How to build a simple frequency doubler for hall effect water flow sensor?

Thread Starter

jbluetooth

Joined May 12, 2019
8
So here's the problem I'm trying to solve. The tankless water heater we had installed requires a certain amount of flow to turn on, I think about .5 gal/min. However, the stupid CA low flow faucet we installed doesn't flow enough water to kick on the water heater. So our new master bath shower and tub have hot water, but the sink does not. I'm trying to modify the water heater to turn on with slightly less flow, before replacing the faucet with a higher flow model. It seems to be a 3 wire hall effect water flow sensor and it must be powered by the two C batteries next to the controller in series (3V). I tried purchasing a different one on amazon to see if it would have any effect on how soon it turns on, but it seems to be about the same, and after searching a lot, it seems the common range for these sensors for a water heater is 1-30l or 2-60l. I purchased a 1-30l sensor and it looks very similar to the one in the water heater. The sensors that are in the .3-10l range I assume would spin faster with the flow in this situtaion and maybe have higher pulse frequency, but don't handle high enough pressure to be reliable for this situation. So I'm pretty new to this stuff, but not a total dummy, it seems like the controller for the water heater is looking for a certain pules frequency before it turns on, so I was thinking if I could wire in a simple frequency doubler, it would turn on with half as much flow. Does that make sense? Is that a simple thing to build that you guys could give me the info on how to build one, parts needed, etc. I can solder and wire in something if you tell me how to build the circuit.
let me know your thoughts, thanks for reading.
Jesse
 

Thread Starter

jbluetooth

Joined May 12, 2019
8
Can I just run a flow on/off switch with relay to send a higher voltage to the signal input or does it need a certain frequency?
 

Thread Starter

jbluetooth

Joined May 12, 2019
8
Do the comparator or exor gate have to be programmed? or just soldered in on the correct pins? Or are these things so small that they have to be put in a circuit board? Any recommendation where I can buy singles? If it's just those, a few resistors and caps, and a 5V power supply, I might be able to swing that with a little help on where to get these 2 parts to make sure I get the right ones and find the right pins.

Thanks
 

Tonyr1084

Joined Sep 24, 2015
3,680
Sorry I can't answer your question. However, I would like to make this cautionary statement: If you change how the heater works you could over-boil the water in the heater, which COULD lead to a blowout on the line. Many water heaters have back flow preventers, meaning if the water heats up and expands and there's not an open faucet then something is going to break. Could be a pipe, could be your heater.

To be honest, I think the solution I would pursue is to change the faucet - or the aerator on the end to a higher flow. I know it's not per CA law, but with your tankless heater, it should be allowed to operate as designed. Modifying it is not advised for a number of reasons. Potential failure of the heater. Potential failure of the plumbing. Potential exposure to high water temperatures and burns. Depending on how the unit fails, there's possibility of electric shock. Not very likely, but always a remote possibility when a machine fails.

For these reasons I'd advise leaving the heater alone and unmodified. I would either get a different aerator or take a small drill and drill out the copper washer with the calibrated hole to one size bigger. If that isn't enough to trigger the heater then I'd go with one size larger a drill. I'd keep doing that until the heater would successfully fire up on demand. Said it before and it's worth saying again - don't modify the heater; you could expose yourself and/or your property (or other persons) to hazards the company has specifically engineered the machine to avoid. You could be liable for injuries and damages should they occur.
 

Thread Starter

jbluetooth

Joined May 12, 2019
8
Or is there somewhere I can buy a simple circuit like this premade that will work if I just add a power supply and connect it up?
 

Tonyr1084

Joined Sep 24, 2015
3,680
I would imagine the manufacturer would have a ready engineered solution. Contact them.

As for doubling a frequency - I don't know how to. I know how to divide by 1/2, but that's not what you're looking for. It's still advisable to contact the manufacturer. Or modify the sink faucet.

[edit] It comes to mind that you could build a frequency to voltage converter then up that voltage then convert the voltage to a frequency. That way you can adjust how the unit works. But I still say contact the manufacturer or modify the faucet.
 

Thread Starter

jbluetooth

Joined May 12, 2019
8
Sorry I can't answer your question. However, I would like to make this cautionary statement: If you change how the heater works you could over-boil the water in the heater, which COULD lead to a blowout on the line. Many water heaters have back flow preventers, meaning if the water heats up and expands and there's not an open faucet then something is going to break. Could be a pipe, could be your heater.

