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FlowconSupportHardwareRepairing .  Relay-fuses

Replacing fuses on relay boards

Opto-22 Relay board: holds 8 quad-relays for a total of 32 relays and 16 fuses.

Each fuse supplies power to two relays.
optobd562x372.jpg (65840 bytes)

Fuse Description and Location:

The two fuses protecting each quad-pak relay are each 5 amp pico-fuses

They are very small, and are located between the relays and the barrier strip.
Each fuse protects two relay connections. Thus, if a fuse blows, two output control wires will die. Fuses virtually never fail on input relays.

Checking for a failed Fuse:

The easiest way to check the fuse is to manually activate the failed control circuit and then measure the voltage drop across the fuse. 

A failed fuse will typically have 120 volts AC across it.
A good fuse has no voltage drop.
Use a good quality voltmeter or DVM for this.


Fuse Location:

There are nine fuses showing in this picture. They connect the common for two adjacent relays, to the common screws of the buss bar.

In this picture, the relay common screws are joined by buss bar.

The fuses pull straight up out of the board.


To replace a fuse:

First, determine WHY the fuse blew and fix the cause!.

Just replacing the fuse with another will usually result in another blown fuse.
Maximum current for any one relay is 2.5 amps. Check with clamp-on ammeter.
Kill all power to the relay panel. You may do this by removing the main 8 amp cartridge fuse with a fuse puller.
Grab one end wire on the pico-fuse with a fine pair of needle-nosed pliers and carefully pull it out of its socket. Repeat with the other end of the fuse.
Note that the fuse is NOT soldered in.
Take a new fuse and, using pliers and side cutters, shape its wire leads to match the old fuse in both length and angle.
Using the needle-nosed pliers, carefully re-insert each fuse lead back into its socket fully.
Replace main fuse / restore power.
Re-test the new fuse with a voltmeter.

Note: NEVER substitute a piece of wire or other object for a fuse!
Doing so could result in traces being blown off of the relay rack, requiring expensive and labor intensive replacement!

Fuse type: Littlefuse Pico II
Fuse p/n: 0251.005
Fuse data sheet

Web Links: fuses available from Opto-22 (Opto-22 p/n: FUSE05)
and Mouser Electronics (Mouser p/n: 576-0251005)