FirstLine UPS
Form No. 003-2323 Rev B
35
Battery Fuse Replacement
If an input line voltage transient well in excess of the UPS rating occurs while the UPS is
running on battery, it is possible for the battery fuse to clear open. The symptom of an
open battery fuse is the same as a disconnected battery: after the UPS is started, the
battery lamp on the mimic display glows red. Prior to starting the UPS, the front panel
display can be used to read the battery voltage. If the voltage is less than 380 Vdc, the
UPS will determine that there is no useable battery present. Possible causes include a
blown fuse, a disconnected battery, and a defective battery.
There are two battery fuses. Either one could be open, so the safe action is to replace both
of them. The following procedure should only be performed by trained, authorized service
personnel. For continued safety, fuses must be replaced by parts of proper rating.
1. Turn off the UPS. If an MBS is present, the load can be maintained by transferring to
Maintenance Bypass mode prior to turning off the UPS.
2. Remove the utility ac power from the input of the UPS.
3. If any external battery cabinets are present, disconnect the batteries in all of them. If the
external battery cabinet is equipped with the optional circuit breaker, it is only necessary to
open (turn off) this breaker which is accessible by removing the front cover of the cabinet.
If not equipped with this breaker, it is necessary to remove the inner panel and unplug the
red and black connectors.
4. Remove the outer panel from the UPS by pulling the top away from the UPS and lifting
the panel.
5. Remove the inner panel by removing the screws around the periphery of the panel and
from the four holes next to the fans. The panel can be lifted off, but it is attached to the
UPS by a ground wire that will limit movement.
6. Unplug the battery by disconnecting the red and black plugs. If the UPS is in the tall
cabinet and has four trays of batteries, also disconnect the second battery connector.
7. For assured safety, measure the dc voltage across the terminal block for the external
battery. If the voltage is more than 10 Vdc, double check that all batteries are disconnected.
8. Also measure the dc voltage between the "-" (minus) terminal on the external battery
connector and the four connections on the two dc fuses. One dc fuse is just below the fans.
The other is on the shelf below and to the right of the fans. If the dc voltage is greater than
40 volts, there must be at least one battery still connected.
9. If voltage measurements are not possible, visually verify that all batteries are
disconnected and wait at least 5 minutes for capacitors to discharge.
10. The fuses can be replaced by loosening the nuts that hold the fuses in place using a 13
mm wrench, slipping out the old fuse, and slipping in the new one. Be sure that the
washers are above the tabs on the fuses. Re-tighten the nuts.
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