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Ian Jackson[_9_] Ian Jackson[_9_] is offline
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Default OT: Car battery volt drop

In message , alan_m
On 26/04/2021 19:06, Michael Chare wrote:
On 26/04/2021 08:54, alan_m wrote:
On 26/04/2021 07:50, RJH wrote:

If only - the first warning I had of a failing battery was the dash
going haywire, and then the car came to a stop.

Albeit on a 5+ year old battery I once had a failure overnight. The
previous day it started the car which had been sitting for 18 hours
in temperatures below 0C.* It started the car a couple of more times
during the day. Previously there had been no indication of a failing
battery and my daily commute was 30+ miles. On the morning of the
failure the dash lights came on for a second or two and then dimmed
to nothing, a turn of the key resulted in zilch. A morning on the
charger did nothing.

A new battery restored everything to working order.

What sort of battery did you have.

This was many cars ago so no idea.

I now have a car with an AGM battery for stop start.* I am now
wondering how long it will last and what a failure will be like.* For
the past 25 years my cars have normally started very easily so I
don't notice that the battery is failing. One car would not start so
I charged the battery, drove about 10 miles to buy a new one and then
the car would not start to come home until I fitted the new battery.
Fortunately I had the tools I needed with me.

Often in the "good old days" part of the problem with a failing battery
was a low starter motor cracking speed coupled with a poor spark. Then
came electronic ignition and then fuel injection and often if there was
enough in the battery to just turn the engine the car would start

Back in the late 60s, add-on electronic ignition was a popular topic in
many hobbyist magazines. I made one design, and although it worked, I
had various problems with it.

The use of ballast resistors was also popular (where the coil primary
was around 8V fed via a resistor which a relay shorts when the ignition
key was being turned).

I have always been of the opinion that the most effective modification
would have been to power the ignition coil from a separate (small) 12V
battery, fed via a diode from the main battery.