New alternator still not charging

[AceOfHearts]

Almost got the car ready for its MOT now, and since it was not charging I decided to replace the very shabby looking old alternator.

Unfortunately this has not fixed the problem and it is still not charging

Is there a fuse anywhere in the line that will stop it?

I guess I will start having to chase all of the cabling through now!

[jmorgan]

Not had a problem with an alternator for many a year, three cars ago it was the ignition bulb blown, it was part of the circuit to tell the alternator to start charging. Not having wiring diagram to hand to check if it is still the case.

I am probably talking out me nether regions though.

[ElvisWedgely]

Not only is the ignition bulb a part of the curcuit but unless its the correct rating bulb fitted the system will not charge. As far as I know, everthing is built into the alternator and there is nothing in between. It could be earth or the wiring.

Tony.TCB

[phazed]

Griffs and chims have a 100 amp fuse next to the sump.

If this is blown, the battery won't charge.

Maybe you have one.

[Wedg1e]

jmorgan said:

Not had a problem with an alternator for many a year, three cars ago it was the ignition bulb blown, it was part of the circuit to tell the alternator to start charging. Not having wiring diagram to hand to check if it is still the case.

I am probably talking out me nether regions though.

I'd go with this, the original alternator may not have been faulty at all

[AceOfHearts]

Wedg1e said:

jmorgan said:

Not had a problem with an alternator for many a year, three cars ago it was the ignition bulb blown, it was part of the circuit to tell the alternator to start charging. Not having wiring diagram to hand to check if it is still the case.

I am probably talking out me nether regions though.

I'd go with this, the original alternator may not have been faulty at all

The 'not charging' light is illuminated, not noticed an ignition light though. Where would it be on the dash (1982 square clock type dash)?

You're right the original alternator might have been Ok, but it was right below where the rats were nesting so it was very rusty and smelly, and I think worth replacing anyways

Edited by AceOfHearts on Saturday 3rd May 13:05

[QBee]

You can test whether you have a (working) 100 amp fuse very easily. You should be able to see the battery from the alternator, electrically speaking.

Take your multimeter (15 quid from Maplins or Halfrauds) and switch to the 20 volts scale.
Engine and ignition OFF.

Stick red probe through the holes at the back of the alternator (opposite end to the pulley). Black lead onto the cylinder head or body of the alternator (or any other earth). Probe around until you find 12.8 volts. If you do, it ain't the 100 amp fuse gone. If you don't, trace the thick wire from the alternator, looking for a fuse or a bad connection.

[ElvisWedgely]

How do you know the alternator is not actually charging? Have you tested the battery terminals with the car running? The reading should be 14.5v or more if it's charging. 12.5v or less if it's not.

This is how an alternator works. When the car starts up, the alternator doesn't automatically start charging.
For the alternator to start charging, it has to receive a signal from the ignion, telling the alternator to start charging. If it doesn't receive this signal, it will spin but not charge. The signal wire on the back of the alternator is one of the thiner wires, and if you look at the wiring diagram, it comes from the back of the ignition, via the ignition light. That is why, if the ignition light is blown, or the wrong rating,the signal that returns to the alternator to tell it to start charging will not work. This action is called exciting the alternator. You can actually exite the alternator manually, when the car is running, and to do this you would need to short the live wire behind the alternator with the signal wire to excite the alternator. This would then get the alternator charging, and it will stay charging untill the car is switched off and back on again. This is why the automstic signal system has to function, in order to make the alternator charge automatically on start up.

I hope that makes sense. I spent a whole day in my garage with a car electrician when I had a similar problem corrected.

Tony.TCB

[AceOfHearts]

Thanks everyone, I understand the alternator needs kicking in as i had the bulb go on my girlfriends old Morris Minor which caused the same issue.

I have just been out with the meter to try and figure out what is going on:

The two top brown wires (heavy cable)

-No voltage with ignition on or off, measured to the engine and the negative side of the battery to make sure.
-No continuity to earth (I know there shouldn't be anyways) or the battery +Ve

The small 'exciting' cable at the bottom

-Showing 1.4v with ignition on
-Not tried with engine running as its a bit late to start it up

The bottom picture is what the dash looks like with the ignition on (ignition light is illuminated)

This makes me think there may be a blown fuse or break in the cable between the battery and alternator as there appears to be no connection. Looks like I need to start rooting round tomorrow

Edited by AceOfHearts on Saturday 3rd May 20:49

Edited by AceOfHearts on Saturday 3rd May 20:51

[Mr Tank]

Hi Lewis

If you haven't sorted it by Monday I have two early FHC's at Rushden you can look at when you come and we can help you trace the fault using these cars.

