Alternator size and amp rating

[James Agg]

Alas, I have tried all suggestions, and the alternator is still not doing anything at all. As far as I’m aware, the alternator only gave charge to the battery a grand total of once and it was over a 3 or 4 mile journey having not worked before, and after that, it stopped giving charge again. I also tested the alternator’s voltage from the B+ terminal without it hooked up to the battery and with the car running and it seems to only give a reading of 0.4volts with it being turned by the engine on idle. I’ve checked the ground, I’ve even sanded back the bracket to ensure that there is bare metal, and it’s still not working. I sadly think I have a duffer of an alternator or a duffer of a regulator built into the alternator. Can’t think of anything else… how disappointing. I don’t think it can be returned as it was an eBay purchase

[alanrichey]

I'm by no means an expert, but you have already commented that the warning light doesn't appear to be working correctly.   I wonder if the alternator is not getting exited enough to sctually kick in (I know it sounds daft but that is the technical term).   What shold happen is that when you switch on the ignition the alternator light should come on, along with the oil pressure light.  This is because one side of the light is fed ignition-switched 12V and the other end is connected to the alternator, which at this stage is at 0V.   Once you start the engine the current flowing through the 'lit' warning light should 'excite' the alternator and it starts to produce power.  Once that reaches 12V then the warning light has 12V on both sides so it goes out.    I know that some alternators can also self-excite on occasions and maybe that is what happened to you on the first trip when it seemed to be working.    So I should check the wiring of the warning light and make sure it is operating correctly.

[phaeton]

9 hours ago, alanrichey said:

I'm by no means an expert, but you have already commented that the warning light doesn't appear to be working correctly.   I wonder if the alternator is not getting exited enough to sctually kick in (I know it sounds daft but that is the technical term).   What shold happen is that when you switch on the ignition the alternator light should come on, along with the oil pressure light.  This is because one side of the light is fed ignition-switched 12V and the other end is connected to the alternator, which at this stage is at 0V.   Once you start the engine the current flowing through the 'lit' warning light should 'excite' the alternator and it starts to produce power.  Once that reaches 12V then the warning light has 12V on both sides so it goes out.    I know that some alternators can also self-excite on occasions and maybe that is what happened to you on the first trip when it seemed to be working.    So I should check the wiring of the warning light and make sure it is operating correctly.

To prove this you need to eliminate all the vehicle wiring, once you have a good known alternator or not you can move forward, you need to systematically work through one step at a time.

1) Temporarily run 2 new wires from the battery one with a 5W bulb & the other without, does the light come on at this point Yes got to 2/No get alternator tested ***test bulb before you do this to ensure it's working

2) Start engine, does light go off Yes alternator is good, fault is in car wiring/No get alternator tested

[James Agg]

48 minutes ago, phaeton said:

To prove this you need to eliminate all the vehicle wiring, once you have a good known alternator or not you can move forward, you need to systematically work through one step at a time.

1) Temporarily run 2 new wires from the battery one with a 5W bulb & the other without, does the light come on at this point Yes got to 2/No get alternator tested ***test bulb before you do this to ensure it's working

2) Start engine, does light go off Yes alternator is good, fault is in car wiring/No get alternator tested

Ah ok, so, when you say eliminate all wiring, you’re suggesting a direct wire from the positive terminal of the battery to the ignition terminal on the alternator so that it isn’t switched at all? I guess that’s ok as a temporary measure as it’s just for testing - I imagine the purpose of the 12v feed to the regulator being switched is so that the regulator doesn’t drain the battery when the car isn’t in use right?

[phaeton]

19 minutes ago, James Agg said:

Ah ok, so, when you say eliminate all wiring, you’re suggesting a direct wire from the positive terminal of the battery to the ignition terminal on the alternator so that it isn’t switched at all? I guess that’s ok as a temporary measure as it’s just for testing - I imagine the purpose of the 12v feed to the regulator being switched is so that the regulator doesn’t drain the battery when the car isn’t in use right?

You could put a switch in there if you wish, but this is just a test to find out if the alternator is charging, personally I'd also have a voltmeter or multimeter on the battery as well. But you must ensure that the bulb works, it needs to be over 5W once you have a known good alternator then you can start to chase down any other fault, if there is one. But until you have a known constant you don't have a base line to start from

[James Agg]

10 minutes ago, phaeton said:

You could put a switch in there if you wish, but this is just a test to find out if the alternator is charging, personally I'd also have a voltmeter or multimeter on the battery as well. But you must ensure that the bulb works, it needs to be over 5W once you have a known good alternator then you can start to chase down any other fault, if there is one. But until you have a known constant you don't have a base line to start from

Yeah sure, I’ll definitely have my voltmeter on there as well to see what it’s doing. Does this diagram look correct for a test? If so, I’ll get to it right now!

[James Agg]

3 minutes ago, James Agg said:

Yeah sure, I’ll definitely have my voltmeter on there as well to see what it’s doing. Does this diagram look correct for a test? If so, I’ll get to it right now!

Oops, that meant to be 5W bulb, not 5V

[phaeton]

Yes, you're trying to replicate the bottom left image in the PDF you posted, but without the ignition switch, unfortunately I can't get my image under 300kb so can't post it I have no idea how to shrink it.

[James Agg]

9 hours ago, James Agg said:

Yeah sure, I’ll definitely have my voltmeter on there as well to see what it’s doing. Does this diagram look correct for a test? If so, I’ll get to it right now!

Oops, that meant to be 5W bulb, not 5V

[James Agg]

Still nothing. See video… I’m stumped, and defeated and am more and more of the thinking that it’s time to return the alternator

[IanS]

Is there any chance that this is a 6V or 24V alternator?

If not then it looks to be bust.

[James Agg]

15 minutes ago, IanS said:

Is there any chance that this is a 6V or 24V alternator?

If not then it looks to be bust.

Yeah, I’m inclined to agree… definitely 12V, unless the advert for it is wrong…

[phaeton]

Yep, I think you've done all the test, the only other if you haven't put it all back together would be to turn on your lights, fans etc. with it running just to see if it needs a bigger draw to kick it in, I have an old tractor which doesn't have a bulb it has a resister that needs to see s bit bigger draw before it starts, . The 5W is definitely 5W?

 

[Foz]

I can't see anything wrong with the wiring on your video but you do seem to have the same connector as me for the ignition and lamp wires.  I found that I had to push the actual ignition spade connection in to get a good connection on mine, as if the connector body didn't push in quite far enough to make a good connection (mine was intermittent).  Could you lose the connector body and try the spade connectors straight onto the alternator terminals ?

 

[James Agg]

Hello all. Thanks for your help with all of this. A replacement arrived today and having compared the two side by side, the problem became alarmingly obvious. The trouble was earthing all along, but not because of my mounting bracket or my wiring, but because whoever did the quality control at the alternator factory failed to spot that they had powder coated over the surface of contact with the bracket (see photos!) My explanation for my theory on it briefly giving charge can be found when you look closely at the lower mounting eyelet which is of course a swing/pivot to allow for belt tension adjustment. Whilst I was faffing around with it, I likely gradually wore away some of the paint on that eyelet at which point it found a tiny bit of earth, but given that it was a fairly bad earth due to there only being very small contact, my guess is that when I drove it, it pushed current through the alternator thanks to that small spot, but resistance would have presumably been very high and the alternator became toast after a fairly short drive owing to needing to push all that current through a lot of resistance. Just a theory anyway - not saying it’s correct.

 

Thanks again. Very happy now and great to see a good steady 14.26v even with a load test!