# Flow switch for controlling UV light on off-grid water system



## K.B. (Sep 7, 2012)

Does anyone here have experience installing/using a flow switch to control a UV light or other component on a water system?

I am neither an electrician or a plumber, and am having trouble getting my head around the way the electronic flow switches are designed to work. 

In my case, I have a UV light sterilizer plumbed in-line with my water filtration system and would like to install a flow switch to control the 30 watt UV light to come on only when water is flowing.

The UV light has a standard cord requiring 120V AC power. My understanding is that these systems are designed to pretty much be left "on" all or most of the time and replaced each year. 

Since I am off-grid, I would like to limit the power usage of the light to only during times that the pump is running (filling the pressure tank).

I have looked at a number of different flow switches, and I can understand the mechanism they use to detect flow (paddle, piston, etc...), it is the electronic control that confuses me. The wiring seems very small and designed for low power to be involved directly with an appliance such as the UV light. 

I think the flow switch wiring needs to be connected to a relay, which then controls the appliance, or run to a controller that plugs directly into the outlet, similar to a timer switch. 

I appreciate any insights, explanations or suggested links to any components that have worked for you.

Thanks in advance!
KB


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## TnAndy (Sep 15, 2005)

I 'think' the reason they are designed to stay on is to actually kill bacteria. I'd suspect the water has to be in the chamber a certain amount of time to purify it. Putting a switch on them might defeat the purpose ?

But if you only want it to light when the pump is on, why not simply wire it to the pump switch contacts ? Pump runs, light is on.


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## K.B. (Sep 7, 2012)

Andy - I think the amount of time that is required for the UV to be effective is based on the intensity of the UV source. The light/chamber that my system came with is supposed to be rated for up to 8 gal/min. The max flow from my pump is less than that (~5 gal/min at the low end of the pressure cycle), so I think it will be OK to just have the light on during the time the pump is on. 

I had not thought of using the contacts on the pump switch, so thank you very much for that suggestion! I will take a look and see if I can make it work.

Please forgive my ignorance, but just to make sure I am thinking correctly: to do this, I would re-purpose the wires within the standard plug leading to the lamp ballast and connect them to the pump contacts that connect back to the pressure switch controlling the pump?


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## TnAndy (Sep 15, 2005)

K.B. said:


> ...but just to make sure I am thinking correctly: to do this, I would re-purpose the wires within the standard plug leading to the lamp ballast and connect them to the pump contacts that connect back to the pressure switch controlling the pump?


Depends on whether your light/ballast is 120v, and the pump is the same. If so, yes, you'd simply connect the leads off the ballast supply wire (cut the plug off, or wire in a receptacle ) to the LOAD side of the pressure switch. (make sure you connect black to black and white to white)

Watch for that on the switch. Square D pressure switches usually put the outside two screws as the LINE side, and the inside two as the LOAD side. It's written on them if you get down and look real close. If it's some other brand, look close at how the incoming and wires out to the pump go to figure out our line/load sides.

If you're using 240v on the pump, and 120v on the light, then you'd only use one of the LOAD contact points, and you'll have to pick up a neutral somehow. THAT might be a bit of a trick. (might pay you to go Relay...see below)

This assumes the ballast doesn't pull much amperage ( I wouldn't think it would) so it overloads your pump circuit. IF you think it's close, you could wire in a relay. 

Relay:

Use the pump contacts to operate the relay circuit, and wire your existing light/ballast circuit feed to one side of the relay, then the other side out to the light. You can get relays (often called contactors in the electrical business) with a 240v coil if your pump is 240v. The coil circuit on the relay only pulls a tiny amount of power, so it shouldn't affect your pump circuit at all.


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## K.B. (Sep 7, 2012)

Wonderful - thank you!

The pump (Grundfos) is wired for 120V, so I think the first explanation in your latest post is the way to go. The pressure switch came with the pump, so I will have to look at the brand, but I recall that the contacts were reasonably accessible when I did the initial installation.

The load from the ballast should be less than 0.5A, so I am hopeful this will be a workable solution... and the price is even better!

Many thanks for your time and help!


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## JeepHammer (May 12, 2015)

I think the guys have you figured out!

I had a different issue,
My well pump is DC, while my UV unit is AC.

And again, there is that flow capacity thing going on...
Your UV unit has to handle the capacity that will be flowing through it.
You usually know what pressure your pump will produce,
But you might want to use smaller lines/fittings to control the flow VOLUME (gallons per minute) through the UV unit.

