Alternator help

Hi members. Not too sure if this is alternator or something else so here goes.
Had battery on charge so multi meter reads 12.58
When engine was running it went upto 12.65 but gradually went down as lights heaters were switched on.
I only had this on tick over by the way. Any advice on this would be great and if i need to replace it what others will fit (2.5 n/a) thanks

what happens when you raise the engine speed , would expect votage to rise and lights to get brighter. There is not many places where you drive at tickover.

There's a meaning behind the "Lucas, get home before dark" joke.

I'm unsure about series 3s but am I correct that Series 2s charge using a dynamo, far less efficient that an alternator? Someone mentioned that to me. Is it true for 3s as well?

They don't charge well and i'm pretty sure don't even break even when using lights and wipers. I may be wrong though.

Is the belt loose?

Blackburn said:

what happens when you raise the engine speed , would expect votage to rise and lights to get brighter. There is not many places where you drive at tickover.

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Thats true mate and no i didn't rev it, was just expecting it to rise to 13+ tho

taylorslandy72 said:

Thats true mate and no i didn't rev it, was just expecting it to rise to 13+ tho

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Not at idle it won't. Hold it at higher revs and see what it does.

Lucas alternator needs to be doing 6000rpm [from the series manual] to give full output of either 34A or 45A depending on model.[16acr or 18acr quoted]
Engine pulley is bigger so you need to compare the size of the pulleys to see what speed your engine would need to be going to give you full output.
On my 200tdi engine
Disco engine pulley 6.25" 158mm
Alt pulley 2.75" 70mm
Ratio 158/70= 2.257
So to get 6000rpm on alternator I need 2667 engine RPM typical tickover is only 600rpm on series engine 200tdi 720rpm
Compare your pulley sizes as may well be different from mine, original 200tdi set up drives the alternator off power steering pump so may reach max output at lower rpm.

The engine was out of a 90 with turbo taken off, still got old pullys attached to alternator

You want a 65 - 80 amp alternator, its not that you need 80 amps, but the higher output means you can get the 30-40amps you need at a much lower RPM, I put a 70amp on my Series with the smallest (sensible) pulley I could get and it charges from about 900 revs which is important with the Perkins engine as I can be driving at under 1000 rpm. I've got a 25 year old 5 ltr Merc and its got a 120amp alternator, it charges on tickover.

Been out this evening to check battery again. This time gave it a good rev as oppose to just tick over. Readings were 13.66 engine off reads 12.78. Thanks for your advice, im learning and picking up tips from this site as i go so appreciate your replies