Rods 'n' Sods - UK Hot Rod & Street Rod Forums banner
1 - 19 of 19 Posts

·
Off the Xmas card list
Joined
·
24,204 Posts
Discussion Starter · #1 ·
Just bought a 40 amp small alternator from E bay . Found a wiring diagram on Google so that's all good . Now I need a nit more info. It has a terminal connection with 3 small terminals in a row which are

1) battery sense
2) ignition switched 12v
3)Warning light

Obviously my original wiring becomes a bit of an issue as all the old alt has is battery terminal and power feed through warning light to alternator.

I'm presuming that terminal 3 is earth switched ie once the alternator is running the power is switched off .


I'm not immediately seeing a way of using my existing warning light set up on this alternator ,any ideas anyone ? Can I use a relay on terminal 3 to switch the existing warning set up off?
 

·
"call 0-800 Apocalypse"
Joined
·
5,229 Posts
is it the daihatsu on Kev, that they use on the westfields?
 

·
Rust buster...
Joined
·
602 Posts
Simples

Sense is normally connected to a switched 12V source in the main loom. The idea being that it regulates the alternators output to give the required charging voltage. If connected back to the B+ connection the alternator will only ever give about 13.5v output.

The warning lights on all alternators work in the same way. With the alternator stopped they are at 0v. Which gives 12v PD across the warning light (as the other side of the warning light is connected to a switched 12v source). Once running the alternator outputs 12v (ish) on this pin which means there is 0v PD across the warning light so it goes out.

Odd for it to have another switched 12v input, but it may just be power feed to the internal regulator. Some have it externally rather than internally. Normally referred to the IG connection if present. You can just link the IG and S connections together if you want to.
 

·
Rust buster...
Joined
·
602 Posts
I assume you mean diag 4 as 7 is the 2 wire alternator.

Same as I said before applies if it's #4 just IG=L

S = sense, connect to a switched 12v source.
IG = ignition live, same as S. Can be looped together
L = connect as I said before. Should be 0v with alternator stopped and 12v with it running. If it isnt then there is a little trick you can do with a transistor so your light works. I'll post it up if it doesnt work, but its only normally on the alternators that have a D+ connection rather than an L connection
 

·
Off the Xmas card list
Joined
·
24,204 Posts
Discussion Starter · #6 ·
Finally sorted the wiring as wasn't operating correctly. This configuration requires S leaving off ( in actual fact it comes up as P, for phase, when checked closer ) .Now all operational.
 

·
Registered
Joined
·
547 Posts
Hi, apologies for recycling this thread but I need a bit of help. I'm trying to wire the same Denso alternator, also having 3 small wires in a row. Unfortunately the wires are not marked but they are coloured,White, Red and black, Yellow and red. I need to know which wire is sense and light e.t.c.
Thanks in advance for any help, Ron.
 

·
Premium Member
Joined
·
3,467 Posts
Hi, apologies for recycling this thread but I need a bit of help. I'm trying to wire the same Denso alternator, also having 3 small wires in a row. Unfortunately the wires are not marked but they are coloured,White, Red and black, Yellow and red. I need to know which wire is sense and light e.t.c.
Thanks in advance for any help, Ron.[/QUOTE

what is the wiring loom off
 

·
Registered
Joined
·
547 Posts
Hi, apologies for recycling this thread but I need a bit of help. I'm trying to wire the same Denso alternator, also having 3 small wires in a row. Unfortunately the wires are not marked but they are coloured,White, Red and black, Yellow and red. I need to know which wire is sense and light e.t.c.
Thanks in advance for any help, Ron.[/QUOTE

what is the wiring loom off
Hi mate, apologies for the delay in answering you. The alternator is going on to my 100E but I don't know what it came off, it just says Toyota on the tag.
Cheers, Ron.
 

