Alternator wiring

Thread Starter

glow376

Joined Feb 10, 2020
8
Hi all ,
Not sure about forums or if I should reply or start new , sorry if I'm off base here.
Denso 1990 ish year model 3 pin inline plug of 1(L), 2(G),3(S) wanting to put this on my
make shift play rod for the dirt . Can I run both wires 2G-3S from the ignition relay output ?
or better yet can i jumper the 2-3 terminals and run one wire back 2(G) to the ignition relay output ?
I think then when I shut off ignition relay both sensing(S) and power control (G) will de-energize
when I want and no battery drain from the 2-3 terminal wires . your thoughts ? thank you
 

bwilliams60

Joined Nov 18, 2012
1,282
Again you are resurrecting an old post and as @shortbus has pointed out, we refer to this as necroposting.
Start a new post, include a picture of the back of your alternator and tell us what you want to do. We will have an answer.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
5,753
The idiot lamp backfeed to the field (to bootstrap the alternator; the old Motorola patent) hasn't been used in cars (exept in Russia) for more than twenty years... Modern alternators (the ones with the regulator built-in) use the Ign input as a control signal (from the ECU or the ignition switch) to tell the regulator to excite the field. The field current comes from the battery lead; not through the Ign wire... Regulation is achieved by the regulator changing the duty cycle of the field current (i.e. PWM).
This response is not related to the question presented.
 

Thread Starter

glow376

Joined Feb 10, 2020
8
Hi all , Toyota/Denso 80 amp alternator . Using this alternator on my dirt rod junker hobby toy. I want to be safe and was thinking of jumping the "IG" and "S" terminal together then just supply 10 amps "ignition" switched/relay to the alternator for total control . The alternator2Jz alternator.jpg output will be #6Awg for 2.5' connected to the starter with a #4Awg for 3.5' to the battery. in case something goes wrong and I open the ignition switch , the alternator will not have an output to back feed to anything . your thoughts ? thanks
 

LowQCab

Joined Nov 6, 2012
23
You really don't need terminal "L" for anything, unless you actually would like to have an indicator
lamp that indicates that the Alternator is not charging, while the ignition switch is "On".
DO NOT CONNECT "L" directly to 12 volts, YOU WILL SMOKE THE REGULATOR.
This "Switched Ground" can only tolerate, "MAYBE" 1 amp maximum current.

"S" is for Voltage Sensing.
So where do you want to sense the voltage ??
directly at the battery Positive Terminal, just like the schematic shows.
THIS WIRE MUST BE FUSED AT THE BATTERY !!!
A 5 amp fuse is way more than is needed.
If you connect it to any other source of power, the Alternator "may" not provide
the ideal charging voltage for the Battery.
It is totally unnecessary to switch this wire, it does not draw any current.
In fact, this wire should NEVER be switched.

"B" is for Battery.
Connecting it to the Starter will work just fine.
MAKE SURE THAT THIS WIRE IS FUSED AT THE BATTERY !!!!
The easiest way to do this is with a piece of "Fusible-Link" wire,
I've forgotten the color codes, but you basically want the largest size they have.
These require a stout crimp connector, and can not be soldered.

"IG" is for Ignition.
I don't know if this particular Regulator actually pulls power from this wire or not.
Probably not.
So this wire can "probably" come from the Ignition Switch through a 5 amp fuse.
Most likely, this wire simply "Disables" the Alternator when the Ignition Switch is turned "Off".
You may find that the Alternator will work just fine with this wire completely disconnected.
If you have the Factory Wiring Harness for the Alternator Connector,
look at the size of the wire that they used,
if it is very small, (like maybe 18ga.),
then it is not used to supply any significant current to the Alternator,
and should be fused accordingly,
in other words, a 5 amp fuse is over-kill.

"IG" is the only questionable wire.
It "MUST BE" switched, (and fused).

"L" is simply a "Switched Ground" connection to turn on the Alt. Indicator Lamp.
DO NOT EVER connect directly to 12 volts !!!!

"S" never pulls any power,
and is only for sensing voltage at an exact point in the Wiring Harness,
(right at the Battery Positive Terminal).
If "S" is EVER disconnected from the Battery while the engine is running,
You may SMOKE every electronic device in the vehicle, Instantly !!!!
This wire is what determines the Output Voltage of the Alternator.
The Alternator is capable of putting out close to 150 volts if it is un-regulated !!!!!!
The Battery MUST NEVER be disconnected while the engine is running !!!!!