To be honest, I think the solution I would pursue is to change the faucet - or the aerator on the end to a higher flow. I know it's not per CA law, but with your tankless heater, it should be allowed to operate as designed. Modifying it is not advised for a number of reasons. Potential failure of the heater. Potential failure of the plumbing. Potential exposure to high water temperatures and burns. Depending on how the unit fails, there's possibility of electric shock. Not very likely, but always a remote possibility when a machine fails.

For these reasons I'd advise leaving the heater alone and unmodified. I would either get a different aerator or take a small drill and drill out the copper washer with the calibrated hole to one size bigger. If that isn't enough to trigger the heater then I'd go with one size larger a drill. I'd keep doing that until the heater would successfully fire up on demand. Said it before and it's worth saying again - don't modify the heater; you could expose yourself and/or your property (or other persons) to hazards the company has specifically engineered the machine to avoid. You could be liable for injuries and damages should they occur.
Not that simple or I would have done it already. The input and output copper lines on the faucet are tiny, it's not just a single point of restriction, I'd have to replace the faucet, and then, it will have to flow a lot more water all the time for the heater to work. That's still an option, I just think a better option would be to have the heater come on with a little less flow so I wanted to investigate that first. I'm pretty used to modifying machines to make them work the way they should have originally been designed lol. I'm not too worried about it coming on with a little less flow since it still won't come on unless there is some flow and I can turn the temperature down a lot from where we are so there's a lot of wiggle room.
 

Sensacell

Joined Jun 19, 2012
2,456
I think you will end up going round in circles with this idea and not achieve a desirable outcome.

Without doing a ton of testing, it's going to be very hard to determine how the unit processes the incoming signal.
Tinkering with a water heating apparatus in a home setting invites many unforeseen possibilities.
 

ebeowulf17

Joined Aug 12, 2014
2,946
On the flowmeters I'm familiar with, the pulse rate is dependent on the size of the orifice, or nozzle, at the inlet side of the meter. If you want more pulses for any given amount of water flow, you just need a smaller orifice.

http://www.digmesa.com/wp-content/uploads/2015/11/digmesa-fh-en-lrint.pdf

BA559977-5DC5-4907-A032-E5204840187B.jpeg

You may be able to buy another flowmeter from the same product line as your existing one, but with a different pulse rate. You may also be able to modify your existing flowmeter to change its nozzle performance.

That said, the more I think about it, the more I also think this is something you should be very careful messing with. There are various safety concerns, plus any of these changes, whether electronic or mechanical, will undoubtedly void any warranty.
 

MisterBill2

Joined Jan 23, 2018
4,068
I have created frequency multipliers for some applications but this one is quite interesting. Such multipliers are sometimes used with encoders to generate positive going pulses on each logic change, rising or falling. The simple way will be to use some CMOS logic gates and delay circuits to do that. he first section can use both sides of a dual one-shot IC, such as a CD4098, with one section set to trigger on a rising edge and the other side set to trigger on a falling edge. Then the second IC would be a simple "OR" gate using the "Q" output of each half of the dual one shot. Probably the same function can be implemented using just one quad nor gate IC, but I have not had my coffee yet and so can't think that one out.
There is no need to modify the faucet or other expensive, messy, and tedious plumbing changes, which might even be illegal in California anyway.

(An additional comment here about California lawmakers is deleted.)
 

Dodgydave

Joined Jun 22, 2012
8,477
Not that simple or I would have done it already. The input and output copper lines on the faucet are tiny, it's not just a single point of restriction, I'd have to replace the faucet, and then, it will have to flow a lot more water all the time for the heater to work. That's still an option, I just think a better option would be to have the heater come on with a little less flow so I wanted to investigate that first. I'm pretty used to modifying machines to make them work the way they should have originally been designed lol. I'm not too worried about it coming on with a little less flow since it still won't come on unless there is some flow and I can turn the temperature down a lot from where we are so there's a lot of wiggle room.
Use a simple Xor gate circuit...

http://www.seekic.com/circuit_diagram/Basic_Circuit/SIMPLE_FREQUENCY_DOUBLER.html
 
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