wiring question. thermostat switch

[capt. apathy]

here's the situation.

I built a solar heater for our pool.  It works great, we actually have to cover 2/3 of it in mid-summer because the pool gets too hot.  

the problem is that since we are short on yard space I had to put it on the roof.  this requires a forced circulation to bring the hot water down to the pool.  

this means running the pool pump for about 8 or 9 hours a day, when it only needs to run about 3 to clean the pool.

the heater has bypass area that holds a about 5 gallons of water so the heater itself will flow just fine by convection.  it just needs the pump to come on every so often (anywhere from 10 minutes to 30) and bring the hot water to the pool.

here's the question-
can anybody tell me an inexpensive way to mount a thermostat into the pipes of the heater (PVC), that will turn on a 15amp pump circuit when the heater water hits about 120-140F, and then preferably run for a set time(5 minutes) or until the heater temp goes below 100F.  ideally the temps would be adjustable but a fixed setting anywhere near that range would be better than what I have going now.

it could also save me repairs to the heater over the sumer by avoiding overheats.  last sumer one of the kids messed with the timers and it went over an hour without circulating.  we had to repair one leak, and a few pieces of PVC pipe had to be replaced because the overheated and where beginning to melt.

I don't want to spend a lot of cash, mostly since I don't have it and also because the main point of this is to have the pump run much less and save me money.

if I can get this to work it should save me about $25-35 a month depending on how much our electric rate increased this year, and maybe avoid some repairs on the heater.

[YUCCA]

Well sir i know you can buy a no hub coupling.  Aka rubber coupling.  Perhaps you could strip the thermostat wire and slide it under the rubber coupling.  Just one idea.

[capt. apathy]

mounting the thermostat shouldn't be a problem.  I can put a threaded fitting in the line if it screws in, or use an epoxy to seal it if it doesn't.

what I need to know is how to set up the circuit to be activated by the thermostat, and what parts I'll need to find to get the job done.

[YUCCA]

Well as far as making it kick a pump on.... Im not sure about the having it run for a set amount of time. I have some experience as an HVAC tech and a little electrical knowledge.  

You could use a step down transformer from 120 to 24volts.  From the transformer you can send 24 volts to the thermostat.  Now the transformer when wiring in the line voltage alot of people will install a fuse inbetween. the transformer and the line voltage.  (i didn't illustrate it in pic)

Anyways the transformer makes 120 volts into 24 volts.  Which goes to your thermostat.  Your thermostat is in a normally open position.  Witch means when your temp falls below say 100' it will make a contact which will send 24 volts to the contactor.

The contactor is also in a normally open position.  When 24 volts gets ssent to the contactor it closes  a switch (much like flippin a light switch on in your house.  The 24 volts basically is the finger that flips the switch.  Then when it makes contact vualah 120 volts is being sent to your pump.

Dont know if i helped much but i was bored and it's been a while since i thought about electricity.  Here's an illustration.

[YUCCA]

Got more questions just ask.  Althought now that i think about it.  The thermostat would have to be special perhaps.   Since you dont want it clickin on and off every 5 mins .  So you could if i recall install a "time delay relay"  on the load side of the contactor.  Kinda like this one.  They make all sorts probably find one with even 3 hour delay.

Time Delay Relay





Contactor:



Transformer:


Fuse:

[Tuomio]

How about this, the pump would be controlled by daylight and temperature. Most of the temperature relays have adjustable temperature "width". You can find them from any place that sells electrical housing acessories.

[StarOfAfrica2]

Why even include the transformer?  Or the fuse?  I'd think the thermostat from an electric water heater would fit the bill nicely.  Temp. range might be a little off, but I think it could work.

[capt. apathy]

Originally posted by StarOfAfrica2
Why even include the transformer?  Or the fuse?  I'd think the thermostat from an electric water heater would fit the bill nicely.  Temp. range might be a little off, but I think it could work.

that would have the right temp range and be easy to find (affordable too). the temp probe and thermostat would already be a integrated.

IIRC the last one I set even had separate setting for on and off temp.  if not I could use it with one of the "time delay relays"  YUCCA mentioned.

I would just have to figure an adaptation to have it come on when the temp goes over the set temp instead of under.

that seems very do-able.  thanks

[StarOfAfrica2]

You could also set it with a basic 24 hour timer where it wont power up at night, save on the electric.  I have a 24 hour dial timer like automatic lights use wired into my hot water heater so it doesnt run at night when I'm sleeping.  At 4 am the power kicks back in and the water heater refreshes the temp in the tank just in time for me to take a shower and go to work.

