When I hooked my OpenSprinkler PI and opened a valve, the associated solenoid buzzes loudly.
I did a couple things to try to diagnose the problem:
* I measured the current directly off of the 24VAC adapter, and it was 27V and 1A.
* I measured the current being output to the solenoid from the OpenSprinkler – it was 27V, but only 250mA.
When I connect the solenoid directly to the 24VAC adapter, it opened and closed quietly, without any buzzing. So it seems like the solenoid works fine, it’s just not receiving enough amps from the OpenSprinkler to work properly.
Is there something further I can do to diagnose the situation? I notice that there are a number of test points on the board, but I’m not entirely sure what each is for or whether they’re relevant to my problem.
The triac (BT1308W) on OSPi can only supply a maximum of 800mA continuous current per channel. In practice this may be lower due to factors such as the base current. I am curious what type of solenoid valve you have — typical sprinkler valves have an operating current of 150mA to 250mA. I’ve never seen a valve that takes as much as 1A current.
There are two work-arounds:
1) you can combine several zones in parallel to increase the current limit. For example, combine zones 1 to 3 together to triple the current output. The downside is that you need to set zones 1 to 3 to always turn on at the same time, and also this wastes 2 zones.
2) alternatively you can replace the BT1308W by a more powerful triac, such as BT137 / BT138. Keep in mind that if you ever run more than 2A current, it will trigger the on-board fuse, so you may have to replace it with something bigger, or simply short the fuse to bypass it.