"B" is directly connected to the Bridge Rectifiers,
and can not possibly drain the Battery.
DO NOT DISCONNECT THIS WIRE FOR ANY REASON, EVER !!!!
.
.
 

Thread Starter

glow376

Joined Feb 10, 2020
8
Don't quite understand what your trying to do. Not all Denso alternators are the same depends on the number of pins. The part I don't understand is when you say you turn off the ignition and back feeding.With how an alternator and regulator work I can't think of a back feed situation? But here is a pretty good explanation that may help you.
http://wilbo666.pbworks.com/w/page/39441708/Toyota Alternators
thanks you for the input. I control the power B+ to ignition coils thru a fused relay and can easily add a fused 10Amp wire from its output to the alternator "IG" pin, was then thinking of putting the sense "S" wire to the starter hot post. then i thought about splicing the IG and S terminals to one wire and connection it to the ignition relay output . there are those times i get my dirt digger vehicle out of shape or to slow roll when in the rocks and I thought it would be nice to make sure i'm shutting down all of the power generation system to NOT back feed during the normal shut down to engine stop or emergency stop.
 

Thread Starter

glow376

Joined Feb 10, 2020
8
You really don't need terminal "L" for anything, unless you actually would like to have an indicator
lamp that indicates that the Alternator is not charging, while the ignition switch is "On".
DO NOT CONNECT "L" directly to 12 volts, YOU WILL SMOKE THE REGULATOR.
This "Switched Ground" can only tolerate, "MAYBE" 1 amp maximum current.

"S" is for Voltage Sensing.
So where do you want to sense the voltage ??
directly at the battery Positive Terminal, just like the schematic shows.
THIS WIRE MUST BE FUSED AT THE BATTERY !!!
A 5 amp fuse is way more than is needed.
If you connect it to any other source of power, the Alternator "may" not provide
the ideal charging voltage for the Battery.
It is totally unnecessary to switch this wire, it does not draw any current.
In fact, this wire should NEVER be switched.

"B" is for Battery.
Connecting it to the Starter will work just fine.
MAKE SURE THAT THIS WIRE IS FUSED AT THE BATTERY !!!!
The easiest way to do this is with a piece of "Fusible-Link" wire,
I've forgotten the color codes, but you basically want the largest size they have.
These require a stout crimp connector, and can not be soldered.

"IG" is for Ignition.
I don't know if this particular Regulator actually pulls power from this wire or not.
Probably not.
So this wire can "probably" come from the Ignition Switch through a 5 amp fuse.
Most likely, this wire simply "Disables" the Alternator when the Ignition Switch is turned "Off".
You may find that the Alternator will work just fine with this wire completely disconnected.
If you have the Factory Wiring Harness for the Alternator Connector,
look at the size of the wire that they used,
if it is very small, (like maybe 18ga.),
then it is not used to supply any significant current to the Alternator,
and should be fused accordingly,
in other words, a 5 amp fuse is over-kill.

"IG" is the only questionable wire.
It "MUST BE" switched, (and fused).

"L" is simply a "Switched Ground" connection to turn on the Alt. Indicator Lamp.
DO NOT EVER connect directly to 12 volts !!!!

"S" never pulls any power,
and is only for sensing voltage at an exact point in the Wiring Harness,
(right at the Battery Positive Terminal).
If "S" is EVER disconnected from the Battery while the engine is running,
You may SMOKE every electronic device in the vehicle, Instantly !!!!
This wire is what determines the Output Voltage of the Alternator.
The Alternator is capable of putting out close to 150 volts if it is un-regulated !!!!!!
The Battery MUST NEVER be disconnected while the engine is running !!!!!

"B" is directly connected to the Bridge Rectifiers,
and can not possibly drain the Battery.
DO NOT DISCONNECT THIS WIRE FOR ANY REASON, EVER !!!!
.
.
hi thanks for this help . I was following the diagram for IG 10 amps . I can easily go to a 5 amp 20Awg wire . I don't need the indication light so that's out . in trying to make it simple by combining the IG and S wires at the alt plug connect to the ignition relay output for a clean no worry shut off .

what about alternator output wire size , was thinking 6awg from Alt to starter and a 4Awg from starter to battery . the starter pulls 105 amps and the starter output is 80 amps . total distance 5.5 feet

thank again !
 

