exceeds the current limit on your alternator your battery does pick up the slack. However this puts tremendous stress on your alternator though and will likely burn it out very quick.

I suggest you have the whole charging system check to see if it's working optimally first. Also it wouldn't hurt to upgrade your main power cables (negative from battery to chassis of car, positive from alternator to positive on battery)

 

[JulesMaximus]

What kind of car? I had underdrive pulleys on a Mustang GT I used to have and my lights would dim at stoplights. I also typically got about 2-3 years out of a battery.

 

[mooseracing]

Originally posted by: Zenmervolt

Originally posted by: Captain Howdy

Originally posted by: mooseracing
...Take your voltmeter, set it on amps (should have at least a 20amp fuse, an dif you are drawing this much you have other issues, very unlikely.)...

I am not sure what cars you are working on, but pretty much every modern car will draw more than 20 amps very easily. Hell, just having a seat warmer on and the blower on full tilt will draw more than 20 amps, not to mention the electronics of the engine.

Not when the engine's off.

He's talking about measuring the parasitic draw, which is measured with the car switched off completely. That should be well under 0.5 amps. On most cars, the parasitic draw should be between 10 and 50 milliamps.

ZV

Yea I should have said off....I would think it would be common to know it draws more than any standard voltmeter when its on. I sometimes forget this is a comp forum and not an auto forum i am on.

Also measure to see if there is a draw across the top of the battery. I forgot to mention as batts get older when they leak they can cause a draw on them selves.

You can measure from one post to the battery top itself with a voltmeter.

 

[Zenmervolt]

Originally posted by: mooseracing

Originally posted by: Zenmervolt

Originally posted by: Captain Howdy

Originally posted by: mooseracing
...Take your voltmeter, set it on amps (should have at least a 20amp fuse, an dif you are drawing this much you have other issues, very unlikely.)...

I am not sure what cars you are working on, but pretty much every modern car will draw more than 20 amps very easily. Hell, just having a seat warmer on and the blower on full tilt will draw more than 20 amps, not to mention the electronics of the engine.

Not when the engine's off.

He's talking about measuring the parasitic draw, which is measured with the car switched off completely. That should be well under 0.5 amps. On most cars, the parasitic draw should be between 10 and 50 milliamps.

ZV

Yea I should have said off....I would think it would be common to know it draws more than any standard voltmeter when its on. I sometimes forget this is a comp forum and not an auto forum i am on.

Also measure to see if there is a draw across the top of the battery. I forgot to mention as batts get older when they leak they can cause a draw on them selves.

You can measure from one post to the battery top itself with a voltmeter.

Just to point out that you said voltmeter. We don't want someone trying to measure amps across the terminals. They'd fry their ammeter. If you're measuring across the terminals be sure to select Volts and not Amps to measure.

ZV

 

[natto fire]

Sorry, I guess the start of the post does mention parasitic drain, and the end talks about loads while the car is on. I know it should be common knowledge that cars pull more than 20 amps, but like you said, this is a computer forum. Hell, even on the car forum I frequent there was a poster trying to tell someone that the difference between a long block and short block is when the engine was made, so you never can be too sure about what is "common knowledge" anymore.

BTW, he is clearly asking two questions with this: "How can you tell how much the car uses under normal driving conditions?" so I just thought you were answering that, considering he stated he was already having it tested for parasitic drain.

Also, if a voltmeter can measure amps, it is technically a multimeter.