Hi all

For a while now my 1.4 8v Grande has being struggling to get any higher than 13.6 volts to the battery it used to sit happily between 14.3 14.4 now can't seem to find out why it's lower I have put a second hand alternator on and it's still the same if anyone's had anything similar let me know

Many thanks

Have you had the battery tested and have you checked all the cables to/from the battery and the engine earth for corrosion?

Battery was replaced 5 months ago and it's a bosh s5 so hope its not that as for earth points most have being checked and were sanded when the engine was replaced so im thinking i may have to go back over them all

Go over the cables not just the attachment points. The cables rot inside the ends

Well there's a surprise haha

Its an high resistance somewhere. Check all your terminations points. Its not rocket science. If you have an healthy alternator diode pack and a good main earth to the block then there is nothing to interrupt a good voltage flow.Your battery will accept what it needs, you cant push anymore into it than it wants. The alternator o/p will always be its nominal, its the current that will drop on demand.

A bit of theory (again...) ?

Ohm's law: U=R * I or Voltage=Resistance * Current , that's it and can't be changed !

Think of it as a garden hose @ home: You got the water pressure (voltage), the hand-gun (resistance) and the flow (current). The more you open the hand-gun (lower resistance): the bigger the flow...

The alternator is voltage-regulated so it outputs always the same voltage in its working range.
An almost empty battery has a relatively low internal resistance, let's say 1,2 Ω and to make it simple 12V for the alternator's voltage.
That would allow 12 / 1,2 = 10 amps to go from the alternator to the battery, thus charging it (hand-gun open).
As it charges, the battery's internal resistance get bigger (hand-gun almost closed), let's say it reaches 12 Ω, the charging current would be reduced to 12 / 12 = 1 amp ...

Got it ?

Also, when current circulates over a resistance, there is a voltage drop (that's why the cable gets warmer or a bulb shines), our garden hose is pretty stiff when hand-gun is closed, but loose stiffness when hand-gun is open...
If TOO much current is drawn, the alternator's would go on its knees and the output voltage would go down. If the pump is too small and the hand-gun fully opened, the flow will decrease once the initial pressure (voltage) drops...

In your case it would be nice to check what current is delivered by the alternator, an Amp clamp will do the job...

ps: I know the purists will say my example is not good since the battery already has a voltage that should enter the equation. I made this purposedly not to add difficulty to understand the basics...

BRs, Bernie

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Thanks guys I'm pretty clued up on electronics normally but this one has me stumped and the mechanic so we have now cleaned all the earth points and the battery connection cleaned the alternator connections and checked all the wires and we have now got 13.8/13.9 so not too far off mechanic seems to think that I may have got a dud battery since that's the only thing that hasn't being changed recently