Alternator Wiring Help Needed

[acdbox]

Hi, having my new starter battery go dead shortly after my leaisures giving out, makes me think the fault lies with the charging, specifically the alternator. I'm thinking it's the wiring to blame.

Basically attached is a picture of the back of the alternator and a picture to the underside of the warning light which is currently half disconnected.

The batteries show a 14+v output but my ammeter doesn't register a charge to them, so thinking again the wiring is to blame?

It's a lucas A127 type alternator on a BMC 1.5.

Also attached is a picture found online that clearly shows a similar alternator with the exact same connectors. Mine only has a single positive and ground connection at present.

 

 

Good Guidance very much appreciated.

Thank you

Andreas

[acdbox]

Ok, so I think the similar alternator image attached just looks the same but at leaset a couple if the terminals are different. Where it says warning lamp, that is actually the ground on my alternator

[springy]

The Thick Red wire is the main positive output for the alternator, the "Ground" wire (if fitted) needs to be a

conductor of the same size as it has to carry the same current, However common practice is to use the

alternator frame as its ground connection which is bolted to the engine which will in turn have a suitably

sized cable bolted to it somewhere else to complete the negative side of the circuit. I would expect the

thinner wire in your photo should be going to the WL terminal - normally fed from the ignition switch via

a warning light, in your case however this may be linked in somewhere else - what is the blue box - an

external regulator of some sort ?

 

springy

[Nickhlx]

If the batteries are showing a genuine "14 volt output" (presumably when the engine is running) it's unlikely that there is too much wrong with the charging. If that is when the engine is off, you either have a 24 volt system (and there is a problem) or the meter is not telling the truth ! I would firstly check the on charge voltage and also the charging current with a clamp-on meter, so you have confirmed data with which to work out the problem. - It could be that the battery is dying (dead) and the system is OK - it is not unheard of that a "new" battery is not as new as it should be and already sulphated before it gets installed, if from a poor shop / outlet.

 

Nick

Edited January 19, 2016 by Nickhlx

[Sir Nibble]

The 14V does not make sense. Without the warning light the alternator would have to be revved like mad to have a chance of cutting in. The "ground" wire you mention is connected to the warning light terminal, for sure, it's not different to the other picture. If that is definately grounded then there is no way the alternator will charge. The single 30A connector the main B+ is connected to is not up to the job on it's own, you need to use the stud connector.

[Tony Brooks]

That is if the OP has properly identified the thin black wire as ground/negative. For all we know (from the information in the original post) it could be a permanent positive feed in which case it would charge (and tend to discharge the battery). Now I know Sir N's post is most likely to be correct we do need the OP to come back and confirm that black wire is definitely a negative one.

 

If it is then apart from the fact the alternator is likely to be earth return the wire is too thin.

 

Cable colours mean little on boats, especially older ones that have suffered the owners' attentions over the years.

 

Not tying to start an argument, just trying to ensure the OP eventually gets the correct answer.

[dor]

The batteries show a 14+v output but my ammeter doesn't register a charge to them, so thinking again the wiring is to blame?

 

 

On most boats, the ammeter will only show current being used coming from the battery. The charging cable from the alternator to the battery will go directly, probably via an isolator and maybe a relay.

 

There is an exception - my blue sea meter shunt is in the negative connection, so shows all current going into and out of the battery. My other panel meter only shows current being used (except for the inverter - which I can see by subtracting the panel current from the blue sea one).

Edited January 19, 2016 by dor

[acdbox]

Hi, thanks for replying. As far as I am aware the alternator doesn't have a bolt connection for the positive, just a secondary 7v aux.

The black wire goes somewhere towards the ignition/console but not sure where exactly. The electrician who came relatively recently said a replacement lamp was needed so I think it was somehow worried to bypass it, but on the recent occourance of a new starter battery dieing now have my doubts. But did seem to charge the previous starter ok, so could be something that has happened since?

 

The blue box is a solar mppt controller separate from the console.

