LT35 alternator - testing voltage regulator

http://www.youtube.com/watch?v=gUCENHqr7b4   

Edited by icky - 28 Jul 10 at 22:28

well, just to put a [temporary?] full stop to this thread:

* i disconnected all the leads from the alternator today and gave them a good clean
* checked the continuity of all leads from alternator to wherever they were going.  all OK no sign of any cracks or short circuits
* did a battery current drain check. disnae seem to be losing anything. strangley - even with the clock in the dash on [should really disconnect it to do a proper check, but i couldnae be bothered] there was absolutely no current drain on the battery at all. at least none that would register on my multimeter.

so i can only conclude that, if there is something wrong with my alternator, it's either that the new belt is slipping slightly as well [worn pulley?] or my voltage regulator is cutting off charging slightly too low. but i'm gonna talke icky's advice and stop fretting about it.  i've got a good hefty 110aH battery in there and the van usually starts within about half a second of turning the key. so, even if the battery's not getting all the juice it deserves from the alternator, it should still have plenty in reserve.

added to which, if the main battery does drop too low to start the van, in the middle of nowhere, i can always press my new cheapo leisure battery into emergency backup use.

dinnae think so.  it's only about 8 months old and only been flattened once [down to about 5 or 6v], when i left the cabin light on over a weekend once.

since i did my various tweakeages and tightenages to the alternator, the battery's usually sitting at just over 12v in the morning now [about 12,05 as opposed to around 11,9 before] so i think it's holding onto whatever it's getting off the alternator but, for whatever reason, it's only being charged up to 12v, instead of around 12,5v.

I've a similar problem that i need some advice on. My charging system is a lot less standard so there in lies my problem. I think it should be fairly easy to put right but any advice would be more than welcome.

Check the battery terminals that are tight and making a positive fit

meant to have another look at this today, but it was too bloody wet [again!]

anyway, one other thing that's puzzling me:

my alternator has the expected connections; one thin wire, leading [presumably] to the charge light on the dash and another heavy duty wire, leading [equally presumably] to the battery positive.  the reason i use the word 'preumably' is that both leads vanish into some hefty sleeving, which snakes its way down and round under the engine, so i cannae see exactly where they go. 

what i'm assuming is the same sleeving then emerges from the other side of the engine bay and feeds into the battery compartment. now, the weird thing is that where the heavy duty lead emerges from the sleeving, it is now two leads, crimped together into one clip at the end and then connected to the battery +ve terminal.

is that normal? - if so, where has this second lead come from? 

[sorry for the long-winded description.  should've really taken a photo and saved myself the typing!]

OK- it's thread archaeology time again!

fingers crossed i have finally sorted this problem.

last time i posted about my alternator, i was labouring under the misapprehension that it had started working again, since the dashboard light was no longer visibly glowing in the daytime.  a couple of days ago, however, i took herman out at night to pick up the missus and noticed that the charge light was in fact glowing dimly [only visible in the dark].

the following day, i went for a run in the van with my circuit tester attached and saw that i was getting  about 12,3V across the battery - better than a kick in the flaps, but about a volt less than i sould have been getting.  with sinking heart, i realised that my alternator was not working properly after all - it was just 'not working' slightly less badly than before.

anyway, today i determined to get to the bottom of the problem, or kill myself in the process:

* once again, i measured the voltage being output from the alternator; 14,8v - so definitely not the alternator then.

* then i measured the voltage across the battery, with the engine idling; 12,3V.  so somewhere 'twixt alternator and battery i was losing 2,5V

* i then began the fun job of tracing from the battery, back to the alternator, to find out whether there was a short in the circuit.  a job made all the more pleasurable by the fact that the lead is routed round the most inacessible and dirtiest parts of the engine.  given that herman's engine is a 17 year old diesel, which would make a seagull which spends it's time floating around the gulf of mexico, look pristine, this meant that i ended up looking like something out of the black&white minstrels, by the time i eventually found...

... a loose connection on the starting motor solenoid, which is where the fat +ve lead from the battery and the fat B+ lead from the alternator meet!

you could have knocked me down with a feather.  i've had a shedload of motors in my time, with a shedload of 'innovative' approaches to wiring, but this is the first time i've seen the output from the alternator channeled to the battery by way of the starter motor solenoid!

anyway, to cut a long story short, i undid the solenoid terminal, removed the battery +ve lead and alternator lead [both of which were covered in oil and muck], gave everything a good cleaning up with a mini file and some wire wool and put it all back together again.   then i started up the motor and stuck my circuit tester across the battery terminals again - and got nearly 14v!

yay!

to say i'm chuffed would be an understatement. 

that intermittent charging problem has been doing my head in since i got the van.  i've swapped alternators, replaced the alternator drive belt, tightened up the alternator, had the dashboard off more times than i care to remember, fiddled and twiddled with the battery terminals, tightened the engine earth strap - and all the time, the problem was a loose connection on the starter motor solenoid.  who would have thought it! [especially given that the starter motor has worked flawlessly all the time - you'd think it would at least have had the decency to be a bit temperamental, so i'd have cast the eye of suspicion upon it].

o well.  at least i've finally cracked it.  until i get off my fat arse and bring my herman blog up to date, here are some snaps for your delight and delectation:

up to my elbows in muck, trying to clean the terminal on the solenoid [actually this pic makes it look positively idyllic - i spent most of my lying under the van with my arms squeezed up through the oil-smeared gaps at the edges of engine bay]


the nice thing about electronic jobs - as opposed to mechanical - is that you dinnae have to get so covered in muck!


still, it was worth it in the end.  behold my mighty voltage and despair!




Edited by madra - 23 Jul 10 at 20:33

so, that's why i've got 5 reverse gears and only 1 forward!

[i bought a new set of leads for my circuit tester after i bust the probe off one of the old ones. for some reason the new ones have the terminals set the opposite way round - so i have to plug them in the wrong sockets. see - i'm not a complete eejit. only a partial one!]

If it's a 'smart' spilt charge relay then it will only charge the leisure battery once the alternator voltage reached a certain level - with min within a minute or 2 or starting. Not necessarily the same as the main battery being fully charged (without wanting to go off about surface charge...)
A standard split charge relay will just switch over as soon as its coil sees 12V - i.e. as soon as the alternator starts giving any output.

To test it why not turn something on connected to the leisure battery, and then disconnect the leisure battery (with and without engine running). With the former it should stay on, the latter it should go out.

Not quite - once the voltage is over a certain level both batteries will be linked. But more current will flow through the one that has less charge, simply because that has the lower voltage.