Adding 2nd alternator to Cummins 6BTA5.9

Several years ago I added the 2nd alternator to the main motor dedicating it to the House Battery.  The following is what I had written and posted at Boatdiesel.com , with some updated information / part numbers.

The DC electrical design on Viking Star has two 100% separate and complete systems: Engine starting / gauges, and the rest. The motor mounted alternator retains it duties of charging the starter battery, while a Leece Neville 270A alternator takes the house battery role. Attached are some picture of the final design I used.

First I went to Cummins and secured an additional pulley for the front of the motor. In this case I used dual V type pulleys, but they have a very wide verity from multi V belts to the flat ‘serpentine’ style, as well as any needed spacers. (I used Cummins option number: AF-9026)   I purchased the accompanying alternator pulley from a local supply house, along with a non-directional fan as the alternator would be spinning ‘backwards’. (No problem with this, but do need the correct fan  A041075594 / 75594??)  make sure it does not have a directional arrow cast into it and that the 'fins' are straight).  Using a external Brush Holder Cover from Leece Neville (part number:  39-5204,  100265, or A038100265S) allows for an external regulator to be connected.

I then used an inverted 4” U channel across the front of the engine. This fit the mounting holes on the bottom of the alternator. By boring ½” holes through the flanges and running a 5” bolt through the lower alternator ears and the holes in the u-channel flanges I could attach the bottom of the alternator. A simple 3/8” x 4” steel strap was bolted to the middle of the U Channel, this provided a riser where I could add the arched top mount for the alternator. (BTW:  The top arch mount can be found for little cost or even free at a local Truck junk yard)

All of this was suspended in front of the Cummins motor on two 2.5” angle irons which were drilled to align up with the forward motor mount holes. Using a small bottle-jack I could relieve the pressure on a forward motor mount, remove the screws and add the angle iron to each side. (I did use longer bolts  to accommodate for the additional metal thickness of the angle irons.)

Sorry, the external regulator cover is not shown in these photos
At this point it still had the standard internal regulator installed.

Total cost, less than $100 for all but the alternator. Tools: Grinder and grinding wheel, skill saw with a metal abrasion cutting blade, drill press. Changes: I note a slight bit more vibration when placing my hand on the new bracket than the motor. If I did it again, would increase the dimensions of the angle iron. Or perhaps add a stiffener to the existing size. (I was limited somewhat by readily available materials).  Note:  I had written this  5+ years ago, and to date have not made any changes.  It works very well and has shown no signs of stress or other issues.

BTW: As alternators go, those Leece Neville alternates are tuff. 270A out of a package about 12” long, and over 8” around. It weighs (I am guessing) 30lbs or so… They are available up to 350A in the same case. At idle, I can pull 150A out of it (measured, warm). Ebay  has them ranging from 200A to 300A, and often for will under $200.