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stmbtwle

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Reply with quote  #51 
I have no experience whatsoever with Arduino, sorry.

The fan pictured is a "shaded pole" motor and they work well with an AC fan speed control and seem to work ok with an AC dimmer switch.   I don't think they'll run on DC.

I use DC fans in my collectors because they'll run directly off a solar panel, and it's easy to control the speed.  However power IS generally limited.  My "space heater" is AC because solar isn't available at night and I don't want to mess with a battery.  I think the choice of AC or DC depends on what's available and what's required.

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Willie, Tampa Bay

mattie

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Reply with quote  #52 
Maybe something like this for dc?


more here

http://www.electroschematics.com/9540/arduino-fan-speed-controlled-temperature/

Regards Mattie
stmbtwle

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Reply with quote  #53 
That could be interesting.

I prefer DC for solar, when it's hooked up to PV it's pretty reliable. Some prefer AC though for larger systems.

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Garage_Hermit

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Reply with quote  #54 
Nice Find, Mattie,

that Post No. 53 looks interesting!

However, it would be even better if the temperature was derived from 2 sensors...
Still, it's a good start...


G_H

(Some folks are never satisfied !)

UPDATED:
======
Comparing the vid at 53 with that at 51, the main differences (apart from AC and DC power) is that the AC is being controlled by a PWM signal (pulse_width modulation); this means, the fan is simply being switched ON and OFF, and left for a certain period (I think he says 15 seconds, and 10 seconds): this is simply altering the duty cycle of the fan...(that's what PWM *is*...).
So it is not truly "variable speed control", it is pulsed control: the fan is being switched.  It's like snap switches, fitted with a timer...
OK, not nit-picking, but that might be OK in some situations.

If you want continuously variable control, then you're looking at vid 53 - the motor speed is slaved to the temperature outputted by the sensor.

As I see it, this the way to be going for Aretha, if you want proportional control of fan speed according to water temp etc.


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mattie

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Reply with quote  #55 
Thanks GH
Looks like your turning into the Mick Jagger of microcontrollers[smile]
Garage_Hermit

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Reply with quote  #56 
I can't get no
Solar Fraction

though I try and I try...

etc.

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
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stmbtwle

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Reply with quote  #57 
Actually, even most dc speed controls use PWM these days, it's more efficient than voltage control.
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Willie, Tampa Bay
stmbtwle

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Reply with quote  #58 
Mattie, I'll have to build that one and see how it works...

Got a test in with the new (more powerful) fans in the Aretha, against the CPVC.   On manual control, I started them at a fairly low speed for an hour and then ran them full for an hour. On "slow" there was about 21F difference between the air entering the absorber section (cool) and the air exiting (warm).  On "high" there was only about 15F.  This is to be expected, but with the higher flow the cooler air doesn't heat the water as much.  So while there appears to be SOME improvement with more power, in the end it was too close to call.

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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #59 
Willie, if it is not too much to ask, what happened to the *water* temps during that test ?

You said that the water does not get heated as much, when the air speed is increased.
Sticking my neck out, this suggests that your water was cooler than it ought to have been...

This in turn would suggest that the water flow rate needs to be adjusted: i.e. reduced...

As I see it, what is of interest is the number of pounds of water, heated thru so many degrees F...

Which in turn suggest that the water flow rate has to be somehow inversely proportional to the air flow rate: faster air flow, lower water flow...

Which in turn suggests that there should -- somewhere -- be an equilibrium point where the water flow rate is just right for the air flow rate...

Whence the need for proportional control...

G_H






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stmbtwle

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Reply with quote  #60 
Water was the same as it always is, 43#. Pump the same too, though the flow is less since I added the second HEX. Haven't checked but probably .5 GPM or thereabouts.

I should have realized in my last test when the exiting air was the same as the water temp, that I had recovered all the heat from it I could. Same thing happened this time. All the higher flow seems to get me is lower internal temps and marginally(?) better efficiency.

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Willie, Tampa Bay
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