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stmbtwle

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Reply with quote  #1 
I've used an arduino controller for my solar space heater for some time, it was powered by a 60w PV panel and a 12v buck converter. Generally worked well except no display and sometimes issues starting up in the morning.  

So I decided to install a small AGM battery in the system to provide the extra "boost" to start the pump and power the arduino display at night.   This of course necessitated a charge controller so I installed an inexpensive pwm controller. 

Now it seems the pulses from the controller are interfering with the Arduino reading the DS18b20 temperature sensors. very often I get a reading of -196 F on both sensors, which won't work.  If I disconnect the charging system the display eventually returns to normal.  

The buck converter only puts out 11.9v, not enough to charge the battery. The solar panel alone is 22v, way too much.  What to do? 

Thoughts?

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Rick H Parker

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Reply with quote  #2 
(1) Try putting the buck converter between the battery and the Arduino. The buck converter might have enough filtering to clear up the noise from the PWM.

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Rick H Parker
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stmbtwle

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Reply with quote  #3 
I think I see what you're saying. It's worth a try, but as I was having problems starting the pump, wouldn't that issue return?

Would a capacitor help?


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Rick H Parker

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Reply with quote  #4 
I think I see what you're saying. It's worth a try, but as I was having problems starting the pump, wouldn't that issue return?

Are you are using the Arduino to switch the pumps on and off OR supply power to the pumps?


If you are using the Arduino to switch the pump on and off, not power the pump.


Use the output of the buck converter to power the Arduino only and keep the pumps on the battery side of the buck converter.  The pumps will draw power directly from the battery. The Arduino will run off the cleaner DC output of the buck converter ... at least it should work if the assumption the sensor error is due to noise from the PWM output. 

A block diagram of your power & control system would be helpful in communicating what you got and how it works.

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Rick H Parker
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stmbtwle

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Reply with quote  #5 
That would work, if the buck provides enough filtering. Space could be a problem though as the arduino and relay are on the same terminal block in a duplex wall box and there is no room in there for this particular buck converter. Will take some fiddling. How about an automotive noise filter? block dgm.jpg 
alt1.jpg 

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Rick H Parker

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Reply with quote  #6 
How about an automotive noise filter

That was kind of next on my list. An automotive noise filter is what we call a Low Pass Filter. If it will work depends on the value of the components in the low pass filter vs the lowest frequency of the PWM. In other words an automotive noise filter is the right circuit but it may or may not be tuned for your application.

In your second diagram the noise filter will need to be able to carry the startup current of the pump.  One way around that would be to filter the current for the Arduino only, two power lines coming from the battery.

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Rick H Parker
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stmbtwle

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Reply with quote  #7 
The auto filters I've seen are good for about 15 amps... It's a 1 amp pump so that shouldn't be a problem. Could also put the filter could be put between the controller (max 5a) and the battery. I want to avoid running extra wires if I can.

Friday I may check the local auto store for a filter.

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Rick H Parker

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Reply with quote  #8 
There is no reason a filter cannot be placed between the charge controller and the battery.  Just keep an eye on it for the first charge to make sure the battery is getting a correct float charge voltage.
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Rick H Parker
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Reply with quote  #9 
Regardless of whether you fit a a hardware filter and whether it resolves the issue I would add a software filter to the Arduino code to discard any temperature reading outside of what you consider to be a valid range.
stmbtwle

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Reply with quote  #10 
Hmmm. Yes that would be the easiest (and cheapest), as long as the pwm noise doesn't totally jam the signal from the sensors. Also thought of increasing the sampling rate (currently 1/sec). Maybe both.

Is there any way I can temporarily connect an old speaker to the circuit (12-14v) so I can monitor this noise without blowing the speaker? Inline capacitor maybe?


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