Wiring help - dual level grant float

[wizardofza]

Instead of forking over almost $200 for Morebeer's dual level float, I figured it couldn't be that difficult (or $$) to build my own.

I want to use it to control the wort level in my brutus grant so I don't have to constantly readjust the valves controlling the pump flow.

I was planning on using two of these : click, one for the top of the grant one at the bottom.

I planned on powering the switches using a DC power supply via a SSR. I this diagram :

This calls for a two pole (DPDT) relay in order to control both floats. I can't seem to find a DPDT solid state relay anywhere online. Do they even exist?

Would it be possible to put two SPDT SSRs in series effectively simulating a DPDT?

Better yet, if anyone has any advice on how to wire this up *correctly* that would be awesome!

 

[mattmauriello]

use a DPST mechanical relay for your high/low control (which looks liek everything from the coil over to the left) and use the second pole to fire an SSR for the pump. the wear on the mechanical should be pretty low per cycle, since you're only switch a few mA oneach pole, and based ont he system I doubt you're going to go through too many cycles per brew (depends on the distance between low and high, the close they are, the more frequent they switch). probably less than 100 cycles. so even a 100,000 cycle relay should get you 1000 brews. probably good enough

 

[erik]

use a DPST mechanical relay for your high/low control

Do you have a specific one you recommend? A link from Grainger or McMaster-Carr (or whatever site sells it) would be MOST appreciated!

 

[wizardofza]

use a DPST mechanical relay for your high/low control (which looks liek everything from the coil over to the left) and use the second pole to fire an SSR for the pump. the wear on the mechanical should be pretty low per cycle, since you're only switch a few mA oneach pole, and based ont he system I doubt you're going to go through too many cycles per brew (depends on the distance between low and high, the close they are, the more frequent they switch). probably less than 100 cycles. so even a 100,000 cycle relay should get you 1000 brews. probably good enough

So a single DPST wouldn't do the trick? I was under the assumption that the picture posted above was a single DPST.

I was thinking something like this from mcmaster : #7170K41. But you're saying I would need a SPST for the pump also?

 

[mattmauriello]

Do you have a specific one you recommend? A link from Grainger or McMaster-Carr (or whatever site sells it) would be MOST appreciated!

whats the voltage of your control supply (what you're running through the float switches)?

 

[mattmauriello]

suppose you have 12VDC as your control voltage, this relay at mcmaster should do the trick: 7266K43. its on page 892 of their online catalog. probably wwant the relay socket too. and the contacts are rated for 10A @ 240VAC so you should be able to run your pump straight off one of the poles on it.

 

[wizardofza]

suppose you have 12VDC as your control voltage, this relay at mcmaster should do the trick: 7266K43. its on page 892 of their online catalog. probably wwant the relay socket too. and the contacts are rated for 10A @ 240VAC so you should be able to run your pump straight off one of the poles on it.

Awesome. I'll use that one.

Thanks for the help.

 

[DrJerryrigger]

I've been more a fan of Mouser than McMaster for this kind of thing (as I've found mouser is usually cheaper), but McMaster is good too.
What I'm not sure about is the two level switches. Rather than being between the two, you could run it on one; if it goes below a point: pump comes on, if it gets back up to the point pump turns off. This would mean the pump would be switching on and off a little more frequently, but you would maintain a more steady level (which would be easier to adjust). I would also go with a more simple switch, like a float out of a toilet, and a simple mechanical switch (off high position, on for low)
With two switches; to put in binary; you have 1 for on and 0 for off on each switch. So with the top switch as the first digit, and 1 as water is above; you have the possible inputs of 00, 01, 10 and 11, but only 00, 01 and 11 are possible when things are working rite (expect things to go wrong). These possibility need to be converted to a 0 or 1 output (pump on or pump off). So you want 00=1, 01=1, 11=0, and (just in case) 10=0. But actually you need 01 to mean 1 until 00, or the pump will come on as soon as it drops below the top sensor.

Or you could just use one switch and the simplest relay you can find (that meets your amperage and voltage requirements). This would give you a 0=0 and a 1=1 (or 1=0 and 0=1 depending on how it's set up). This will take less work, fewer parts, and give you fewer things to screw up.

Many relays on the market use 12V DC as their signal. I have had luck with old ac to dc transformers from various small appliances, If you look around you may find you have a 12VDC transformer from an old printer in your basement (just check the rated amp. to the relay).

 

[wizardofza]

I've been more a fan of Mouser than McMaster for this kind of thing (as I've found mouser is usually cheaper), but McMaster is good too.
What I'm not sure about is the two level switches. Rather than being between the two, you could run it on one; if it goes below a point: pump comes on, if it gets back up to the point pump turns off. This would mean the pump would be switching on and off a little more frequently, but you would maintain a more steady level (which would be easier to adjust). I would also go with a more simple switch, like a float out of a toilet, and a simple mechanical switch (off high position, on for low)
With two switches; to put in binary; you have 1 for on and 0 for off on each switch. So with the top switch as the first digit, and 1 as water is above; you have the possible inputs of 00, 01, 10 and 11, but only 00, 01 and 11 are possible when things are working rite (expect things to go wrong). These possibility need to be converted to a 0 or 1 output (pump on or pump off). So you want 00=1, 01=1, 11=0, and (just in case) 10=0. But actually you need 01 to mean 1 until 00, or the pump will come on as soon as it drops below the top sensor.

Or you could just use one switch and the simplest relay you can find (that meets your amperage and voltage requirements). This would give you a 0=0 and a 1=1 (or 1=0 and 0=1 depending on how it's set up). This will take less work, fewer parts, and give you fewer things to screw up.

Many relays on the market use 12V DC as their signal. I have had luck with old ac to dc transformers from various small appliances, If you look around you may find you have a 12VDC transformer from an old printer in your basement (just check the rated amp. to the relay).

I have a comp sci background, so I dig your example, but I think if I only use one switch I would need to use either use a timed delay, or a switch with hysteresis. The former being more than I want to spend, and the latter I have yet to find.

 

[DrJerryrigger]

I have a comp sci background, so I dig your example, but I think if I only use one switch I would need to use either use a timed delay, or a switch with hysteresis. The former being more than I want to spend, and the latter I have yet to find.

Oh good, I glad you followed that.
If you were to only have one switch you would be cycling your pump on and off much more frequently, which is a problem for some pumps, and not as much for others. Or better yet, if you had a gravity fed system with out a pump, but instead a solenoid valve, it would have no trouble switching on and off many time per min.
Anyway, I think this frequency of the cycles problem is best addressed mechanically with a not so super sensitive switch, on the end of a long lever/float. If rigged up right, this could give a inch or more of range between pump off and pump on. This would be a rather "fiddley" job, which may not be your cup of tea (but it is mine).