Ever have nuisance animals stealthily add feces to your garden, eat your plants, or otherwise become a complete bother? If you ever lived in a house with a yard, its quite likely. Usually a neighbour’s free range cat or dog is to blame although it may be stray dear or crazy raccoons too. Trapping the animal for relocation is an option but likely more work than its worth. Besides, raccoons tend to trash most cheap cages and your not going to catch a dear. So what is the solution?
Many years ago a nifty product came on the market – the motion based sprinkler. Relatively inexpensive but seemed plagued with issues. Setup was a pain involving testing the trigger and range inevitably getting one wet. Despite best efforts to set motion detection, they often didn’t trigger on the animals themselves. When it did work, it was magic, scaring off any potential threat.
The devices are still available but with a pretty hefty price tag. The actual components are inexpensive and common. A PIR sensor (dime a dozen), set of rechargeable batteries (likely the most expensive part), a small solar panel, standard sprinkler, and a solenoid. At best the thing is likely worth $10 and should retail for under $45 yet they list for anywhere from $75 to well over $100. If you think you are getting higher quality for the money, guess again. The components are pretty much the same for all these units and have been around for ages.
Most people assume the device will work for a few seasons. Despite the cost, that won’t happen and in fact, you may not even get a full season from one of these. If the batteries don’t fail the solenoid surely will. One would think it was some sort of conspiracy because actual sprinkler solenoids work for many seasons without issue. So why is it these devices fail so frequently and quickly?
The answer is not immediately obvious. Disassembling the unit will reveal exactly what we said to begin with. A short list of commonly available cheap parts. The solenoid is the interesting piece. Unlike underground sprinkler solenoids, this one is battery powered. That means its DC current, not AC. When current is applied, the metal plunger is drawn up by magnetic forces generated by the current on a winding. Typically, this process tends to leave residual magnetism which has to be countered by a spring to help release the plunger. Over time, the spring gets weaker and the residual magnetism becomes more permanent.
If this were AC driven, the reverse current provided would counter the effects helping to ensure the whole thing doesn’t become one big charged magnet. Unfortunately, these devices are solar charged DC battery driven and there in lies the biggest problem. With increased usage comes increased magnetic force and decreased spring tension. Sure the spring tension can be increased by stretching it out a bit, but often this is still not enough to counter the forces on the plunger.
The result is a perfect marketing dream where the product will always fail and the consumer will always have to purchase yet another one. This wouldn’t be so bad if the price reflected the cheap nature of the product and the fact that it is prone to failure. Instead, manufactures including the Chinese themselves seem to feel its worth gold. Markup is crazy high leaving consumers high and dry (or at least the critters they are trying to scare away stay dry).
The only real way around this nonsense would be to use an old motion light sensor to power up a small transformer that sends AC current triggering a standard sprinkler solenoid attached to the garden hose. Any cheap sprinkler could then be used in any configuration reliably and for multiple seasons. Alas, the old incandescent motion sensors are harder to come by and more pricey than they should be too. Most are $40 new if you can even find one without led lights attached.
Once again, they have you so either you cough it up for a season, moved to a Condo, or ignore the animals pilfering on your garden, trees, and bushes.