14 replies to this topic

[bluesprite]

1992 Rover mini sprite carb, 45a alternator
Hi,
For the past month or so when I'm driving at night if I put the rear screen heater on then the ignition light comes on VERY faintly, then if I put the heater fan on it is more noticable, and with the wipers on too you probably couldn't miss it but it still isn't on fully.
I've no reason to think it doesn't do the same in the day it's just not as often I need to use the heaters in the day and the faint light probably wouldn't be as visible so I just haven't seen it.

Oddly turning the headlights from dipped to full doesn't seem to make a difference to the red light's brightness.
I don't think the fan belt is slipping but I could be wrong.
I'm pretty sure I've checked whether the brightness of the light changes with revs and it didn't.
The car's never missed a beat and starts first time even when it's freezing so I'm pretty sure the battery is charging ok even when I have needed to use the heaters/wipers and driven home with the faint red light.
If the fan belt was slipping wouldn't it have snapped by now?
Could it be the brushes are wearing out?
Could the light be wired up wrong?

Thanks for any help!

[ryan22_lgm]

the fan belt can be tightened using the adjuster at the bottom. This light lights up when the is a problem with the power going to the alternator. Have you checked the connector going into the alternator? clean any connections apply wd 40

[tiger99]

Check the ignition switch. Does it get slightly warm? If so, replace it. Check its connections for cleanliness and tightness anyway.

The reason I say ignition switch is that the warning lamp is on when there is a very different voltage on each side of it, e.g. 12V nominal from the battery on one side, and somewhere near zero (just some resistance to earth) on the alternator side when the engine is not running. When the voltages on each side are balanced, the net result is zero as far as the lamp is concerned. But if the alternator end has a significantly higher voltage imposed on it than the ignition switch side, the lamp, which does not care which way round the voltage is, will glow again.

The loads you are switching to bring it on are downstream of the ignition switch, the headlights are not, so your symptom is completely explained, because the voltage downstream of the switch is dropping. And yes, it has happened to me on 2 cars, one a Mini.

[Glenn S]

If it is a Lucas 18 acr 45amp alternator it really sounds like the warning light diode gone. new diode pack in the alternator required.

[tiger99]

Oh, amd if you have a multimeter, put it between one of the white wires downstream of the ignition switch (around the fusebox possibly) and the upstream feed from the battery (brown on solenoid will do). If you see a volt or two when the light is glimmering, the case is proved, except that you need to check the relevant wires as well as the switch, i.e. brown from solenoid to switch and white from switch to fusebox, because it is just possible that a wire is damaged or one end corroded. But 9 times out of 10 it will be the switch itself.

[Dan]

The difference between main and dipped beam is 10 watts, the heated rear screen is 60 watts. Not surprising that the screen puts more load on the system than changing the headlights over.

[bluesprite]

the fan belt can be tightened using the adjuster at the bottom. This light lights up when the is a problem with the power going to the alternator. Have you checked the connector going into the alternator? clean any connections apply wd 40

I'll see if I can tighten it up a bit, it just looked really awkward to get to and there's no guarantee that I can definitely tighten it and not accidentaly loosen it haha! The terminals on the alternator did look a bit corroded but I didn't have anything with me to clean them up a bit so I'll give that a go too.

Check the ignition switch. Does it get slightly warm? If so, replace it. Check its connections for cleanliness and tightness anyway.

The reason I say ignition switch is that the warning lamp is on when there is a very different voltage on each side of it, e.g. 12V nominal from the battery on one side, and somewhere near zero (just some resistance to earth) on the alternator side when the engine is not running. When the voltages on each side are balanced, the net result is zero as far as the lamp is concerned. But if the alternator end has a significantly higher voltage imposed on it than the ignition switch side, the lamp, which does not care which way round the voltage is, will glow again.

The loads you are switching to bring it on are downstream of the ignition switch, the headlights are not, so your symptom is completely explained, because the voltage downstream of the switch is dropping. And yes, it has happened to me on 2 cars, one a Mini.

If it is a Lucas 18 acr 45amp alternator it really sounds like the warning light diode gone. new diode pack in the alternator required.

I've never noticed the key being warm when I took it out?
If it's a diode that's gone, is its purpose solely for the dash light? Because I swapped all the other dash lights for LEDs except this one, and if that is the case, I can just pop an LED in here as well and problem solved?

The difference between main and dipped beam is 10 watts, the heated rear screen is 60 watts. Not surprising that the screen puts more load on the system than changing the headlights over.

I'd been wondering the power rating for all the bits thanks! do you happen to know what the heater fan is, and the wiper motor by any chance?

[tiger99]

No, you can not use a LED in this position. The voltage across it may be in either direction, and with your problem, it is almost certainly in the wrong direction. 12V in the wrong direction will blow a LED, even with the correct series resistor for 12V operation.

Also, the current through the bulb is necessary to give the alternator field winding some magnetisation, otherwise it will never generate anything. Without the correct bulb, the alternator will just not start to work when the engine starts.