Thread Starter

glow376

Joined Feb 10, 2020
8
Thanks everyone !So Much great information ! I see I can't tie the "IG"&"S" wires together or the alternator will just pulse , although this is what i see in new vehicles . So I will control the alt from my switched Ignition relay and the sensing wire will be tied to my fuel pump relay output . electric fuel pumps require a lot of current when the throttle changes . this way the battery buss will be maintained and proper fuel delivery also . any thoughts ?
thanks again
 

shortbus

Joined Sep 30, 2009
7,599
Don't think I would connect the sense to anything but the battery, like it says in the link I gave. Your only wanting to keep the battery charged, it acts like a big capacitor to cover any of the voltage drops that occur when the motor is running.

When you say 4Ga from starter to battery, aren't you using a regular battery cable there?
 

Thread Starter

glow376

Joined Feb 10, 2020
8
Don't think I would connect the sense to anything but the battery, like it says in the link I gave. Your only wanting to keep the battery charged, it acts like a big capacitor to cover any of the voltage drops that occur when the motor is running.

When you say 4Ga from starter to battery, aren't you using a regular battery cable there?
Hi, thank you for the help !

As I look at my engine data , I see fluctuation on battery buss as low as 11V when fuel pressure is under demand or running full throttle , was hoping to shorten the lag time of the alt to bring battery buss back up to 12.5V quicker. I'm using a capacitor battery optima yellow top 450 Amps

This 80 Amp alternator wire of 6Awg is 2.5' to the starter (hot) from starter to battery is a 4Awg which is 2.5' and the starter draws 118Amps max
The wire I have from the local salvage is silver coated copper stranded Teflon insulation mil-spec wire with 133 strands of 27Awg.
 

shortbus

Joined Sep 30, 2009
7,599
was hoping to shorten the lag time of the alt to bring battery buss back up to 12.5V quicker.
Think you'll find that's built into the regulator, to help prevent spikes in the system. Look at it like this, the volts drop due to a motor starting in the system, and if the regulator responded instantly and upped the voltage fast, and at that time the motor shut off, there would be a spike from both the shutdown of the motor that caused the drop plus a higher out put from the alternator. The whole system in a vehicle is a balancing act, and spikes do happen.
 

Thread Starter

glow376

Joined Feb 10, 2020
8
Think you'll find that's built into the regulator, to help prevent spikes in the system. Look at it like this, the volts drop due to a motor starting in the system, and if the regulator responded instantly and upped the voltage fast, and at that time the motor shut off, there would be a spike from both the shutdown of the motor that caused the drop plus a higher out put from the alternator. The whole system in a vehicle is a balancing act, and spikes do happen.
thank you , I had not thought about a spike issue and let you know how this mod goes .
 
As I look at my engine data , I see fluctuation on battery buss as low as 11V when fuel pressure is under demand or running full throttle , was hoping to shorten the lag time of the alt to bring battery buss back up to 12.5V quicker. I'm using a capacitor battery optima yellow top 450 Amps
How long exactly are the fluctuations? What are you measuring with?

Assuming this is an electronic injection system and not a carb...
The fuel system I would think would be relatively constant since injected systems pump the excess gas back to the tank anyways. Full throttle may make the injector pulse longer, but in the end not enough to bring the voltage down significantly.

If it's not injected you have bigger problems.

11 and 12.5 volts are low numbers unless you are talking drops detected with a scope or something better than a multi meter. There may be a bigger issue if that is the case.
 

Thread Starter

glow376

Joined Feb 10, 2020
8
How long exactly are the fluctuations? What are you measuring with?

Assuming this is an electronic injection system and not a carb...
The fuel system I would think would be relatively constant since injected systems pump the excess gas back to the tank anyways. Full throttle may make the injector pulse longer, but in the end not enough to bring the voltage down significantly.

If it's not injected you have bigger problems.

11 and 12.5 volts are low numbers unless you are talking drops detected with a scope or something better than a multi meter. There may be a bigger issue if that is the case.
hi , thanks for the help . engine data shows a 1.5 sec lag so yes the injectore are using more power fuel pump and if throttle is stabbed above
 
More or less there should be no lag whatsoever. It should never drop to 11 Volts when you stuff it to begin with. If it drops at all it should only happen at idle. Either your alternator is bad, your alternator isn't big enough, you have a broken wire, junk battery, or loose connection that when you stuff it and as the engine twists it looses connection.
 
Did you actually figure out the alternator wiring? It seemed like you had it at one point. If you are not seeing over 13 Volts the alternator isn't even working to begin with is what I was trying to get at.
 
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