Alternator fault ?

[Steven Smith]

I noticed today that for the first minute or so after starting the voltage display on the dash is showing 17 volts but then drop's down to around 14 volts.
Before I start looking for a fault just wanted to ask if this was normal, I haven't checked the accuracy of the display with a multimeter yet.
1985 C4

 

[Oneball]

It’ll drop the voltage when the battery is charged. But that does seem high so it’s worth a check. Have you got the digital dash? It might be that it’s not entirely accurate.

 

[Stingray]

As the voltage is dropping back to normal level you know the voltage regulation is working.

First step is to check all the voltage readings with a decent digital voltmeter. Check them right at the battery terminals.
How old's the battery? I'd suspect a weak battery causing the system to try to overcharge before the regulator pulls things back to normal. Just because a battery can crank the engine doesn't mean it's "good". The best test is a high current drain test at your local battery centre (or Halfords) although you can get a pretty good guide from DIY voltage checks.

Check the voltage in three different circumstances,
1. Check after the car's been left standing overnight on a mild night and before anything is switched on or the engine is started. (Use the car previous day to make sure the battery was fully charged before parking up.) A "good" battery will show at least 12.6v. Anything under 12.4v and your battery is on the slide. Below 12.3 and it's time to replace it.
2. Check again during the first minute after starting, while the dash is showing 17v.
3. Check again after the dash voltmeter has settled back to 14v.

I'll be interested to hear what you find.

If a battery is weak I don't spend money on chargers/tenders - they can't breathe new life into an old battery. Just buy a new one.

 

[Steven Smith]

As the voltage is dropping back to normal level you know the voltage regulation is working.

First step is to check all the voltage readings with a decent digital voltmeter. Check them right at the battery terminals.
How old's the battery? I'd suspect a weak battery causing the system to try to overcharge before the regulator pulls things back to normal. Just because a battery can crank the engine doesn't mean it's "good". The best test is a high current drain test at your local battery centre (or Halfords) although you can get a pretty good guide from DIY voltage checks.

Check the voltage in three different circumstances,
1. Check after the car's been left standing overnight on a mild night and before anything is switched on or the engine is started. (Use the car previous day to make sure the battery was fully charged before parking up.) A "good" battery will show at least 12.6v. Anything under 12.4v and your battery is on the slide. Below 12.3 and it's time to replace it.
2. Check again during the first minute after starting, while the dash is showing 17v.
3. Check again after the dash voltmeter has settled back to 14v.

I'll be interested to hear what you find.

If a battery is weak I don't spend money on chargers/tenders - they can't breathe new life into an old battery. Just buy a new one.

Thank you, battery at 12.59 when I got to car after being left overnight.
Dropped to 12.25 when ignition turned on
Digital dash showing 16.9 v but multimeter reading 14.84 at battery.
Dash went up to 17.8v but multimeter never went above 14.6v so I suspect it's a fault with the dashboard display.

 

[Steven Smith]

Update: after contacting Bryan Thompson at Batee.com he had the following advice "It is common for the power supply in the cluster to output less than the required 5.00 volts. The power supply is the reference for the analog gauge measurements including voltage. When the output drops, the gauges read higher than they should."

So looks like a new power supply for the digital dash is on the shopping list.