A car electrical question
28 October 2011, 05:02 PM
#1
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A car electrical question
How long roughly would it take a car battery to not hold enough charge to work the starter motor if their was a constant 12V drain on it?
I know this is a difficult question to answer but I will even accept guesstimates!
I know this is a difficult question to answer but I will even accept guesstimates!
Last edited by Jamz3k; 28 October 2011 at 05:05 PM.
28 October 2011, 05:07 PM
#3
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Yes it does.
Really the story behind the thought is that my car battery keeps dying if i dont drive it for 24hours or more. I have spent quite a bit of time testing the circuits on the car and the only one which I can see that is drawing serious power is for the aftermarket satnav at the car came with.
Really the story behind the thought is that my car battery keeps dying if i dont drive it for 24hours or more. I have spent quite a bit of time testing the circuits on the car and the only one which I can see that is drawing serious power is for the aftermarket satnav at the car came with.
28 October 2011, 05:13 PM
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2001 car - is it the original battery?
It depends on the size (amps) drain on the battery and how good the battery is in the first place and also if it is being charged effectively by the alternator - a lot of variables...also how the car is driven, if you do a lot of short journeys with he electrical toys/radio/fan, etc on then the alternator may not have the time to charge up the battery. Starting a car takes a lot out of the battery.
It depends on the size (amps) drain on the battery and how good the battery is in the first place and also if it is being charged effectively by the alternator - a lot of variables...also how the car is driven, if you do a lot of short journeys with he electrical toys/radio/fan, etc on then the alternator may not have the time to charge up the battery. Starting a car takes a lot out of the battery.
Last edited by The Zohan; 28 October 2011 at 05:16 PM.
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28 October 2011, 05:15 PM
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It could be an alternator issue, there is a quirk on certain impreza models where the battery will not charge unless the car senses a drain thus not putting extra load onto the engine creating more emissions 
The work around we have found is to drive around with the side lights on so the alternator will kick in and charge the battery.
This problem obviously only effects users who don't do a lot of night time driving.
This could be worth a try, I'd get the alternator checked out anyways just to be sure.
good luck!
The work around we have found is to drive around with the side lights on so the alternator will kick in and charge the battery.This problem obviously only effects users who don't do a lot of night time driving.
This could be worth a try, I'd get the alternator checked out anyways just to be sure.
good luck!
28 October 2011, 05:16 PM
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Thats a good point, check the condition of the battery with a hydrometer, then check what the voltage is with a multimeter, which ideally should be between 12.5 and 12.8 volts. then start the car and see what the voltage is across the terminals.
http://www.halfords.com/webapp/wcs/s...egoryId_255205
http://www.halfords.com/webapp/wcs/s...egoryId_255205
Last edited by Dedrater; 28 October 2011 at 05:19 PM.
28 October 2011, 05:21 PM
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28 October 2011, 05:34 PM
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28 October 2011, 06:12 PM
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Could just be a duff battery, even though it's relativley new, whats the voltage when it's running, should see around 14volts, if your only doing short journeys with everything on then it's not enough,and the battery is probably fooked especially if it was a velly cheep i make special price just for you 
28 October 2011, 07:19 PM
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Just 'cos the alternator is "new" doesn't mean it works. Had this a few years back on a Chevette. Alternator was dead so got a new one from Halfords. That one was duff too (it WAS duff - zero output from the alternator terminals when spinning). Some argie bargie with the branch and they reluctantly swapped it for another. That did work.
Went back and told the branch (was 5 minutes walk away) that the first one definitely was duff and they went to pick it back off the shelf (for a customer to buy) where they'd put it thinking it really was OK and it was just me. .......
Dave
Went back and told the branch (was 5 minutes walk away) that the first one definitely was duff and they went to pick it back off the shelf (for a customer to buy) where they'd put it thinking it really was OK and it was just me. .......
Dave
28 October 2011, 09:59 PM
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28 October 2011, 11:14 PM
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I would always advise checking which is the highest capacity battery ( that will fit ! ) available. Subaru "trackers" not switching to sleep mode are the usual culprit.
I have a PC in mine, that draws just enough current to ensure that the alternator gets a work out every time I drive.
dunx
I have a PC in mine, that draws just enough current to ensure that the alternator gets a work out every time I drive.
dunx
29 October 2011, 06:23 AM
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You could always fit a battery isolator until you find the current drain.
Put a multimeter in the circuit set for looking at amps, check what amps are being drawn when stood with ignition off then remove the fuses one by one and check meter after each one and note if it has gone down. Replace each fuse before removing the next so you don't get in a mess. Hopefully that will tell you what circuit the device that is sucking power is on.
