Alternator - Help, i cant work this one out on my own

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billiam

billiam

Member
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Herts
Hi
Its been years since I've posted but I constantly use the forum. Every question I've had has been answered in the archives, until now. (gonna be embarrassing if someone posts me a link to a thread with my answer.

A couple of years ago my '91 110 defender 200tdi decided to go bang, a rod came out the side of the block. I've finally got round to fixing it and all was going well. I split the body and chassis, cleaned/repaired/painted/protected the chassis. Got a good engine (god there expensive!!!) a put it all together, replacing parts that were easy to replace with the body off, hard with it on. She started well and drove well.

But the bloody alternators playing up...

Right first of all, light was on, no charge. So i swapped it for the one off my knackered engine, no charge. Swapped the cables, no charge. Blamed the alternator and took it to the shop. It was tested and was working fine, he blamed bad terminals or slipping belt, so i put new terminals on the wire, spent ages with sandpaper cleaning the terminals on the alternator and fitted a new belt, making sure it was tight (and a brand new battery). Still no charge...

With the ignition on, the charge light is on, so no bulb problems, but when i start the engine, it goes out (which seems strange). I put my tester to the battery and it reads 12v, so not enough. When I floor it, the voltage does start to go up, maybe reaching 12.5v, but not the 14v you want. I have 2 brown wires from the alternator to the starter, and tapping into them I get 12.5v with ignition off so my leads to the battery must be ok, with ignition on it drops, and with engine on it doesn't rise, just stays around 12, 12.5v. The brown and yellow wire is all there, connected into the dash. With ignition on it reads a slight voltage (maybe 1.5v, is this enough?), then with engine on, no voltage, which presumable would make the light go out.

Sorry to ramble on but i wanted to be as comprehensive as possible.

Any ideas, I'm proper stuck and am dying to take it for its mot tomorrow so i can drive it again, Thanks, Will
 
what do you get between batt warning light and earth with volt meter?
secondly is the loom like v8 where it uses starter terminal to battery cable as a connection?
 
Had exactly the same problem, tried everything you have, turned out it Was the wires in the plug to loose, Got rid of the black plug cut wires and put new push fit terminals on so they were a tight fit Straight to the spades on alternator, and has worked perfect ever since. Battery now charging over 14 when engine running.
I have a new plug but never got round to fitting it yet.
.
 
Stupid question possibly but has it got the right size pulley to match the new engine type -- i.e.. might be too big in diameter and so not spinning quick enough... just a thought....
 
billiam said:
With the ignition on, the charge light is on, so no bulb problems, but when i start the engine, it goes out (which seems strange). I put my tester to the battery and it reads 12v, so not enough. When I floor it, the voltage does start to go up, maybe reaching 12.5v, but not the 14v you want. I have 2 brown wires from the alternator to the starter, and tapping into them I get 12.5v with ignition off so my leads to the battery must be ok, with ignition on it drops, and with engine on it doesn't rise, just stays around 12, 12.5v. The brown and yellow wire is all there, connected into the dash. With ignition on it reads a slight voltage (maybe 1.5v, is this enough?), then with engine on, no voltage, which presumable would make the light go out.

Any ideas, I'm proper stuck and am dying to take it for its mot tomorrow so i can drive it again, Thanks, Will
Click to expand...

Not necessarily, the 12.5v you are measuring doesn't prove the cables have good continuity only that you have a connection (as there is minimal current flow. If you have a slight resistance in the cable it will drop voltage proportional to the current flowing. Example - assuming your alternator is putting out 14v at its terminal and is charging the battery at 5 amps, if you have 0.25 ohms resistance in the cable it will drop 1.25 volts. 14v-1.25v=12.75v at your battery. If you have minimal current flowing in that wire (engine off / ignition on) then you wont produce any voltage drop so you get a higher reading. Try starting the engine and measuring the voltage at the terminal on the alt, if it is 14ish then alt is working and you have a poor cable/connection somewhere.

one side of the light normally gets its power from the battery, the other side connects to the alternator. The purpose is two fold, firstly it provides a 'kick start' current for the alternator via the bulb (the alt effectively provides the earth return for the bulb which is why it lights up). secondly once the alt is up and running it puts 12v onto that wire, as there is now 12v on each side of the bulb it is effectively turned off.
 
