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Post by jeoff82 on Dec 16, 2021 23:50:34 GMT 1
Have a Corsa that keeps draining the battery until it will not crank over after a few days of standing. Its had 3 batteries and a new alternator. I have fully charged the newest battery and checked for a drain, after around 20 mins it is 0.004 amps on the scope. If I leave the scope on it all night and check the min/max in the morning it's still draining extremely slowly. Although if I check that fully charged battery after a night of standing it will be down to around 11.6 volts. Leave standing all day and recheck voltage, 11 volts. How is this possible?!
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Post by Rhubarb on Dec 17, 2021 0:13:28 GMT 1
Your scope is lying?
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Post by wightdiag on Dec 17, 2021 0:42:39 GMT 1
Well one battery could have an internal short, but 3 sounds highly unlikely - to check, charge and leave disconnected from the car and see if it drops over 24hrs
4mA sounds unreasonably low for a modern car - (assuming it is), so I'm with Rhubarb it's your measuring device or method that is incorrect.
Try doing a voltage drop from the negative post to a good ground on the body, set your scope to mV - with no current flowing you should see no voltage drop, if you are getting a few mV you have a current flowing (no current no drop)
If it is dropping the battery that fast it's a big leak.
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Post by jeoff82 on Dec 17, 2021 7:47:09 GMT 1
Well I thought might be my scope so I tried my multi meter and it's the same.
I also tried removing the battery and seeing if it dropped but it does not. It does not make any sense that I cannot see any current flow even though the battery is draining.
OK I'll try the voltage drop test, I know this can be done across fuses to find drains.
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Post by jeoff82 on Dec 17, 2021 7:53:50 GMT 1
As for method for checking for the drain i thought I know how to do this but I am obviously missing something. I disconnect the battery ground and attach my meter in line with the battery ground post and the ground cable. Not sure of other methods apart from the voltage drop test?
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Post by wightdiag on Dec 17, 2021 10:32:37 GMT 1
As for method for checking for the drain i thought I know how to do this but I am obviously missing something. I disconnect the battery ground and attach my meter in line with the battery ground post and the ground cable. Not sure of other methods apart from the voltage drop test? That is correct, you might need to move the meter leads depending on the meter, usually 200mA with the leads in the normal position and up to 10A in the Amps position with the switch set appropriately. What sort of scope are you using - you would need to use a DC amp clamp, unless you mean a graphing meter? If you have a fully charged 60Ah battery, 11.6v is 20% charged so you have lost 48Ah in 12 hrs that's a constant 4A drain, or 8A on and off for 50% of the time - Use your meter on the 10A position !
Yes, the idea was to treat the ground wire like a big fuse. |
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Post by chippie on Dec 17, 2021 12:32:04 GMT 1
If you still have a discharge then here's what I'd do:
Remove the battery from the car and fully charge.
Disconnect the alternator altogether, this will exonerate the alternator and associated circuitry.
Replace the battery on the car and reconnect it.
Leave overnight and see what terminal voltage you have in the morning.
After that, its a case of isolating loads by fuse removal and pinning down that which is causing the drain....
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Post by jeoff82 on Dec 17, 2021 12:36:35 GMT 1
As for method for checking for the drain i thought I know how to do this but I am obviously missing something. I disconnect the battery ground and attach my meter in line with the battery ground post and the ground cable. Not sure of other methods apart from the voltage drop test? That is correct, you might need to move the meter leads depending on the meter, usually 200mA with the leads in the normal position and up to 10A in the Amps position with the switch set appropriately. What sort of scope are you using - you would need to use a DC amp clamp, unless you mean a graphing meter? If you have a fully charged 60Ah battery, 11.6v is 20% charged so you have lost 48Ah in 12 hrs that's a constant 4A drain, or 8A on and off for 50% of the time - Use your meter on the 10A position !
