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Alternator Problem

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I have the following symptoms on a 1984 3.5 V8 90:

Charge light comes on as normal before starting engine, When I start the engine it goes dim but as you rev the engine it gets brighter. According to the bible it is the main output diode that has gone open circuit. Is this something that

1. I can do anything about (without complete new Alternator)

2. My normal landrover garage can deal with

or do i need a specialist auto-electrician to refurb the alternator.

also why does my alternator not look like any of the ones in the manual :unsure:

Any advice is appreciated

Rob

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Personally, I would have a good Auto Sparky check it out. He/she is in the best position to check & rectify problems on & off the vehicle. Besides, your LR Garage may probably send it out for repairs anyway.

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I am no sparky but owning a Defender has forced me to start dabbling in the dark art. To do this you will need a simple avometer or voltmeter which can be got at places like radioshack, halfrauds, ace and so on for very cheap.

If you have a avometer/voltmeter then do the following checks:

Volt reading at battery terminals with switch off and no drain on battery - should be at least 12 V

Volt reading with switch open and no other drain on battery - should be around 12 V

Volt reading as starter turns - should not drop below 9 volts.

Volt reading with engine running and no throttle and no other drain on battery - shouold be about 13.5 V

Volt reading with engine running and no throttle but plenty of drain (ie. Air con + window heater + head lights) should not drop below 12 V and with say 1500 rpm should be back at 13.5 V

Volt reading with engine running at around 2000 rpm snd no drain on battery - volt reading should be around 13.5 V

If volt readings are lower than these then re-do the tests with the voltmeter attatched to the battery cables BEFORE the battery terminals and compare the results.

If the volt reading is higher than 14.5 V during any of the above then the alternator regulator is shot and your battery if not allready cooked is well on it's way to being cooked.

Come back with the test results for more info.

Adam

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Alternator red light not going out stays on but not bright and it will flicker slightly as the revs are increased.

1995 Defender 300tdi

Managed to find this info and will try it out tomorrow, but is there anyway to identify if the resister/part behind the dash is at fault and not the alternator?

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The resistor is there to provide a load for the warning lamp, with the circuit passing through a diode and into the alternator.  The lamp is on when the alternator isn't spinning. So I'd say that it is in-circuit and is working. 

When the alternator spins up, it should start to generate volts and once it does, it equalises the volts across the lamp, so that it goes out. If it doesn't it's an indication that the alternator is faulty. A new rectifier pack will possibly sort it (around £10) or you could remove the unit and take it for testing at an auto electrician.

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Get it fixed ASAP.  The AC voltage that comes with a dead diode kills other items in the vehicle really fast.  If you do not already have a 100 A alternator, it is a good opportunity to upgrade to one.

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Will do, don't need to use the vehicle. Trying to chase up a repair kit for the alternator, proving not as easy as I thought it would be. A few part nos to check out.

Is it worth putting in a 100A. I have thought about it, but some say do some say don't?

Edited by bushwhacker

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If it's been muddy you might find the brushes are stuck and a quick clean & wiggle will free them for zero pounds.

If you put in a higher capacity alternator you need to upgrade the main charging wire to suit - and if your truck doesn't have any big loads (like a winch or fridge or a million spotlights) it won't do much other than refill your battery a little faster after each start.

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9 hours ago, FridgeFreezer said:

If it's been muddy you might find the brushes are stuck and a quick clean & wiggle will free them for zero pounds.

No, because the current through the indicator lamp is the current through the brushes. When it lights, the brushes must have contact. Sounds like a diode.

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1 hour ago, Sigi_H said:

No, because the current through the indicator lamp is the current through the brushes. When it lights, the brushes must have contact. Sounds like a diode.

Stuck brushes can have very light/intermittent contact, enough to give the symptoms described, that's why I suggested it... also it's a 5 minute check that costs nothing.