Iv'e just cured this issue on mine. Same engine just re-fit into an 87 ninety. What had happened was that the wire insulation had perished next to the starter motor.

First check your earth straps, from battery to Chassis and block, and Alternator terminals and clean them up.

I always put a cable tie around the solenoid after replacing a starter. Unfortunately the wire insulation had cracked so the wiring was earthing out on the casing of the starter. Remove your exhaust down pipe and starter then you can trace the wires around the back of the engine and check for damaged insulation etc. The thin wire from the Alternator is your excitation current of which the current goes from the battery, through the battery indicator lamp then to the terminal on the alternator. If your battery light is functioning correctly it still could be damaged between the light and the alternator. The 2 large brown wires are the 12v feed from the alternator to the battery of which go to the positive terminal on the starter.

I think all of the wires were earthing out so I went mad with electrical insulation tape. Ill replace the wires............. one day.

Hope this helps.
 
Last edited:
Thanks for the replys, lots to try today.

I think i'll start with the earth and put a new one on, it cant hurt to have more.

Might it be a good idea to get a good thick cable, insulated well, and run it straight from the alternator terminals to the battery? It will remove any issues with the connection at the starter... If it still doesn't work after that then i know there is something wrong with the brown yellow wire behind the dash.
 
Just discovered, with help for a great guy here on LZ Kwakerman, that the purpose for an inline resistor on the Brown/Yellow wire in the main loom was to allow the alternator to charge if the charge bulb blows.

Cant see it being coincidental, but make sure the charge light works and the resistor is not open, also trace the Brown/Yellow wire to make sure its connected.

See thread here
http://www.landyzone.co.uk/lz/f7/anyone-knows-what-resistor-281777.html
 
Barbados said:
Just discovered, with help for a great guy here on LZ Kwakerman, that the purpose for an inline resistor on the Brown/Yellow wire in the main loom was to allow the alternator to charge if the charge bulb blows.

Cant see it being coincidental, but make sure the charge light works and the resistor is not open, also trace the Brown/Yellow wire to make sure its connected.

See thread here
http://www.landyzone.co.uk/lz/f7/anyone-knows-what-resistor-281777.html
Click to expand...

not sure that's standard. don't remember it on the 300 anyway.

anyhoo, barb i think you might have misunderstood a little.

the resister is in parallel with the bulb. you need some resistance on the wire to get the alt excited. this is usually done by the bulb.

if the bulb goes, then current will go via the resistor which will now also give a load and excite the alt.

so since he has the warning light on, then the resistor isn't used. hope that made sense :)
 
billiam said:
Hi
Its been years since I've posted but I constantly use the forum. Every question I've had has been answered in the archives, until now. (gonna be embarrassing if someone posts me a link to a thread with my answer.

A couple of years ago my '91 110 defender 200tdi decided to go bang, a rod came out the side of the block. I've finally got round to fixing it and all was going well. I split the body and chassis, cleaned/repaired/painted/protected the chassis. Got a good engine (god there expensive!!!) a put it all together, replacing parts that were easy to replace with the body off, hard with it on. She started well and drove well.

But the bloody alternators playing up...

Right first of all, light was on, no charge. So i swapped it for the one off my knackered engine, no charge. Swapped the cables, no charge. Blamed the alternator and took it to the shop. It was tested and was working fine, he blamed bad terminals or slipping belt, so i put new terminals on the wire, spent ages with sandpaper cleaning the terminals on the alternator and fitted a new belt, making sure it was tight (and a brand new battery). Still no charge...

With the ignition on, the charge light is on, so no bulb problems, but when i start the engine, it goes out (which seems strange). I put my tester to the battery and it reads 12v, so not enough. When I floor it, the voltage does start to go up, maybe reaching 12.5v, but not the 14v you want. I have 2 brown wires from the alternator to the starter, and tapping into them I get 12.5v with ignition off so my leads to the battery must be ok, with ignition on it drops, and with engine on it doesn't rise, just stays around 12, 12.5v. The brown and yellow wire is all there, connected into the dash. With ignition on it reads a slight voltage (maybe 1.5v, is this enough?), then with engine on, no voltage, which presumable would make the light go out.

Sorry to ramble on but i wanted to be as comprehensive as possible.