Yes, the idea was to treat the ground wire like a big fuse. So I used my snap on vantage on the internal amp setting graphing scale. Now I am using a snap on multi meter incase the vantage was giving me incorrect readings but it's the same. I agree it's a big drain but it's not showing on meter which don't make any sense to me. |
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Post by rhyds on Dec 17, 2021 13:24:04 GMT 1
Silly question, but can you do a scanner/multimeter check over the course of an hour/two hours or so? My thinking is an ECM or other module (e.g radio head unit/alternator) that's floating/flapping somehow between its powered down state and its "awake" state often enough to produce a significant current draw, but not when you're actually testing it.
Also, more silly questions: do you park the car near your house and have the keys in your back pocket? I keep accidentally unlocking/locking my car from my living room, and on a Focus MK2 that keeps a fair few modules "awake"
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Post by Rhubarb on Dec 17, 2021 16:23:36 GMT 1
Disconnect the negative terminal and instead of your meter/scope use a bulb..If the bulb lights you have a drain.
Pull each fuse one at a time until the bulb goes out.
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Post by remmington on Dec 17, 2021 16:47:35 GMT 1
Disconnect the negative terminal and instead of your meter/scope use a bulb..If the bulb lights you have a drain. Pull each fuse one at a time until the bulb goes out. I got one - what a thing of beauty! - I use mine as well to load up circuits with the bulb drawing current for testing. |
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Post by jeoff82 on Dec 17, 2021 17:50:20 GMT 1
Thanks for all the advice and feedback, I have noticed that when I left it unlocked today in the workshop the battery voltage has stayed the same all day 11.86. Going to leave it in the workshop all weekend and recheck it Monday.
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Post by givusaclue on Dec 17, 2021 22:06:39 GMT 1
Can you set a voltage trigger with a long time base & hook your vantage to the mains overnight?
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Post by givusaclue on Dec 17, 2021 22:14:55 GMT 1
That is correct, you might need to move the meter leads depending on the meter, usually 200mA with the leads in the normal position and up to 10A in the Amps position with the switch set appropriately. What sort of scope are you using - you would need to use a DC amp clamp, unless you mean a graphing meter? If you have a fully charged 60Ah battery, 11.6v is 20% charged so you have lost 48Ah in 12 hrs that's a constant 4A drain, or 8A on and off for 50% of the time - Use your meter on the 10A position !
Yes, the idea was to treat the ground wire like a big fuse. So I used my snap on vantage on the internal amp setting graphing scale. Now I am using a snap on multi meter incase the vantage was giving me incorrect readings but it's the same. I agree it's a big drain but it's not showing on meter which don't make any sense to me. To amplify your readings you could loop the cable through your amp clamp a couple of times assuming you have the slack to make it stand out, just remember to divide the reading by the amount of loops for the actual figure, have you got access to a thermal camera? |
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Post by valhalla on Dec 18, 2021 1:00:48 GMT 1
Agree with all of the above, and something I would add;
It appears that you have a big current draw that only happens intermittently. If it seems to happen wherever the Corsa is parked, it is less likely to be the alarm/imob/central electrical system, but nothing can be ruled-out. However, the main consumers that are permanently connected across the battery are where you should concentrate your investigations;
As well as the alternator, the starter motor and the electric power-steering system will be permanently live, and if something is causing these to discharge the battery intermittently, the currents will be huge. To find if the current is large, use something like Remmington's "soap-on-a-rope" (bulb and leads), but instead of a bulb, use a 5A inline fuse. The theory is that you can shut the car down, making sure it is all turned-off, then connect your fuse across the battery -ve to the main ground connection point, then disconnect the battery -ve lead, so that your test-lead is now the battery cable. If your SnapOn meters are correct (there has to be a first time for everything), nothing will happen.
After leaving the car overnight, reconnect the battery -ve lead before you do anything else, then check your test-lead to see if it has blown the fuse. If it has, that confirms you have an intermittent, high-current draw, and therefore no further gain can be had by trying to measure the thing with a meter, you will need a logger.......or just isolate each of the "big consumers" in-turn overnight, and try this test with a new fuse each time until you have eliminated the problem.
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