Hi all,

Noticed yesterday wipers speeding up and slowing down on their own. Checked voltage today and it starts off at about 13.6 idling and then rises to about 14.8 all on its own and when revving goes to 16. But it's not consistent - readings on the multimeter do things like 13.8, 13.4 13.9, 14.5, 15.2. Battery has definitely been boiling and deposited sulphates on the clamp and inner wing.

I swapped for another regulator and the symptoms are the same. Cleaned up the connections to the earth by the washer bottle and not a difference.

Any ideas? I thought I'd see if I could keep the voltage down by having the lights on but that actually seemed to make it worse.

Any ideas apart from two dud regulators?

We had the alternator off a month or so ago to take the manifold off, but it seems to be fitted ok and the belt goes round and isn't too tight.

you need to look for a high resistance in the earth or anywhere in the charging circuit look for blackened copper wires where they go in to the crimps cut the old ones off clean the copper or replace the wire

are you using old resistor/mechanical try cleaning the contacts with emery paper

I've been thinking about the last things I did. Would a poor alternator earth have this effect? the long alternator fixing bolt wasn't in the best condition. I was going to redo the spade connector to the alternator but couldn't find a new one in the dark.

What about the battery / gearbox earth - is this a likely contender. I didn't check it earlier.

They're not the most likely culprits Richard, it's poor connections to the voltage regulator that cause overcharging. The way the regulation system works is that the regulator needs to be fed with the same voltage that is charging the battery, if there is a bad connection in the feed or the earth for the voltage regulator, then the resulting resistance will cause a voltage drop, and the the regulator is effectively being 'lied to' about the alternators output. So the regulator may actually be working fine, but is inadvertently over charging the battery to compensate for it's own lower voltage feed.
One of the possible sources of a bad connection/high resistance, is the fuse box. It is possible putting the lights on to make things worse. The extra current drawn by the lights lowers the voltage to the regulator even further, and if this appears to be happening then it is likely that the high resistance point is somewhere in the wiring that feeds both the lights and the regulator, which would narrow it down to a fat yellow wire between the starter motor and the bulkhead.

Right I'll look later. I did wonder if it could be the battery? It's not terribly new, but would a dead cell have this effect? It's starting fine.

Hmm - turns out battery is about 6years old. I've not got the car with me today and can't remember what size/type it's got. Is is 063?

Well I think I've fixed it. It seems that the battery earth clamp which is attached to a security theft device rather than directly to the battery terminal was only finger tight. I tightened it up and voltage is steady at 12.8 on tickover and 15.2 max on revving.

Thanks for the advice.

Richard

Isn't 15.2 volts a little on the high side? I thought about 14.7 max. How accurate is your voltmeter? Had it calibrated?

Above 14.4 volts, a lead acid battery can start 'gassing', so 14.4 was the usual 'target' alternator output voltage for regulators fitted to A series vehicles.

Not calibrated John, I thought it a touch high but both my electronic regulators are giving identical readings. And they're stable to 2DP and not fluctuating.

Could it be the battery? It was showing 12.8 before starting the car.

If both are giving the same reading maybe it is your meter over reading. Have you got access to another one to confirm?