 

So if a second negative is wired direct to the battery to carry a heavier load is that ok practise or it should go via the whatever is wired into the console? Thanks

[Sir Nibble]

Right below the wiring you have now is a plastic dome. Pull that off and the +ve stud is underneath. What you need to have is an ignition supply to the warning light, (it appears from the pic you have that) and a wire from the other side to where that black wire is. If the electrician has fixed a blown bulb by shoving that wire on to a +ve supply then he's a very, very bad boy and that could explain why you have ended up with flat batteries in the first place. Sort that out to be going on with.

[acdbox]

Hay Sir Nibble, thanks for the reply. Got round to wiring up the battery directly to the connection under the rubber some you said. The strange thing is there is a .15 - .2 voltage drop useing the new connection? Brand new wire/lugs and same even with the old wire attached too?

Is that deffinetly where to wire the positive to?

Thanks again mate.

Sorry just read read your post. And no wonder there's a voltage drop! Will wire properly and report back

[Tony Brooks]

As long as you have identified the correct stud (may have D+ cast into the case by it) then I can confirm it is the same as the two large 9 mm blades. If you are trying to use the other (W) rev counter stud the voltage will be lower than at the D+ stud an it will also half wave rectified with a limited current supply so make sure yo have the correct stud.

 

The small 6mm blade in your photo needs a cable from the warning lamp connected to it.

 

I would ignore the black lead and insulate the end until you know where the other end is connected.

 

How are you measuring the voltdrop? Where have you connected the meter cables to the circuit?

[acdbox]

Hi, ok thanks once more. Warning lamp is correctly installed and have also run a new cable for positive to the stud instead of the blade connection.

Though if I could ask one more question and that is what about the negative? There isn't an obvious place to run a negative back to the battery... Does this mean it is an insulated return alternator and if so how does it connect back to the battery? Thanks again

[nicknorman]

Hi, ok thanks once more. Warning lamp is correctly installed and have also run a new cable for positive to the stud instead of the blade connection.

Though if I could ask one more question and that is what about the negative? There isn't an obvious place to run a negative back to the battery... Does this mean it is an insulated return alternator and if so how does it connect back to the battery? Thanks again

An insulated return alternator has the casing electrically isolated (ie not connected to anything) and has a -ve stud to which is connected a fat black lead that goes to battery -ve.

 

A non-insulated return alternator has the case connected to -ve. The case is bolted to the engine. Somewhere, probably near the starter motor, there will be a fat negative cable connected between the engine block and the battery negative. Thus the -ve return is via the engine casing. It seems you have this latter type. Voltage drop can occur just as much in the -ve return as in the +ve so I would check for voltage drop between the alternator casing and battery negative too.

Edited January 25, 2016 by nicknorman

[acdbox]

Hay nicknorman, think you are correct in that the alternator is of the latter type you mentioned.

And pointed out exactly what my next question may have been... Where is the main battery negative connected to the engine.

Will check this out tonight as I think that there is a slight voltage drop in the return which you said.

Thank you very much

Kind regards mate

[bizzard]

Hay nicknorman, think you are correct in that the alternator is of the latter type you mentioned.

And pointed out exactly what my next question may have been... Where is the main battery negative connected to the engine.

Will check this out tonight as I think that there is a slight voltage drop in the return which you said.

Thank you very much

Kind regards mate

Often found attached at an engine mounting bracket or starter motor attachment bolt.

[nicknorman]

Hay nicknorman, think you are correct in that the alternator is of the latter type you mentioned.

And pointed out exactly what my next question may have been... Where is the main battery negative connected to the engine.

Will check this out tonight as I think that there is a slight voltage drop in the return which you said.

Thank you very much

Kind regards mate

Just to mention (in case you hadn't already realised) that the cable from engine to battery -ve is also the return for the starter motor and some sensors (oil pressure switch etc). Edited January 25, 2016 by nicknorman

[Sir Nibble]

Now I am left wondering about a split charge relay. Presumably on the end of that black lead somewhere, and presumably still engaged.

Edited January 25, 2016 by Sir Nibble