·
Premium Member
Joined
·
3,467 Posts
Hi Ron Google Toyota Alternator Wiring then go down the page a bit to Search For Images of Toyota Alternator Wiring click on that, then in the second row down click on the third image to see the diagram for the socket on the alternator that is the same as yours. From this you will be able to tell where each of your wires should go to e.g. which colour is warning light, which colour is ignition feed and colour is battery sense. Then follow the wiring diagram second row down fouth image. Hope I have made this is wiring clear. You will also need 84/03 ( for a 42 amp alt ) 97/03 ( for a 50 amp alt ) or a 120/03 ( for a 60 amp alt ) size cable from the large terminal in your picture to either to the starter motor battery side or direct to the battery

Paul
 

·
Registered
Joined
·
547 Posts
Hi Paul, that's fantastic, thanks for taking the time to sort me out. I'm getting straight to it.
Cheers, Ron.
 

·
Premium Member
Joined
·
3,467 Posts
Finally sorted the wiring as wasn't operating correctly. This configuration requires S leaving off ( in actual fact it comes up as P, for phase, when checked closer ) .Now all operational.
kapri just wondered where you got your configuration from. As flak monkey says normally the sense controls the amount of voltage going to the battery ( hope I am not teaching to suck eggs here ) as you need less voltage going to the battery when it is charged than when it is discharged. If it keeps charging at a high rate all it will do is cook the battery
 

·
Off the Xmas card list
Joined
·
24,204 Posts
Discussion Starter · #13 ·
...and back to the top :(

Just swapped from 40 amp to 60 amp alternator , ignition light works if S ( battery sense ) is left off ( as previously ) but not if you connect it ? Am I missing something obvious here ? Why have it if it doesn't work when connected ?

Last time I had this trouble I took the alternator to a local auto electrician ,he tested it and said to leave off the sense feed.
 

·
Gym Junkie
Joined
·
6,213 Posts
Is your Charge Lamp connected to the L Terminal on one side and the switched side of the ignition switch on the other, when the alternator starts charging a current flows through some diodes inside the alternator to apply an equal positive voltage out the L terminal to one side of the warning light so the light goes out, when the alternator stops charging the current through the diodes stops flowing and the voltage drops causing the light to come on to let you know there is a problem.
 

·
I'm Not Jed Clampett
Joined
·
2,725 Posts
...and back to the top :(

Just swapped from 40 amp to 60 amp alternator , ignition light works if S ( battery sense ) is left off ( as previously ) but not if you connect it ? Am I missing something obvious here ? Why have it if it doesn't work when connected ?

Last time I had this trouble I took the alternator to a local auto electrician ,he tested it and said to leave off the sense feed.
some 3 wire Densos have a W output instead of S (sense). W stands for Wave and is an AC reference output. I *think* that having a permanent 12V on the stator wiring from connecting the W terminal to the battery positive might well screw up the alternator operation.
 

·
Off the Xmas card list
Joined
·
24,204 Posts
Discussion Starter · #16 · (Edited)
Is your Charge Lamp connected to the L Terminal on one side and the switched side of the ignition switch on the other, when the alternator starts charging a current flows through some diodes inside the alternator to apply an equal positive voltage out the L terminal to one side of the warning light so the light goes out, when the alternator stops charging the current through the diodes stops flowing and the voltage drops causing the light to come on to let you know there is a problem.
I work from ignition out ( ;) ) but switched power though ignition bulb to alternator , so yes.

I've just run it up and it putting out 14.2 violts constantly regardless of revs.

From what Stu is saying it looks like connecting the battery Sense lead is making the diode switch the light off before it starts ? Maybe the battery sense wire needs to go through an ignition switched relay ?
 

·
Gym Junkie
Joined
·
6,213 Posts
With no wire connected to the L terminal and the ignition on are you getting a voltage from the L terminal, if you are then that is what is making the bulb go out, you should only be getting a voltage out of the L terminal once the engine starts and the alternator starts charging, allowing current to flow through the Diode Trio.

This diagram shows the internal wiring on a typical alternator:

 

·
Gym Junkie
Joined
·
6,213 Posts
I'd try it without the S wire first first as you know that works so I am assuming that there is no voltage on the L pin at this stage then connect the S to the battery (or any live 12V feed) and see what happens to the voltage on the L pin, it should remain at 0V if it goes to 12V then there is something amiss probably inside the alternator.
 
1 - 19 of 19 Posts
Top