Smartgauge " stuck "' at 76

[nicknorman]

If it's any consolation, my twin alternator system has worked immaculately forever until the day a few weeks ago when I took my red alternator sparking light out to prove that the Finchers system was potentially working, but not sparking. It proved a point, and the Finchers continued to a mooring where they can do some serious work on the lovely boat.

However,sticking the light back in has not worked, it will not illuminate and I have had to excite the alternator by crossing the wires.

Unfortunately, I have not had time to investigate further.

As someone's signature says, "no good turn goes unpunished"!

[chubby]

Cheers guys ,

 

I thought by carrying out that test of the thick cables i was testing alternator output .

I ve rechecked the back of the alternator and will attempt description of the remaining wires .

 

At the back of the alternator , adjacent to where the thick red cable is bolted there is a grey plastic harness that appears to click into the back of the alrernator . It has a green wire & a yellow wire . When i removed this harness there were 2 female (?) spade type connections which fitted to the two " spades " actually inside the alternator

 

At the top of the alternator is a black plastic " housing " with 4 wires . Red / yellow & black / green / black . This is cable tied to the metal arc onto which the alternator is bolted , along which you would slide the alternator to tighten the belt ( i think )

 

The reason it then become annoying is because theres a bunch of bullet connectors crimped on & they connect other wires of other colours that then are very difficult to trace .

 

It looks like somehow these all connect together but i can t really follow where they go ?

 

Does any of help ? is it the two wires , green & yellow that are connected to the alternator via the grey plastic harness that i need to test with the ignition on but not running the engine ?

 

sorry & thanks again

[nicknorman]

Cheers guys ,

I thought by carrying out that test of the thick cables i was testing alternator output .

I ve rechecked the back of the alternator and will attempt description of the remaining wires .

At the back of the alternator , adjacent to where the thick red cable is bolted there is a grey plastic harness that appears to click into the back of the alrernator . It has a green wire & a yellow wire . When i removed this harness there were 2 female (?) spade type connections which fitted to the two " spades " actually inside the alternator

At the top of the alternator is a black plastic " housing " with 4 wires . Red / yellow & black / green / black . This is cable tied to the metal arc onto which the alternator is bolted , along which you would slide the alternator to tighten the belt ( i think )

The reason it then become annoying is because theres a bunch of bullet connectors crimped on & they connect other wires of other colours that then are very difficult to trace .

It looks like somehow these all connect together but i can t really follow where they go ?

Does any of help ? is it the two wires , green & yellow that are connected to the alternator via the grey plastic harness that i need to test with the ignition on but not running the engine ?

sorry & thanks again

With the alternator thick red and thick black wires being connected directly to the batteries, measuring at the alternator will show as a minimum the batteries's voltage. If the alternator is charging, the voltage will increase to say 14v or more. The reason for testing directly at the alternator was to ensure that there wasn't a bad connection in the wiring whereby the alternator was working fine, but high resistance wiring meant virtually no current was getting through. Anyway, we have proven that the alternator is definitely not working, but we haven't yet proven why.

 

I am quite familiar with the principles of how alternators work, but I have limited experience of specific models other than those fitted to my own boat, in terms of the terminal layouts. I am therefore the wrong person to be specific about your alternator, however I am confident that one of the small wires should be carrying a couple of volts or so with the ignition on but not running, whilst the other wires will either be at zero or battery voltage. Hence my suggestion to check the voltage at all the wires going into the alternator Don't disconnect anything though, hopefully you can get the meter probe into the back of the connectors in the alternator. Everything needs to remain connected to get the few volts, if you disconnect the relevant wire, the few volts will become 12.6 volts.

 

If you find one wire has a few volts on it, this will be the D+ excitation coming from the warning lamp. It doesn't particularly matter which wire it is, for the purposes of deciding whether the fault lies with the alternator or the wiring / panel, the presence of the few volts will indicate that the fault lies with the alternator. On the other hand, if no wires have that slight voltage it points to a wiring or panel issue with the alternator itself most probably being fine, once the excitation is sorted. Process of elimination!

 

Edit: just checking my facts and I think the voltage at the D+ terminal should be less than I stated, probably less than 1v (depends on the size of the warning lamp bulb etc) but the important point is that it is not zero, and not 12.6v or whatever the battery voltage is.