Also, the thermostat has a built in "reset switch" for overload protection.

As for reversing the on/off function, there's a way to do it but my brain is too mushed right now to think of it.  I'm heading to bed.

[capt. apathy]

Originally posted by StarOfAfrica2
You could also set it with a basic 24 hour timer where it wont power up at night, save on the electric.  I have a 24 hour dial timer like automatic lights use wired into my hot water heater so it doesnt run at night when I'm sleeping.  At 4 am the power kicks back in and the water heater refreshes the temp in the tank just in time for me to take a shower and go to work.

 

thats what I had last year.  but the pump had to run continusly from about 9am to 7pm or the heater would overheat.  at about 12 amps, thats a lot of electricty to waste.

[FiLtH]

Pool heating is a bit out of my realm, but perhaps a strap on aqua-stat that could be wired to your pool pump that breaks on temperature rise.

[Gunslinger]

Originally posted by capt. apathy
thats what I had last year.  but the pump had to run continusly from about 9am to 7pm or the heater would overheat.  at about 12 amps, thats a lot of electricty to waste.

As far as time delay goes, I know they have them that have a cycle that runs from 2, 4, 6, or 8, hours and repeats this cycle every 24 hours.

Example.

Activate it at 9AM on the 2 hour setting.  Everyday at 9AM it will run till 11AM.  

I think a time delay would be easier and cheaper than running a thermostat set up.  And IMHO it's better on the motor to actually run for a bit then shut of  then it is on/off on/off all day long with temp. shifts.  

G/L and let me know how ya did.  I've been pondering doing this myself.

[StarOfAfrica2]

Ok let me make sure I've got this right.

When the water in the tank reaches a certain temp, you want to circulate it.  Warmer water goes to the pool, cooler water flows into the tank and when it drops below a certain temp the pump shuts off and the heater does its work.  Correct?  Then rinse and repeat, so the pump only has to run when its circulating the water?

Assuming that, and using a hot water heater thermostat ...........

The thermostat is designed so that when the sensor reads below a preset temp, a contactor closes and juice flows through to the heating element.  In this case though, the juice flows through to a flapper valve installed inside the pipe and closes the water flow off to the pool.  Water refills in the tank, and a float valve shuts the water pump off when the water level in the tank is full.  Heater heats up the water, then when its hot enough the thermostat opens its circuit and cuts power, gravity opens the flapper valve and hot water flows out of the tank.  Water level drops, float valve turns on the pump again and tank refills.

[capt. apathy]

I don't think the valve thing will work since the heater doesn't have a real tank.  more of a large by-pass area.

the heater itself is made out of rows of 3/4" PVC pipe inside a box made from a sheet of plywood with a 2x4 frame with a glass cover.  it sets on the roof tilted at about a 40deg angle.

the 1-1/2" line from the pump goes up to the roof and to the heater.  at the heater it has the 3/4" line go into the heater, and the rest goes into about 12' of 4" line that runs up the back side of the heater.  at the top of the 4" pipe it goes back to 1-1/2" and the 3/4" line from the heater conects back in and the 1-1/2" goes back to the pool.

when the pump is off convection causes the hot water in the heater to rise up into the top of the 4", which pulls cold water in from the bottom of the 4" pipe.


I wonder if I could I could get a 15amp switch that the waterheater thermostat could control with a solenoid.  one that was set so that the power from the thermostat would hold the circuit open and close the circuit when the thermostat tripped off at the higher temp.

[WhiteHawk]

i dunno.  Id go with an anolog temperature sensor in between your pump hot supply wire and the pump,  mounted TO your pipe.  Internal sensors tha rely on touching the liquid require a pretty good metered and constant flow.  If there is no check valve in the piping, you will get the "slish slosh" thing. The pipe will maintain a more constant temperature. The anolog temp sensor sohould have a "time on" and "time off" delay so you can run your pump at whatever temperature you select, (make sure you have the right range on your sensor), and for the amount of time you find meets your needs.  For ex.  The temp hits 120 (your pipe may only be 100, but you can adjust) your sensor closes the internal contacts and your pump runs until your "time off" delay elapses.  It is critical that whatever you go with, you have the ability to tweak it so you arent buying 3 or 4 different sensors.  I work with both kinds of sensors, but all the piping is precision engineered for each kind of sensor.