Fan speed

Halfandhalf

Halfandhalf

Well-Known Member
So I bought heatsink/fans for my vero 29's that are way too strong. They were pulling more in air than I was taking out of the tent until I ramped up the exhaust but the noise inside and out is unbearable now. Is it possible to control 3 fans in parallel with a potentiometer?

All three fans are 230 ma 12vdc. I know a lot of these fans have a mininum starting voltage of 5 or 7 but even that might be enough to reduce the speed to a comfortable level. I'm fairly sure the vero's will be fine with less fan power as these are rated for 200 watts dissipation and the veros are only running at ~73 watts.

What size potentiometer and wattage should I get? I calculated ~20 ohm? v=ir 12=(.23*3)R, R=17.4.
I ordered this 25 ohm 5 watt pot. Will that work? Am I missing something? Am I going to have a burning up pot? Should I just order new fans and try to attach them to these heatsinks instead of going for potentiometer control?

I just spent the last week trying to convince myself that the fan noise and extra intake/exhaust was fine but I really don't like it :(
 
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SupraSPL

SupraSPL

Well-Known Member
Ya even if you reduce it to 9V there will be a lot less noise. How are you powering the fans? Adjustable power supplies are pretty cheap. You can make a simple dimmer, although I cannot confirm the electrical details.

http://www.ebay.com/itm/Switching-Power-Supply-Converter-AC-110-220V-12V-1A-12W-for-LED-Strip-Light-T7W8-/272613735531?hash=item3f790b7c6b:g:g2MAAOSwA29Y31oO

http://www.ebay.com/itm/Adjustable-AC-DC-Adapter-3-12V-1A-Power-Supply-Motor-Speed-Controller-US-Plug-/401288081488?hash=item5d6ea23050:g:kdkAAOSwB-1YwNQF
 
Halfandhalf

Halfandhalf

Well-Known Member
Unfortunately it's only two wires. I regret buying these honestly. On top of the fan being too powerful the star design of the heatsink might not be dissipating heat very well. The heatsink itself doesn't get hot and I'm getting a lot of heat pointed down it seems. Not sure if its actually doing its job? If its rated for 200w could it be too much and not work at all? I'm not really sure how much heat these cobs are supposed to put out at a certain distance, it increases my temps to high 70's low 80's atm.

Still if I can reduce the fan speeds that would at least make it quieter. I dunno I hope that pot I bought is good enough for this. I'm fuzzy on the electrical calculations and implications of turning down the voltage. I am guessing it turns into heat and that the pot should be rated for as many watts as its dissipating? So with my 5 watt pot that I ordered that should be enough to bring it down to 5v from 12v? (8.28w total - 5w=3.28w 3.28w/8.28w=~.4 .4*12v=~5v). The ohms are approximately the resistance of the whole parallel circuit. .23a*3=.69a v=ir 12v=.69aR 12v/.69a=17ohms. Closest I could find was 25 ohms. Can anyone confirm the math/electronics?

or maybe i could just go with that second link supra. that does look like it should work. lul i typed this all out before checking that. Still would like to know about the pot math and I think using the pot would be cleaner since I could just use one ac plug then but if all else fails! Thanks for the link.
 
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CobKits

CobKits

Well-Known Member
a 9V battery will tell you everything you need to know about how quiet they can be. im sure you have one around
 
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