yo-yo-t

Hi All, apologies for the novella but I've found with gremlin like issues, detail matters. I am posting to see if anyone else has experienced an issue as below:

1. Battery died (think Dodo, literally nothing in it) after 2-3 weeks rested up
   
2. When jumped it wouldn't hold a charge and the dash was flickering so my cheap eBay reman jobby had given up the ghost, thing was never as it should, most I can remember seeing on a multimeter was 13.6V
   
3. Fitted a new alternator, much better quality unit, producing a very healthy 14.4 - 14.6 volts and dash is back to normal
   
4. As soon as I got to maybe 15Mph I got a Battery/Charging system light, which seemed to be intermittent and will not, ever, come up when the car is sat still and revving
   
5. Confused, I checked all my work including the 4 pin connector and verified that each terminal in the connector was providing the right voltage as laid out by Spartarus in this forum post - https://www.s2ki.com/forums/s2000-un...alled-1165917/
   
6. Car worked enough, assumed light was in error and called it a day, drove it later that night and realised the light didn't come on at all. Later determined this was due to the headlights being on
   
7. Contacted the company who said it was very unlikely to be the alternator but would send me out another one to be sure, turns out I'd had their last one but they instead sent me out a new brush holder and regulator. I fitted those, refitted to the car and no change
   
8. I then "fitted" a 12V USB Adaptor with a built in Voltmeter to the cigarette lighter port and realised that the readout would be 14.4 when idling but would drop to 12.6 for stretches, seemingly at random, even when the charging warning light wasn't on. However, with the headlights on, the voltage was absolutely consistent
   

So... I have an inconsistently charging car, but only when moving, which is fixed by turning the headlights on (full beam or dipped work but sidelights do not). I must seem very odd to my fellow road user as I drive in brilliant sunshine at 1PM in this current heatwave the UK are experiencing.

I am hoping someone out there has had this before but I'll settle for any ideas anybody has too, TIA!

aleksboch

Perhaps try a brand new battery

chrispayze

Do the 'low voltage' occurances coincide with something else such as air con cutting in/out?

yo-yo-t

Hi Mate, no, all peripherals have the normal effect on voltage. I.e: Headlights on, car will read 14.3-14.4v, adding the roof mechanism or windows or AC etc will cause a minor/normal drop in voltage

Nottm_S2

Sitting and flattening the battery is normal S2000 behaviour
what year is your car?
Is it modded?
If it's only the headlights making it charge ok maybe there is a fault in that circuit somehow?

The alternator should always be giving you c14v
I would buy a used working one and try it, it could be something in the unit

martin j

Battery may have given up, old batteries don't like going flat, altenator may be trying to charge a corpse as well as run car, many decent factors will check it FOC but battery will need a full charge on it to do so, think off car and 240v powered charger. HTH.

Chuck S

A few deep discharges will kill starting batteries. I'm missing the results of your battery test. Or didn't you test the battery?

-- Chuck

yo-yo-t

It hasn't been load tested but is a recent battery (roughly 6 month old), reads 12.6 Volts (on both an actual multimeter and the questionable 12V socket Voltmeter) after a trickle charge (and still does after being in the car despite the inconsistent charging) and the wholly unreliable indicator shows Green for "Fully Charged". (Black would be "Needs Charging" and Red Cross "It's dead Jim")

Chuck S

Battery needs to be load tested. Simple voltage test will only see the surface change which will reach 12.7v in a few minutes on a charger. If you can't load test -- and every auto parts store in the universe will do this for free -- measure the voltage after the battery has been sitting with neither load or discharge for 24 hours (or at least overnight if you're impatient).

-- Chuck

BenRNBP

Just a thought, but are all your ground/earthing straps in good shape? - in particular the one from the engine to subframe