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

[Phil Auten]

Aaahh! Good old farmer field expiedency fixes. I love 'em!

Phil in TX


On 9/29/2019 9:30 AM, Cecil Bearden wrote:
> 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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