Alternator Amperage and failure??
Discussion
Ok, so a couple of years ago at the Griff Growl my alternator blew up.
RAC turned up and replaced it. He wasn't sure if it was the right amperage one, but the car stated ran and all looked good, aside from the charge light being stuck on. A year later still no problems and all looks dandy.
Recently I have noticed that my in car voltmeter is now reading 12V when the lights are on, and drops to 11-10.5 when the lights and blower are on.
My car is supposed to have an 85amp alternator in it and it may only have a 45amp one in it.
From my understanding this means that the alternator has to work at a higher capacity, more of the time, to keep everything charged, which will lead to premature failure. Where as an 85 amp alternator will be working at a less capacity.
This along with being right next to the exhaust manifolds.
Am I correct in this assupmtion?
I am an electrical numpty, so what is the best way to check it's doing it's job?
RAC turned up and replaced it. He wasn't sure if it was the right amperage one, but the car stated ran and all looked good, aside from the charge light being stuck on. A year later still no problems and all looks dandy.
Recently I have noticed that my in car voltmeter is now reading 12V when the lights are on, and drops to 11-10.5 when the lights and blower are on.
My car is supposed to have an 85amp alternator in it and it may only have a 45amp one in it.
From my understanding this means that the alternator has to work at a higher capacity, more of the time, to keep everything charged, which will lead to premature failure. Where as an 85 amp alternator will be working at a less capacity.
This along with being right next to the exhaust manifolds.
Am I correct in this assupmtion?
I am an electrical numpty, so what is the best way to check it's doing it's job?
I think your volt drop with all the loads on is already giving you the answer... you need the bigger (correct size) alternator to support the electrical load.
The current alt will not suffer but at the same time cannot keep up with the demand so if you continued with the high load eventually the battery would go flat. If the load is only there for a while the alt. will catch up when the load is removed and bring the battery back to full charge. If you return from a journey under load (wet, cold, night) and park up the battery will be low on charge and could suffer long term damage if left that way.
Steve
The current alt will not suffer but at the same time cannot keep up with the demand so if you continued with the high load eventually the battery would go flat. If the load is only there for a while the alt. will catch up when the load is removed and bring the battery back to full charge. If you return from a journey under load (wet, cold, night) and park up the battery will be low on charge and could suffer long term damage if left that way.
Steve
A Griff doesn't have a massively complex electrical system does it? I think the spec for my car is a 70A alternator but that's massive overkill, even with everything on it doesn't eat anything like that much. Lights and blower is... 10A for the headlights and maybe 20A for the blower (they can use a surprising amount of power) plus say 5A for the ignition system... a 45A alternator ought to have no trouble keeping up.
I suspect that if it is an alternator fault you've got a unit which was at the lower end of the reliability distribution and also doesn't like being cooked by the exhaust. Also there was something wrong with the installation in the first place if the charge light was stuck on. I'm not sure quite what sort of cock-up would do that without stopping it charging at all so I can't say whether that might have had anything to do with it.
However it's also worth checking for bad connections... measure the voltage on the battery posts, then measure it directly on the alternator terminals and see if it's higher there... if it is check every joint and connection between alternator and battery... don't forget the earth side either, have seen similar results on an Astra due to the earth connection from alternator to engine block going high resistance.
I suspect that if it is an alternator fault you've got a unit which was at the lower end of the reliability distribution and also doesn't like being cooked by the exhaust. Also there was something wrong with the installation in the first place if the charge light was stuck on. I'm not sure quite what sort of cock-up would do that without stopping it charging at all so I can't say whether that might have had anything to do with it.
However it's also worth checking for bad connections... measure the voltage on the battery posts, then measure it directly on the alternator terminals and see if it's higher there... if it is check every joint and connection between alternator and battery... don't forget the earth side either, have seen similar results on an Astra due to the earth connection from alternator to engine block going high resistance.
I'm definitely going to check the earth's tomorrow.
I think something behind the dash blew when the last one packed up, which is causing the charge light to stay on.
Quickly on measuring the output, do I measure it across the battery posts with the engine running?
How can I check the resistance?
I think something behind the dash blew when the last one packed up, which is causing the charge light to stay on.
Quickly on measuring the output, do I measure it across the battery posts with the engine running?
How can I check the resistance?
Yep... measure across the battery posts with the engine turning over at about 1500rpm. A brick or something to hold the throttle fractionally depressed is often useful 
Measuring resistance isn't completely straightforward because the resistance ranges on multimeters aren't up to the job, so you have to do it by an indirect method... Engine at 1500rpm with the lights and blower on to give some load, and use the voltage range on the meter. Positive meter lead on battery negative post, negative meter lead on alternator body (or alternator earth terminal if it has a separate terminal for it). Should see negligible voltage... if it reads a significant amount then move the negative meter lead step by step along the path to the battery... engine block, bodywork, negative battery lead (as opposed to post)... the step that gives a significant change in reading is the step that stepped over a high-resistance point. And the same on the positive side - negative meter lead to positive battery post, positive meter lead to alternator main output, then step positive lead back along the path to the battery.
Measuring resistance isn't completely straightforward because the resistance ranges on multimeters aren't up to the job, so you have to do it by an indirect method... Engine at 1500rpm with the lights and blower on to give some load, and use the voltage range on the meter. Positive meter lead on battery negative post, negative meter lead on alternator body (or alternator earth terminal if it has a separate terminal for it). Should see negligible voltage... if it reads a significant amount then move the negative meter lead step by step along the path to the battery... engine block, bodywork, negative battery lead (as opposed to post)... the step that gives a significant change in reading is the step that stepped over a high-resistance point. And the same on the positive side - negative meter lead to positive battery post, positive meter lead to alternator main output, then step positive lead back along the path to the battery.
Wildfire said:
Recently I have noticed that my in car voltmeter is now reading 12V when the lights are on, and drops to 11-10.5 when the lights and blower are on.
You may have already fixed the problem but if not then think back to the S. The symptom quoted above is what happens when the yellow connector under the steering column starts to burn out. Is there a similar connector of the Griff? Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff