[AT] Cummins scan tool was OT Buck-Boost convertor for charging auxiliary battery

[Cecil Bearden]

I have a 98 Chevy C8500 w/ 3126B Cat and Allison HT750.  It has a speed 
control when using the PTO that has been disconnected.  It was a former 
Mechanic service truck.  In order to get the high idle switch connected 
I have to take the truck to a Cat dealer and they hook up the computer 
to the truck and reprogram the computer to work with the high idle 
switch.  This is a minimum of $500.. When the computer is connected to 
the truck and then connects to Cat there is a $250 charge to connect to 
the Cat service site that $250 goes to Cat.  The other charges are to 
the stealership.   As much as I love Cat equipment, this is a ridiculous 
charge.  I use a piece of 1x2 cut to the right length and wedge it form 
the accelerator to the seat.

Cecil

On 9/29/2019 9:09 AM, James Peck wrote:
> That vocational truck was a Navistar with a Cummins engine. We had been told that we could use the cruise control setting to regulate PTO speed when stationary. The engine load was going to a shiftable transfer box that had pumps bolted to it. The Navistar dealer brought over a Cummins rep with a laptop type diagnostic tool.  We ended up adding a potentiometer that provided a voltage speed command to the engine in place of the fly by wire type accelerator pedal when the truck was stationary.
>
> [James Peck] I worked on a 12 volt battery vocational truck that used voltage converters to get 24 vdc to run a plc and  electrohydraulic valves.
>
> I personally would try to determine if the problem is just a poorly performing voltage converter. I would avoid modification if the problem can be rectified by replacing a poorly performing component.
>
> ]Cecil Bearden] To update the VC problem, after measuring the voltages and looking at diagrams again I am beginning to understand the system, but I don't understand the reasoning behind it.   In a nutshell, the alternator charges the main battery, at the same time the VC charges both batteries in series at 24V.  Definitely something lost in translation in their engineering. All I can think is What the H*#L ?!?!?!?
> I have found a 24V alternator of the same size and connections.
>
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