Edited December 15, 2014 by nicknorman

[chubby]

Cheers again Nick ,

 

Very grateful for your help & patience . I now understand what you mean when testing the thick red cable .

I ' ll have look again at all those cables and see if i can put probe on them but to be honest there doesn t really appear to be anywhere to put a probe on them .

 

I googled about Barrus Shire Alternator & a few old threads came up from the forum & other forums . Seems like theyre pretty unreliable , but im not sure of my next move if i cannot test the alternator as replacement doesn t seem stroghtforward if i need a new one .

 

I refused to let my eberspacher beat me earlier in the year but i ve a feeling the alternator will win this time . Bugger !

 

i ll have a mooch tomorrow ,

 

cheers again

[BruceinSanity]

It may just be worth trying revving the engine up towards it's safe max, not in gear. Alternators can be persuaded to excite at high revs sometimes. If you do that (briefly) and see the voltage at the SG rise, then you know it's an excitation problem and will be putting some charge into the batts.

[nicknorman]

Cheers again Nick ,

Very grateful for your help & patience . I now understand what you mean when testing the thick red cable .

I ' ll have look again at all those cables and see if i can put probe on them but to be honest there doesn t really appear to be anywhere to put a probe on them .

I googled about Barrus Shire Alternator & a few old threads came up from the forum & other forums . Seems like theyre pretty unreliable , but im not sure of my next move if i cannot test the alternator as replacement doesn t seem stroghtforward if i need a new one .

I refused to let my eberspacher beat me earlier in the year but i ve a feeling the alternator will win this time . Bugger !

i ll have a mooch tomorrow ,

cheers again

One would expect an alternator, properly installed by a mainstream engine mariniser, to activate a warning light or alarm if it failed. Since there seems to be only 1 warning light for both alternators, this should be connected to both alternator D+ terminals via diodes. So if the domestic alternator has failed it should leave the warning light on. There are 3 reasons that I can think of, why the light is not staying on:

 

The first is that the installation is in fact poorly designed and the light is not in fact connected to the alternator.

 

The second is that there is a break somewhere in the wiring between the light and alternator. Connectors can be a weak point here.

 

The third is that within the alternator, the D+ terminal is not connecting through the field windings and this is typically due to worn slip ring brushes. These are relatively easy to replace once you know the make and model of alternator. The only thing is that the slip rings themselves can be in a bad state once the brushes are fully worn out so a new set of brushes may not last long unless the rotor is overhauled at the same time.

 

If the alternator is totally caput I would really expect the light to stay on so hopefully it is nothing too drastic, hence the need to persevere with fault finding before contemplating buying a new alternator.

[chubby]

ok

 

I spent several hours late last night & this morning googling barrus shire + alternator etc to see what came up . There were several previous questions on here , other forums & blogs .

This is what i think i ve found out . My engine has a " deluxe " instrument. ( oohh listen to him !!!)

Next to the ignition switch is an orange lamp with a picture of a battery . On the voltmeter there is a single red bulb located on the left side of the gauge , much smaller than the orange one .

I believe , from reading blogs & other forum posts that the large orange lamp is for the engine alternator . When i turn the key 1/2 way it lights up & a loud buzzer sounds . Turn the key 1/2 way further & engine starts , the buzzer stops & the light goes out . The other " theory " i have that makes me think its connected the engine alternator is that the loud buzzer is there to alert you to a problem

whilst underway as you would definately hear it over the engine & combined with the big orange lamp which is very prominent .

My understanding of such things is that the engine battery is more important than the cabin batts because , all being well , if u flatten your cabins batts then the engine battery should & must be able start in order to then recharge the cabin batts . Therefore it ought to have a very noticeable warning system .

The voltmeter itself has a small red bulb . When turning on the ignition this does not light up at all . Once the engine is running the needle moves just past 14 V .

 

Frrom Nicks advice & internet reading i think i may a grasp of how it is meant to work if all is well .

The lamp is indicating that a small voltage is going from (? somewhere / something ) INTO the alternator in order to EXCITE (?) the alternator . To prepare it for functioning .

The presence of this light on the engine alternator indicates that it is receiving this small charge & when engine is started it deliver 14.4 to the engine battery .

No light on the voltmeter indicates no " exciter " voltage going into the larger alternator & when engine starts the alternator fails to function . If it were working correctly it would function like the large orange battery lamp . ie - the small lamp comes on when ignition is 1/2 way , go out when engine fires up , & only come on again whilst underway to indicate a problem .

