Hi All,

Car has been killing LED's of late making them strobe and flash. So I cracked the multmeter out to check the voltage.

Battery was at 12.1v before starting. On starting the car jumps to 14.3 for a few seconds then drops down to 12.5v. Turn lights, full beam, fogs, heater, heated screen etc all on and it drops to 12v, then 11.9, 11.8 etc, revving the engine makes no difference to the voltage.

The car isn't throwing any CEL and never has an issue starting or driving, has never cut out etc. I've managed to get hold of a good used alternator to replace mine with but find it odd the car isn't reporting a fault? I'm going to replace it on weds to see if that cures the issue.

Scott

 

Can't see why a low voltage would kill LED's?

Unless the alternator rectifier has gone and it's producing AC?

 

Well I don't know what the voltage is doing higher up the rpm range, up to about 4k there was no change. Also if its not making 12 volts the LED's wouldn't light up correctly, most LED's you can't use on a dimmer as they start strobing. It's eaten 8 LED 501's so far, rear plate lights and front sides (Blobeye).

It was only the LED's going that made me have a look at the voltage in the first place, and it seems very low?

 

mine dropped to 11.9 but never after alternator belt change for new one
normal leds(cheap) gone on mine before and after change

 

Ok so from what you said it was belt slip causing your issue? Belt isn't slipping on mine.

 

Both my newages sit at between 13.8 and 14.3v when under load and around 12.8 with everything off. Sounds like your alternator isnt regulating the voltage correctly so hopefully new unit should sort it out and only a 5 min job to swop over. I leave my sidelights on all the time when driving to keep the battery topped up.

 

Sounds like the brushes on the reg have had it, or the sliprings have worn, so they can't pass enough current into keep the field windings going - what you typically get is good voltage at first, then it tapers off rapidly . You won't always get a warning light as the alternator can still produce enough current to extinguish it....but not anywhere near enough current to meet the load being placed on it - hence the voltage dropping.


Pity its not a Bosch alternator...because guess what...that's a £25 part and is held by just a few bolts onto the back. Denso though...ha! not so easy

 

Yeah I know, i've had to replace one on a BMW previously, nice and easy.

I'll be swapping it tomorrow so hopefully it'll cure the problem .

 

Replaced the alternator, problem solved