Any ideas, I'm proper stuck and am dying to take it for its mot tomorrow so i can drive it again, Thanks, Will
Click to expand...

you've got that a bit mixed up.

when your turn the ign on, the batt light comes on to warn you there is not enough charge. this is as kwacker said, due to 12v going through the bulb and earthing via the alt. so that's good!.

when the you start the engine, the alt kicks in, stops grounding the light and puts 12v back up the bulb wire. 12v down and 12v up cancel each other out, so the bulb goes out. you say this happens, so good stuff!

now, measure your bat voltage across the posts after the engine has been off for a while.. what is it?

also it sounds like you've been swapping parts about. are you sure the alt pulley is the correct size?

google says it is 64mm diameter and looks like

(rinsed image)
gallery_3439_602_17362.jpg
 
I've been at this bloody land rover all day and its still not working.

Headline is that ive run a thick cable from b+ straight to the battery. With the engine running and alternator cable off the battery, straight onto the tester, 14v. When i connect it to the battery, it drops instantly to 12.5v and only raises to 13v when revved. This makes no sense and im pulling my hair out.

Here's what ive done. Put both alternators on, the one off the new engine and the one off my knackered engine, same result.
New earth strap from engine to chassis, also jump cable from negative to chassis, same result so i can rule out an earth.
Disconnected the brown yellow wire, ignition on, no charge light, earthed the cable, light came on. Everything checkes out there.
Connected the brown yellow wire to a bulb and the other to positive. Engine off, light on. Engine on, light off. No charge.
Removed the entire engine loom and replaced it with the one off my old engine incase of bad wires. No change.

Any thoughts...
 
billiam said:
I've been at this bloody land rover all day and its still not working.

Headline is that ive run a thick cable from b+ straight to the battery. With the engine running and alternator cable off the battery, straight onto the tester, 14v. When i connect it to the battery, it drops instantly to 12.5v and only raises to 13v when revved. This makes no sense and im pulling my hair out.

Here's what ive done. Put both alternators on, the one off the new engine and the one off my knackered engine, same result.
New earth strap from engine to chassis, also jump cable from negative to chassis, same result so i can rule out an earth.
Disconnected the brown yellow wire, ignition on, no charge light, earthed the cable, light came on. Everything checkes out there.
Connected the brown yellow wire to a bulb and the other to positive. Engine off, light on. Engine on, light off. No charge.
Removed the entire engine loom and replaced it with the one off my old engine incase of bad wires. No change.

Any thoughts...
Click to expand...

answer the q's above
 
Sorry, I posted that without flicking to page 2.
Pully is correct.
Voltage at the battery is 12.5v at rest. all normal.

I've just gone out to do another test. I started the engine and pulled the terminals off the battery, leaving the alternator connected and it didn't die. Ran for a good minuet until i turned it off. So i'm getting something from the alternator. Are the standard 200tdi alternators just rubbish? am I asking too much from it to expect 14v across the battery?
 
billiam said:
Sorry, I posted that without flicking to page 2.
Pully is correct.
Voltage at the battery is 12.5v at rest. all normal.

I've just gone out to do another test. I started the engine and pulled the terminals off the battery, leaving the alternator connected and it didn't die. Ran for a good minuet until i turned it off. So i'm getting something from the alternator. Are the standard 200tdi alternators just rubbish? am I asking too much from it to expect 14v across the battery?
Click to expand...

don't do that, you'll kill the alt.

you got a trickle charger? go stick the battery on charge over night and then try with the multi again.
 
Analogue multi meter, digital alternator tester, both read the same. I put it on my ford ranger and it reads 14v at tickover.

Batterys giving out 12.5v, brand new thursday. Its a right big bugger. Would the alternator cut out (not charge) a fully charged battery? I've tried it with all the lights and blower on...
 
billiam said:
Analogue multi meter, digital alternator tester, both read the same. I put it on my ford ranger and it reads 14v at tickover.

Batterys giving out 12.5v, brand new thursday. Its a right big bugger. Would the alternator cut out (not charge) a fully charged battery? I've tried it with all the lights and blower on...
Click to expand...
Alternator should give a minimum of 13.8 volts at 2K rpm, preferably 14.2 or more regardless of battery state unless the battery is fecked and holding the output down.
Disconnecting the battery with the alternator running will destroy diodes in the alternator unless you are very lucky.
Use a pair of jump leads to connect the alternator direct to the battery, alternator case to battery negative, alternator output to positive and see what you get. You may need to raise the revs to 2K to see the correct voltage depending on the pulley size.
 
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