Alternator not charging my battery

[Spitfire74]

Hi all

I have discovered that my alternator does not seem to be charging the battery in my Spitfire MkIV/1500 (Mk IV engine). I have used a voltmeter on the battery to test for charge while running and it displays only around 12V and never over which says to me that it isn't charging. Likewise when using an alternator tester on the negative and positive terminals of the alternator I do not get the 6 lights to indicate correct working. 

I have replaced the brushes in the alternator and tested again but still do not get a charge in the battery. 

When taking the connector off from the alternator I did notice that one of the cables appears to not be connected to anything. However, there also appears to be no cable for it to connect to and all last summer the battery was charging properly from the alternator so I do not suspect that this is the issue...but maybe it is? The cable I'm referring to is the blue one, that I've circled, in the picture below.

I'd be very grateful for any info on the rogue blue cable and any suggestions on what else might not be working in the alternator and need fixing!

Cheers, Nick

[RobPearce]

The blue wire isn't the only rogue in that photo - the black that becomes green is also not correct. Some DPO has messed with the wiring, which could mean there are all sorts of things wrong. However, assuming you've not changed anything since it worked, it's probably not that.

The bottom fixing of the alternator is not tight in that photo. Probably the most common cause of alternator not working is the fan belt being loose, so make sure that's right first. Second most common is worn brushes - you say you've changed them but did you also check the rectifier pack and regulator? Were the new brushes a good set?

[Spitfire74]

Hi Rob

Cheers for the reply. Should have mentioned that I took that photo having taken off the alternator and in the process of putting it back on the car...hence the loose fixing at the bottom. 

Any idea what that blue wire is/should be doing? Also what's wrong with the black/green wire please? But yes I've not changed anything since it worked. Strangely though the alternator stopped working a few days after I bought the car (a couple of years ago) and I replaced it with a straight swap out for a new alternator (the one currently fitted) which has worked fine for about 3 years now, so I'm hoping it's not a problem with the loom!?

The new brushes were from Rimmer Bros and looked decent to me! I've not checked the rectifier and regulator, could you direct me as to how/what I should be looking for with those?

[RobPearce]

I don't think the blue wire does anything. The alternator plug should have only three wires - two brown and one brown/yellow. It looks like something that's been added for reasons unknown and then the reason removed.

The black/green wire... looked as if it also goes to the alternator? If that's just an illusion, and it's actually the temperature gauge sender wire, then it's OK apart from having apparently been repaired at some point.

If an alternator suddenly packs up, it's not necessarily the brushes that are to blame, especially if it's a relatively new (low mileage) unit. The condition of the old ones will give some indication but if replacing them made no difference then the chances are the fault is one of the other things.

Most likely is the rectifier (diode) pack. This consists of nine diodes in a 3x3 matrix to convert the three-phase AC stator output into DC to battery and field winding. Since (six of) these diodes have to carry the full 35A output of the alternator, they have been known to fail.

The field winding is grounded through the regulator, which adjusts the current (and hence field) to get the required output on the main feed. If that fails open, the field winding doesn't provide enough magnetic field to charge the battery.

There are some fairly good alternator diagnostic write-ups on the web. Google should find them for you.

[Velocita Rosso]

Make sure the small diameter wire from the alternator is still continuous to the red warning light (ign ) light.....or that the bulb has not gone. Either of the two will not allow a charge .Go on ask me how I know! So...continuity test wire at alternator to red warning light bulb and check bulb  

[RobPearce]

Quoted from Velocita Rosso-

Either of the two will not allow a charge

That's not actually guaranteed - my Spitfire still charges absolutely fine despite the bulb not working - but agreed it's usually the case. The bulb provides some current to the field winding to "kick" it into action. Once the alternator has started up, it's no longer needed. If the rotor retains enough magnetism in the iron core then the alternator can self-start without the bulb.