Put a multimeter in the circuit set for looking at amps, check what amps are being drawn when stood with ignition off then remove the fuses one by one and check meter after each one and note if it has gone down. Replace each fuse before removing the next so you don't get in a mess. Hopefully that will tell you what circuit the device that is sucking power is on.
29 October 2011, 01:11 PM
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The rate of flattening of the battery does not rely so much on the 12v drain as the amount of current that the item is pulling from the battery.
The condition of your battery is also a factor of course, but if the battery is in good condition it should not go flat that quickly unless the item which is still connected is a pretty high current user.
You either have something with unusually heavy current use constantly connected, or your battery is knackered.
Les
29 October 2011, 01:19 PM
#24
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Good news is that the car *seemed* to spark into life a bit shaprer thismorning so I think the satnav definitely has contributed to the battery drain.
Thanks everyone who replied.
09 November 2011, 09:30 PM
#25
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Well talk about being pissed off! After thinking i had solved the riddle of the mysterious battery drain on the motor, its back with vengence.
Now that its getting colder and wetter the battery is draining quite rapidly ie. its noticeable that it aint fully charged after sitting for a night. The alternators output seems o be sweet to the beat and I also took a trip up to halfords to buy a few bits so they checked out the battery (its under 5year warranty) and it seems grand also. They use some pretty nifty bosch device to check battery so I have no reason to doubt them. I have to say it was a very different Halfords visit than usual as they were not only very helpful and polite over the phone but extremely decent when I popped in.
So summing up, it looks like I need an auto spark as i'm fooking stumped but I really think water ingress has something to do with it now, I just don't know what to do or how to fix it.
Now that its getting colder and wetter the battery is draining quite rapidly ie. its noticeable that it aint fully charged after sitting for a night. The alternators output seems o be sweet to the beat and I also took a trip up to halfords to buy a few bits so they checked out the battery (its under 5year warranty) and it seems grand also. They use some pretty nifty bosch device to check battery so I have no reason to doubt them. I have to say it was a very different Halfords visit than usual as they were not only very helpful and polite over the phone but extremely decent when I popped in.
So summing up, it looks like I need an auto spark as i'm fooking stumped but I really think water ingress has something to do with it now, I just don't know what to do or how to fix it.
09 November 2011, 11:49 PM
#26
If you want a rough figure: roughly 50% -60% of its amp hour rating is a safe figure.
So a 60 amp hour batter with a 1 amp draw would take 60 hours to get entirely flat. 50% of that would be 30hours whilst allowing more than enough juice for starting the engine*
*depending on the battery's quality, state of repair and initial state of charge.
Remember if the battery has been discharged to the point it won't start the car too regulaly or used with a state of charge below 12.4volts for a long period of time (weeks, months etc), it will permanently reduce the battery's maximum capacity (in other words it'll go flat quicker and get worse and worse). Allowing voltage to drop below 10.5volts WILL damage them irrepairably.
Also driving the car does not fully charge the battery - especially if it has gone flat, or is serverely discharged. Its a common misconception that is difficult to get across to people; That their alternator will not 100% charge their battery unless they go for a non-stop 24hour road trip. You see, even if you have a 90amp alternator...it'll happily dump in the first 50% of charge pretty quickly as the battery will readily accept current (not 90amps, as a 90amp alternator is typically rated at 90amp @6000rpm
, so tpically its dumping in a healthy 20-30amps when driving, minus any other electrical loads), But when the battery approaches 80-90% capacity its voltages and internal resistance raises making it less willing to to accept more current (unless you raise the voltage - which will cause gassing, so don't use fast chargers 
). So basically what you end up with is a 90amp alternator only feeding 1 amp into the battery. And if thats, say, a 60amp hour battery at 90% charge...it take another 6 hours of driving to bring it to 100% charge.
Seeing no mention of a battery charger has yet to have been said, I thought it was worthwhile pointing the above out.
As for battery chargers, that is another can of worms - Unless its a multi-stage charger, assume it will either undercharge or overcharge your battery.
So a 60 amp hour batter with a 1 amp draw would take 60 hours to get entirely flat. 50% of that would be 30hours whilst allowing more than enough juice for starting the engine*
*depending on the battery's quality, state of repair and initial state of charge.
Remember if the battery has been discharged to the point it won't start the car too regulaly or used with a state of charge below 12.4volts for a long period of time (weeks, months etc), it will permanently reduce the battery's maximum capacity (in other words it'll go flat quicker and get worse and worse). Allowing voltage to drop below 10.5volts WILL damage them irrepairably.
