Battery Light

[Joel]

I love electrics

 

Battery went flat over the weekend. I'd been fitting the wipers and checking they worked, so I figured it must have just drained the battery. Plus the car hasn't run for more than a few minutes at a time for the past 6 months, which probably hasn't helped.

 

So I charged the battery, but now the battery warning light on the dash stays on after you fire the engine?

 

Does that mean it's not charging? Have I got a short somewhere? Where do I start looking?

 

I should add that all the electrics seem to be working (lights/dash instruments etc), and there's no blown fuses. The battery was new about 6 or 7 months ago and it's heavy duty.

 

Knackered alternator maybe?

 

Help

[Longboarder]

Sounds like alternator not charging. A strip and clean may help, particularily the terminals and slip rings. To test for a short in the blue wire ,alternator pin 61 to instrument panel, pull the plug out of the alternator and switch on ignition but DON'T start the engine. The ign light shouldn't come on unless the is a short.

 

Nigel

[Joel]

Hi Nigel,

 

I pulled the plug on the alternator with the ignition on as you suggested, and the dash battery light went out so I assume there's no short.

 

Must be the alternator then I guess.

 

Just as a reasurrance, there's no way a problem elsewhere could make the battery warning light come on is there?

 

For instance, the last thing I was doing was connecting the wipers, which incidentaly are working fine, but if I'd wired them wrong, it wouldn't affect the warning light? I don't see how the two could be connected, surely just a fuse would blow?

 

Anyway, I'll give the alternator a once over and see if that makes a difference.

 

Cheers.

[Guest Ant]

Put a volt meter across the battery. With the engine running the voltage should rise from about 12 or 13 volts to 14 or 15 volts. If it doesn't then the alternator isn't charging. If it does then it's probably a fault in the warning circuit, or the warning circuit within the alternator itself.

 

Ant

[Joel]

ok, I tried the volt test across the battery - a steady 13V at all times, running the engine didn't budge it at all.

 

So next question, how do you bench test an alternator?

 

I thought by attaching the spindle to a battery drill I might be able to spin it fast enough to get a reading across the pins, but not a sausage.

 

Does that solve my problem or am I doing it wrong?

[Guest Guy]

You have to energise the alternator to get it to generate more electricity, it won't simply run on the bench. It's best to test it in the car, try for a bad connection (most probable) or try a new alternator.

[Guest Andy Rathbone]

if you get no joy i have a spare alternator (history unknown) you could try you seem fairly close i'm in nuneaton. one thing i did pick up, you say your only getting 13v from your alternator, it should be more (13.8v plus)realy. is your battery topped up with water?, what about trying a diffrent battery you could have a bad cell which means your battery is weak, it will still work but wait till that cold frosty morning.

[Guest Ant]

Sounds to me like it's an alternator problem. The voltage should definitely be higher with the engine running than without. One final test would be to put the volt meter on the back of the alternator rather than on the battery. If it's still constant then get yourself off to the scrappy for another alternator, and keep the current one for spares. Chances are only the brushes are worn out, or possibly a rusted wire inside it.

 

Regarding keeping a battery in tip-top condition on a car which isn't used regularly - race technology (http://www.race-technology.com/WebPage/Products/CHARGERS/ChargersMain.html) do a low current charger which you can leave permanently connected to your battery int he garage and it will keep it in tip-top condition by constantly monitoring the voltage, and doing small charge / discharge cycles. They're only 25 quid.

 

Ant

[Joel]

Right,

 

I dug out an old but unused alternator from the garage. I think it may have been from a Sherpa Van. Anyway, it fits and works. The dash battery warning light goes out when you start the engine and the voltage across the battery increases with the engine running too.

 

Am I likely to have trouble using any old alternator though? Obviously I don't want to be frying my whole system.

 

I don't know if it's possible to identify it's spec from the markings on the case, but if it helps it says:

 

Lucas B90 Service Unit

LRA101

23801 7 81 B

 

Also there are a few other differences from the original, which had some kind of red device attached to the back (see attached pic). Radio interferrence suppression maybe? Also there was a blue/white wire which attached to one of the bolt ends, which I think was something to do with engine management or auto-choke.

 

The new(ish) alternator has neither of these.

 

Any enlightenment on the above would be much appreciated.

[Guest Andy Rathbone]

to answer your questions, as long as the alternator is not for 24v (big lorry ones)you should be ok. The red box , yes you are quite correct radio suppression. its basically a capacitor that reduces the sparking from the brushes in the alternator. as for your blue/white, wire if its connected to anything to do with the case it will be an earth and could be moved to some where more convinient, but must be connected, else it could cause so realy odd symptoms.

ATB

[Guest Ant]

I reckon you'll be fine with it. the main differences between alternators for different cars are:

 

- Physical size and mounting point locations.

 

- Overall power rating.

 

So long as it's 12 volt it'll be fine. If it's over-rated in wattage then you're wasting energy by driving a bigger alternator than you need. If it's under rated then if you drive with headlights on, wipers going etc etc for a long period of time you'll gradually run the battery down. Remember though that Sierra alternators are rated to cope with heated rear (and front sometimes) screens, power windows, central locking, warning modules, courtesy lights, etc etc. The hood's only high current devices are headlights and wipers.

 

You'll be fine!

 

Ant

[Longboarder]

The blue white wire on the old alternator was probably for electric choke. Do you need it? Ditto supressor. As long as its charging at 14.5-15 ish then you got yourself a bargain. Is the pulley size and alignment OK?

 

Nigel

Edited June 25, 2003 by Longboarder

[Joel]

Thanks for the replies everyone,

 

To answer a few questions, the new (Sherpa?) alternator is almost identical in size to the old Sierra one. the pully size and allignment is identical, and it's a perfect fit for the bracket.

 

The only noticeable difference apart from those I mentioned earlier, is the weight - it's a fair bit lighter.

 

Voltage across the battery with the engine running is 14V, dropping to about 12.5 when I switch off. That might sound a bit low, but it seems to turn the engine over with a fair bit of ummph (technical term).

 

According to Haynes, the blue/white wire for 87-89 2.0 OHC carb, is for the auto-choke, and yes I would have thought I needed it as I'm still using the ESCII and all that business. Having said that, the car seemed to run fine this morning, though I only ran it for a few minutes.

[Longboarder]

Good enough I should think. 14v and no auto choke. But you're a kit car builder. Splice in a 6v take off (thats what I was told the auto choke runs on,no idea why) or make a manual one. Volts might perk up a bit after the cobwebs have blown away. Wasn't B90 a Lucas exchange reconditioned scheme somewhen?

 

Nigel

 

Just had the thought, if you take the duff alternator apart you could probably see where the blue/white wire comes from and copy that in your 'new' alternator.

Edited June 26, 2003 by Longboarder

[Joel]

Wasn't B90 a Lucas exchange reconditioned scheme somewhen?

 

Quite likely, there's something about a 1 year Lucas service guarantee on the alternator casing. I would think it expired a long time ago.