S & L on alternator

[penguin_patrol]

On my alternator there is a 2 pin plug which has a S and L terminal plus the +ive and –ive output.
What I would like to know is the S terminal is a sensing for the battery voltage and the L is for the ignition to energise the alternator. Is this statement correct?

Also if the S terminal had no voltage on it what would happen? No charge or a lot of charge. And If the L terminal had nothing across it would not charge at all and the charge lamp would come on?
The reason I ask this is my alternator was just rebuilt on Saturday and now it is not working again so I thought it could be something in these plugs.
For trouble shooting purposes i am going to run a new +ive cable from the alt to the battery,
can I hook up the S terminal straight to the battery bypassing the factory loom and can I also do the same for the L terminal via a switch which I turn on when car is running and off when not running or is this not going to work? All i want to do is test the alt and the S & L terminal to try and find the problem for the auto elec.

Any help greatly appreciated
Ps can 99 Nissan patrol st 2.8td 143000km

Thank tom

[mgundle]

hi there
um if this is on a late model gu s is battery sense which can be looped straight to the b+ terminal on the alternator this senses battery voltage to the regulator thus correcting the charge rate on the car depending on load

if you were not to run it it would over charge because the regulator would be sensing no or low battery voltage and would try and correct it this sounds like a idea to get full grunt out of an alternator but it will melt the internals

the L terminal is the warning light circuit of the regulator this needs to have an ignition feed though a small dash globe ie.Charge light, To excite the regulator & diodes in the alternator to cause charging to occur if you have hooked straight +ve or -ve to the L terminal you have probably blown the regulator

may i ask what did you have replaced when you had the alternator rebuilt
did you have the regulator replaced or just the brushes that make contact with the slipring, because if you just replaced brushes the regulator was probably faulty from the begining because when brushes run low on a slipring the make poor contact during this they generate excessive voltage to make contact and when they eventually make contact the excessive voltage runs into the regulator blowing or causing it to malfunction.
i would have it checked to see if the wiring is ok and then have the alternator checked over again and get the reg replaced if it wasnt providing the rectifier, Rotor & stator test fine

hope that helps you with your drama
cheers
my two cents

[murcod]

From my playing with alternators I'd agree - S for sense and L for the dash warning light.

For testing, hooking the sense straight to the alternator output is fine, but for a permanent install you'd be much better off running a separate light gauge wire to the battery positive terminal. That way the output voltage will be bumped up to compensate for high current loads (ie. voltage drops across the main charging lead to the battery) and your battery will charge faster. That's the whole idea behind having the remote sensing capability.

[penguin_patrol]

when it was done on saturday the regulator and brushes were replaced and they machined the (insert thimimygig name here) the recipts at work.
I decided to check the connections at the join in the harness to the alt and when i disconected it the engine spead up and then pluged it back in and it was charging javascript:emoticon(':lol:'). did the same after work and it started charging and i turned my lights on cause it was dark in the carpark and when i got out and turned them off again it stoped charging.

So that would mean that the Alt is fine. it was charging @ 14.3V and 2500rpm. I can't work out why it didn't happen after work. Could there be a fault in either the S or L wire befor the plug or something similar.

Thanks
tom

[mgundle]

fault can be in either

alt or in wiring its highly unlikely its in the wiring
does the dash warning light come on and go out??
if it has no battery sense it will overcharge
sounds to me dodgy exciter diode or regulator in alternator take it back and let them warrant it

[penguin_patrol]

thanks everyone
the dash light has never come on but it does work on startup
mgundle:
this exciter diode that you are talking about. It supplys the initial charge/excitement to get the alt charging. Is this in the diode pack?

Will they(auto electrican)/should they warrent it even though when they bench tested it all worked fine and then i bought the alt home and installed it myself.
i don't know much about the legal side of warrants. there was nothing stated on the recipt about a warranty.

Thanks