Unexplained amp draw! - Alfa Romeo Forum
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(Post Link) post #1 of 14 Old 11-02-10 Thread Starter
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Unexplained amp draw!

Hi, long time reader, first time poster!

I've recently had my battery drain to flat overnight (on numerous occasions) even replaced the battery but same problem.
I thought it might be the diode in the alternator but no joy. There is a constant amp draw on the battery of about 10amps even without the earth being connected.
Yesterday we removed the battery and checked with an amp guage and multi-meter and it would appear that some parts of the engine are actually charged/magnetised (especially the fuse plate). The battery still drains to flat over a period of about 8 hours with nothing left on.

This has me and my mechanic completely stumped! Can anyone help/shed light/have an educated guess?!

Many thanks
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How are you measuring this draw? If the earth isn't connected then how can the battery have a load on it?
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(Post Link) post #3 of 14 Old 11-02-10 Thread Starter
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That's the exact question I've been asking myself!! Never known anything like it. I measured with a hand held analogue draw guage, connected it drew about 10amps, disconnected it varied between 2-8, not just around the battery, couldn't believe it so took it to my mechanic, he removed the battery and re-tested, his only diagnosis was that the engine is somehow charging/magnetising in certain areas, esp. the fuse plate.
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To be brutally honest, unless you are living in an area not governed by the usual laws of physics, what the mechanic said is just wrong.

What exactly did you connect to what to measure the current? Did you take the cable of either the + or - of the battery and insert the ammeter in between the battery terminal and the cable you just disconnected from it?
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Have you recently changed you in car stereo?

Had a similar problem not so long ago - diagnosed to the CD player drawing power from the battery even when it was switched off.
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(Post Link) post #6 of 14 Old 11-02-10 Thread Starter
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[email protected] mate, I am living in Devon, there are many 'usual laws' that they aren't governed by down here, such as having innapropriate relations with pets and siblings, I think physics still applies!lol

I just connected a multi-mater to the terminals with both cables attached and then the earth removed, didn't think to try testing between terminal and cable.

Someone has suggested that it could be a wire either not connected or mis-connected to the live post on the batt.

Hazey- nope, haven't changed the stereo, same unit that's been in there for 2 years!

I did have a replacement engine about 6 months back
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Quote:
Originally Posted by oisav View Post
[email protected] mate, I am living in Devon, there are many 'usual laws' that they aren't governed by down here, such as having innapropriate relations with pets and siblings, I think physics still applies!lol

I just connected a multi-mater to the terminals with both cables attached and then the earth removed, didn't think to try testing between terminal and cable.

Someone has suggested that it could be a wire either not connected or mis-connected to the live post on the batt.

Hazey- nope, haven't changed the stereo, same unit that's been in there for 2 years!

I did have a replacement engine about 6 months back

OK, if you connect a multimeter across the 2 terminals of the battery and it is set to measure voltage, it will, unsurprisingly show you the voltage, which should be around 12V.

If you do the same set to measure current (amps) then the fuse is likely to blow in your multimeter, or if it doesn't happen, it will trash it so DONT DO THAT!

Ammeters have to be connected in series, and voltmeters in parallel!

Olly.

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'There is a constant amp draw on the battery of about 10amps even without the earth being connected'

If there is nothing connected to the the battery earth then there is no possibility under the laws of physics that there is current draw. The most likely explanation is that the battery has failed, probably one plate as you are still able to charge it, and the current discharge is taking place within the battery itself. Take the battery to a reputable garage and get them to load test it. Also do you know how old the battery is?
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Quote:
Originally Posted by olly6969 View Post
OK, if you connect a multimeter across the 2 terminals of the battery and it is set to measure voltage, it will, unsurprisingly show you the voltage, which should be around 12V.

If you do the same set to measure current (amps) then the fuse is likely to blow in your multimeter, or if it doesn't happen, it will trash it so DONT DO THAT!

Ammeters have to be connected in series, and voltmeters in parallel!

Olly.

.
Exactly!

The ammeter has a very low resistance and must be connected as Olly says. I'm always having to point this out to my 6th form physics students, and do they listen? I have a pouch of spare fuses for the multi-meters ready during practicals.
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I have a similar problem with my 156. I bought the car with no stereo and finally fitted one about a month ago. Since then the car has had a slow turn over to start and if left for more than 3 days without starting it would not start. I thought the battery was at fault as there was a good level of charge from the alternator 14.5V so I assumed it was a battery problem. I bought a new Bosch one and it is doing the same thing! Maybe I am having the same problems as Hazeyblue, does anyone know how I would test for that? The cd player seems to have a problem as when I connect the steering wheel controls block to the back of the unit it locks up all the controls on the front. I thought this was a wiring problem as the guy who had it before me had a none Alfa head unit fitted.
Does anyone have any ideas about this? I can not find any wiring details on the net which might help me!
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Do you turn the head unit off using the button rather than just popping the front off? The Sony I had fitted for a while needed turning off manually, otherwise there was a drain on the battery.
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Quote:
Originally Posted by MikeyP View Post
I have a similar problem with my 156. I bought the car with no stereo and finally fitted one about a month ago. Since then the car has had a slow turn over to start and if left for more than 3 days without starting it would not start. I thought the battery was at fault as there was a good level of charge from the alternator 14.5V so I assumed it was a battery problem. I bought a new Bosch one and it is doing the same thing! Maybe I am having the same problems as Hazeyblue, does anyone know how I would test for that? The cd player seems to have a problem as when I connect the steering wheel controls block to the back of the unit it locks up all the controls on the front. I thought this was a wiring problem as the guy who had it before me had a none Alfa head unit fitted.
Does anyone have any ideas about this? I can not find any wiring details on the net which might help me!
Quote:
Originally Posted by armoore View Post
Do you turn the head unit off using the button rather than just popping the front off? The Sony I had fitted for a while needed turning off manually, otherwise there was a drain on the battery.
If you look in the ICE forum it will tell you that the alfa wiring in the stereo plugs power is opposite to most normal stereo's, I had to find this out myself took me a while. The wire which provides main power and the memory back-up wires are in the wrong position for a standard stereo and need swapping. As I said search on the ice forum and there are detailed instructions

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Renone is probably correct about the discharge being in the battery which could have shorted plates due to being fully discharged by something in the car. One problem I had once with a renault was a faulty switch on the boot which made the boot light stay on constant, which drained the battery overnight and eventually killed it I only found out because of the melted plastic smell off the bulb cover.
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SOLUTION

Main Bus A Undervolt is caused by 1 thing - Cable failure ! There is an electrical cable running between the alternator and the main Bus A interface in the engine bay (hides under a black box, and is the recommended engine jump-start point)

Wear and tear cause this wire to have internal fractures.
Solution is to make a nice big 200A wire with two spade terminals long enough to reach between Alternator + terminal and Bus A + terminal (look for red wires)

The resulting parallel connection does not void warranty, permits battery to charge properly, and saves you money and horror. Many systems will also come back from the dead.

Worth checking out - my 164 is still on its original alternator brushes, so its unlikely to need more done.
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