Andy

[jmorgan]

"no charge", that the ignition lamp? If so it ain't that unless its the wrong bulb? How about that earth bolt if it is indeed what it is. Meter it out?

[AceOfHearts]

jmorgan said:

"no charge", that the ignition lamp? If so it ain't that unless its the wrong bulb? How about that earth bolt if it is indeed what it is. Meter it out?

I assume so as there is no other lamp in the dash that would make any sense, and that is the only one that comes on with the ignition

[AceOfHearts]

Progress!

Cleaned up the connection on the back of the 'No Charge' lamp. Am now getting battery voltage at the exciter cable on the alternator. I started the engine up, and the 'No Charge' lamp is now going out (which it wasn't before) but the battery is still not charging (showing 12v)

Now I just think there is a break in the cable between the alternator and battery but at least I am getting somewhere

[jmorgan]

Just been nosing at my wiring diagram as you find this. On my 400, and I assume it is not 400 only, Battery to alternator. Alternator to bulb. Back of the bulb then goes into the dash on a common rail if I am following the diagram correctly. This rail feeds the volt meter first then shoots off somewhere else. Still chasing it out but doing other stuff as well.

[phazed]

AceOfHearts said:

Progress!

Now I just think there is a break in the cable between the alternator and battery but at least I am getting somewhere

As mentioned before, must be a fuse.

Coincidentally, this happened to me yesterday!

No spare fuse so temporarily took the fuse out of the equation and bolted the 2 cable ends together.

[honestjohntoo]

jmorgan said:

Back of the bulb then goes into the dash on a common rail if I am following the diagram correctly. This rail feeds the volt meter first then shoots off somewhere else.

That mentioned rail should carry 12 volts brought to the instrument cluster on a white wire from the ignition switch - usually un-fused because a blown fuse can shut down the charging system.

The voltage thro' the bulb excites the field coils of the alternator and if the alternator is duff - ie not charging, the bulb is effectively earthed inside the alternator and is illuminate to warn of 'not charging;.

If the voltage from the ignition switch to the rail is missing the alternator cannot get going.

Likewise, If the bulb is duff, the alternator cannot get going.

For both the above the bulb is not lit.

If the alternator is OK and charging, the voltage on the other side of the bulb goes to 12 volts and the bulb is extinguished because both sides of the bulb are at the same voltage, - ie everything OK.

If the bulb glows dimly the alternator is not putting out full voltage, the voltage across the bulb is thereby reduced, ie not sufficient to light the bulb brightly.

The common cause of the above is a duff rectifier inside the alternator.

If you want to see a typical circuit go to here

http://www.vintagemodelairplane.com/pages/Download...

and eyeball components No 1 and No 44 on my PDF therein.

The circuit is not TVR, but your charging stuff will be similar.

Apologies if you already know this!!!

[Jack Valiant]

Looking at the pictures, and its difficult to see, but it looks to me like its connected wrong fella..... The 2 brown cables are normally connected to the screw connector with nuts on the heavy output side of the alternator? It looks to me like you have them connected to the spade connector .?? Quick test, put your meter onto the big connector with the black insulator post while its running, put the meter in the 12v dc range with the neg of the meter connected to the battery neg and look for 13.5 to 13.7 v.... If its there you have connected it wrong matey.

Chris

[wooly350i]

You have given the throttle some welly once started to kick in the charging,yes?

[adam quantrill]

There is no fuse and the two thick wires should be permanently connected to battery +ve so you should always see 12V there at that terminal. They go straight there from the battery pretty much as I recall?

If there are no volts then either the far end at the battery has dropped off the clamp or there's a break in (two) cables.

That's why you have to be careful when spannering around the rear of the alternator as the spanner can easily short this terminal to earth with a big spark!

Fix this and I'm sure it will spring into life.

[jindle]

adam quantrill said:

There is no fuse and the two thick wires should be permanently connected to battery +ve so you should always see 12V there at that terminal. They go straight there from the battery pretty much as I recall?

Don't they go via the starter motor?