Also driving the car does not fully charge the battery - especially if it has gone flat, or is serverely discharged. Its a common misconception that is difficult to get across to people; That their alternator will not 100% charge their battery unless they go for a non-stop 24hour road trip. You see, even if you have a 90amp alternator...it'll happily dump in the first 50% of charge pretty quickly as the battery will readily accept current (not 90amps, as a 90amp alternator is typically rated at 90amp @6000rpm
, so tpically its dumping in a healthy 20-30amps when driving, minus any other electrical loads), But when the battery approaches 80-90% capacity its voltages and internal resistance raises making it less willing to to accept more current (unless you raise the voltage - which will cause gassing, so don't use fast chargers ). So basically what you end up with is a 90amp alternator only feeding 1 amp into the battery. And if thats, say, a 60amp hour battery at 90% charge...it take another 6 hours of driving to bring it to 100% charge.Seeing no mention of a battery charger has yet to have been said, I thought it was worthwhile pointing the above out.
As for battery chargers, that is another can of worms - Unless its a multi-stage charger, assume it will either undercharge or overcharge your battery.
Last edited by ALi-B; 10 November 2011 at 12:09 AM.
10 November 2011, 05:47 PM
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If your battery has been left discharged for any time then the plates may have sulphated. Or if it's a poor quality battery the plates can lose material which falls to the bottom of the case and effectively shorts some cells out. Get a good battery and find out why the sat nav is draining it. Rewire it to an ignition on circuit.
10 November 2011, 09:09 PM
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If you want a rough figure: roughly 50% -60% of its amp hour rating is a safe figure.
So a 60 amp hour batter with a 1 amp draw would take 60 hours to get entirely flat. 50% of that would be 30hours whilst allowing more than enough juice for starting the engine*
*depending on the battery's quality, state of repair and initial state of charge.
Remember if the battery has been discharged to the point it won't start the car too regulaly or used with a state of charge below 12.4volts for a long period of time (weeks, months etc), it will permanently reduce the battery's maximum capacity (in other words it'll go flat quicker and get worse and worse). Allowing voltage to drop below 10.5volts WILL damage them irrepairably.
Also driving the car does not fully charge the battery - especially if it has gone flat, or is serverely discharged. Its a common misconception that is difficult to get across to people; That their alternator will not 100% charge their battery unless they go for a non-stop 24hour road trip. You see, even if you have a 90amp alternator...it'll happily dump in the first 50% of charge pretty quickly as the battery will readily accept current (not 90amps, as a 90amp alternator is typically rated at 90amp @6000rpm, so tpically its dumping in a healthy 20-30amps when driving, minus any other electrical loads), But when the battery approaches 80-90% capacity its voltages and internal resistance raises making it less willing to to accept more current (unless you raise the voltage - which will cause gassing, so don't use fast chargers ). So basically what you end up with is a 90amp alternator only feeding 1 amp into the battery. And if thats, say, a 60amp hour battery at 90% charge...it take another 6 hours of driving to bring it to 100% charge.
Seeing no mention of a battery charger has yet to have been said, I thought it was worthwhile pointing the above out.
As for battery chargers, that is another can of worms - Unless its a multi-stage charger, assume it will either undercharge or overcharge your battery.
So a 60 amp hour batter with a 1 amp draw would take 60 hours to get entirely flat. 50% of that would be 30hours whilst allowing more than enough juice for starting the engine*
*depending on the battery's quality, state of repair and initial state of charge.
Remember if the battery has been discharged to the point it won't start the car too regulaly or used with a state of charge below 12.4volts for a long period of time (weeks, months etc), it will permanently reduce the battery's maximum capacity (in other words it'll go flat quicker and get worse and worse). Allowing voltage to drop below 10.5volts WILL damage them irrepairably.
Also driving the car does not fully charge the battery - especially if it has gone flat, or is serverely discharged. Its a common misconception that is difficult to get across to people; That their alternator will not 100% charge their battery unless they go for a non-stop 24hour road trip. You see, even if you have a 90amp alternator...it'll happily dump in the first 50% of charge pretty quickly as the battery will readily accept current (not 90amps, as a 90amp alternator is typically rated at 90amp @6000rpm
, so tpically its dumping in a healthy 20-30amps when driving, minus any other electrical loads), But when the battery approaches 80-90% capacity its voltages and internal resistance raises making it less willing to to accept more current (unless you raise the voltage - which will cause gassing, so don't use fast chargers ). So basically what you end up with is a 90amp alternator only feeding 1 amp into the battery. And if thats, say, a 60amp hour battery at 90% charge...it take another 6 hours of driving to bring it to 100% charge.Seeing no mention of a battery charger has yet to have been said, I thought it was worthwhile pointing the above out.
As for battery chargers, that is another can of worms - Unless its a multi-stage charger, assume it will either undercharge or overcharge your battery.
Oh and yes, i've used a charger on the battery but its a cheap yoke I lend off a friend.
When I was at Halfords they used this Bosch battery tester on the battery and it seemed to show that it was in fit condition? Do you know what this Bosch piece of kit is and is it accurate?