 

Is this more or less correct . Please chastise me if i m miles off .

 

If correct , & having tested the thick cables bolted to the alternator with a multimeter to see if there was a rise in voltage with engine running , i now have to find which of the small cables ( 6 in total ) is the one that is connected to the voltmeters red bulb ?

 

I will probe each wire with the red probe & connect the black probe to the engine mounts with the key turned 1/2 way & buzzer sounding .

 

The readings should be 0 , 12.6 ( or .7 ) or another v of small value - 2V or less . This low voltage is the " exciter " Voltage coming from the voltmeter .

 

If none of the wires tested indicate the 2V or less exciter voltage then regardless of which wire may be from the voltmeter , it isn t working & the fault lies with the back of the panel ?

 

If i do find the 2V or less current then the voltmeter / panel IS functioning correctly ( perhaps bulb has blown ?) & the fault lies within the alternator itself .

 

I ll head out to the engine bay & check using the above as a guide . Am i using the correct process of elimination ?

 

ETA : thanks guys - i wasn t hoping for further replies this early . I ve considered the idea of revving up the engine to excite the alternator & so i did this whilst cruising yesterday . My idea of big revs is 2000 so whether thats enough i wouldn t know .

Frustrating !

 

cheers again

Thanks again

Edited December 16, 2014 by chubby

[nicknorman]

ok

I spent several hours late last night & this morning googling barrus shire + alternator etc to see what came up . There were several previous questions on here , other forums & blogs .

This is what i think i ve found out . My engine has a " deluxe " instrument. ( oohh listen to him !!!)

Next to the ignition switch is an orange lamp with a picture of a battery . On the voltmeter there is a single red bulb located on the left side of the gauge , much smaller than the orange one .

I believe , from reading blogs & other forum posts that the large orange lamp is for the engine alternator . When i turn the key 1/2 way it lights up & a loud buzzer sounds . Turn the key 1/2 way further & engine starts , the buzzer stops & the light goes out . The other " theory " i have that makes me think its connected the engine alternator is that the loud buzzer is there to alert you to a problem

whilst underway as you would definately hear it over the engine & combined with the big orange lamp which is very prominent .

My understanding of such things is that the engine battery is more important than the cabin batts because , all being well , if u flatten your cabins batts then the engine battery should & must be able start in order to then recharge the cabin batts . Therefore it ought to have a very noticeable warning system .

The voltmeter itself has a small red bulb . When turning on the ignition this does not light up at all . Once the engine is running the needle moves just past 14 V .

Frrom Nicks advice & internet reading i think i may a grasp of how it is meant to work if all is well .

The lamp is indicating that a small voltage is going from (? somewhere / something ) INTO the alternator in order to EXCITE (?) the alternator . To prepare it for functioning .

The presence of this light on the engine alternator indicates that it is receiving this small charge & when engine is started it deliver 14.4 to the engine battery .

No light on the voltmeter indicates no " exciter " voltage going into the larger alternator & when engine starts the alternator fails to function .

Is this more or less correct . Please chastise me if i m miles off .

If correct , & having tested the thick cables bolted to the alternator with a multimeter to see if there was a rise in voltage with engine running , i now have to find which of the small cables ( 6 in total ) is the one that is connected to the voltmeters red bulb ?

I will probe each wire with the red probe & connect the black probe to the engine mounts with the key turned 1/2 way & buzzer sounding .

The readings should be 0 , 12.6 ( or .7 ) or another v of small value - 2V or less . This low voltage is the " exciter " Voltage coming from the voltmeter .

If none of the wires tested indicate the 2V or less exciter voltage then regardless of which wire may be from the voltmeter , it isn t working & the fault lies with the back of the panel ?

If i do find the 2V or less current then the voltmeter / panel IS functioning correctly ( perhaps bulb has blown ?) & the fault lies within the alternator itself .

I ll head out to the engine bay & check using the above as a guide . Am i using the correct process of elimination ?

Thanks again

We have a habit of crossing posts!

 

Yes the above is pretty much correct except for the last bit when you talk of bulb blown

 

The power for the exciter comes from the ignition switch, via the bulb, and then down via wiring and a connector, to the alternator D+ terminal, then internally through the regulator and a carbon brush, to the rotor field coil where a magnetic field is created, and then back through a brush to -ve. So if the bulb is blown, or any other break in the chain mentioned above, there is no exciter current and the alternator doesn't start working.

