Fuses – What You Need to Know

There are two fuses in Lakewood 1500 series controllers. One is a 100mA, 250VAC Slow-Blow fuse. The other is a Fast-Blow 10A, 250VAC fuse. This article will discuss why they can blow and how you can troubleshoot the source of the problem. Remember that the fuse protects the components on that circuit, so learning the root cause is important! On our NexSys controllers, the power supply is more advanced and handles protection of the low voltage components, while there is a separate fuse for the high voltage relays – but the same principles apply.

Why Fuses Blow

The 100mA fuse protects the “LOW VOLTAGE” portion of the controller (water meters, display, flowswitch, 4-20mA output, etc.). The 10A fuse protects the “HIGH VOLTAGE” portion of the controller (relays).

When a fuse blows, there are a few possible causes:

  • A power surge in the supply circuit that caused the fuse to blow
  • A component connected to the controller has failed – this could be a process input or output device.
  • There is a failed component on the circuit board.
  • Another component on the same circuit is causing voltage fluctuations to the controller.

How to Troubleshoot

The most common issue regarding the fuses is telling when they have blown. The European style fuses MUST be checked out of the controller with either a multi-meter or a continuity tester. There is a high probability that the fuse will blow in the end-cap, not in the middle of the fuse – meaning you may not see the failure.

Once you have determined a fuse is blown, follow these steps:

  1. Power down the controller.
  2. Remove all terminal blocks from the controller:
    1. Water meters
    2. Flow switch
    3. 4-20 mA inputs
  3. Disconnect all relay outputs (valves, pumps)
  4. Replace the fuse.
  5. Power up the controller.

If the fuse immediately blows, then there is an issue with the controller circuit board. No blown fuses? Then replace the terminal blocks one at a time. If the fuse does not blow, re-attach the pumps and bleed valves to the pigtails. After everything has been reconnected, turn on the relays manually, one at a time.

If at any time the fuse blows, you have found the cause. For example, if the fuse blows after connecting the water meter, then the water meter or cable is the problem.

As always, contact Lakewood Instruments technical support with any questions.