Inexpensive DIY Auto Water Change System (AWC)

[Harrison Gordon]

This is my thread where I will document (and ask questions) about my AWC system that I have just started to build.

I used to fill buckets with water from the tap, detoxify and pour them into a 20g bin on wheels, and mix the salt in there. Then I would pump the water into the tank after draining the old.

Currently I have an RODI system, so now I have the saltwater container pump water into the bin, which I wheel to the tank and pump into there.

Now I want to make my life ten times easier, by using peristaltic pumps to precisely exchange water between the RODI system, my tank, and the drain.
For this, I have purchased a double-headed Cole Parmer with Thermofisher Scientific motor, connected to a variable-amperage power supply.
The idea is to have a supply line from the saltwater basin going up to the attic, over to the pump, down to the tank. Back up to the pump, into the drain in the attic. The motor will be controlled with a smart outlet which will be timed to swap a certain amount of water per day.
In addition I'm splitting my RODI line to go to a float valve in the sump.

Things I'm missing are sensor in water basin to prevent running dry (but I think I can handle checking it every once in a while).
Total cost should hopefully be $150 - $175

Lets see how it goes and hope many other people can do the same thing!

 

[Harrison Gordon]

UPDATE:
The DC controller I have gives off 15v, but the motor is rated for 12v.
Does anyone know if/why the voltage matters, but not the amperage, that is supplied to the motor?

And if I should lower the voltage, what would be the best way of doing so? Thanks!

 

[User]

UPDATE:
The DC controller I have gives off 15v, but the motor is rated for 12v.
Does anyone know if/why the voltage matters, but not the amperage, that is supplied to the motor?

And if I should lower the voltage, what would be the best way of doing so? Thanks!

Quick answer- the power brick supplies UPTO the rates amps. It doesn’t send all 5amps (for example) unless the load calls fir it.

The power brick doesn’t SEND amps, the load PULLS it. The motor will pull as many amps as it needs, upto the max possible by the power supply

Make sense?

Please note- extremely simplified version of the magic that happens in a circuit


To lower the voltage- id get a 12v rated power supply. No mods, and will be more efficient than ‘burning’ a bunch of volts to reduce the 15v to 12v

 

[User]

... duplicate

 

[Harrison Gordon]

Quick answer- the power brick supplies UPTO the rates amps. It doesn’t send all 5amps (for example) unless the load calls fir it.

The power brick doesn’t SEND amps, the load PULLS it. The motor will pull as many amps as it needs, upto the max possible by the power supply

Make sense?

Please note- extremely simplified version of the magic that happens in a circuit


To lower the voltage- id get a 12v rated power supply. No mods, and will be more efficient than ‘burning’ a bunch of volts to reduce the 15v to 12v

Maybe I'm a little unclear. It seems you're saying I can supply it with however many amps I have, but it will only take what it can handle? But, what does the voltage have to do with it?

My power supply (photo soon) has a dial that goes from not moving the pump to making it spin fast even with heads attached. It also has reverse direction switch.

I tried a 12v 4.5a supply before this one, but I think it's a little underpowered; 10a would probably be better. Anyways I would rather keep my variable supply.

Is the extra 3v bad even?

Thank you!

 

[Skydvr]

The power supply provides a voltage.
The load determines how much current is drawn from the power supply.
The power supply design determines what happens when the maximum current is exceeded.

Say you have a 10 volt power supply with a maximum current rating of 1 amp.
If you put a 1k ohm load on the power supply, the load will draw 10mA (0.01A). Everything works fine.
[V=I*R => I=V/R 10V/1000ohm=0.01A]
If you put a 10 ohm load on the power supply, the load will draw 1A. Everything works fine.
If you put a load on the power supply that is less than 10 ohms (+/- a small percentage), you exceed the max rating of the power supply. If you pull slightly more than what the power supply can handle, you likely won’t notice anything other than the power supply getting warm, but it would do that at max power anyway. If you draw a much higer current, you risk damaging the power supply.

Most consumer stuff runs on ICs (integrated circuits, a single silicon based device that performs the function of large complex circuits) that manage the output because they are so cheap, simplify the design and assembly process, and the older technologies are becoming more expensive. These ICs are typically current limiting. Once they hit max current, the output voltage starts dropping. If you put too large of a load on a power supply and cause the voltage to drop significantly, different things can happen. Some devices will run slower, some will over heat, others will power down due to under voltage (or flicker off and on as the power supply cuts out every time it powers up and the load starts pulling current). The device determines what will happen at lower voltages.

