Hi guys!
I am about to install a second solar collector and I need to install a second temperature sensor in the second solar panel. However my controller device has only one input foir the respective sensor. How I could use 2 separate PT1000 sensors in parallel and measure one and/or both highest resistances? I understand that simple parallel wiring will not work properly.
Alternatively I have to istall additional pumping station and controller that I' d like to avoid.
Thanks in advance!
First thought would be to use a relay with low impedance contacts to switch between the sensors. Do you have a digital output available?
Thank you for the idea. However timewise I need 1/3 of time to use one sensor, 1/3 to use both, 1/3 of time to use second one. So I am not sure how to use switch. I think there should be some additional resistance wiring that would make possible to measure highest resistance out of 2.
If both panels are in the same position, the temperature should be similar.
faidons:
Hi guys!I am about to install a second solar collector and I need to install a second temperature sensor in the second solar panel. However my controller device has only one input foir the respective sensor. How I could use 2 separate PT1000 sensors in parallel and measure one and/or both highest resistances? I understand that simple parallel wiring will not work properly.
Alternatively I have to istall additional pumping station and controller that I' d like to avoid.
Thanks in advance!
You have not stated what your control device is. Is it a commercial unit or an Arduino? If we don't know how you are controlling the device we cannot give meaningful advice.
Weedpharma
My controlling device is standard controller that came together with existing solar system http://www.sokdoo.com/SR868C8.pdf . That has only one collector T input. I plan to expose panels to about 40 degrees diferent directions hence I expect different T.
My latest solution is to instal simple day time timer that switches relay that consequntly switch temperature devices as well as closes/opens valve for liquid circulation. With such semi-automation I could use collectorsand liqid circulation in parallel. One period both, second period only one collector.
It would have been helpful to supply this in your OP. I thought we were talking about a PV panels rather than a HWS.
If you have two panels you need two pumps. Simply pumping when one panel is hot will pump cold water from the cooler one as well so you will get a mixture of hot and cold water.
Weedpharma
Hello,
I have the same need as the original post. (I'll continue this thread as I stumbled upon it while searching for solutions and it may help others).
Unfortunately my water solar collectors are already in place and have been for a while (it's a long story!), changing the plumbing isn't a viable option.
While it's not the optimum solution the panels do work well.
With the temperature probe on the in the panel that receives the sun first, the pump activates sooner but also turns off while the 2nd panel is still producing heat.
With the prob in the panel that received the sun later, the pump activates later but the 1st panel may be too hot. As soon as the water circulates the second panel's temperature goes up and the system shuts of because it has reached 110°c.
I don't have much knowledge about electronics, so this may sound silly.
The idea of using a switch with a timer seems to be the simplest and most effective, would a simple timer with a mechanical relay be ok? or do I have to worry about the solar controller (integrated with the heating system) receiving spikes from the voltage transients (the temp. probe is ohmic (PT1000), but I don't know what's inside the controller).
The second option, is connect to two probes to an Arduino (Adafruit has PT1000 temperature sensor amplifier), and output the highest value using a digital potentiometer.
The only problems I can see with this setup is:
Thanks!
Antonio
The accuracy problem is easily solved, use the pot in series with a fixed precision resistor - for instance if only
interested in 0C to 70C range a variable 200 ohm resistor in series with a fixed 1k resistor could do the job.
Unfortunately digital pots aren't available in very low values like 200 ohms so you'll probably need to transform
to a parallel circuit, fixed 1k2 in parallel to 5k digipot? Non-linear response would have to be fixed in software.
If I use a 1k potentiometer with 256 taps in series with a 920ohm resister, it should be fairly linear.
(I've read the 1k also includes internal resistance of the wiper?) so every step of the pot won't be ~3.9 ohms but shouldn't be far off.
With the PT1000 i should more or less get the following range with 1°c step:
-20°c => 921.6 ohm
245°c => 1922 ohm
Do you think I can wire the potentiometer's output directly to the solar controller's input? I wouldn't imagine it draws much current 