 

So you have a string of stuff with 12v at one end of the bulb (when ignition turned on), and a field coil of some (lowish) resistance, resulting in let's say 11v dropped across the bulb and 1v or so dropped across the field coil. The presence of the 1v or so indicates exciter current is flowing through the rotor field coil and generating the startup magnetic field.

 

Just so you understand how it should work, once the alternator starts working the voltage on the D+ terminal should rise to the operating voltage of the alternator (say 14v) by means of internal circuitry, so now the bulb has 14v from the ignition switch at one end, and 14v from the D+ terminal at the other end, so there is no voltage across it so it goes out.

 

Edited to add, you mention the buzzer but typically the buzzer means several things, alternator issue, engine overheating or low oil pressure. The various sensors are all connected to one buzzer via diodes. When you turn the ignition on, the low oil pressure sensor will activate the buzzer regardless of any alternator issues, so it is not helpful in this context.

Edited December 16, 2014 by nicknorman

[chubby]

Cheers Nick

 

So if theres no red bulb when keys 1/2 turned in the ignition then the " circuit " cannot be complete & the alternator cannot receive the necessary voltage to " excite " ?

 

I m probably making it over complicated & doing myself no favours .

 

If the bulb doesn t light then theres nothing going to the alternator from the ignition

 

is that correct . Have i misunderstood ?

 

I m off a probing now

 

cheers

[nicknorman]

Cheers Nick

So if theres no red bulb when keys 1/2 turned in the ignition then the " circuit " cannot be complete & the alternator cannot receive the necessary voltage to " excite " ?

I m probably making it over complicated & doing myself no favours .

If the bulb doesn t light then theres nothing going to the alternator from the ignition

is that correct . Have i misunderstood ?

I m off a probing now

cheers

Correct.

[chubby]

Cheers Nick

 

Youre a legend .

 

I ve probed the 6 wires that exit the alternator with the ignition 1/2 turned .

 

. Theres a group of 4 that connect to a black plastic " thing " that is strapped to the arc frame that the alternator is mounted on & i could probe the back of the black plastic connector .

 

Of these 4 two displayed the battery voltage 12.7 ( black probe was on -ve battery post as i couldn t hold the probe anywhere myself & read the meter , its very cramped back there . I hope thats acceptable for testing ?)

 

The other two showed zero .

 

There are then two wires - green & yellow going into the back of the alternator via a grey plastic housing that clips into place , connecting spade connectors inside the grey plastic connector . This is located next to the thick red cable already tested .

 

One wire showed 12.7 . The other zero

 

.So theres no cable indicating the lower voltage required to excite the alternator .

 

I ve got an awful feeling your going to suggest removing the instrument .

 

I shall fortify myself with more tea

 

cheers again

 

something else i noticed is that with key 1/2 turned the only red light that comes on is the oil pressure one . No light on the temp gauge either .

Might not be relevant but i thought i d mention just incase

Edited December 16, 2014 by chubby

[nicknorman]

Cheers Nick

Youre a legend .

I ve probed the 6 wires that exit the alternator with the ignition 1/2 turned .

. Theres a group of 4 that connect to a black plastic " thing " that is strapped to the arc frame that the alternator is mounted on & i could probe the back of the black plastic connector .

Of these 4 two displayed the battery voltage 12.7 ( black probe was on -ve battery post as i couldn t hold the probe anywhere myself & read the meter , its very cramped back there . I hope thats acceptable for testing ?)

The other two showed zero .

There are then two wires - green & yellow going into the back of the alternator via a grey plastic housing that clips into place , connecting spade connectors inside the grey plastic connector . This is located next to the thick red cable already tested .

One wire showed 12.7 . The other zero

.So theres no cable indicating the lower voltage required to excite the alternator .

I ve got an awful feeling your going to suggest removing the instrument .

I shall fortify myself with more tea

cheers again

something else i noticed is that with key 1/2 turned the only red light that comes on is the oil pressure one . No light on the temp gauge either .

Might not be relevant but i thought i d mention just incase

I wouldn't expect the temperature light to come on - it just comes on when the engine is too hot.

 

So it now gets a bit tricky since I don't know which lead is the D+ one. Any chance of posting a photo of the back of the alternator? Have you looked closely for any markings? It does seem to have quite a lot of wires!