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Agree. In the same way my daughter’s washing machine wouldn’t spin. It did the other rotations but no spin. The brushes were worn right down and consequently little pressure from the springs. There was enough contact for the low current demand but not on spin cycle. 

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Sorry, but the AC Motor in a washing machine is completely different!

If the charge indicator lamp has 2W the current will be around 200 mA. Since the indicator is lighting before start, there must be going current through the brushes.

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2 minutes ago, Sigi_H said:

If the charge indicator lamp has 2W the current will be around 200 mA. Since the indicator is lighting before start, there must be going current through the brushes.

No-one's said there's not current going through the brushes - just that it's possible to have a poor contact. I've seen this exact thing many times due to muddy brushes.

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16 minutes ago, Sigi_H said:

Sorry, but the AC Motor in a washing machine is completely different!

Why is it?

Impedance or resistance but the same issue - it might be too high.

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Please look at Wikipedia to see the differences between AC an DC Motors/Generators.

but it doesn't matter anyway, because he has to look for the regulator and it is connected to the brushes. I would remove the generator completely and measure the diodes and the brushes on the workbench.

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I may have forgotten some aspects since graduating, as it has been a fair few years. I don't see why my description of dodgy brush contact on an AC motor is any less relevant in this case.

Edited by Peaklander
Deleted my arrogant words - sorry

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ok, no need to consult Wikipedia 😉

The difference is that the generator in the car has an indication of whether a rotor current is flowing. Sometimes I had the problem with different generators that the slip rings weren't round anymore. The brushes therefore had no contact at higher revs due to jumping, but almost always when stationary.
As I said before, the thing has to be out anyway. Then you can look for all possibilities.

Edited by Sigi_H

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1 hour ago, Sigi_H said:

Please look at Wikipedia to see the differences between AC an DC Motors/Generators.

An alternator is an A/C generator.  Exactly the same as an A/C motor.....

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Yes, but without the diodes, which are very important in this application and which make it a DC application. This became a very theoretical discussion, which does not really help.

Best to do is to put the generator out and test all mentioned points. Mud in the brushes, non-circular slip rings, short or interrupted diodes or connections. All this can be done stationary and measured ohmic.

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Alternator removed and looking a bit rough, if the date on it is anything to go by it has been there for 25 years. Going to put a complete new alternator, belt, waterpump, gasket and p gasket on. I will maybe do up this old one. How does the center shaft come out, is it pressed in? If anyone thinks it is not worth it looking at this pics please say so. 20191128_154524.thumb.jpg.c180b46a03db6d5c33a9ffcaf17919f5.jpg20191128_154513.thumb.jpg.f4efa14097cfe9a09416e6ecf1167400.jpg20191128_145508.thumb.jpg.6c7410db32706a57cd67ebd2e7379ee8.jpg

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Oh dear. There is some muck in there. Have you taken the diode packs off? I'm no expert on alternator disassembly but I don't think that you have to go too mad on the mechanical strip down but you could clean up the electrical stuff where you have already exposed it. I believe you will find links to diode packs if you google AMR3412.

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I can see, the upper slip ring has a deep groove. It is only worth to be done by yourself if you are able to replace the slip ring. If it's possible to get a generator on exchange base, do it.

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I'd question if it's worth the manual labour Vs replacing it with a good rebuilt one. Also, unless there's something obviously wrong with the bearings don't fiddle with them, 99% of problems are the regulator pack or brushes. Last person I know pressed new bearings into his alternator it seized up not many miles later... on the way to a ferry... mentioning no forum moderators... :ph34r:

https://jasm.co.uk/ are good guys for proper refurb.

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^^ yeah unless it's a hard to find alternator I wouldn't bother spending hours refurbing one.  Last time I did one I found it was a lottery with the diode packs and regulators - had to rebuild it twice due to rubbish components and it lasted less than 12 months before the diode pack went bad again, nearly wrecking a battery at the same time. £50 and 30 mins changeover, job done. 

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