Need some electrical edjumakashun...

[laknox]

I'm trying to cobble together a small exhaust fan, solar powered. I have a bunch of old computer fans, both 5v and 12v, and am having trouble figuring out what I can run and how much panel I need. Main questions are:

1. With 12v fans, how far down in voltage can I run them before I start damaging the motor? (Assume the usual cheap computer case fans you're likely to get in a desktop.)

2. When voltage goes down, amperage goes down; will low amperage damage the fan?

3. If I use a "quick and dirty" 12v to 5v USB car charger to run a 5v fan, will the loss of voltage (and amperage) between 12 and 5 as the panel becomes less effective cause any issues?

4. What's more important to fan speed; volts or amps?

I know there are a lot of DIY "instructions" out there, but they're usually not real detailed, nor do they explain a lot. Any info is appreciate.

Lyle

[jwmII]

#2 on your list I am sure is a misquote. Actually when voltage goes DOWN amperage goes UP.

[MrWizard]

thats a good point
my 12 PC fan is a real Zinger at 16v, i can hear Whine, when ever i am near the fridge

but that voltage will get reduced when i resolve my Chassis Battery Solar issues that panel is put back in use floating the chassis batteries, the load will reduce the voltage

[MEXICOWANDERER]

You can find a range of voltages in surplus fans from 5- volts to 48-volts. In my humble experience overvolting a fan can make many of them complain noise-wise
I routinely have chosen an 18-volt fan for use at 12-volts when max possible air flow isn't an issue. These fans are very hard to hear running.

[laknox]

Thanks for all the good info, guys. I guess I was over-thinking this and, frankly, was a bit paranoid about overheating the fan if it stalled. I'll go ahead with my little project and see how it works. If it =does=, I'll post pics; if not, I'll just disappear into the sunset... 🙂

Lyle

[reed_cundiff]

Glad to find this thread since this is something that we should do fairly soon. We have our LFP battery bank (8.6 kW-hr at 48 V nominal) and Magnum 4.0 kW PSWI in the front bay of our 5th wheel. The inverter can give off a lot of heat when running the a/c from battery/solar and LFP can degrade at high temperature. The bay is below the front overhang and has a large door to front and access doors to propane canisters on either side.

So we will just install a couple of 12 V receptacles in the front bay for 12 V fans (12 W) for cross-ventilation.

Reed and Elaine

[reed_cundiff]

Glad to find this thread since this is something that we should do fairly soon. We have our LFP battery bank (8.6 kW-hr at 48 V nominal) and Magnum 4.0 kW PSWI in the front bay of our 5th wheel. The inverter can give off a lot of heat when running the a/c from battery/solar and LFP can degrade at high temperature. The bay is below the front overhang and has a large door to front and access doors to propane canisters on either side.

So we will just install a couple of 12 V receptacles in the front bay for 12 V fans (12 W) for cross-ventilation.

Reed and Elaine

[DrewE]

Volts and amps are not independent of each other. Your fan will consume a certain amount of current at a specific voltage (and other operating conditions).

For most devices, a higher voltage leads to a higher current and higher power consumption. For electric motors, the curve is rather more complicated; lower voltage generally leads to higher current use and may or may not lead to greater power consumption. The nature of the load on the motor and the motor design play a huge role here.

Technically speaking, it's neither low voltage nor low or high current that harms a fan or other motor, but excess heat. At the limit, you can "run" a fan all day without damage at 0V and 0A, though the air flow will be extremely low.

[GordonThree]

simple answer = hook up those fans to whatever panel you have on hand or fits your space and budget, they'll endure just fine.

running the 5v fans off a 12v+ panel, if you have two fans, wire two fans in series, then you don't need the voltage adapter.

[wa8yxm]

1. With 12v fans, how far down in voltage can I run them before I start damaging the motor? (Assume the usual cheap computer case fans you're likely to get in a desktop.)

Quiet a ways. the Brushless DC fans used in computers will stall if you go too low.

2. When voltage goes down, amperage goes down; will low amperage damage the fan?

Wong, as voltage goes down, speed goes down, current increases believe it or not.

3. If I use a "quick and dirty" 12v to 5v USB car charger to run a 5v fan, will the loss of voltage (and amperage) between 12 and 5 as the panel becomes less effective cause any issues?

Well any time you use any device to change voltage there is a loss of effiency.. However you coudl loose half the panel output voltage and it might still work.. Depending on the USB thingy.

4. What's more important to fan speed; volts or amps?

Both... But they both become voltage.. IF the power source can not provide the amps.. the result will show as low voltage.

[1492]

Moved from Technology Corner

[magicbus]

I hooked 4 computer fans in parallel to a 12x18 inch solar panel to ventilate a crawlspace. Two intake and two exhaust. That was 4 years ago. I leave them on all summer so they run with the sun. I flipped the switch this spring and they started right up.

Dave

[MrWizard]

Gordon pretty much nailed it
I have 12v PC fan wired directly to a 40w 16v panel output
spins all day stops at night
that panels power does go someplace else
it was just the easiest way to get that fan powered, it sees full panel voltage

[GordonThree]

Computer fans are amazingly durable. A 12v fan will run as low as 7v no problem or as high as 17v (from my own experience). They are electronically commutated so the winding switch on and off as needed to make it spin.

Low amps or volts will not harm the fan. They have protection against that as well as a locked rotor.

High volts will eventually kill the microchip inside the fan.

For these tiny DC brushless fans voltage is the only thing that matters. They'll not draw more amps than needed.