There's no real need to continuity check though. If the bulb comes on then it's working. 😀

[Velocita Rosso]

Quoted from RobPearce-

Quoted from Velocita Rosso-

Either of the two will not allow a charge

 

There's no real need to continuity check though. If the bulb comes on then it's working. 😀

...but if the bulb does not come on....then its in need of continuity....unless the bulb has gone👍

[Spitfire74]

Thanks for all the help everyone. Which wire is the one that goes to the warning light please? I've got the wiring diagrams but struggling to get my head around them haha! Is it the yellow/brown one? Also, assuming then I'd be alright to remove that random blue wire?

The black/green wire doesn't actually go to the alternator, I think it is actually the temperature gauge sender wire.

Also, not related to the alternator but I was wondering if anyone could I.D what the relay on the right of this picture (ok, top of the picture, it's rotated it on here!) is for...I know the left hand one is for the horns but curious as to the reason for the right hand one (and why it isn't currently connected to anything!)

[Clive]

Brown/tellow is indeed the WL wire.

You need to check where that blue wire goes to.

Relay, could be for aftermarket accessory, maybe spotlights or similar. Or possibly an overdrive. 

 

That alternator plug has definitely been "played" with. The main thick brown wire is soldered, something not done in the factory. It all needs thorough checking. But the likely suspect if teh wiring is working is the alternator itself, possibly the diode pack. Have a google, there are youtube videos etc on testing an alternator.

[RobPearce]

The warning light is, indeed, the brown/yellow wire, which should also be the small (1/4") connector. If your warning light doesn't come on with the ignition, then a quick "continuity" test would be to connect that terminal to ground, at which the light should come on.

Yes, I don't see a problem removing the blue wire. Incidentally, the two brown wires are very different sizes. This is a legacy of the early "battery sensed" alternators, where one of the big terminals was the power to battery and the other was a "sense" wire for monitoring voltage. You almost certainly have a later "machine sensed" alternator, in which the two big terminals are connected together.

As to the relay... do you have overdrive? On a MkIV or earlier with a D-type overdrive, that would be the overdrive relay. On 1500s with a J-type the relay is not used, as the solenoid draws much less current. My guess would be that yours is a slightly earlier car that's been converted to J-type (or, possibly, to non-OD, but that's not a common thing to do).

[Spitfire74]

Thanks for the help again guys!

Rob, when you say "connect the terminal to ground" can you explain, do you mean just use a cable from the terminal to the earthing cable off the battery and then with the electrics turned on the WL should turn on?

Also, are you saying that the two brown wires ought to be going to the same terminal? Slightly confused by what you mean here.

Yes, the car does have a working overdrive. Having done some research the car originally left the factory in 1974 as a MkIV but was sold to me as a 1500/MkIV, but still has the MkIV engine in it. I'm guessing you are probably right about it having been converted to a J type overdrive seeing as the overdrive still works correctly and nothing is connected to that relay!

 

[RobPearce]

Sorry for confusing you on the brown wires. They are correct as they stand - the two terminals are probably connected together inside the alternator, in which case it doesn't matter which way round they are, but on some early units it did matter. It was just an aside, not anything to worry about.

For the bulb test... The ignition warning light is connected between the ignition switch and that brown/yellow wire. It's supposed to come on if the alternator isn't producing a field.

So first, does the ignition light come on when you turn the key on with the alternator connected? If not, you need to figure out why. An easy test is to use a bit of wire to connect that brown/yellow terminal to a ground - could be battery but the engine block or alternator body should do just as well. In that condition the light should come on with the key. If it does then you have a faulty alternator - usually the brushes but equally could be the regulator. If not then check for a blown bulb or a wiring fault, as Mike said.

 

[Spitfire74]

Thanks Rob, no worries haha, like I said, the electrical side of this is all new and a learning experience for me (so apologies for any stupid questions haha!)

As you say the bulb isn't coming on, there's continuity at the alternator end of the wire on the terminal connection but when I pulled the lamp out the back of the Speedometer I was presented with this (photo taken after removing the bulb!)...

