What does the Gen 2 relay do?

[erasedhammer]

Been staring at the wiring diagrams for a little while, what does the relay do? What is the purpose of the 2 pin connector on the back of the alternators?

 

[cucvrus]

Been staring at the wiring diagrams for a little while, what does the relay do? What is the purpose of the 2 pin connector on the back of the alternators?

The 2 pin plug on the alternator is the voltage regulator plug. That is part I do know. Just wanted to answer for you.

 

[Barrman]

A relay is just a switch remotely controlled through electricity. If you look at a CUCV battery wiring set up. No power is pulled from the front battery (Battery 1). It just has a negative lead going to ground and the positive going to the back battery (Battery 2). Basically, the batteries are wired as a series circuit to get 24 volts for starting.

Only at the negative of the second battery is 12 volt positive pulled to run the rest of the truck. So, how do you wire up a 12 volt and a 24 volt system on the same truck with the same ground point? Several switches are needed. Switches that have to turn on and off at the same time.

GM used relays to automatically do the switching. The starter relay switches on with 12 volts to send 24 volts to the starter. Since both alternators are isolated ground to their respective batteries. Relays again were used to turn on the exciter wires (brown wire on plug at alternator). The red wire on the same plug comes from the negative of Bat 2 for Gen 1 or the positive of Bat 2 for Gen 2.

It is almost impossible to run an internal regulator alternator without a relay. On any vehicle that the battery stays plugged in on. It also makes it so you can turn the engine off and the alternator won’t keep back feeding the ignition system with power.

The CUCV system is weird at first glance. But, having had and currently driving both 24 starters and 12 volt starters on 6.2 or 6.5 Diesel engines. The 24 volt starter is worlds better. With that in mind. When I put a 6.2 in my M715. I put a complete CUCV dual alternator set up in it and ran my own relays for the alternators. The system works very well.

 

[erasedhammer]

A relay is just a switch remotely controlled through electricity. If you look at a CUCV battery wiring set up. No power is pulled from the front battery (Battery 1). It just has a negative lead going to ground and the positive going to the back battery (Battery 2). Basically, the batteries are wired as a series circuit to get 24 volts for starting.

Only at the negative of the second battery is 12 volt positive pulled to run the rest of the truck. So, how do you wire up a 12 volt and a 24 volt system on the same truck with the same ground point? Several switches are needed. Switches that have to turn on and off at the same time.

GM used relays to automatically do the switching. The starter relay switches on with 12 volts to send 24 volts to the starter. Since both alternators are isolated ground to their respective batteries. Relays again were used to turn on the exciter wires (brown wire on plug at alternator). The red wire on the same plug comes from the negative of Bat 2 for Gen 1 or the positive of Bat 2 for Gen 2.

It is almost impossible to run an internal regulator alternator without a relay. On any vehicle that the battery stays plugged in on. It also makes it so you can turn the engine off and the alternator won’t keep back feeding the ignition system with power.

The CUCV system is weird at first glance. But, having had and currently driving both 24 starters and 12 volt starters on 6.2 or 6.5 Diesel engines. The 24 volt starter is worlds better. With that in mind. When I put a 6.2 in my M715. I put a complete CUCV dual alternator set up in it and ran my own relays for the alternators. The system works very well.

I've done the roscommon 12v conversion, so I only have Gen 2.

The way I understand it is that the brown wire is the exciter so the alternator will start charging at idle. But after some testing I see that it self excites at a quick rev to 3k rpm or so.
So IF the relay was completely disconnected from the system, then only after a rev would the alternator start charging the batteries, and wouldnt drain anything from batteries after shutdown since the brown wire is already 0v.
I am considering finding a one wire alternator for my truck. Simpler is definitely better in my book. (also plan on getting the dakota digital dash cluster, which doesn't have an indicator light, just voltmeter)