Griffith charging

[steveknowles]

HELP!! Having voltage probs with my Griff. When driving voltmeter drops to 11 volts, if you rev the nuts off it the voltage recovers to 14ish and will stay there for a while, then drop again (at night lights go dim). Thought it was the alternator/rectifier. Removed alternator and had it professionally checked, all came back okay ! Any ideas anyone ?

[steve-V8s]

Would suggest the first thing to do would be connect a decent voltmeter across the battery and see if that agrees with the dash mounted one. Could be that the voltage is actually correct but the earth connection for the dash instruments has gone high impedance so the gauge is reading incorrectly. Are the other gauges working normally ? If the supply really is hovering around 11v then I would have expected you to eventually have starting problems.

[steveknowles]

Yes, the battery eventually goes dead, so voltage drop isn't just to dash display, which is why my first port of call was the alternator

[steve-V8s]

If the alternator is working but the charge is not getting back to the battery then I guess you need to start checking the wiring between the two. On the alternator there is a thick cable that should take the charge back to the battery and a thinner cable which is the energising supply for the coil. Would suggest checking that there is a good healthy 14v at the thick wire and then trace it back to the battery to see where the voltage is disappearing. A favourite problem area, so I understand is the 100a fuse that is located in a small plastic box attached to the chassis rail under the car about in line with where your feet are, apparently the contacts corrode on this part. If there is no output from the alternator then check that the energising supply is present.

[HRG]

3V voltage drop.. Sounds like a bad cell in the battery to me.

[steve-V8s]

HRG said:

3V voltage drop.. Sounds like a bad cell in the battery to me.

Interesting idea. I guess you are thinking of one cell being short circuit, not seen that for a while. If that is the case then would expect the car to struggle to turn over on the starter.

[HRG]

Batteries fail in odd ways these days, I had one die overnight recently. No warning, no slow turnover, it just expired

It's a very easy fault find to swap the battery out and see if the problem goes away.

[Uncle Fester]

TVR had an odd habit of sometimes crimping the main wires, rather than soldering them, so check them.

Over time, water gets into the joint and dries out, gradually depositing dissolved road salt in the joint. When the engine heat causes this to expand, it cracks the terminal away from the wire. You can get odd resistances that change with moisture and temperature.

If your alternator and battery wires are poorly made like that, replace them with properly soldered joints.

If you have them out for any reason, replace them with proper ones as a precaution. If the alternator, starter and battery aren’t properly connected, you will always have troubles.

[Loubaruch]

Had an identical problem a few weeks ago, took little notice of the voltmeter dropping to 11 volts intermittently until after filling with petrol the battery failed to turn the engine. Called RAC as I was on the A1 and they concluded after testing it that the battery was completely US, seemed reasonable as it was at least 8 years old. Bought a new battery from the patrolman at great expense only for the same thing to happen again a few days later. Checked the wiring and found the main charging cable loose on the alternator. Removed cables, cleaned contacts and everything now OK with constant 13volts on the Voltmeter.
As SteveV8 says check all wiring including the large Fuse! Poor contact most likely cause.

Edited by Loubaruch on Sunday 5th October 22:51

Edited by Loubaruch on Sunday 5th October 22:53

[steveknowles]

Cheers everyone will check all suggested and let you know the result. My guess is the fuse under the floor as have had cables off alternator and all looked clean and tidy, will also have battery checked.