bloomin battery light.

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jon-ovlov
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Joined: 30 Jul 2010 09:45 pm
Location: Bristol/Birmingham

Re: bloomin battery light.

Post by jon-ovlov » 08 Nov 2010 11:42 pm

Ride_on wrote:What is the actual battery voltage with the engine running? I presume its low, ie 12.5v or something.

The small red wire goes to the warning light, and the blue/red one should be at battery voltage. There maybe a small ground wire for the field coils so make sure that is solid at both ends (or 0v between the alternator ground and battery ground, a small voltage will indicate a bad ground).

The warning light is part of the circuit and also needs a good connection, according to the circuit diagram there is also a resistor on the dash panel (gauges PCB) which is also needed. What the correct voltage for the small red wire is I don't know off hand, but I suspect this is where your problem maybe, assuming you havn't had 3 faulty alternators. A 360 dash has a white block ceramic 120ohm resistor in parallel with the light, I'd check around this for corrosion and correct resistance.
Around 12 volts yes. Blue/red wire is at battery voltage. surely the warning light circuit cant have that much affect on the alternator charging the battery? The voltage at the terminal on the fuse box that belongs to the red wire was at battery voltage, which would lead me to believe that it is the red wire thats the problem. it just doesn't make any sense really. i was getting 6 volts from another terminal, the brown one on the fuse box. cant remember what exact terminal it was though (i know the lead coming out was blue). On the 340 circuit diagram, there is no resistor as far as i can see. Where would i find the grounds for the circuits? It wouldnt be that ive disconnected the front wiper motors at all? (stupid question).

Btw cheers for your response, its given me something else to go on. :mrgreen:
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Speedy88 wrote: Leave choke on, idling obnoxiously until neighbours peer out windows at the noisy exhaust
Give neighbours thumbs up
Rev engine to 7K
Exit street sideways
Win at life.

themightybaggins
Posts: 49
Joined: 28 Dec 2008 09:52 pm
Location: bromley

Re: bloomin battery light.

Post by themightybaggins » 09 Nov 2010 12:17 pm

The wire that goes to the battery light is absolutely vital for the alternater to charge properly (if at all).

The usual set up is (not sure about v300's specifically, this is general) the lakp in the dash will be fed from a live source, like an ignition live, and the other terminal is wired to the alternater. The alternater will supply the earth for the lamp, which is why it lights when the engine is not running. As soon as the alternater turns, if its working correctly, it will remove the earth supply to the lamp, and the light goes out.

You will have a large wire from the alternater to the battery positive, or the starter motor possibly, this carries the real charge to the battery.

You may also have an ignition live feed directly to the alternater.

All the above need to be working for the alternator to charge properly.

You can test the battery light wiring circuit, by using a small lamp like a number plate light, or interior light or something, wire one side directly to the battery positive, other to the correct wire on the alternator. It should light when the engine is off, and go out as soon as the engine starts, almost regardless of the battery condition.

Put a volt meter accross the battery with the engine running, then try it with the test light as i described, and note the voltage. You need about 13.5 at least. Ideally it should be 14.4, but rarely is in real life.

If you're not confident doing that, take it to an auto electrican, who should be able to diagnose it quickly. I can highly recommend one if you're anywhere near the south east of london.

themightybaggins
Posts: 49
Joined: 28 Dec 2008 09:52 pm
Location: bromley

Re: bloomin battery light.

Post by themightybaggins » 09 Nov 2010 12:20 pm

I should mention that what i described, is only a roadside test, you wouldnt really want to go driving it like that!

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jon-ovlov
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Re: bloomin battery light.

Post by jon-ovlov » 09 Nov 2010 07:40 pm

cheers for that reply. i'll give it another go tomorrow. I replaced the small red wire today, and that didnt work. I understand what your saying about the earth on the alternator etc, so will give that a go tomorrow too. As far as i can see, its the alternator again. judging by doing several tests, replacing bits, and getting a volt metre on it. I get 10 volts from the small red lead. 12 from the blue/red one, and 12 on the large red battery cable. It has to be the alternator.

argh!
Image
Speedy88 wrote: Leave choke on, idling obnoxiously until neighbours peer out windows at the noisy exhaust
Give neighbours thumbs up
Rev engine to 7K
Exit street sideways
Win at life.

themightybaggins
Posts: 49
Joined: 28 Dec 2008 09:52 pm
Location: bromley

Re: bloomin battery light.

Post by themightybaggins » 09 Nov 2010 08:04 pm

It sounds like that could be the case,

was it a new alternator you put on? Must be under warrenty surely?

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jon-ovlov
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Location: Bristol/Birmingham

Re: bloomin battery light.

Post by jon-ovlov » 09 Nov 2010 08:08 pm

Yeah it was. Reconditioned anyway. and it is in warranty. Just cant believe its my third one! First one went that was on the car when i bought it, second the pulley gave way, this one isnt producing charge any more. 3rd times a charm!!! :lol:
Image
Speedy88 wrote: Leave choke on, idling obnoxiously until neighbours peer out windows at the noisy exhaust
Give neighbours thumbs up
Rev engine to 7K
Exit street sideways
Win at life.

themightybaggins
Posts: 49
Joined: 28 Dec 2008 09:52 pm
Location: bromley

Re: bloomin battery light.

Post by themightybaggins » 09 Nov 2010 08:32 pm

Well its obviously as arse ache taking it off again, but at least they should give you a new one free!

Reconditioned original parts are often better than aftermarket new parts. Depending on who reconditioned it of course!

Ride_on
Posts: 2262
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Re: bloomin battery light.

Post by Ride_on » 10 Nov 2010 07:37 pm

jon-ovlov wrote:
Surely the warning light circuit cant have that much affect on the alternator charging the battery? The voltage at the terminal on the fuse box that belongs to the red wire was at battery voltage, which would lead me to believe that it is the red wire thats the problem. it just doesn't make any sense really. i was getting 6 volts from another terminal, the brown one on the fuse box. cant remember what exact terminal it was though (i know the lead coming out was blue). On the 340 circuit diagram, there is no resistor as far as i can see. Where would i find the grounds for the circuits? It wouldnt be that ive disconnected the front wiper motors at all? (stupid question).

Btw cheers for your response, its given me something else to go on. :mrgreen:
The resistor is on my 340 haynes diagram, but it just doesn't say what value it is thats why I mentioned the 360 one as I have a dash out. Its hidden in the dash image, but I need to use a USB microscope to read the drawing ;-)

It is funny how the alternator works and I'm not sure I have got fully yet (even though I am an Electronics Engineer), there are no magnets, so the field coils need some power to start with to enable the rotor to start generating. Most alternators are self excited now (as opposed to battery excited), as this enables the voltage drop due to high current draw to be compensated for (at low rpm) rather than just maintain a constant voltage. You do however need a small current to get things going and this normally comes via the warning light+resistor which is also linked to the battery.

My wild guess is that the resistor is not connected/badly connected and you are fully reliant on the warning bulb to provide starting current but this is probably not enough hence the need for the resistor.
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

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jon-ovlov
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Location: Bristol/Birmingham

Re: bloomin battery light.

Post by jon-ovlov » 13 Nov 2010 06:55 pm

Fixed! got the alternator swapped under warranty, getting a nice 13V + across the battery.no battery light warning. Great! Cheers for the replies guys! Lets hope 3rd times a charm!

Jon :D
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Speedy88 wrote: Leave choke on, idling obnoxiously until neighbours peer out windows at the noisy exhaust
Give neighbours thumbs up
Rev engine to 7K
Exit street sideways
Win at life.

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