Hello,

Does anyone know the amp draw on the IG wire (12V key on) for the Denso 90A alternator? I've searched the net and can't find any conclusive number.

Thank you,

Steve

That would depend on the output of the alternator.

More alternator output means more field current.

Whatever it is it isn't much. Look at an OEM harness in the wrecking yard and you'll see that they don't use heavy wire. Probably 16 or 18 ga. If the OEM guys aren't worried about it then hot rodders don't need to worry about it.

Buy a good 0 to 100 amp gauge and find out
Please let us know also

Thank you everyone.

Cab-That will be a while. Drivetrain is out of the car and I'm laying out the wiring plans for the EFI, ignition, in tank pump and Denso conversion.

What am I doing....

You can probably find a schematic on line for a car with a 90A alternator in it. The schematic will show you the wire sizes that the OEM engineers used. I'd trust that information over anything else.

Thanks Andy, good idea. I looked at some schematics and although the wire gauge wasn't indicated, I did find a few that show a 7.5A fuse in the ignition line. I took a look at your website for the 90A alternator install instructions and I see what you mean regarding small wire gauge on the pigtail connector.

The load pulls mostly away from the battery. The wire for the alternator is rated for the amount of amps going to the battery. The length of the wire is also factored in. If you want to check the amps running threw the wire you need a DC amp probe. The load on the battery will effect output.
[img]https://mowgli-adventures.com/wp-content/uploads/2021/02/Wire-gauge-calculator-table.jpg.webp[/img]

You didn't understand the question.

Maybe I don't, IG wire? Ignition wire? The alternator had nothing to do with the draw of the ignition. A amp probe will tell you the draw on any wire.

[video:youtube]https://www.youtube.com/watch?app=desktop&v=VNZgm0hatzU[/video]

What feeds the (usually) blue wire that connects to one of the field terminals?

The ignition circuit. The other field terminal connects to the regulator green (usually) wire.

Blue wire(one going to the regulator) is battery power(key on), The green is the way the regulator "regulates" the alternator output. This is relatively low amperage and the regulator varies voltage to the field to control output.

The blue wire is the IGNITION ONE circuit.

That's how the factory labeled it, that's how the OP referred to it. You can call it a ham sandwich if you want, but no one's going to have it for lunch.

For those interested, I found the following link interesting. It provides a good operational description of Toyota alternators:

http://wilbo666.pbworks.com/w/page/39441708/Toyota%20Alternators

Good link.

So the “IG” wire on Denso alternators only has to carry enough current to “bias on” a transistor switch inside the Regulator IC Chip - probably a low current.

Only if it's an internally regulated alternator though, which may or may not apply to the OP's alternator because Denso made both styles.

Me too, on two cars under construction, one drag race (150.00+ MPH 1/4 mile, 130 MPH in the 1/8 mile) only and the other street only

How many horsepower does an alternator consume at high rpm during a quarter-mile run?

Guess maybe max of
90 amps x 14 volts divided by .85 efficiency = 1482 watts

1492 divided by 745 watts per horsepower
= 2

but could a gain of two win by a distance of a inch to a foot at the finish line.....

at real high rpm the belt/pulley efficiency might be way less than 85%

Yes, 90A alternator, internally regulated. AndyF's (AR Engineering) conversion.