over the road 12v power source.

[Rodsmc5c]

     I know this has probably been asked before but I see that the "R"  terminal on my bus generator is  12 volts.   Can I connect from there to my house battery bank with like a 4/0 wire or is this a fool's errand. I haven't  looked to find the terminal yet. Is it out in the open or buried inside the gen.  ? 
   Thanks
      Rod


   

[Len Silva]

No, you cannot draw any appreciable current from the "R" (regulator) post.  The 12 volts there does not come from the alternator (directly) but rather from the regulator which tells the alternator what to do.

There can be some VERY light loads there such as relays or tach drive.

[Ed Hackenbruch]

The PO of my 5A took one of the belts from the 24v alternator and used it to turn a 12v alternator that he installed on a bracket.

[Jerry32]

I used a 12 V converter plugged in to my 24 V inverter to keep the 12 V charged on the road. When plugged in to a pole the transfer sw taskes care of it Jerry

[Rodsmc5c]

  thanks,  that's what i thought. I see in the manual that there is a black #10 gage wire  12 volts in the ac junction box (that the PO sawed out and threw away).  is it safe to assume that that serves the same purpose as the "R" terminal?  I"m thinking I am going to go back to plan A  and mount a  1 wire alt. back where the old ac compressor was.
  Rod











rod

[Len Silva]

Typically, that 12 volts comes from the regulator to control the alternator.  It is also used to operate a 12 volt relay in the AC compartment to prevent the AC from coming on when the alternator is not charging.

[Sean]

Folks,

There seems to be some confusion here about the "R" terminal.

First, to answer the OP's question, no, you can not power anything with 12 volts from this terminal.

"R" does not stand for "Regulator," it stands for "Relay."  The 12 volts on this terminal does not come from the regulator, nor is it used to control the alternator.  Rather, it goes the other way -- this signal is a half-wave rectified DC output from the alternator stator, whose sole purpose is to communicate whether or not the alternator is producing power.  Because it is a single tap on one diode, the output voltage is approximately half of the alternator's rated voltage (so roughly 12 volts for a 24-volt alternator), however the signal is not straight DC -- it's half a sine wave.

Note that there is generally no connection between this terminal and the regulator.  The only thing that should be connected to this terminal is the coil of a 12-volt relay.  That relay's contacts are then generally used to control two things -- the passenger A/C and heater blowers, and the "Not Gen," "No Charge," or similarly labeled tell-tale on the dash.  The idea here is that the energy-hungry blowers will not run unless the alternator is putting out charge.

The way the regulator is involved here is that if the regulator stops calling for charge for whatever reason (such as it is controlled by an air pressure switch, or there is an alternate charge source such as a battery charger supplied by a generator bringing the voltage up above the regulator's set point), then the voltage on this terminal will drop to zero.  This will be true even though the batteries (or alternate charge source) are still maintaining the voltage at the alternator's main output terminal at 24 volts.

-Sean
http://OurOdyssey.BlogSpot.com

[Len Silva]

Thank you Sean,

I stand corrected.

[Sean]

My pleasure, Len.  I meant to add that absence of voltage on this terminal could mean that the regulator has stopped calling for charge (as I already wrote) or is otherwise damaged, but it might also indicate that the alternator itself has developed a problem.  This is one reason the signal comes from the alternator itself and not merely the regulator.

I also meant to answer this:

..  I"m thinking I am going to go back to plan A  and mount a  1 wire alt. back where the old ac compressor was.

I guess I would ask why "Plan A" is not simply to use a 24-volt house bank?

There is a ton of material in the archives about this choice, but basically what it comes down to is that using a 12-volt house system on a 24-volt coach means you will be giving up the tremendous advantage of all that available energy from the massive 50DN alternator (capable of producing 6,500 watts -- more than many RV generators), you will have to double the size of all your cables and fuses to run on 12 volts, and you will be limited to ~2,500 watts or so in inverters (should you choose to install one) vs. up to 4,000-5,000 watts for 24-volt models.

-Sean
http://OurOdyssey.BlogSpot.com

[DaveG]

Wow Sean, nicely put.

Okay everyone, from now on Sean gets all the A/C questions...from 12v to 120KV