I solved the capacity issue by splitting the system after the pump into potable (human consumable) and utility water.
The outside faucets/hydrants, toilet, cloths washer all get utility water that isn't consumed,
While the kitchen sink, dish washer, bathroom sink (cold water) all get potable water.

I had to build a switch, simply a magnet on an arm that moves to the side of a plastic fitting, a long leg pipe 'T' and some creative small components to make the switch body.

That activates a 'Reed' switch on the OUTSIDE of the plastic fitting.
Water flow in the potable water pipe activates the switch, which kicks on a 110 volt AC timer.

When we are using water and the pump kicks on, with no flow through the potable side,
We can do watering of gardens, wash cars or cloths without the UV kicking on since there isn't any potable water being used.

If when the pump kicks on and the potable tanks are low,
The UV only kicks on until slightly after the potable water tanks are filled, and then kick off.

One word of caution,
The UV bulb can burn out, leaving you with no biological protection.
When I could afford it, I added a second UV unit in series.
The water gets treated twice, but I don't have to worry about capacity/consumption,
The well pumps are on timers, so they normally run during peak sun hours,
Or when my welder/generator is running for something else.

I can run the pump/UV units off Batteries, but I've only rarely had to do that.
Normally the tanks have enough capacity to cover the gaps between peak sun to peak sun...
Better to let the sun power everything when you can...

The Reed switch/magnet works reliably, and could care less about the plastic fitting wall.
I tried all those pressure switches, keeping up on maintenance drove me crazy!
Since the Reed switch is on the OUTSIDE of the plastic fitting,
And since the magnet never needs changed,
On the rare occasion the switch goes bad, its a 5 minute repair without opening the pressure system.

I've only had to replace one switch in 10 years, but I bought 10 when I ordered them, so I have plenty of spares...
And they are about $3 each, since they are simple and commonly used.

Just some ideas from a guy that's been doing this close to 20 years,
Use what you want to! Forget the rest...

A little something on reed switches,
Link: http://www.epowerwash.com/wp/archives/1956


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## where I want to (Oct 28, 2008)

I would worry about the constant switching on and off would have bad effect on the longevity of the UV unit. And they are so expensive to replace plus if they fail do you have an alarm to keep from pumping untreated water through your pipes?


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## TnAndy (Sep 15, 2005)

I use a "Sterilite" brand on our system. The ballast does have an alarm if the bulb fails (and if you're in the basement to hear it, it ain't loud), but if the ballast fails, no, there isn't anything that would tell you except for the LED being out (it has a countdown timer on it for days of bulb life left....365 to 0 )

I'm personally not TOO concerned about it even being there....we used the spring for 15 years before I saw these systems, and I added it as a "it can't hurt" deal. We had no gastrointestinal problems I could attribute to water in those 15 years.


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## wy_white_wolf (Oct 14, 2004)

Is there any warm-up time on the light before it's effective? If so the pressure switch might not be a good idea.

WWW


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## JeepHammer (May 12, 2015)

I'll be glad when there is an LED UV unit.
Its just got to be cheaper to buy & operate than the current units are.


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## where I want to (Oct 28, 2008)

http://www.hexatechinc.com/uv-c-led.html

There was one in development- I don't know where it stands now.


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## JeepHammer (May 12, 2015)

Instead of one bulb in the center and reflectors on the outside of the tube,
LEDs could be on the outside as well as the inside,
Fully around the water supply, so it could be saturation without the possability of a single bulb failing and leaving you without protection.


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## K.B. (Sep 7, 2012)

I found some time to test out powering the light from the contacts on the pump connecting to the pressure switch as discussed above. 

All seems to be working well. The UV light comes on right when energized along with the pump, and the LED on the ballast/control box shows a green (happy) light. I can't see any visible delay with regard to the light illuminating and the pump beginning. I suspect there is at least a few milliseconds to several seconds delay in warming up the UV source to full intensity, but I do not have any additional info for this particular unit.

For my purposes, I think this should work well. I am currently using well water that is pumped to a larger holding tank that supplies the house water. Later this year or next year I will be switching to rain-catch off the house roof. My plan is to filter through a sand/charcoal filter before it goes into the holding tank that is connected to the house supply. The additional sediment/charcoal filters that are downstream of the house water pump are intended to "polish" the water to a higher quality.

We use a separate (off-line) ceramic water filter on the tap water for our drinking water. The UV sterilizing unit is probably redundant, but my wife requested it when I was putting in the plumbing system. 

I appreciate the helpful suggestions!


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