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Bert

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Reply with quote  #11 
I used that high temp paint on my first collector. Seemed to be OK. GH said that his never cured because it has to get up to 300 to do so.

So I'm trying to decide on which paint to use.  When I take my old collector apart this Spring, I will see how it looks inside.

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Bert K.
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gbwillson

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Reply with quote  #12 
I tried Rustoleum grill paint and it stunk, took a long time to dry and had terrible coverage, like it was watered down. Krylon grill paint seems to cover well, dries fast and doesn't stink. But neither one required heat to cure them. Just be sure to check the label for dry times and curing requirements. If you are not sure of a products specs, look up the MSD.

I don't think any water-based(enamel) spray paints are bad to use. I prefer Krylon ultra black camo paint as it has a built in primer. Any brand should be fine handling the heat in a collector, unless a stagnation event occurs. But are you planning for a stagnation event?

Greg in MN
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Reply with quote  #13 
Quote:
if painting screen, cut it to size, roll it up, spray it in the roll form. There is less paint wasted as it passes thru the screen. The pass-thru spray collects on the inner layers of screen. After one coat, unroll it, then roll it in the opposite direction to finsh paintiing what was the inner layers.


Neat idea, Jeff !

I think this deserves to be reproduced in the "Quick Tips" section --- what do the webmasters think ?

G_H

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SolarInterested

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Reply with quote  #14 
Sounds like a good tip.
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Both temperature rise and airflow are integral to comparing hot air collectors
Bert

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Reply with quote  #15 
Quote:
Originally Posted by gbwillson
 Any brand should be fine handling the heat in a collector, unless a stagnation event occurs. But are you planning for a stagnation event?

Greg in MN


I don't want stagnation, but I may have to plan for the possibility. May have to incorporate some vents/fans for the Summer. I would also like a DC backup for the AC fan. Have to figure out how to do that without interfering with the airflow.

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Bert K.
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Garage_Hermit

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Reply with quote  #16 
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I would also like a DC backup for the AC fan. Have to figure out how to do that without interfering with the airflow.


Bert, how about using a DC fan, period.
If you run it off a battery (served by a battery charger...and/or a solar panel), the right fan should consume  peanuts power-wise.

In the event of a mains power outage, your battery will keep the fan running, so (theoretically) no stagnation at the collector...

Or run the fan directly *off* the battery charger - I am currently using an automobile radiator fan this way...
The fan motor is rated at 90 watts at 12 Volt, = 7.5 amps; the charger output is 3.7 amps, so the fan runs at half-power, which is fine, as it is not supposed to run full speed, full time...  So instead of the full 1600 CFM, I guess I am getting around 800, which is all I need anyhow.

I have the charger plugged in to a mechanical timer, which controls when the fan is 0N and OFF.

G_H

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Bert

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Reply with quote  #17 
GH

I will probably test it both ways and see how the airflow compares.
I have a 12v 1700 cfm fan on my current panel with a speed control.

I have an 8" 740 cfm AC fan that I was planning on using. I notice that it puts out a lot more air than the DC fan even though the dc fan as twice the cfm rating.

Will be interesting to see the actual output when I get it built.

I could build it so the the AC and DC fans are exchangeable, but I would have to be home to change them out.


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Bert K.
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Reply with quote  #18 
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I notice that it puts out a lot more air than the DC fan even though the dc fan as twice the cfm rating.


Hmm, Bert, those fans merit a comparison test !

What are their respective power ratings, by any chance ?
The DC one looks similar to mine, which is rated at 90 watts...
Is it running at maximum power, That Is The Question ?

Also, I suspect that fan blade type has a role to play, as in forward- or backward-inclined etc.

Also diameters, number of blades...

================

I could build it so the the AC and DC fans are exchangeable, but I would have to be home to change them out
Quote:


Well, you could maybe run them off a relay: the main fan is AC, running off your mains, via  a normally closed relay: when the mains is outed, the relay loses its holding current, and opens, so making the battery circuit to the second (DC) (backup) fan, which therefor runs... No Collector Stagnation...

When the mains current returns, the relay closes, thus energizing the AC fan, but breaking the battery circuit, so that the DC fan goes off.

Or Something Like That...

cf.  http://hydrosystemsco.com/wp-content/uploads/2014/06/triton-relays-normally-open-vs-normally-closed.pdf

G_H



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Bert

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Reply with quote  #19 
The DC fan is 34 watts. It's a car radiator fan
http://www.amazon.com/gp/product/B003908L3Q?psc=1&redirect=true&ref_=oh_aui_search_detailpage

The AC fan is about 195 watts
http://www.amazon.com/gp/product/B006Z1JLN0?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I could do the relay and perhaps damper if necessary.

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Bert K.
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Garage_Hermit

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Reply with quote  #20 
Bert, I think the secret is in here...

http://www.pelonistechnologies.com/blog/axial-vs.-centrifugal-fans

and in this graph...

http://www.engineeringtoolbox.com/fan-types-d_142.html


The car ("propellor") fan will shove 1700 CFM in still air; but once the pressure increases the airflow will drop right off.

The centrifugal fan does better sucking through a duct (where there is higher static pressure);
so the car fan is probably not giving U anything like its rated 1700 CFM, which is basically what you said... less airflow compared to the AC fan...

? any thoughts ?

G_H

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