STECA controller not controlling speed of circulation pump

[Promero]

Hi all,

I was astounded by the pricing and lack of availability of self controlled variable speed pumps, so I bought a variable speed pump that would be controlled by my STECA TR A503 TTR U controller. This unit states it will control up to two pumps based on the differential temperature of the STECA sensors. However, upon following the instructions on the manual in connecting the 12v speed control wiring from the pump to the controller, the pump always goes full speed, until the STECA controller turns it off. My hot water storage tank does not get hot because the flow rate is too high, and the heat just goes right back out to the panels. My goal is to have the most efficient heat transfer possible. My suspicion is that maybe the STECA controller needs to be in a certain system configuration to enable differential control, but I've already spent a day on trying to figure it out without any luck. Does anyone have some advice or can link to a person who can consult on this situation? I have tried both the thermal solar panel manufacturer and the Grundfos company, and they were not helpful.

Bright Skies,

Paul Grundfos Alpha 1 26-99 F.jpgSTECA A503 TTR U.jpg

[bcroe]

I am wondering, is variable speed operation required? For a handful of $
I built a 12VDC control that turns on the pump when the differential is too
large, turns it off when it closes by my set hysteresis. A cheap meter reads
out the temps at both ends, or the differential via a 3 pos switch, no fancy
screens. Bruce Roe

[Promero]

Hi

No, it’s good way. I already have a speed controller, so I wanted to take advantage of the feature. Variable speed saves on energy costs and my pump needs a higher head capacity than most.

I have been working on the variable speed issue, and I think I have a solution. The settings are buried 4 layers deep on the setup menu!!

Paul

[LucMan]

Hi all,

I was astounded by the pricing and lack of availability of self controlled variable speed pumps, so I bought a variable speed pump that would be controlled by my STECA TR A503 TTR U controller. This unit states it will control up to two pumps based on the differential temperature of the STECA sensors. However, upon following the instructions on the manual in connecting the 12v speed control wiring from the pump to the controller, the pump always goes full speed, until the STECA controller turns it off. My hot water storage tank does not get hot because the flow rate is too high, and the heat just goes right back out to the panels. My goal is to have the most efficient heat transfer possible. My suspicion is that maybe the STECA controller needs to be in a certain system configuration to enable differential control, but I've already spent a day on trying to figure it out without any luck. Does anyone have some advice or can link to a person who can consult on this situation? I have tried both the thermal solar panel manufacturer and the Grundfos company, and they were not helpful.

Bright Skies,

Paul Grundfos Alpha 1 26-99 F.jpgSTECA A503 TTR U.jpg

Check the specs of your controller. Does it have the capability of variable speed output for AC line voltage?
You have a 115 v pump you will need to connect it to the 115v output pump relay which may be speed controlled, not the 12VDC. Depending on the controller it may not be able to vary speed of your line voltage pump. Some Steca controllers have the variable speed option for line voltage pumps, they use an SCR to pulse voltage to the pump motor to control the speed. Be careful not to exceed the rated amps of the SCR usually only 1 amp, they smoke easily.

[Promero]

Hi Lucman,

The pump has three low voltage wires used to control speed (one is an output for an alarm?). The STECA has 1-10v low voltage connections and temperature probe connections on one side of the unit, while the 115v AC connections are on the other side. The manual states this and gives a how to on choosing pump type and speed curve type in setup for software. I’m still working on it and lost, though!

Paul

[LucMan]

That's a new to me expensive pump! I"ve always used valves to regulate the flow rate set and forget, 1-1.5 gpm per panel. Grundfoss says 0 volts = full speed check your polarity on the dc control connections, then check your dc output voltage to the motor.

[Promero]

Hi all,

yes, the pump sure is shiny! Well worth the huge cost for looks alone. Thank you for the advice on the Grundfos low voltage scheme. I set the STECA controller to 10 volts = zero and 1volt equals max speed. Uncertain still about how the speed control is working though. Learning a lot!

my panels run off the main loop three ways and it appears as evidenced by the top of panel sensor that the are feeding each other heat, causing the temp to go up over 200 and the pump to go to high speed.

This is the main reason why I’m having a hard time determining if thethe speed control settings are correct.

UPDATE: Once the panels cooled down from the circulation, I was able to listen to the pump, snd I found out the Grundfos does have what I would say is the standard 0 volts dc = low speed and 10 volts high speed. I set the minimum rpm to 20%, a little lower than the default.

Now to adjust the flow valves….

Paul