So, yeh...I think I may have identified the issue, the yellow/brown wire was hanging on by about two strands and the connection to the bulb holder is tacked on with a small bit of solder!! I'm amazed it's worked in the past since I bought it!!

I've taken the bulb out and that looks fine so am thinking I need to get a new bulb holder. I've been looking on Rimmer Bros and Moss-Europe to try and find the right part. I don't suppose anyone has a parts list or happens to know the part code for these bulb holders? It's a screw thread interior/bulb rather than bayonet.

Also, was thinking of maybe upgrading the lights to LEDs such as these from Moss

https://www.moss-europe.co.uk/led-bulb-screw-mes-e10-12v-2-2w-white-negative-glb987ln.html

In order to do that though would I need to put an adapter into the circuit (https://www.moss-europe.co.uk/led-bulb-kit-bayonet-bay15d-12v-21-5w-red-glb380lrk.html ) The only ones I can find are for the bayonet bulbs rather than for the screw bulbs.

 

Also another (unrelated to original post, sorry!) question. The tachometer hasn't worked since I bought the car and has been on my to do list since then! As I've been getting in and about the electrics I've taken a look at it and I appear to be missing the cables circled in blue and red below. I'm guessing the red one is an earth but can't work out where it then connects to and also what the blue one is and where it is meant to connect to (been studying the wiring diagrams but can't work it out still!) The cable above the blue one is yellow and connects to the coil:

Thanks again, Nick

[Clive]

Don't bother with a LED on the alternator light, more trouble than it is worth. You may well be able to repair what you have with a soldering iron.

Re rev counter, the earth eye (circled in red) is a black wire, should be lurking in there but otherwise you can earth it off the knurled nut on the back of the speedo. 

The spade (circled blue) should be a dark green wire. That should come from the voltage stabaliser attached to the back of the speedo. connected to the B terminal (the other terminal on the voltage stabaliser feed the fuel and temp gauges)

The problem possibly arises because the mkIV spit used a cable driven rev counter, driven from a delso distributer via a cable that is like a speedo cable. The 1500 used the electronic rev counter, so if your has a mkIV wiring loom those wires may be missing. BTW the bullet connector on the rev counter goes direct to the coil negative connection.

[Spitfire74]

Hi Clive, thanks for the reply

Roger that re LEDs. Would you say the same for headlights etc. or would these be worth 'upgrading'?

For the tachometer earth is that just a short cable from the tacho to the speedo nut then?

Yep, the bullet connector is the only one that actually has a wire and is connected in my car and it does go to the coil. For the dark green wire to the voltage stabiliser, do you know what amp wire should be used for this?

Unfortunately the Haynes and the Owners Workshop Manual don't mention wire gauges/amps anywhere (just colours) and there is of-course a wide selection of wires at different ratings available! I have tried googling but can't find a definitive answer, was rather hoping that somewhere out there there might be a list of what gauge wires are necessary for each connection in the loom!

Cheers, Nick

[RobPearce]

LEDs are fine for side-lights, instrument illumination, stop/tail and, if you use good ones, headlights. That doesn't mean it's necessarily worth using them, though. What thay aren't any good for is bulbs that are in current-sensitive circuits, where some other device relies on the current being drawn. LEDs hardly draw any current so that other device won't operate. The obvious examples of this are the alternator light (current is needed to kick-start the alternator field) and the indicators (current needed to make the flasher unit work). Stick with normal bulbs for them.

The tach earth can be connected to the speedo nut but best to use the one with the earth wires on it.

The green wire doesn't carry much current. If you use a red crimped connector, they are intended for 5A wire IIRC, which is plenty.

[Spitfire74]

Thanks Rob. Maybe I won't bother with LEDs then, atleast for now anyway!

I've managed to reconnect the bulb holder and can now report that the alternator is finally working properly again! So thanks to everyone for the help, I would never even have thought that that could have been the problem!

Next job trying to reconnect the tachometer (amongst some other, more cosmetic jobs!)