 

If doing it by trial and error here is a suggestion:

 

Either one of the 12v wires goes to the bulb but is not finding a -ve via the alternator, or one of the 0v ones should be connected to the bulb but isn't. Can you obtain a small 12v bulb (eg car side light bulb)? If so, if you connected one side to -ve and the other side to each of the wires carrying 12v one at a time, one of them might cause the lamp in the panel to come on (ignition needs to be turned on of course). This would show that there is an alternator fault, maybe brushes or maybe something worse, but that the panel wiring, bulb etc was OK.

 

If you can't get the panel alternator warning light bulb to work in this way, try starting the engine, running it at around 1200 rpm and then connecting the bulb between +ve and each of the wires that is at 0v one at a time. If the problem was in the panel/wiring then this might cause the alternator to excite and start working until you next stop the engine. You only need to touch the bulb on briefly, once the alternator starts working, the circuit to the warning light is superfluous. If this is sucessful it points to a wiring issue to the panel, bulb blown in the panel etc.

 

Do be careful with running engines /belts and your clothes and wires/leads!

Edited December 16, 2014 by nicknorman

[chubby]

Cheers Nick

 

I can t put up photos on here as i find it too complicated . im not a big user of computers . i can take pics with my phone email them to you if you PM me .

No worries if not .

Ive rechecked again & there are no markings on the alternator to indicate which is the D+ terminal . Theres just the two plastic connectors . One with 4 wires . one with 2 . Thats it .

 

I ll dig out a test bulb & start checking as you advised

 

cheers again

[chubby]

ok

 

Progress ?

 

I cobbled together a test lamp . I did as you suggest .

 

 

 

cheers

 

So with ignition on , engine off i put the negative end of the test lamp on the negative battery terminal held by a crocodile clip .

The positive cable i inserted into the grey harness ar the back of the alternator .

Two wires . Yellow & green . On the previous test the green read 0 V . The yellow read 12.6 V

 

With key turned & buzzing alarm sounding i inserted the +ve from test lamp & connected it to the Yellow cable .

 

The red lamp on the voltmeter came on .

 

Is this indicating that

Yhe wiring from ignition switch to D + connection is working & that the fault is within the alternator itself & will need removing & servicing / replacement ?

 

Thanks again

 

ETA : re read Nicks last post & my question above is already answered . Faulty alternator , wiring ok .

 

Also , its a gloriously sunny day today . Smartgauge has climbed from 74 to 76 so far . It s working as it ought to . Happy days

Edited December 16, 2014 by chubby

[nicknorman]

Well done for following my rather complicated but vague instructions! You have just carried out thorough fault finding which proves that yes, the alternator itself is faulty, although it could be something as simple as the brushes. I would recommend removing it and taking it to an auto-electrician specialist since procuring a new alternator of identical size sounds tricky from what other poster have said elsewhere. Alternatively you could contemplate trying to get a new one whilst having the old one overhauled an then keeping it as a spare.

[chubby]

Cheers Nick

 

Im very much grateful to you for your help & your patience . I do struggle with this stuff but you ve gotta learn it somehow . I ve been to see an auto electrician who was recommended by another boater near me . I'll get it to him tomorrow morning . Hopefully it 'll be straightforward .

I did think actually about maybe fitting a new one even if this one is repaired but because it s simpler to put this one back in because the 2 wire grey plastic harness will obviously just clip back in . If i got a new one i might have to go cutting wires & crimping on new connections etc so providing it can be repaired i 'll stick with it .

 

Cheers again , youre an absolute gent & im very grateful for your time & trouble

Edited December 16, 2014 by chubby

[Tony Brooks]

From the description of the plastic "plug" with two thin wires in it I suspect it may be a Hitachi alternator as some Vetus use. One thin wire is a battery sense wire and should read battery voltage all the time while the other is the warning lamp wire.

 

The sense wire - if that is what is is, should have battery voltage on it all the time.

 

The warning lamp wire is as Nick says except I think he did not (only scan read the thread) give the voltage to expect if the alternator is suffering from worn brushes. Normally with the ignition on that wire will only show a few volts - if that. However if the brushes have failed then you should get close to battery voltage on it UNLESS the warning lamp or whatever has failed. Then it would read all but zero.

 

If you push a piece of wire into the back of the thin wire with zero volts on it and run the other end on the alternator case with the ignition on the warning lamp for that alternator (if there is oen) should light up. If not, its blown. Do not do that to the one with battery voltage on it.

