Any Auto Sparkies out There?

[Chlorate]

Hi all,

Well my car hasn't been particularly kind to me over the last few months - new clutch, cat converter fell off, few bits on the MOT and now some lectrickery troubles.

I noticed when driving back to Kent last weekend that having the headlights, seat heaters, stereo, wipers and rear screen demister on at the same time was causing the battery discharge light to illuminate dimly. On inspection the naff bit of wire connecting my battery positive to the rest of the car has gotten worse and appears to be limiting current draw (although no trouble starting). So replacement loom purchaced from the stealership for picking up today (£120 thieving b*stards, but it's a breakdown waiting to happen so it needs doing ASAP).

I've also just noticed that with the engine running the voltage goes up to 20v as opposed to the usual 14v...

The alternator is a year old - admittedly it's an aftermarket job.

Is this likely to be a failed voltage regulator in the alternator or the alternator acting as a current source and supplying higher voltage to maintain its output current at higher load?

Either way I need to sort this before the battery or something more expensive goes pop...

Cheers,

Alex

[Peter.N.]

Firstly I would check the accuracy of your voltmeter on another car because I can't imagine that the output of the alternator could get the voltage that high without cooking the battery and the alternator, even you had a have resistance in the battery circuit the regulator should keep it down to about 14.4. I don't think the electronics or bulbs would survive long at 20 volts either

Peter.

[Chlorate]

You raise a good point Peter. I'll pop a fresh battery in the meter over lunch and test it again...

[Chlorate]

Haha... panic over, yes the battery in my meter was a tad low and reading higher than it should.
Lesson learnt there, it's not always as bad as you think.
Cheers again.

[citronut]

i might be wrong here but i though a battery in a multi meter was not in play whilst reading voltage,

also i have seen a car charging system chucking ouyt 18 to 19 volts, although that had fried the battery beyond use

[Hell Razor5543]

Well, if it is a digital multimeter its battery will be needed to get the display working, as well as the rest of the electronics.

[Chlorate]

Some digi meters (mine included) use their internal voltage as a reference, if the battery is low it causes it to over-read.
Fresh battery in the meter and it reads 14.4v across the battery now with the car running.

[Hell Razor5543]

That would do it as well. IIRC in the past some very expensive test equipment had 2 power sources, one of which was the real power supply while the other was a very accurate reference power source, usually with a very long working life (several years). The supplier would usually stick a date label in the normal supply compartment with the date when the reference supply would need to be changed (and the unit checked for accuracy and calibration).