Can I use an external power supply to provide Excitation voltage?

When your application requires more than the recommended maximum number of load cells,  utilize an external excitation voltage to power your load cells. Most current model Hardy controllers utilize a 5vdc excitation voltage, and the external power supply voltage must match the excitation voltage. 
NOTE:  The older HI 2160RC, HI 2151/20 and HI 1771WS use 10vdc excitation (+5v & -5v).

When using an external power supply the excitation monitor will not function properly.  You should ignore the error bit or turn the excitation monitor off.   Excitation monitor is the current draw on the excitation voltage from the weight controller.  The internal excitation voltage is not being used, therefore no current draw, and the excitation monitor will improperly report a failure.

You cannot use a higher voltage power supply due to over voltage damage to your Hardy controller.

C2® calibration, if equipped, will still operate under these conditions as long as you are not exceeding the max number of C2® cells for the unit.  Maximum number C2 load cells equals eight.

Wiring considerations would be to verify the +Exc is not used on the Hardy controllers.  Remove any jumpers from  Excitation + and Sense+  terminals.  The +5 volt supply is connected to the load cells and then attached to the +Sen connection on your Hardy controller. The external power supply - (or return) connection is to the jumpered -Exc and -Sen terminal on the unit. +SIG & -SIG would be attached to the load cell outputs in the normal manner.

Attached is a Tech Note Schematic that shows how to connect an external power supply to a Hardy controller.