 

If I am right about that alternator make and it can not be repaired I suspect you may well be changing connections etc. to keep the cost down!

[Eeyore]

Well done for following my rather complicated but vague instructions! You have just carried out thorough fault finding which proves that yes, the alternator itself is faulty, although it could be something as simple as the brushes. I would recommend removing it and taking it to an auto-electrician specialist since procuring a new alternator of identical size sounds tricky from what other poster have said elsewhere. Alternatively you could contemplate trying to get a new one whilst having the old one overhauled an then keeping it as a spare.

Hi Nick

The OP mentioned four wires connected to a black block, which is usually the relay that connects the domestic alternator ignition or "I" (sense) terminal to the domestic bank. It's functionaly the similar to the one that Beta usually cable tie to the back of the panel. I would have expected 3 terminals to show battery voltage with the key in the on position. 1x permenant live from domestic battery, 1 x 12 volt from key switch to relay coil, and 1 x 12 volt switched output to the "I" terminal

Note that the gauge often indicates start battery voltage, whilst the small lamp within is associated with the domestic alternator!

The wiring is often messy as the relay was a modification added when powering both "I" terminals direct from the key switch proved troublesome.

Hope this is of some help.

Steve (Eeyore)

(Hope I didn't miss anything - it's a long tread to read on a phone screen!)

Edited to reference feed to "I" terminal, and remove reference to warning lamp - senior moment; sorry about that.

Edited December 16, 2014 by Eeyore

[Eeyore]

If I am right about that alternator make and it can not be repaired I suspect you may well be changing connections etc. to keep the cost down!

The alternator was fitted to some Mazda RX7 models; my local boat yard manager is an enthusiast who also looks after the Barrus engine in his fathers boat!

I have edited my previous post to refer to the sense supply to the domestic alternator.

[nicknorman]

If you push a piece of wire into the back of the thin wire with zero volts on it and run the other end on the alternator case with the ignition on the warning lamp for that alternator (if there is oen) should light up. If not, its blown. Do not do that to the one with battery voltage on it.

 

No, if you connect a wire between something with zero volts on it, to another point with zero volts in it, absolutely nothing will happen!

 

You have to do it to the one with 12v on but by using a bulb instead of a wire you don't come unstuck if it turns out to be the battery sense wire.

[nicknorman]

Hi Nick

The OP mentioned four wires connected to a black block, which is usually the relay that connects the domestic alternator ignition or "I" (sense) terminal to the domestic bank. It's functionaly the similar to the one that Beta usually cable tie to the back of the panel. I would have expected 3 terminals to show battery voltage with the key in the on position. 1x permenant live from domestic battery, 1 x 12 volt from key switch to relay coil, and 1 x 12 volt switched output to the "I" terminal

Note that the gauge often indicates start battery voltage, whilst the small lamp within is associated with the domestic alternator!

The wiring is often messy as the relay was a modification added when powering both "I" terminals direct from the key switch proved troublesome.

Hope this is of some help.

Steve (Eeyore)

(Hope I didn't miss anything - it's a long tread to read on a phone screen!)

Edited to reference feed to "I" terminal, and remove reference to warning lamp - senior moment; sorry about that.

Yes I hadn't quite read the OP's descriptions properly but when I do so again I think you are right, it is a relay whereas I thought it was just some connector block actually in the alternator. Anyway, despite my lack of knowledge of how different installations are done in practice, it seems we got there in the end by hook or by crook and the wiring is fine whilst the alternator is duff.

[Tony Brooks]

No, if you connect a wire between something with zero volts on it, to another point with zero volts in it, absolutely nothing will happen!

 

You have to do it to the one with 12v on but by using a bulb instead of a wire you don't come unstuck if it turns out to be the battery sense wire.

 

Come on, read the post. I gave a simple diagnostic test , not just for the OP but for all readers. If the wire with zero volts on it is in fact the W cable then with the engine stationary and the ignition on you will get zero or close to zero volts. However if it is the D+ wire (note I twice warned about not using the sense wire) the with the engaging stationary and the ignition on the warning lamp should come on if it does not then there is a blown bulb or a warning lamp fault. If it does then the rotor circuit is open circuit so the alternator is faulty.

