OpenSprinkler › Forums › Hardware Questions › Add MOV to 26VAC input Pins? › Re: Re: Add MOV to 26VAC input Pins?
The limitation of jumpering the Poly Fuse is that now the only thing protecting you from an overcurrent condition is the internal fuse link within the 24V AC step-down transformer. These fuse links are non-replaceable. So when they blow , you have to change the entire transformer.
The causes of overcurrent conditions are typically either bad solenoids on the water valves or short-circuits in the interconnect wiring from the controller to the valves. Typically, this effects only one zone. Therefore, the symptom is that one day nothing works and you find no 24V AC input to the controller. Now, the 24V transformer could also be damaged by a lightning strike or power surge, so you replace the transformer. Everything appears to work for a day or so until you turn on the problem zone, then the transformer dies again. Each new transformer is going to cost you $15 to $25 bucks.
Again, you will only have this problem if your system develops a defect that causes an overcurrent condition. If you want to help reduce the cost of such overcurrent conditions then you can add an inline fuse holder and fuse. Typical over-rating on the fuse is at least 20% over the specified output. Therefore, if the transformer is rated at 750mA, I would suggest starting with a 1A fuse minimum. In-line fuse holders can be found at many auto parts stores, big box department stores, etc.
If you have a properly sized in-line fuse, then should you develop an overcurrent condition, the cost of repair is replacing a 50 cent fuse, not the entire transformer. Of course, you still have to locate and repair the short, but the cost of troubleshooting goes way down.