Charging, voltage and battery.

[Redfox 10]

HI all,

Having owned my Corrado G60 for a month, I came home from a drive tonight, and I turned off the engine while opening the garage.

When I wanted to start again, it just wouldn't turn the starter, I waited a little, and this time I could hear the starter spin a little slowly.

Anyway, open the hood, put a voltmeter on the battery, 9,6 Volt, and after a break - 12,05 Volt, which is of course too little

Battery is a Bosch Silver 45 Ah (came on the car), generator seems to be the 65 Ah model (ring like holes in the end type).

 

I pushed the car in, put a charger on it - wouldn't charge, so I thought okay, dead battery.

After a few minutes, I tried again, and this time my c-tek would start up and charge.

 

After two hours, I wnet out in the garage to have a look, and took the charger off. After having just been charging, the battery shows a high, but slowly falling Voltage, as normal.

Started the car first time, and this tiem the measuring of charging volt from the generator was 14,04 Volt.

Is this normal?

And upon stopping the engine, Voltage showed 12,63 Volt but slowly dropping. So continue to charge the rest of the night until early morning tomorrow.

What should be the ideal Voltage on a working battery? 12,7?

 

I cannot measure the cranking Ah and see if the battery have collapsed to some extent, as this is not possible.

Can I asume that when started the 14,04 Volt means the generator is okay, as I son't want to replace it, if it is okay?

 

How long time after a charge, should a battery rest, before having dropped to actual Voltage?

 

Can I also amuse, that no wires are bloken or defect, like bad earth for example, as the Generators output seems to be 14,04 Volt, and all electrics work as normal?

 

Other good suggestions?

 

Cheers,

Redfox ;)

[RW1 0]

14.04 volts across the battery terminals when alternator is charging is normal. Alternator is OK.

 

12.63 Volts is about what I'd expect if the battery is fully charged and is left standing for a while.

 

Ignition won't fire up if the voltage drops during engine start cranking below about 10 volts.

 

How long time after a charge, should a battery rest, before having dropped to actual Voltage?

On car very quickly within minutes.

Off car, an hour to two hours depending on the age of the battery.

 

Measure the voltage with DVM to 0.** volts across the battery earth to alternator body earth while the engine is running at normal idle and report back.

 

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[Redfox 10]

Hi RW1,

Thanks for the answer. I just came home, read it, and hurried out and started the car. Before starting I measured 12,65 Volt between + and - on battery.

Upon starting, when the idleing is around 1000 rpm's, I measure 14,3 Volt same place. After warming up, idle drops to 750 rpm's and charging is now 13,95 Volt between poles on battery.

Anyway, I also measured what you told, and between - on battery and - on the generator is 0,03 - 0,05 Volt, but it seems to fluctuate quite much, holding the testpins steady, I suddenly reads Voltage rising to 14 Volt and dropping again.

Does this mean anything?

I tried both my digital meters, and they show the same, and have fresh 9Volt batteries.

 

Q: Does this mean that the battery, a wire or the generator is faulty?

 

Cheers,

Redfox.

Edited September 2, 2011 by Redfox

[RW1 0]

Ignore the across battery voltage with the battery and with alternator running, that is as expected. The fact the battery has held 12.65volts suggests it's OK.

 

Clean up the battery connections with emery paper. Run an earth strap from the alternator body to the cylinder head (strap has eye ends, available from a motor factors). 8v's are bad for the earth between the alternator and engine block earth in earth return circuit of the alternator/battery. That voltage if its 0.05 volts is a little high. Ideally its usually around 0.02 to 0.03volts.

 

The 14volts is ????. That suggests something is not normal with the alternator. Which way round with the DVM leads. Positive on the alternator = +14volts reading? Shouldn't be happening between the earth sides of the battery and alternator. All you should be seeing on the DVM is a few millivolts as above.

 

The alternator earth side relies on the metal alternator mounting brackets to the engine and they go resistive with time. The check is the voltage drop between earths you have just done. Putting the earth strap on bypasses the resistance.

 

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Edited September 2, 2011 by RW1

[Redfox 10]

Hi, and thanks for the answer.

I have measured the battery again and now it dropped down to 12.45 volt. So I guess it had it. I cleaned up all the positive and earth points to be really clean, and put on a new battery, this time 61 Ah as VW says it have to be.

I started the car, and I measure 13,95 Volt across the battery. 12,8 when stopped.

From Battery negative to generator cover is 0,02-0,03 Volt. If I measure from battery negative to the bloe wire on the altenator is shows 13,95 Volt.

At no time (also yesterday) could I see the alternator lams light up, which it should I guess, if the alternator was faulty.

I'll report back as I find something (or not).

 

Will do the earth direct wire asap.

 

Cheers,

Redfox.

[RW1 0]

That battery voltage 12.45v confirms the battery, don't think you will find anything else but the 0.05volts originally across the earths will not have helped its charging.

 

Strap will be a good precaution. On the cylinder head sometimes there is a 10mm bolt hole between plugs 1 & 2. A short length bolt will secure the strap there but make sure it tightens up before bottoming out. Alternatively, find somewhere on the rocker cover securing points. On the alternator if its a Bosch, a nut can be treaded onto one of the 4 bolt end sticking out towards the centreline of the car to secure the strap eye. The earth strap is like the ones that earth the bonnet to the inner wings on the car.

 

Just measured my 8v Scirocco. Earth to earth reading is 0.028 volts rock steady.

13.95volts across the battery terminals with engine running.

 

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[Redfox 10]

HI all,

Just want to report back, that all seems to be fine now. Drove a few houndred yesterday and voltage etc. is good.

I guess the old battery was coming to it's end and when current was being drawn from it, it sort of failed.

 

Cheers,

Redfox.