Freshwater UV light Flow Switch

Freshwater UV light Flow Switch

We have had a UV light fitted to Hannah now for 2 years. You can read more about our water filtering setup in a previous post.

UV light kills harmful microorganisms such as viruses, bacteria, and parasites that may be present in the water, making it safe to drink and reducing the risk of waterborne illnesses. Unlike chemical treatment methods such as chlorine, UV water treatment does not leave any residual taste or odor in the water, and it is environmentally friendly. A UV water treatment system is generally low-maintenance and easy to install.

You can see our UV light below on the back wall.

The UV light of this setup draws roughly 1.2 amps, and out of the box, it is on all of the time. So to save power for the last 2 years we have actually been flicking the “water pump” switch on and off whenever not using the water taps for longer periods of time.

This is a lot of effort for some taps on the boat, as the switch is centrally in the main switchboard, so if you are brushing your teeth in the heads, you need to venture into the corner of the saloon, flick the switch and go back to the heads if you want fresh water.

Since leaving the UK we have had all of the components to fix this problem for us thanks to Matt, a colleague of Kathryn, but we didn’t bring it all together until April 2023…

The solution is made up of a flow switch which will be put after our water pump and accumulation tank that will detect the flow of water through pipes. This will be used to turn the UV light on and off whenever water is flowing. In order to make sure the water does get to see the UV light, and also to avoid the light flicking on and off too often we also then have this switch going through a 555 timer chip circuit to delay the turn off once water flow has stopped.

We were following the following circuit diagram also provided by Matt.

We have multiple soldering irons onboard, but not of the highest quality (on a boat you normally need them for simple jobs), so soldering a circuit board together on a slightly moving boat was a bit more of a challenge than normal. (So let’s ignore the small mess in the top right of the backside of the board 😜)

This circuit board has 5 cables leaving it that need to be connected: +/- 12v power for the board, 2x cables connecting to the flow switch, 1x + for the UV light itself.

This circuit board was then enclosed in a little waterproof case with external LED and mounted near most of our other electrical water components (such as the 12v regulator and UV ballast)

Finding the correct adapters to get the flow switch from a 3/8ths of an inch pipe thread all the way up to 19mm hose proved to be a bit of a problem, but once we had visited all the nearby chandleries we finally had a setup that should work.

We cut the pipe after the accumulator, added the flow switch, fitted everything back together, wired it in, and it all looked fairly nice. The water filter area also has these 2 nice metal bars which are perfectly placed to protect the flow switch from our pots and pans!

Now we can leave the water pump and UV light on all-day knowing that the 1.2 amps will only be drawn when water is actually flowing. The UV light then stays on for a few seconds before switching off.

The switch is nice and sensitive, so even if you just trickle water out of the tap the UV light will be switched on!

Perfect, and thanks Matt!

2 thoughts on “Freshwater UV light Flow Switch

  1. You’re very welcome guys. Glad to see you got it working nicely. First time?

    1. First time it didn’t actually work, but checking back on all the connections we were totally missing one. 1 week out from the Azores now and it’s still working well, absolutely amazing not needing to turn it on and off by hand constantly!

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