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Fordboi

Nippon Denso alternator woes

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14v with a few revs. Just over 13v at idle and then 11.8v with lights on and that's when the instruments fluctuate.

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Have u cleaned battery terminals, use jump leads to battery neg to chassis and chassis to engine, got to be bad earth or live from alternator, check starter motor terminals clean and tighten, basically check all earth's remove clean and tighten, what did they say was wrong with old alternator? 

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Main Lights, fuel pump, heater, etc will pull at least  20a from that battery.   The little denso alternators are only 40a at max.    So I’d expect the voltage to drop with lights on etc when on tick over.   If the car starts fine and does not need charging when used regular then it’s probably ok.  

Note the wording in adverts... denso style alternator.    These are copy’s and probably not as good as genuine denso.

Your Gauges going mad could be something else...   wonder if it’s more of a problem at your gauges having a dodgy shared earth, or dodgy voltage stabiliser.   I think from memory voltage stabilisers pump out 10v. So analogue gauges should still work and not get upset below 10v.   The voltage stabiliser should only be running the gauges..  Hopefully  no ones plumbed in something else into the 10v circuit like  alternator excitation current etc as that might feed back.  

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I've disconnected the battery and connected a large battery off my Mondeo. The behaviour was the same although the starter motor sounded a bit more powerful! Speaking of which I will check the starter motor connections. They said there was a problem with the windings in the old alternator but I'm slightly sceptical of that diagnosis now.

 

DamperMan....My XE is on carbs so the fuel pump is low draw and there is no heater or blown air etc so the electrical system is purely running the pump, ECU and headlight circuit. I wonder if you're right therefore that although my voltage is dipping low at idle, perhaps the gauge issue is another problem. I don't know if there is a voltage stabiliser on the gauges at all to be honest....behind the dash is very neat and tidy for a change and there doesn't appear to be anything resembling a voltage stabiliser. Would that be required with the VDO gauges? I've already checked they have the correct senders fitted.

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With a Fully charged fat boy Mondeo battery the car would run for ages without an alternator, lights on, fan... and have more than enough power for a few gauges.    The fat boy mondeo battery will have more cranking amps so i'd expect a better turn over speed compared to a smaller battery usually used on a Westfield.       I don't know about your VDO, but normal old fashion analogue smiths type gauges just measure the voltage drop across the sender.   The sender running to earth.  Full scale deflection when the sender fully earths out.     More voltage supplied to the gauge the higher the reading ...That's why they need a stablised supply, not one varying between 12 and 14 v.         I'm afraid  I have no idea what your VDO's need  there may be some some electronic magic inside, or built in voltage stabilisation.     

I'll just say that just because a mechanical Oil pressure sender vs a Electric one have different readings that could be calibration, also mechanical ones are much quicker acting and in my view much better.   When I had some sort of strange oil pressure issue the needle would bounce.   An electric one with its slow damped action would have not moved at all.      The Fuel level  in my car is a loose guide to what might or might not be then tank the only thing to be sure of it will need filling very soon...         

                                

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I agree with you there, a mechanical gauge would always be preferable I think! I've found a set of installation instructions for the VDO gauges and it says that each gauge must have its own dedicated ground. Currently all the gauges are daisy chained together from the illumination ground into the gauge ground and so on across the dashboard. I guess its possible that this may be causing the issue. Where do people normally ground all the gauges keeping in mind that the bulbs can continue to share a common ground but I will need to create 5 new grounding points for the individual gauges? I'm going to try isolating the oil pressure ground initially as a trial.

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Hi, u can get metal earth distribution blocks just run all earth's from gauges to 1 side and sizeable earth cable or cables to earth obviously short as possible. 

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Got to say, lots of separate grounds everywhere is normally a recipe for disaster, especially from a measuring point of view with sensors and gauges; it tends to promote lots of ground offsets etc, which then gives false signal levels.perhaps VDO are suggesting it for some other reason, I’d be curious as to why.

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10 hours ago, Fordboi said:

14v with a few revs. Just over 13v at idle and then 11.8v with lights on and that's when the instruments fluctuate.

I had similar before. Check your pulley measurements and see what speed the alternator is turning at. Mine was too slow at idle, changed the pulley and all was good again. Off the top of my head; the alternator should max out at 18k rpm when the engine reaches its max rpm.

The faster it turns the more current you will get out, and it’s current that the headlights are eating, not voltage.  

R

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