0439006 JOHNSON GEARCASE ASSY.

Illustration 1 g00481725
Functional Block Diagram Of AC Voltage Display in EMCP II
Table 1
AC Voltage Range Selection
GSC P20 Setpoint External Potential Transformer Input Voltage Range For AC Transformer Box (ATB) GSC Internal Multiplier Jumper
700 None 0 - 700 5 Required
150 None 0 - 150 1 None
300 2:1 0 - 150 2 None
500 3.33:1 0 - 150 3.33 None
600 4:1 0 - 150 4 None
750 5:1 0 - 150 5 None
3000 20:1 0 - 150 20 None
4500 30:1 0 - 150 30 None
5250 35:1 0 - 150 35 None
9000 60:1 0 - 150 60 None
15000 100:1 0 - 150 100 None
18000 120:1 0 - 150 120 None
30000 200:1 0 - 150 200 None The AC voltage and/or current values are inaccurate.Note: For related information, see Testing And Adjusting, "AC Voltage Range - Adjust".The P20 setpoint determines the proper AC voltage range and the internal multiplier that are used by the GSC for calculating AC voltage. The GSC uses the internal multiplier in order to compensate for the turns ratio of the external potential transformers. The turns ratio of the external potential transformer must match the internal multiplier in order to ensure an accurate AC voltage calculation by the GSC.The jumper block is located in the relay module. The jumper block connects a "divide-by-five circuit" to the ACV input of the GSC. The "divide-by-five circuit" reduces the ACV input to a controllable level for the GSC when P20 is 700. When setpoint P20 is 700, a multiplier of five is needed to compensate for the presence of the "divide-by-five circuit". This is done even though no external potential transformer is present.Note: In order to prevent an inaccurate calculation of the voltage by the GSC, the jumper block should NOT be installed when P20 is programmed to a value that is different from 700. The other values (150 through 30 000) are used with an external potential transformer. The values result in input voltages from 0 to 150 ACV at the AC Transformer Box (ATB). No further reduction of the input voltage is required.Do the following procedure to determine the cause of inaccurate AC voltage and/or current values on the GSC.
Check setpoints P20 (full scale voltage) and P21 (full scale current). In order for the GSC to operate correctly, the current transformers (CT) must have 5 amp secondaries. See Testing And Adjusting, "Engine/Generator Setpoint Viewing OP2" and Testing And Adjusting, "Engine/Generator Programming OP5". Typical factory setpoints are as follows: 700 V for P20 and 600 A for P21. The setpoints should be correct for the generator set application.
Refer to table 1 and illustration 1 in order to help determine the proper setpoints and any necessary external potential transformers.
If only the voltage is inaccurate, check the jumper for the AC voltage range for correct installation. The jumper should be installed for systems with a full scale AC voltage input of 700 volts (P20 = 700). The jumper should NOT be installed for systems with 150 volt full scale AC inputs. Also, the jumper should NOT be installed for any unit with external potential transformers. For information regarding the installation of the jumper, see Testing And Adjusting, "AC Voltage Range - Adjust".
Check Systems Operation, "Voltmeter/Ammeter Programming OP8". OP8 is the option for programming the calibration value of the voltmeter and the ammeter. The calibration values, written on the ATB bar code sticker, must be programmed into the GSC to ensure accurate voltage and current values.