Odd electrical behaviour

[Fraser]

Hi all,

Had some odd behaviour this afternoon when I took the Zed out. I've just charged up the battery as it had gone completely flat after coming back from Scotland a couple of weeks ago, put the charged battery back in the car this morning reading 12ish volts. Car started OK, it's raining so I've had the lights on and the wipers, no radio. The ABS and traction light came on, then the airbag light came on. I noticed that the wipers had slowed down too. I'd intended to fill up with fuel whilst I was out, but as I pulled into the petrol station, I switched the lights off, and as I did so, all of the other warning lights went out and the wipers went back to their original speed. I guessed that the battery wasn't doing too well, so I didn't turn the engine off and just came back home.
I don't know if its coincidence, but when I turned the engine on, there is an unusual whining from the engine bay and it's the first time it's ever done it.
When I got back home I tested the battery voltage and it was reading 11 volts. I had a look at how to test the alternator, so I turned the engine back on and it was still reading 11 volts.
Based on this, I'm guessing that a new alternator is required?
Before I go and get one, can anyone confirm that this sounds like the right route to look at?

Thank you in advance.

 

[t-tony]

You can test the output from the back of the alternator. Connect a volt meter between the big terminal and earth. You want around 13.8 volts. But, it the whining noise is coming from there it sounds like the bearings are giving up anyway.

Tony.

 

[colb]

Had an undercharging alternator on my Z3, only noticed it after being out in the night using headlights, next day had a flat battery. Checked output with a voltmeter after jump starting it and it was only putting out 12v at best so couldn't maintain the battery when using headlights. Fitted a replacement alternator which restored the charging rate to 13.8 - 14v, been fine ever since. Having gone through that I fitted a volt meter with two usb sockets into one of the vacant switch positions so I can monitor what state the battery is in and monitor the charging rate. Always thought they should have put a battery condition meter in when they built them.

 

[gookah]

another way of checking your alternator output is when its dark, with the engine idling, switch on your main beams and the heated rear window, then rev the car and see if they brighten up, that shows that the alternator is giving out more voltage than the battery is when its idling

 

[Fraser]

Thanks for the responses guys, I'll have another play and see what happens. Another thing to spend out on.

Any advise of replacement alternators? I've seen that they're output can vary between 80A and 120A. Does it really matter, or is it just best to get a quality unit no matter what the output is? I bought a heavy duty battery last year as the last one died (could have been down to the alternator now in hindsight), I think it's around 80A output. Will this make a difference?

 

[Synclare]

.

 

[colb]

Best of luck finding someone who refurbishes alternators these days, looked for someone when mine went duff but couldn't find anyone, a guy I knew elsewhere had a business refurbing alternators, he closed down as it was no longer viable, seems we have gone to just replacing withnew or refurbs by larger companies. Shopped around for best price checking all the online suppliers starting with Carparts4less, web based arm of Europarts but cheaper. Fitted a like for like alternator 80Amp as far as I remember.

 

[t-tony]

There will be a plate or Decal on the alternator telling you the output etc. Replace like for like, don’t go for smaller rated output, it has what it has for a reason.

Tony.

 

[Fraser]

There will be a plate or Decal on the alternator telling you the output etc. Replace like for like, don’t go for smaller rated output, it has what it has for a reason.

Tony.

I was thinking of going for a higher rating because of the higher rated battery, do you think would it be worth it?

 

[andyglym]

With your engine running, lights on and blower on full you should be getting 12v reading if your battery is good, as stated circa 14v straight from the battery with engine running and nothing on.

 

[t-tony]

I was thinking of going for a higher rating because of the higher rated battery, do you think would it be worth it?

I would replace like for like Fraser, after all it’s done alright up to now.

Tony.

 

[Oddly Godly]

I bought a cheap voltage adapter of ebay that plugs into the cigarette lighter. It seems quite accurate. It shows just over 12 volts and 13.7 with the engine running. They are very cheap. I dont leave it in when not in use as the cigarette lighter is permanently live. It's handy for checking everything is fine with the battery and alternator.