Alternator/Battery gurus help please :)

-Mike-

-Mike-

-Mike-

Soldato
Joined
22 Dec 2002
Posts
10,165
Location
Minehead
I'm hoping someone can help me with this -

Just wondering if you can tell me whether my diagnosis is correct/incorrect.

Battery voltage with car left overnight between 12.01 and 12.10 = Duff battery

Resistance between alternator casing and battery negative is almost 0 = earthing between the two is ok

Car voltage with engine running all ancilleries off 14.04

Car voltage with engine running, headlamps, heater, rear demister on 13.65 .......... Alternator in reasonably good health?



Thanks :)
 
Under cranking the battery voltage drops to 7.52v according to vagcom and pretty much the same with a multimeter.

Code: 
Voltage        
12.01
7.52        <<<CRANK>>>
8.51
10.18
11.1
12.46
12.69
12.69
12.69
12.84
12.84
12.92
13.15
13.15
13.22
13.38
13.3
13.45
13.76
13.76
13.91
13.98
14.14
14.29
14.29
14.21
14.36
14.36

Time frame of the above readings is five seconds.

A flat 12v is not fine for a car battery at all. A healthy one is usually around 12.5 -12.6v

I haven't charged it off the car overnight, but its a genuine VW battery and given I have invoices for wiper blades and other small items with the car and no invoice for a battery - its possible by some miracle that its the original one.

I haven't tested resistance down the charging cable back to the battery but I can do so now and will report back :) Thanks for help SS.
 
Thanks for the reply mate -

I wouldn't know how to disable starting for cranking as its a pd tdi engine. I can go to a battery place and get a drop test done I suppose.

Why am I flapping over it - Well it starts VERY slowly as in the actual crank speed is poor and I worry it won't start when I need it to.

I've always been of the mind that prevention is better than cure and as such if I can avoid it coming to the point where it just won't start I'll be very happy. I've looked at the battery and it has VW part numbers on it and only rated at 570cca (If I've interpreted the label properly).

The battery I want to replace it with is a Bosch Silver 5 with 800CCA. I realise batteries are expensive but at £79 delivered I believe this to be good value for a battery I have had on a previous vehicle and it never let me down.
 
Again, thanks for your reply. Problem is I'd feel cheeky getting a garage to do a drop test hoping to get a battery sale and then buying it from the interwebs!

The car is right outside the house so the alarm doesn't go off and the boot light doesn't work ;) The car is driven daily pretty much and usually at least 15/20 miles so it should be getting a reasonable charge.
 
numnutz said:
All the Halfords I've ever been too can do a battery test using a handheld bosch device, I assume it's a drop tester as they input battery capacity etc and it simulates a load. If you know someone with a trade card, Halfords is good value for buying a new battery.
Click to expand...

Halfords want £120 for an 096. I can get a 110 delivered for £79. I don't know anyone with a trade card either.
 
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