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Normal charging voltage


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What should the charging voltage be to the battery when the car is just idling?  

I've replaced the battery and just out of curiosity I checked the voltage which was reading 17 to 18 volts. Is this right for a spitfire?  

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Do you have an alternator or dynamo ??

As Pete has mentioned, 17 to 18 is too high.

If dynamo the control box may not adjusting the current output properly and if it is an alternator the diodes may be at fault or similar within the unit.

Depending on what type of control box you have (if you run a dynamo) they can be adjusted.

A bit more info from you will help us to assist - hopefully !!! :blink:



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Alternator Health check

Tick-over - ignition only                                 13 v - 13.5 v

Tick-over - Headlights on                               11.5 v - 12.5 v

2000 rpm - ignition only                                  13.5 v - 14.5 v

2000 rpm - Headlights on                                13 v - 13.5 v


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17/18v is way too high - moderns often run around 15V to increase the power, but then have to be a bit clever in voltage management - my old Discovery is one such beast and when halogen bulbs were fitted, the ECU soft starts the bulbs and gradually increases the voltage so as not to shock them - you can tell if you change to Xenon headlamps (Complete unit change, not just an illegal bulb swap) and unless you change the cars configuration, the Xenon's flicker on startup because they do need more volts (about 50000) to get going before dropping back to about 15,000v) 


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  • 2 weeks later...

Back to this old nugget. Fuel and temperature gauges aren't working. Checked the voltage stabiliser on the back of the speedometer and not getting any voltage from that. Also noticed that the indicators were intermittent and when they did work on increase of engine rpm they flashed quicker. I think I have been getting a surge in voltage but no fuses have blown. 

So I'm thinking I'm going to need a new regulator but how do I know which one I need? There appears to be 2 types available 2 or 3 lead and 4 lead

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 Across the battery while the engine car is running; you want a minimum of 13.8 and a max of 14.5 ish. 13.8 or below on full electrical load and at 2K plus would have me checking for volt drops as 13.8 and below will ensure a low capacity battery.



Edited by Spitfire6
Changed engine to car
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