Alternator madness

Alternator checked out ok by vehicle electrician. Refitted and voltages as follows battery 12.38. @ warning light 12.38 other side bulb 1.88 (static) 9.4 running. Resistance alt out to batt +ve 0.1 ohms engine to batt -ve 0.08 ohms warning light just slightly glowing. Left engine running and after few minutes voltage started creeping up very slowly reaching 12.92 after about 20 minutes warning light out ! is the battery sulphated or something
 
Sulphated would give a rapid rise due to resistance.
Have you a ammeter?, sounds more like a big battery bank, or low output alternator, check output current..
Does the battery voltage rise slowly like the warning light terminal, ie 9.4 to 12.92?

Brian
 
Just a thought ... aren't Lister engines notably low revving ? Does the light go out quicker and charge voltage rise if you increase revs ? Maybe need to adjust pulley size for a long term fix if increasing revs fixes the problem.
 
Yes Lister very slow revving pulley quite small already.
Sorry Brian the battery volts reached 12.92 didn't check output to warning light other than just after starting ie 9.4 will do the next time. Battery 110ah and I suspect this charging problem been there for some time longer than I know. Maybe I should try another battery just to check. Will put ammeter back in circuit now there is something coming out of alternator
Thanks for helping only 2 volts to go !!
 
Sounds like low speed, alternator is starting to charge at around 2500/3000 alternator rpm. You need to be up around 7000 / 8000 rpm, sounds like your charging at 2 -5 amp at a very low rpm.
My Volvo run the alternator of the flywheel, with a small pully on the alternator, we get around 5 times the engine rpm at the alternator.

All the best

Brian
 
Have you got the correct wattage bulb, in the warning light?
If the wattage is too low alternator will struggle to start charging, fitting a higher wattage bulb will enable alternator to start charging at lower revs.
 
thanks all, I'm using a 2 watt festoon bulb during testing but did try a 5 watt bulb earlier I think it's a combination of pulley speed plus big battery and old age and poor joints ( a bit like myself) at least now I've got something working as opposed to absolutely nothing a week ago thanks for your help and perseverance.
Jim
 
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