I think that the diode theory is unlikely for two reasons, firstly the field circuit and warning light diodes are far less stressed than the main rectifier diodes and likely to last a lot longer (your main diodes are ok, or your battery would be flat), and secondly a mechanical switch is less reliable than a lightly stressed diode. But it is not impossible that it is an internal alternator fault, just unlikely, and unlikely things happen sometimes.

But if the switch is not faulty (don't bother measuring it with a multimeter, the best you can usually measure, 0.1 ohm, is way too high, the switch needs to be better than that) the connections in the main brown and white circuits are still suspect.

If the headlights are switched from off to on, not just dipping, does the light change? If it does not get brighter with headlights on, there is nothing wrong with the alternator, and it is the ignition switch or its wiring.

The brown wires from the ignition switch and alternator are probably joined at the solenoid, and that is one place to check for good contact, if it is not the switch itself.

[Dan]

The wiper motor's name is Lucas 14 Watt wiper Motor, the clue's in the name!

The plastic cased heater is also 60 watts, I think. I'm not certain though, i did measure one once but it was a while back. Motors of course draw more power to start than to run and are inductive loads so determining load on the system is not as straightforward as with a plain old resistive heater or tungsten lamp.

The Mini hasn't had an ACR alternator for a very, very long time. I'd be surprised if yours has had one fitted, it's probably an A127 like it's meant to be and these are pretty good little units which were fitted to an awful lot of cars for a very long time. Doesn't mean it hasn't failed, but it wouldn't usually show up with a dim warning lamp if it did. They tend to either fail completely or drop a phase.

I'd tend to try checking the drive belt first myself. It should be tight (not over tight, you can wreck the alternator and water pump bearings) but it's also important the pulleys are clean, and in line. And if it's worn out, it won't work properly however tight it is. The belt should not be sitting deep down in the grooves, if it is then it has worn to be to narrow to grip the sides. Don't get me wrong though, corrosion in the system is the main cause of most of the Mini's wiring issues and causes things to overload. It could be corrosion in switches or joints as Tiger99 says. A single bad joint in a dash connector caused a very similar issue in my own car and drove me mad for weeks, which is irritating because my wiring is all custom.

[tiger99]

I did not even consider belt slip, because he did not mention it screeching, and you would need quite a lot of slip to lose alternator output, as the alternator is almost constant current regardless of speed, above a certain minimum. But it should be checked anyway.

These belts are a pain. Modern cars seem to use a Poly-V belt, which is tensioned automatically by a spring-loaded roller. Obviously you need completely new pulleys, but they never seem to slip and last for ages. I guess these will appear on Minis eventually, if they have not already.

[bluesprite]

Yeah there was a squeak but it changed with speed and not revs and stopped when the car was stationary so I convinced myself it's the pesky front left brake seizing again.

I'll go and have a look tomorrow and report back, thanks to everyone for your help! It's on axle stands at the minute so would rather not start the car until it's back together but I'll check everything mentioned short of the fan belt slipping for wear or corrosion. Thanks again!

Edited by bluesprite, 20 February 2012 - 11:08 PM.

[Dan]

Fan belts only squeal when they are seriously failing. They can be slipping for a long time before you notice any noise.

[bluesprite]

I can't believe this was two weeks ago! my mini's still in the garage in bits and I've been too busy sorting other stuff to try much mentioned here because I can't start the car yet

Someone mentioned the regulator, would this be a good replacement, or something I should consider getting anyway?
http://www.ebay.co.uk/itm/LUCAS-A127-TYPE-ALTERNATOR-REGULATOR-HEAVY-DUTY-75AMPS-/310150553115?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item483669de1b

There is a bit of slack on the fan belt but not too much, how do you know how slack it should be? I've read it can be damaging to have it too tight?

Thanks again for all your help!

[Rented]

start with the simple basic checks first - charging rate . with no load - e.g no lights etc . you want around 13.8 to 14.2 .

Then check the charging rate under load e.g with lights on and the rear heated windscreen and hazards say . you still want the same charging rate of 13.8 to 14.2 roughtly .

Check your battery to ensure its not sulphated at all and lost some of its capacity or that its not taking a charge very well . check its voltage with it disconnected from the car , you want around 12.4v up to say 13.2 maybe .

i think from the soudns of it you have a weak altenator thats not picking up the charging rate enougth when it comes under load but it could be becuase thge battery has lost some of its capacity possibly .

All abit vauge on possibilities but check the simple things first - charging rates and battery !

If you cant test it or able to google how then take it to a garage or mate who knows how to show you for another day .

[bigmatt4]

I can't believe this was two weeks ago! my mini's still in the garage in bits and I've been too busy sorting other stuff to try much mentioned here because I can't start the car yet

Someone mentioned the regulator, would this be a good replacement, or something I should consider getting anyway?
http://www.ebay.co.u...=item483669de1b

There is a bit of slack on the fan belt but not too much, how do you know how slack it should be? I've read it can be damaging to have it too tight?

Thanks again for all your help!

my rules for fanbelts is if you can turn the engine over by turning the alternator pulley it is tight enough if it slips it too loose