Cheaper or older power supplies (typically those with special keyed connectors that were intended for a specific device and may only have a fuse for short circuit protection) might not have self protection. These may overheat, causing a component to fail (power supply no longer works), or causing fires in extreme cases. If the load has a high enough current or has a short circuit, a component may fail immediately, killing the power supply.

If the load exceeds the power supply current rating, but is not high enough to switch the power supply off, and the output voltage drops enough, you can cause overheating and damage to some devices. Some types of motors can’t handle lower voltages and will overheat, breaking down the winding insulation, eventually leading to shorts, or broken wires or solder joints.

A few extra volts probably won’t cause a problem, especially if it is a continuous duty motor, which is likely coming from Cole-Parmer seeing as how they make stuff for chemical processing and some medical applications. If it doesn’t get hot, you’e fine.



What is the current rating on the motor? Your power supply needs to be able to supply at least that much current. There isn’t much mass to get moving, so the starting surge should be pretty short, so you shouldn’t need to worry about oversizing your power supply for that.
Are there any details other than the manufacturer and voltage rating?
Is this a two wire motor?

Have you checked the maximum lift on the pump? Pulling that high and over that long of a run may be an issue.
I’d also really reconsider not putting a float on the supply basin. If that runs dry while you are away, you are still going to be pumping water from the tank. You could end up diluting the salinity too much with your ATO or pumping your sump dry and damaging equipment (depending on tubing depth). Might not be an issue as long as you have additional circulation pumps in the display if your drain line isn’t set low enough to run the sump dry and that what ever volume of water your pump is left with is sufficient to prevent overheating.

Remember to calibrate both pump heads to eachother (if they are adjustable). The restriction on the intake (due to lift height and run length) and outlet will effect how much volume each head moves, so this needs to be done with the tubing run in place.

Sorry this got so long.

 

[Harrison Gordon]

The power supply provides a voltage.
The load determines how much current is drawn from the power supply.
The power supply design determines what happens when the maximum current is exceeded.

Say you have a 10 volt power supply with a maximum current rating of 1 amp.
If you put a 1k ohm load on the power supply, the load will draw 10mA (0.01A). Everything works fine.
[V=I*R => I=V/R 10V/1000ohm=0.01A]
If you put a 10 ohm load on the power supply, the load will draw 1A. Everything works fine.
If you put a load on the power supply that is less than 10 ohms (+/- a small percentage), you exceed the max rating of the power supply. If you pull slightly more than what the power supply can handle, you likely won’t notice anything other than the power supply getting warm, but it would do that at max power anyway. If you draw a much higer current, you risk damaging the power supply.

Most consumer stuff runs on ICs (integrated circuits, a single silicon based device that performs the function of large complex circuits) that manage the output because they are so cheap, simplify the design and assembly process, and the older technologies are becoming more expensive. These ICs are typically current limiting. Once they hit max current, the output voltage starts dropping. If you put too large of a load on a power supply and cause the voltage to drop significantly, different things can happen. Some devices will run slower, some will over heat, others will power down due to under voltage (or flicker off and on as the power supply cuts out every time it powers up and the load starts pulling current). The device determines what will happen at lower voltages.

Cheaper or older power supplies (typically those with special keyed connectors that were intended for a specific device and may only have a fuse for short circuit protection) might not have self protection. These may overheat, causing a component to fail (power supply no longer works), or causing fires in extreme cases. If the load has a high enough current or has a short circuit, a component may fail immediately, killing the power supply.

If the load exceeds the power supply current rating, but is not high enough to switch the power supply off, and the output voltage drops enough, you can cause overheating and damage to some devices. Some types of motors can’t handle lower voltages and will overheat, breaking down the winding insulation, eventually leading to shorts, or broken wires or solder joints.

A few extra volts probably won’t cause a problem, especially if it is a continuous duty motor, which is likely coming from Cole-Parmer seeing as how they make stuff for chemical processing and some medical applications. If it doesn’t get hot, you’e fine.



What is the current rating on the motor? Your power supply needs to be able to supply at least that much current. There isn’t much mass to get moving, so the starting surge should be pretty short, so you shouldn’t need to worry about oversizing your power supply for that.
Are there any details other than the manufacturer and voltage rating?
Is this a two wire motor?

Have you checked the maximum lift on the pump? Pulling that high and over that long of a run may be an issue.
I’d also really reconsider not putting a float on the supply basin. If that runs dry while you are away, you are still going to be pumping water from the tank. You could end up diluting the salinity too much with your ATO or pumping your sump dry and damaging equipment (depending on tubing depth). Might not be an issue as long as you have additional circulation pumps in the display if your drain line isn’t set low enough to run the sump dry and that what ever volume of water your pump is left with is sufficient to prevent overheating.

