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Post by remmington on Dec 18, 2021 17:50:11 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.
I have done that with an BMW X5 - taken battery earth terminal off - and left 5A fuse in between battery earth and removed terminal - to find something has gone live overnight and blown it. I like the "soap on a rope" description - made me an old man smile LOL.Plus giveusclues - suggestion of looping and amplifying readings my maths/turns of coils - is something I have done as well. |
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Post by studabear on Dec 19, 2021 0:28:35 GMT 1
Brilliant thread this, some great pointers for fault finding, need to make me one of those bulb holders.
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Post by remmington on Dec 19, 2021 9:07:02 GMT 1
Brilliant thread this, some great pointers for fault finding, need to make me one of those bulb holders. First as Rhubarb described above.  Second = you think you have a wire or teminal with high resistance - and you drop it off for continuity with a 40ohm test ciruit on a multimeter - you get a bleep. But what you actually are doing is putting the battery of your multimeter in circuit and the multimeter makes the calculation for volt drop by ohms law - you are puting volts in the circuit but no load - no current (energy). So if you load the curcuit up with 12 volt and your bulb holder in circuit - you can measure the volt drop with a multimeter - or see the volt drop with the brightness or lack of brightness of the bulb in your bulb holder. ---------------------
Xmas is coming - Christmas crackers will be everywhere - score yourself a mini compass. Then declare it a "field coil tester" - no I am not joking - I kid you not. Magnetic compass. Is a very-very usefull tool for auto electrical diagnostics. The simple facts are: electricity causes a magnetic field when traveling thru metals. Most automotive sensors use magnetic fields. All motors use magnets. All solenoids use magnets. All "hall effect sensors" have magnets in them. All standard relays, will deflect a compass when switching. So you can test several types of automotive sensors operation without the need to disconnect the sensor.
A little home study course for you: Place a silva type compass on the positive cable on your battery, when you activate your starter you will see the compass needle deflect one way, when the starter stops pulling current and the alternator starts putting current back into the battery the compass needle will deflect 180 degrees, as the current flows in the other direction. |
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Post by remmington on Dec 19, 2021 14:46:07 GMT 1
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Post by remmington on Dec 19, 2021 14:50:58 GMT 1
Attachment DeletedYou will note: The fuse puller on the lead - check fuses no need to get a set of pliers to pull a fuse. You will note: Xmas cracker mini compass hanging of multimeter to check relays/metering solenoids. Plus proper Silvia compass - I use this allot. ------------------ Put the expensive scan tool down - along with the expensive scope - back to basics... (I am teasing now!) 
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Post by Rhubarb on Dec 19, 2021 15:13:09 GMT 1
Doesn't matter how technical vehicles get we always have to go back to basics  |
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Post by wightdiag on Dec 19, 2021 23:00:12 GMT 1
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Post by valhalla on Dec 21, 2021 0:56:16 GMT 1
Doesn't matter how technical vehicles get we always have to go back to basics I would go one step further and say;
"The more techinical vehicles get, the more necessary it is to go back to the basics, as complicated tools cannot adapt to every situation presented"
One reason why the Picoscope et-al will always reign supreme over scantools, as you are looking at the raw information, not someone's interpretation of it.
Basic electromagnetics as-shown by Remmington is definitely the way forward for most things now, especially as EV's start to come onto the scene. It won't be long before we have to diagnose motor faults by irregular flux patterns around the casing.
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Post by remmington on Dec 21, 2021 8:35:04 GMT 1
Doesn't matter how technical vehicles get we always have to go back to basics I would go one step further and say; "The more techinical vehicles get, the more necessary it is to go back to the basics, as complicated tools cannot adapt to every situation presented" One reason why the Picoscope et-al will always reign supreme over scantools, as you are looking at the raw information, not someone's interpretation of it. Basic electromagnetics as-shown by Remmington is definitely the way forward for most things now, especially as EV's start to come onto the scene. It won't be long before we have to diagnose motor faults by irregular flux patterns around the casing.
I been thinking in my simple mind - FLIR camera maybe where it is at? I shall not be gearing myself up for EV's - I will be retired - I will be needed a new greenhouse/armchair... |
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Post by wightdiag on Dec 21, 2021 10:43:36 GMT 1
Not at all sold on FLIR - all the demo's I've seen (and having used one) always seem like a "going to/got to use this because I have it" sort of thing, never seen one that resulted in a quick diagnosis that could not have ben done just as easily any other way. One issue is "known goods" - too many variables
To no-ones surprise I would love to get involved in EV's - right up my street. Unfortunately there are about a dozen on the island so not enough demand 
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Post by valhalla on Dec 22, 2021 0:32:47 GMT 1
I'm a big user of FLIR camera. I have had an E5 unit for several years now, and I wouldn't be without it.
Examples are; * Poor connections on lamp clusters (especially French, rear clusters, vans......) * Electrical discharges overnight - come back in the morning, sweep the camera over the car, see the hot-spots - there's your answer * Cooling system circulation problems * Heater developments on Defender (something I am still refining)
I have loads of happy memories and photos with the FLIR, and the customers are always very, very impressed with the reports - the E5 overlays a real outline photo with the IR image, so it looks the part.
The main thing is, it can be quicker than anything else for a first-look at an electrical issue. It doesn't always work, but then again, if it isn't warm, then it shouldn't be a problem.
I think I may have posted (some time back) a funny photo of why my Dog (at the time) could never get away with anything; I was like "Preditor" with my camera, and could see where he had been for several minutes after he had done something, especially where he had sat on the furniture in the house!
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Post by trickydicky on Dec 22, 2021 5:56:17 GMT 1
This is how I would do it
Disconnect battery (fully charged)
Connect ammeter in series between battery neg post and ground lead on 10amp scale and select min/max (to record max current)
Lock car and wait until current drops to min (0.04a in your case)
Go have lunch or come back in 24 hrs 😉
When you get back check to see what the max amp reading was to confirm you have an intermittent draw
A good meter will go into stand by after 15 mins but still save the min/max results
Along with the volt drop test across fuses I have taken to using a thermal imaging camera or infra red thermometer to quickly locate "hot spots" in fuseboxes etc.
This works very well in our current climate where cars haven't run for a while.
A scope will work with a really high quality amp clamp but cheap ones will drift and aren't ideal looking for small parasitic drains
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Post by develin on Dec 22, 2021 11:34:04 GMT 1
In our shop we have a hydrometer to test specific gravity of batteries for occasions such as this.. Due to damp weather in Ireland batteries sulfate quickly causes the electrolyte not to be able to pass through the cells properly and that can make them discharge themselves quite quickly once connected to a car, or they lose their cranking power but that would be a constant issue not intermittent
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Post by jeoff82 on Dec 23, 2021 12:51:21 GMT 1
Just to update this. I left the car in the garage last weekend unlocked and the voltage when I left it was 11.89v and when I checked it again Monday it was the same and the car started fine. I then recharged the battery to 12.8v and locked the car and within 3 days the voltage had dropped to 11.4v and refused to crank. Still no draw in amperage showing on the meter but clearly a drain. I now suspect it could be a door lock motor as only appears to drain when locked. I have recharged the battery again to 12.8v and disconnected the drivers door loom and relocked the car. Hopefully can narrow it down to this motor or door at least.
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