Separate 12 volt alternator

[Lin]

I know that some have separate 12 volt alternators for charging the house bank.  Where would one be attached to an MC5 8v71?

[robertglines1]

Ran off pulley on right side of motor looking at it from back of bus...use to charge gen battery...ran a exciter wire from rear junction box...8v92 detroit

[chris4905]

Lin,

Don't have an MCI, but I hope my GM pictures help you anyway.  I believe my 8V71 is similar to yours.

The alternator is a Delco Remy "1 wire", available at just about any automotive supply store.

Charged my 2 6V deep cycle batts wired in series for our 12V house system.

[chris4905]

Another picture of alternator.

[Ed Hackenbruch]

Lin, the PO put one under my air filters on my 5A and ran the belt for it off of the 24 volt alt.

[travelingfools]

Anyone have one mounted on a 6V92 ? With that mounted "backwards", is the rotation an issue ?

[Chopper Scott]

If I remember correctly an alternator doesn't care what direction it is turned to make juice however the fan is directional. I mounted a 12 volt alternator and ran 12 volt power from it to the house batteries and also clear to the front of the bus to  power the headlights, radio and various other 12 volt systems.

[RickB]

You can use a pulley driven by the rear of the blower as Robert suggested but I don't think there would be room for your 24 volt alternator. I'm hoping to use my front   a/c  mount to run mine.

[Gary '79 5C]

Lin,

If you have deep sixed your coach A/C, another idea would be to get a Vanner equalizer to pull 12V from your start batt's.

The OEM alternator certainly has the capacity, and I would install a 24V relay such that it separates your start batt's from your house batt's when the engine is not running. That relay can be cannibalized from the condenser motors of the previously used coach A/C. Mine was located on the ceiling of the forward bay.

FWIW, I have gotten rid of the OEM alternator and have installed a standard truck J180 alternator 24V in its place.

Good Luck,

[Tom Y]

Lin, I have 2 alternators on my Cummins also. Keep in mind if you use a 1 wire unit and your batteries are not close they may not get fully charged. It sees the voltage at the alternator, I think a 3 wire will allow you to see the voltage somewhere else.  Tom Y

[Gary '79 5C]

Lin, I have 2 alternators on my Cummins also. Keep in mind if you use a 1 wire unit and your batteries are not close they may not get fully charged. It sees the voltage at the alternator, I think a 3 wire will allow you to see the voltage somewhere else.  Tom Y

Tom,

I read, but did not fully understand. My read of your comment is that if the start batt's are forward, with 20+ feet of 30 year old cables, the voltage drop will not allow full charge of those batt's.

I may be missing something here and just looking to clarify. Slow morning so far for me...
Thanks.
Gary

[Tom Y]

Gary, This is my take on it only. I was reading about the 1 and 3 wire units. If you have a load on your batteries ( they show 12v ? ) your alt may be seeing 14v so it stops charging. With the 3 wire unit 1 wire is checking voltage at a terminal point seeing the 12v and keeps it charging. I MAY BE WRONG. That being said, I put in 1 wire alts but my batts are a few feet away.  Tom Y

[bevans6]

the idea is that an alternator with an internal regulator uses a reference voltage to determine it's output voltage.  With a one wire alternator, the output voltage and reference voltage are identical, so the opportunity for the alternator to be putting out say 14.5 volts and have that voltage reduce to a lower number at the battery over a long cable exists.  The bus alternator for the start batteries, in my MC-5 with a stock setup, uses an external, adjustable regulator so you can set the voltage at the batteries to what you want.

I think, although I haven't thought it through and haven't checked voltage loss tables, that a house battery charging alternator won't be putting out that much current unless you are asking it to run inverters for high wattage loads like AC units and such on the road, which isn't the best application for a small 12v alternator anyway, so the voltage drop will not be an issue.  if you do plan to be pulling a lot of current, then look up the proper size cable for the application.  And it's always good practice to measure charging voltage at the battery itself, since it's the thing that cares what the voltage is or is not.

Brian

[luvrbus]

Lin, you can run the alternator from the front cam shaft pulley



good luck

[JackConrad]

Anyone have one mounted on a 6V92 ? With that mounted "backwards", is the rotation an issue ?

Only issue with a "backwards" rotation is the direction of the cooling fins on the alternator pulley.  They are available in left & right rotation as well as straight fins that will work in either direction.  Jack