 

I agree that your test sequence has identified a faulty alternator but in my view it was rather long winded. However in the case of the OP it was probably necessary.

 

IN fact with an open circuit rotor and the engine stationary with the ignition on you should get around battery voltage on the D+ wire because there is virtually zero current flow so there can be no voltdrop across the bulb. This is a Lucas recommended test, except they say do it with the D+ cable disconnected.

[nicknorman]

Come on, read the post. I gave a simple diagnostic test , not just for the OP but for all readers. If the wire with zero volts on it is in fact the W cable then with the engine stationary and the ignition on you will get zero or close to zero volts. However if it is the D+ wire (note I twice warned about not using the sense wire) the with the engaging stationary and the ignition on the warning lamp should come on if it does not then there is a blown bulb or a warning lamp fault. If it does then the rotor circuit is open circuit so the alternator is faulty.

 

I agree that your test sequence has identified a faulty alternator but in my view it was rather long winded. However in the case of the OP it was probably necessary.

 

IN fact with an open circuit rotor and the engine stationary with the ignition on you should get around battery voltage on the D+ wire because there is virtually zero current flow so there can be no voltdrop across the bulb. This is a Lucas recommended test, except they say do it with the D+ cable disconnected.

 

Tony, you have massively more real world experience in such matters than I do, but you can't change the laws of physics! You post said to connect a wire between a wire with zero volts on it, and another place with zero volts on it. Think about it, this can never bring the warning light on.

 

The wire going to the warning light, and presuming a faulty alternator (open circuit field circuit) so the light is off, will have battery voltage at the alternator terminal. As such it is superficially indistinguishable from a sense wire or other wire connected to battery hence, in the absence of having any clue where the wires go, the instruction to use a bulb to ground rather than just a wire.

 

In summary, connecting a wire to ground on the terminals having zero volts will achieve nothing, connecting a wire to ground on a terminal at 12v will either bring the light on, or cause a dead short circuit. The latter is too much of a risk to take hence the bulb.

[Eeyore]

Yes I hadn't quite read the OP's descriptions properly but when I do so again I think you are right, it is a relay whereas I thought it was just some connector block actually in the alternator. Anyway, despite my lack of knowledge of how different installations are done in practice, it seems we got there in the end by hook or by crook and the wiring is fine whilst the alternator is duff.

Hi Nick,

Back at a big screen now, and spotted the OPs readings on the yellow and green wires to the back of the alternator.

These two wires are the same as the start battery alternator on your Beta, one is the warning light, the other is an ignition feed from the key switch. On yours they are probably labeled "I" and "L", and probably the same on the OPs. The green "I" wire has been variously described here as excite, permanent or sense; but whatever we call it will need to be live with the key switch on for the alternator to charge. The green wire is fed from the domestic battery bank by a relay controlled from the key switch. The OP has already taken readings at the relay indicating a lack of output, so a relay change is a "dirt cheap" and worthwhile thing to try.

The only small "fly in the ointment" is that there are two configurations for those small relays, absolutely identical in appearance, but with the terminal numbers in different place - standardisation, ho hum.

I would be seriously impressed if this Hitachi alternator is original, as they do seem to get a lot of "bad press". Could still be real benefit from having the alternator serviced regardless of outcome with the relay. Tony has already mentioned that they may not be repairable; so best to have it serviced to extend life before a failure renders it un repairable.

Steve (Eeyore)

Edited December 17, 2014 by Eeyore

[Tony Brooks]

Tony, you have massively more real world experience in such matters than I do, but you can't change the laws of physics! You post said to connect a wire between a wire with zero volts on it, and another place with zero volts on it. Think about it, this can never bring the warning light on.

 

The wire going to the warning light, and presuming a faulty alternator (open circuit field circuit) so the light is off, will have battery voltage at the alternator terminal. As such it is superficially indistinguishable from a sense wire or other wire connected to battery hence, in the absence of having any clue where the wires go, the instruction to use a bulb to ground rather than just a wire.

 

In summary, connecting a wire to ground on the terminals having zero volts will achieve nothing, connecting a wire to ground on a terminal at 12v will either bring the light on, or cause a dead short circuit. The latter is too much of a risk to take hence the bulb.

 

I agree with all you say BUT as I pointed out I was trying to give a more complete set of results, via a simple test for other readers. The Lucas test card recommendation was to unplug/disconnect the wire in question and sue a voltmeter. Expect the results you have stated here.