Slomofo Posted May 7 Report Share Posted May 7 So I ran some tests on the battery installed in my Boxster, I was curious about slow cranking - Health is ‘Good’, Cranking is ‘Good’ although a bit slow in my opinion, Load/No Load Voltage is ‘OK’ (12.3/11.6) Live Charging was the one that puzzles me. I’m getting a stepped wave of charge (engine running, accessories off) that fluctuates between 12.5v and 14.3v, whereas the same trace on my BMW, Disco or SWMBO’s Mazda are all a constant 14.5v charging trace. C’est normal or something to investigate? If any have similar experiences do tell! Quote Link to comment Share on other sites More sharing options...
Paul P Posted May 7 Report Share Posted May 7 Interesting observation. My thoughts / questions - no experience or answers Engine running at idle if so does it smooth out to the higher end if you raise the revs ? any squeal from the belt ? Quote Link to comment Share on other sites More sharing options...
Slomofo Posted May 7 Author Report Share Posted May 7 6 minutes ago, Paul P said: Interesting observation. My thoughts / questions - no experience or answers Engine running at idle if so does it smooth out to the higher end if you raise the revs ? any squeal from the belt ? Constant charging profile at idle and up to 2.5k, no squeaks! Quote Link to comment Share on other sites More sharing options...
Paul P Posted May 7 Report Share Posted May 7 48 minutes ago, Slomofo said: Constant charging profile at idle and up to 2.5k, no squeaks! Hmm - that feels like an issue with the regulator - the 987 is "old school" ( no stop/start agm cleverness) - so I would expect "charging" to be at a fairly constant level (small variation for idle I guess ) - I couldn't say if thats unusual - never observed it close up - but it feels wrong especially if it's an irregular fluctuation. I have only observed a couple of cars with a multimeter for charging - and I seem to remember that was "about 13.7 ish" when running - so seems you may have an kicked ants nest, be intersted in hearing other folks thoughts and experience. Quote Link to comment Share on other sites More sharing options...
Slomofo Posted May 7 Author Report Share Posted May 7 4 minutes ago, Paul P said: Hmm - that feels like an issue with the regulator - the 987 is "old school" ( no stop/start agm cleverness) - so I would expect "charging" to be at a fairly constant level (small variation for idle I guess ) - I couldn't say if thats unusual - never observed it close up - but it feels wrong especially if it's an irregular fluctuation. I have only observed a couple of cars with a multimeter for charging - and I seem to remember that was "about 13.7 ish" when running - so seems you may have an kicked ants nest, be intersted in hearing other folks thoughts and experience. Thanks - I use a TopDon20 battery analyser with the phone App, clever bit of kit but also opens Cans of Worms 😜 Quote Link to comment Share on other sites More sharing options...
Paul P Posted May 7 Report Share Posted May 7 I have a topdon battery tester - no app, but a good bit of kit - just never used it in anger on a battery in situ for charging - just the "static" tests - and not needed to use it for charge testing since I got it. Quote Link to comment Share on other sites More sharing options...
Sword Posted May 8 Report Share Posted May 8 I had slow crank on mine and found that if you follow the positive battery cable to where it enters the car there is a push fit connection. This corrodes over time and leads to poor connection and slow crank. Push the red tab down and pull off to look inside the connector. My solution was to thread the metal post, take the connector apart and used a nut to hold in place rather than push fit. Cranks no problem now Just a thought.. 1 Quote Link to comment Share on other sites More sharing options...
Slomofo Posted May 8 Author Report Share Posted May 8 Good to know - will have a shufty! Quote Link to comment Share on other sites More sharing options...
Paul P Posted May 8 Report Share Posted May 8 30 minutes ago, Sword said: I had slow crank on mine and found that if you follow the positive battery cable to where it enters the car there is a push fit connection. This corrodes over time and leads to poor connection and slow crank. Push the red tab down and pull off to look inside the connector. My solution was to thread the metal post, take the connector apart and used a nut to hold in place rather than push fit. Cranks no problem now Just a thought.. That’s a good point. There is a “repair “ kit from Porsche for that issue I think. I remember it could be the cause of non starting issues but makes sense that it could also affect charging as well as cranking speeds. Quote Link to comment Share on other sites More sharing options...
nelmo Posted May 8 Report Share Posted May 8 17 hours ago, Slomofo said: fluctuates between 12.5v and 14.3v The 2005 Ford Zetec engine in my kit car does the same, low at idle and increases to a maximum as the revs rise, which seems logical; higher revs -> faster speed on the alternator -> higher charging voltage. Never checked on my more modern Skoda - I assumed it would be the same but maybe not? Quote Link to comment Share on other sites More sharing options...
Slomofo Posted May 8 Author Report Share Posted May 8 Mine fluctuates at idle (like an ecg trace), so the exam question is ‘normal or not?’. Lots of theories abound, I’m after an experienced based opinion - though it is charging so not crucial! Full Wave Rectification is my pet theory based on a dim & distant recollection of Physics A Level - but curious as to why only the Porker displays this. I think Paul P might be close with the regulator being in control- but if it’s supposed to look like that then shovel down😜 Quote Link to comment Share on other sites More sharing options...
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