Remember to calibrate both pump heads to eachother (if they are adjustable). The restriction on the intake (due to lift height and run length) and outlet will effect how much volume each head moves, so this needs to be done with the tubing run in place.

Sorry this got so long.

Wow, I much enjoyed reading this! Thank you for such an in-depth explanation.

Two-wire motor, rated at 12v and 150 RPM. No other important info.
If you think the extra 3v shouldn't hurt I'll run it for like half an hour and see if it's warm. I also got a 12v 3a supply that will do constant full speed.

Yeah this thing can definitely handle the lift, it's 10 feet up and then over a bit but these things are rated for a lot more. Of course I must verify that myself first to be sure.

And about the float. Originally I was gonna do it no question, then I read a thread and there was someone saying if you aren't checking your basin once a week and don't know when you should, then you've got things wrong.
So I realized yes I should check the room with lots of water moving through tubes on the second floor of my house every so often.....
Now on my system if it gets below five gallons the circulation pump is exposed and that is very noisy. Still a float is a great idea that should make it into the design once I get everything else sorted out.

On another note I unfortunately realized that the tubing size on my Cole Parmer pump heads are 1/16th.....super tiny! Will take longer to change the water I guess.

Thanks for all the help

 

[reefwiser]

I did this for 15 years using a stenner dual head pump and a multi timer
Pump came on once an hour removing and adding water. Time was based on how much water was removed in a minute. Real simple

Now I just don’t change water doing the DSR method.

 

[Harrison Gordon]

I did this for 15 years using a stenner dual head pump and a multi timer
Pump came on once an hour removing and adding water. Time was based on how much water was removed in a minute. Real simple

Now I just don’t change water doing the DSR method.

Yeah I looked at the stenners, didn't want to do the $300 though.

 

[Skydvr]

I didn’t find any technical information on that motor doing a quick search.

That train transformer varies the voltage as you turn the knob. It has a pretty low output power, but that motor shouldn’t have a very high current draw.

Running it at 80% would give 12VDC, assuming the drop off is linear.
You have just under .5A available at full voltage.
As long as that power supply is driving the motor at a suitable speed and the motor isn’t getting hot, you should be fine.

Personally, I’d prefer running it on a cheap wall-wort power supply or throw something together with stuff I have kicking around. But that would require a meter, or finding a data sheet, so you know what the motor is actually pulling.

 

[Harrison Gordon]

I didn’t find any technical information on that motor doing a quick search.

That train transformer varies the voltage as you turn the knob. It has a pretty low output power, but that motor shouldn’t have a very high current draw.

Running it at 80% would give 12VDC, assuming the drop off is linear.
You have just under .5A available at full voltage.
As long as that power supply is driving the motor at a suitable speed and the motor isn’t getting hot, you should be fine.

Personally, I’d prefer running it on a cheap wall-wort power supply or throw something together with stuff I have kicking around. But that would require a meter, or finding a data sheet, so you know what the motor is actually pulling.

Ok. I tested it for half an hour on a 12v 3a power supply, running pretty fast but only got 0.5gal/hr, 10ft head height and didn't notice any strain or different noise from when running dry.
I guess I will probably just use that because it was spinning as fast as the train power supply could do on full power so no reason for it anyways.

Would be nice if I could find larger tube size pump heads though.

 

[Ranjib]

UPDATE:
The DC controller I have gives off 15v, but the motor is rated for 12v.
Does anyone know if/why the voltage matters, but not the amperage, that is supplied to the motor?

And if I should lower the voltage, what would be the best way of doing so? Thanks!

You can use a lm2596 module to convert 15V to 12V. Voltage and current both matters, but specifics will vary depending upon your use case

 

[Ranjib]

Ok. I tested it for half an hour on a 12v 3a power supply, running pretty fast but only got 0.5gal/hr, 10ft head height and didn't notice any strain or different noise from when running dry.
I guess I will probably just use that because it was spinning as fast as the train power supply could do on full power so no reason for it anyways.

Would be nice if I could find larger tube size pump heads though.

you can add an potentiometer to control the speed

 

[Harrison Gordon]

Well, here we are -- time for an update!
So overall the system has been running great. Yup, the whole thing has been running for a few months now. Learned early on (as I had suspected) that the attic gets very cold--and luckily the pump runs off a smart plug, so I simply set it so that it won't run when the outdoor temperature drops below 25º. The mixing station was already setup so I just ran some lines into there; the hard part was putting the lines through the wall between my closet and my tank, because we couldn't move the tank! Anyways, it worked out, and here are some pics: