MPR25 Rectifier Adjustment

MPR25 Rectifier

The following steps are necessary to adjust and align Nortel MPR25 Rectifier groups used in DC power (battery) PBX installations.

These steps may be performed under load (i.e., with Switch, Inverters, etc. powered on).

The adjustments must be performed in two stages. First each individual rectifier must be adjusted, and then the rectifiers must be aligned as a group.

Note: The final 'group' adjustments (load balancing) should be repeated as a periodic routine maintenance.

Tools required: Multi-Meter (set to DC volts), and a small flat blade screwdriver.

Preliminary 'Individual' Adjustments:

Repeat the following procedure for each MPR25 in your system. Units not being adjusted must be powered OFF.

  1. Place the multi-meter test leads into the front panel test points (V+, V-), and measure DC voltage.
  2. Turn the HVSD (high voltage shut down) potentiometer 10 full turns clockwise.
  3. Adjust the FLT (float charge) potentiometer for approximately –57.Vdc.
  4. Patiently turn the HVSD potentiometer counterclockwise until the rectifier shuts down.
  5. Turn the FLT potentiometer clockwise for 2 full turns.
  6. Cycle the AC breaker OFF/ON. The unit should power up, and remain on.
  7. Adjust the FLT potentiometer for –52.6Vdc (float voltage).
  8. Holding the FLT/EQL switch in the EQL position, adjust the EQL (equalize-charge) potentiometer for –53.8Vdc.

This completes the preliminary adjustment of one unit.

Final 'Group' Adjustments:

Upon completion of the preliminary 'Individual' adjustments, turn all of the rectifiers on.

Note: The battery voltage must be below the rectifier(s) float voltage for the rectifier(s) to come on-line - i.e., the red LED display on the MFA150 must read less than –54Vdc before any final adjustments can be made.

To equally balance the load between rectifiers, some fine FLT adjustment may be necessary. Turn the FLT potentiometer VERY SLIGHTLY until the MPR25 front panel LED displays are similar -  i.e. within +/- .2 of each other. Turn the FLT potentiometer Clockwise (increase) on lower readings, and Counterclockwise (decrease) on the higher readings. This adjustment must be repeated until all rectifiers are equally loaded.

See also: Replacing M1 Batteries

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