The 'E' Type Forum

My S1 4.2 spends its off time plugged into a battery conditioner with the battery isolated from the rest of the vehicle. On most recent 2 early year (UK) drives the ameter has shown charging the battery (1/2 deflection) for all the drive, over half hour each. Charge will drop to almost nil when idling. This is a new behavior and Ive learned to suspect changes :-)

Any thoughts on (a) is there a problem (b) steps to diagnose & rectify most welcome

Hi, how old is your battery, is it on an alternator or dynamo?

Your alternator (or generator) will charge the battery when the voltage produced by the alternator is higher than the battery voltage. A fully charged battery typically has a voltage of 12.6 to 12.8 volts. Alternators are usually set to produce 14 to 14.4 volts, but their output is rpm dependent. Your alternator is probably not at its full voltage when the engine is only at idle rpm. This is why voltmeters are more useful than ammeters.

kind regards
Marek

I would suspect the battery could be ageing. Try leaving it off the conditioner for a while, and see what the voltage drops to. Also, see how well it turns the engine over when it's been off the conditioner for a while. Even better, use a battery tester!

I use CTEK battery conditioners all the time. My original Ammeter behaved similarly to your findings with no apparent affect. I have since swapped it out for a CAERBONT supplied and period looking Voltmeter, which is more accurate.
viewtopic.php?f=3&t=16418&p=153249&hili ... er#p153249
The Lucas voltmeter is listed under the Smiths S2 section on their site:
https://www.smiths-instruments.co.uk/pr ... -series-2/

DWW wrote: ↑

Sat Mar 08, 2025 5:58 pm

Hi, how old is your battery, is it on an alternator or dynamo?

battery is probably about 5 or 6 years old and on an alternator

malcolm wrote: ↑

Sun Mar 09, 2025 10:18 am

I would suspect the battery could be ageing. Try leaving it off the conditioner for a while, and see what the voltage drops to. Also, see how well it turns the engine over when it's been off the conditioner for a while. Even better, use a battery tester!

Thanks, Ill try that and report back in a few days..........

Ok so after a week off the conditioner the battery is still showing 12.8v, will see how it starts up (or not !) during the week

Just an update, after a few weeks off the conditioner still turns and starts fine, showing 12.8v on the battery before start up. And running still shows half deflection on the ammeter when more than idle.
Am beginning to suspect the 4TR so going to replace it before it (maybe) causes damage to the battery or worse battery splits due to over charging....

I would suggest checking the alternator output voltage with the engine at speed. If this voltage is between 13.5 and 14.8, I would assume the VR is probably okay.
Tom

Yes, see what's actually going into the battery with a good multimeter.

After a short delay (caused in part by an XK120 that declined to start after 17 months parked up.....lord knows why ) ; replaced the 4TR and all good so far............

Now got 2 mobile cars for first time in a while.