A127 Alternator - Indicator Light

[gandy]

Hi,

I think our alternator has failed, the charge warning light doesn't come on. It does light if I disconnect the terminal from the alternator, and touch it to ground so the lamp and wiring appear not to be the problem. Also checked the alternator ground which also seems OK.

Does anyone know whether the warning light circuitry is something that can be checked out readily? Currently my plan is to fit a replacement alternator, and get this one fixed as a spare so there's not a great rush. Would be interested to see whether I can fix it myself rather than doing my usual which is to take it to the local auto electrical place. In case it's relevant the failed alternator is a marine version with isolated return.

Thanks,

Tony S

 

[alahol2]

The charging lamp on my alternator has never come on. As soon as the 'ignition' switch is turned on 12V is output on the 'L' indicator light pin. I've been round and round in circles trying to figure out what is going on but never worked it out. The alternator works perfectly well and has done for the last 12 years in this state. So maybe not an urgent problem to solve.

 

[rogerthebodger]

Hi,

I think our alternator has failed, the charge warning light doesn't come on. It does light if I disconnect the terminal from the alternator, and touch it to ground so the lamp and wiring appear not to be the problem. Also checked the alternator ground which also seems OK.

Does anyone know whether the warning light circuitry is something that can be checked out readily? Currently my plan is to fit a replacement alternator, and get this one fixed as a spare so there's not a great rush. Would be interested to see whether I can fix it myself rather than doing my usual which is to take it to the local auto electrical place. In case it's relevant the failed alternator is a marine version with isolated return.

Thanks,

Tony S

Check the resistance between the terminal on the alternator and the engine or alternator negative with the charging light disconnected. If it is open circuit (no reading on a multimeter) the alternator needs fixing.

Take it to a local auto electrician who will check it out and repair it.

 

[VicS]

Hi,

I think our alternator has failed, the charge warning light doesn't come on. It does light if I disconnect the terminal from the alternator, and touch it to ground so the lamp and wiring appear not to be the problem. Also checked the alternator ground which also seems OK.

Does anyone know whether the warning light circuitry is something that can be checked out readily? Currently my plan is to fit a replacement alternator, and get this one fixed as a spare so there's not a great rush. Would be interested to see whether I can fix it myself rather than doing my usual which is to take it to the local auto electrical place. In case it's relevant the failed alternator is a marine version with isolated return.

Thanks,

Tony S

Check the brushes! and the state of the slip rings.

 

[superheat6k]

I have recently bought an A127 size alternator 12v 70amp (replaced a 55a) from a supplier in Plymouth. The service was excellent. You need to specify left or right hand for the mounting bracket position. Was about £140 inc next day, prompt delivery.

The Starter Motor & Alternator Co. Ltd
01752 339871

 

[JVL]

I have recently bought an A127 size alternator 12v 70amp (replaced a 55a) from a supplier in Plymouth. The service was excellent. You need to specify left or right hand for the mounting bracket position. Was about £140 inc next day, prompt delivery.

The Starter Motor & Alternator Co. Ltd
01752 339871

+1 have used them more than once excellent company

john

 

[William_H]

Check the brushes! and the state of the slip rings.

I agree. Not much goes wrong with alternators except the slip rings and brushes. Unless ti also has a regulator built in as some car alternators do. good luck olewill

 

[jimmyk]

Have you checked if it's charging with a multi meter.

 

[gandy]

Thanks everyone. I didn't check whether it charged as I didn't have a meter with me, so I removed the alternator and have it at home. I'll check resistance on the warning lamp circuit as suggested, also the brushes and slip rings. I'm trying to think how I can test it other than taking it back on board and refitting it.

 

[jimmyk]

tony brooks website on electrics is excellent

 

[peteK]

I have recently bought an A127 size alternator 12v 70amp (replaced a 55a) from a supplier in Plymouth. The service was excellent. You need to specify left or right hand for the mounting bracket position. Was about £140 inc next day, prompt delivery.

The Starter Motor & Alternator Co. Ltd
01752 339871

About half that price on ebay

 

[superheat6k]

About half that price on ebay

Not isolated return. I checked that out, although possibly refurbished, but not new.

 

[Redwing228]

Thanks everyone. I didn't check whether it charged as I didn't have a meter with me, so I removed the alternator and have it at home. I'll check resistance on the warning lamp circuit as suggested, also the brushes and slip rings. I'm trying to think how I can test it other than taking it back on board and refitting it.

If you can rig up a temporary 12v supply to feed the warning light circuit (excitation) via a small stand-in warning lamp and spin the alternator using an electric drill you can test it whilst clamped in a bench vice. I did this when I fixed the faulty Denso alternator off our Beta 20 recently. In our case it was the regulator that had failed.. Still don't know why it failed.

My Land Rover 110 has a A127 unit and it is a tough and reliable machine in my opinion.

 

[jakeroyd]

Bit late perhaps if you have removed the unit.
however , just check any outlet or across the battery wit the engine running.
if you see around 14.5v you are charging.

 

[Birdseye]

Bit late perhaps if you have removed the unit.
however , just check any outlet or across the battery wit the engine running.
if you see around 14.5v you are charging.

If he sees anything more than 12.8v he is charging.

 

[Birdseye]

Hi,

I think our alternator has failed, the charge warning light doesn't come on. It does light if I disconnect the terminal from the alternator, and touch it to ground so the lamp and wiring appear not to be the problem. Also checked the alternator ground which also seems OK.

Does anyone know whether the warning light circuitry is something that can be checked out readily? Currently my plan is to fit a replacement alternator, and get this one fixed as a spare so there's not a great rush. Would be interested to see whether I can fix it myself rather than doing my usual which is to take it to the local auto electrical place. In case it's relevant the failed alternator is a marine version with isolated return.

Thanks,

Tony S

Been through all this aggro and a few alternators over recent years until I found that my problem was overheating of the diodes. Anyway what I did find was that it simply want economic to repair alternators and the trade had died out locally. I accept that Scotland is likely to be a bit behind the times so you may be able to get some work done up there cheaper than buying new, but I found that they simplest and most economical way forward was to junk the old one and buy a new guaranteed alternator. Whats more |I found it best to buy one made in europe - the chinese ones werent to the same electrical standard

 

[gandy]

Thanks everyone. I didn't have a meter on board which was why I couldn't test at the time. Taking the assembly off the back it looks as if brush or slip ring is the immediate issue. One slip ring is nice and shiny, the other one is not. I haven't yet dismantled further to see if the slip ring looks like it's damaged or worn, or just tarnished because the brush isn't making contact. I thought the brushes looked OK, but don't know how long new ones should be.

I'm now puzzling a little about how it is supposed to work. The removable module with the brushes is described as a regulator. As far as I can see the path goes - 12V -> Lamp -> Brush -> Field windings -> Brush -> Regulator -> Ground. I can't see any other connection, which means I can't see how the regulator can sense the output voltage. I was expecting to see a connection to B+ as well.

 

[earlybird]

In, say, the Yanmar Hitachi alternator, a rotor coil brush is connected internally to one bank of the diodes, hence sees the output voltage. (The indicator lamp is connected to this point also).
There is therefore a series connection from the diode output to the regulator via the rotor coil.
Isn't the AC127 similar?

 

[gandy]

I've just had a look around, and according to some diagrams there are diodes from the stator windings to the indicator light connection, that must be inside the back plate of the alternator, but that would explain how it senses output voltage.

 

[VicS]

I've just had a look around, and according to some diagrams there are diodes from the stator windings to the indicator light connection, that must be inside the back plate of the alternator, but that would explain how it senses output voltage.

The field diodes ?