Have a reasonably ancient spa that works all ok. Have fitted a Tempercon digital thermostat that is switching the 1500w heater element inside the pump body. All works fine - heats from cold at about 4C/hr and then disconnects at set temperature. All of the safety works, ie the heater gets no juice until the flow switch is opened by the pump running etc. So far so good.
But here is the problem. Once it gets to 38.9C, the heater disconnects (confirmed by putting a meter across it) but the temp continues rising at about 0.8C/hr. I suspect that this unwanted heat is coming from the pump motor (1800w) but how the heck is this issue usually dealt with? Should the pump usually be turned off at the set max temp? and if so, how to over-ride that when using the spa? This is certainly not how the original wiring dealt with it when it originally had a mechanical thermostat.
Any ideas/suggestions?
fremo,
Jan 26, 4:10am
Get an infrared temp tester and measure the temp of the pump etc.May be poor circulation of cooling air,really hot day etc. Try it at night and see what your temp readings are etc.What did it get to leaving it going? Take the top temp reached and deduct difference from 38.9 and set at lower level. Is it enclosed in a glass house type building? Lots of variables.Where does the tempercon sensor get its readings from,is it too close to a heat source etc.Maybe you need to have a sparkie look at it.Hope your running it off an RCD being an older system it may be due for some attention. They tend to have condensation amungst the electronics and a bit of rust here and there when they get on a bit. Electricity and water are not the best of friends.
aredwood,
Jan 26, 5:02am
Is your pump one of the davy celcior models? As instead of fan cooling they use water cooling. (which is good for energy efficiency) And confirm that the thermostat is switching the live side of the element and not the neutral. Rough calculations on your figures suggests you have 300w of net heat input when the heater is off. Could the pump impeller be inefficient enough to add 300W to the water? Could be.
nzjay,
Jan 26, 5:08am
I'm guessing you may have fitted a "smart" digital temperature controller, that "learns" and anticipates the needs of the pool. You may well have set the temperature required incorrectly into a "set point" instead of the upper limit required, Is the element now wired directly to the controller and not being switched by a contactor? If so, wire a lamp across the element, so you can see what is actually happening. I think you may find that the Temp controller, is pulsing the element so the temperature rises more slowly to the actual cut off temp. It does this, so the final point temp doesn't overshoot, and the controller will learn from any overshoots and pulse slower or less to compensate. Reread the instructions for the controller, or talk to the suppliers if this is the case.
moltenfire,
Jan 26, 1:18pm
Many thanks. Yes good point - the whole unit is in a fairly unventilated place - the temp sensor is bonded to the pump body where the water flows (same as original). Yep certainly have an RCD. a 10mA one! No rust and electrically all pretty top-notch as have rewired to pretty industrial type of standard.
moltenfire,
Jan 26, 1:20pm
Thanks. yep it is a Celcior and tempercon is switching the live via a relay. I wonder if the heat is coming from the impellor or the motor itself. in any event will stick a fan on it and ventilate it to the outside world as it is very enclosed.
moltenfire,
Jan 26, 1:23pm
Thanks. No it's a just a dumb sensor and there is no pulsing - I was aware of that issue. It does have an indicator showing when the heater contacts are closed but might add a decent big indicator on the pump wire box to show when there is actually juice on the heater.
moltenfire,
Jan 26, 1:24pm
Yep, will report back once have added a fan to cool the pump. aredwood I think you may be on the money as yes it is very enclosed - I assumed that this likelihood would have been considered with the pump design. ! Have just pulled the cover off the pump area and taken the thermal image of the thing. the windings area of the pump appear hotter than the water!
ira78,
Jan 26, 4:51pm
Normally you wouldn't have the pump running long enough without the heater for it to be significant. And if you're actually using it you'll have the lid off and it will cool far faster than that .8°C/hour anyway so it won't overheat then.
aredwood,
Jan 27, 3:20am
Your pump is water cooled. So the heat is coming from the motor. Look up the data sheet. Even the smallest model adds about 600w of heat to the water while running. In other words everything is working as designed. Be happy as you are getting quicker heating times and better energy efficiency. If the pump is on a timer. Reduce the thermostat setting a bit so the last few deg will be heated by the pump instead of the element. Otherwise get a dual output digital thermostat. And configure 1 output to control the element. and the other to control a solenoid to add cold water. Just program a fixed deadband between the 2 outputs.
moltenfire,
Aug 18, 6:27am
Yep thanks everyone. Now understand that it's more likely my running the pump for prolonged periods that's the essential issue. Have fitted a timer that gives it a two hour on cycle during cheap juice hours and have added a manual overide switch so that when the pump is needed, the timer can be over-ridden. So far so good and motor will last a lot longer.
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