Pride came before a fall. Advice please.

[Bandit1200]

With such a beautiful day I took the Stag on a planned 100 mile round trip through the Shropshire hills. Leaving a roundabout on the dual carriageway A5, on the outskirts of Shrewsbury, the traffic came to a crawl and it took almost an hour to travel the next 2 miles to the next roundabout.
My Stag has a computer-controlled Davies Craig external electric water pump, electric fan, and Stagweber header tank. I was pleased that this set up successfully maintained readings on the temp gauge between N and 2/3 N, the reading fluctuating between the two as the EEWP and electric fan worked together. I did not turn off the ignition during this time as to do so would have caused engine heat soak to cause problems restarting with the indignity of passing motorists telling their fellow passengers "Those Stags are known for overheating you know"
However, upon reaching the next roundabout, I diverted to a Sainsbury's petrol station where I filled up with petrol. When I attempted to exit the forecourt the battery was almost flat and would not turn the engine.
Fortunately, I was able to get a jump start from a very king chap on the forecourt who was driving an appropriately liveried RSPCA 4X4.
My initial thoughts were that crawling at idling speed for an hour, the alternator had not fed the battery to compensate for the drain from the EEWP, electric fan and petrol pump.
Then I thought that an alternator should charge fully, even at idling speed.
My battery is 10 yrs old and the terminals are clean and tight.
I'd be grateful for any observations and advice to avoid future similar problems.
Thanks in advance
Steve

[mike@thenook]

Does sound like your battery may not be holding the charge, at 10 years old I’d be very surprised if it is of much use at all. While I don’t have a DG pump or electric fan neither should drain a good battery or over power a sound alternator at idle.
I’d get them both tested but if you’re voltmeter shows it is charging then my bet would be battery

Cheers

Mike

[new to this]

I would say you need a bigger alternator, your drawing more power than your ariginal alternator can replace

[sujitroy]

+1 on checking the battery. Can you get it load tested at a shop for free?

[Phil S]

+2 a drop test will kill your battery if it is that old. New battery and a 70amp alternator should cure the problem

[flying farmer]

Old battery might not have a lot of capacity left, but I bet if you look at the voltmeter while stuck in traffic with the fan and everything else on that you have less than 12V showing.
I have similar problems on most of my cars even with 65amp alternators fitted, night times are even worse with the lights on but I have never suffered a flat battery as if necessary I have had to give the engine a few more revs to keep the voltage up.
Probably worse on an auto with a low idle speed

[wilf]

Do some proper diagnosis first - invest in or borrow a DC clamp-on ammeter and see what currents are flowing around the circuits. You will be able to see total battery current by clamping over either of the battery leads, fan load by clamping over its feed cable etc.
Then you can decide if a higher rated alternator is needed or not.

At 10 yrs old, I too would suspect the battery not to be at its best.

[richardthestag]

nip down to your nearest Halfords, they will test the battery in seconds and for free

[Neil in Deal]

Morning all,
Here's another "hand up" for a less than healthy battery.
Remember, the car was originally fitted with a battery sized (both physically and electrically) to meet the requirements of the car as it was designed.
At 10 years old, I'd agree it's probably lost some capacity, replacement would be a sensible move, now "the nights are fair drawin' in, aye....)
Just for info, the ships I used to sail on all relied (if all else failed) on 24v batteries, for providing vital services and starting of the Emergency Generator.
Some in my rank (Electro-tech.) used to try to prove to "The Office" ashore they were clever at saving money, by not renewing these batteries. However if the batteries were anywhere NEAR 5 years old I would tell The Office I WAS replacing them. When I was a Radio Officer, you HAD to ensure your Em.Batteries were in tip-top condition, the Radio Surveyors would come down really heavily if they were not.
Luckily, my first boss was really good, and taught me well, emphasising just how important good batteries were - the "heart" of things.
Your nice RSPCA man jump started you, not so easy to jump start many thousands of tonnes of ship rolling around mid-Atlantic!
Stay safe,

Neil.

[brian0443]

Again I'm with the battery. Assuming you have checked the drive belt to the alternator is tight.

[PJB]

This is most definitely not the case (for OEM Stag alternators - and many others) - "I thought that an alternator should charge fully, even at idling speed".

A "modern" alternator will pump out much more at idle but as they say - check it all before replacing anything and the battery may well be past it's best. Regards

[trunt]

Another vote for the battery but also think about a modern alternator down the road due to the load, they do provide more current at idle.

I have the Davis Craig pump and a 16” fan, they run on after switch off and I have not had any problems. The alternator is a more modern 55A that seems to cope well, the voltage output is a full 14v even when the car is idling with both fan and pump running full speed and I estimate that’s about 25A. Not driven it much at night but I did spend a sweaty hot evening adjusting the beams and though I did not note the voltage I had no problems e.g. the lights did not seem to dim when the fan came on.


Terry

[RNF]

This is cheap insurance and takes very little room. I've used it to start my 5.0L V8 farm truck without any battery at all, then with no recharge it fired up a 3.0l diesel without any battery connected to the truck. It's a powerful little bugger.

https://themicrostart.com/xp-10-hd/

[Bandit1200]

Thanks for all your comments. Fortunately, the 10-mile drive back to my home was sufficient to recharge the battery and start the car the following morning.
Accepting that the battery, at 10yrs old, maybe approaching its last legs so I have purchased a new battery to keep the jump leads company in the boot.
That Microstart device looks interesting but I'd still need a new battery when the time comes.
Thanks again.
Steve

[RNF]

Thanks for all your comments. Fortunately, the 10-mile drive back to my home was sufficient to recharge the battery and start the car the following morning.
Accepting that the battery, at 10yrs old, maybe approaching its last legs so I have purchased a new battery to keep the jump leads company in the boot.
That Microstart device looks interesting but I'd still need a new battery when the time comes.
Thanks again.
Steve

Yes, it's just there for emergencies