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Old 23-09-2018, 07:38   #1
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Adding PC fans to solar circuit

Hi
I wondered if anyone can see any problems with adding 1 or 2 low powered pc fans to my existing solar rig ( see pic )
Would I need diodes? Will it have a bad effect on the charging? ( they would be very low power ( 0,05 A )
My solar panels add up to 150W
(I'm using the controller in the pic)

My solar panels are on the transom and it would be great to add the fans for the aft cabin ventilation, I appreciate they will only run during the day!

many thanks
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Old 23-09-2018, 08:06   #2
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Re: Adding PC fans to solar circuit

48v Booster into a 12V battery?



You say solar panels Are they wired series or parallel? What is the output voltage of the panels? Even if it's only 17V, it won't be good for a 12V fan.
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Old 23-09-2018, 08:13   #3
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Re: Adding PC fans to solar circuit

oops sorry, it looked like mine! its more like this...
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Old 23-09-2018, 08:17   #4
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Re: Adding PC fans to solar circuit

Run them off the load output terminals, or batt charge output, not directly off the panels.
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Old 23-09-2018, 08:17   #5
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Re: Adding PC fans to solar circuit

The panels are wired in parallel, I'll need to check the top end voltage, I guess I may need a DC to DC converter, I'll check the top end allowed on the PC fans as well.
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Old 23-09-2018, 08:18   #6
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Re: Adding PC fans to solar circuit

'run them off the load output terminals, or batt charge output, not directly off the panels.'
yes, that makes sense. thanks

But in the interest of not draining the batteries, its not what I originally had in mind, I ideally just wanted to tag on to the solar power without going near the batteries.
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Old 23-09-2018, 09:03   #7
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Re: Adding PC fans to solar circuit

Most PC fans are not really that efficient (at least ones large enough to move any noticeable air) The problem your going to run into is the fan needs 12v but your solar panel EVEN if its a 12v panel is most likely putting out 14-18v in full sun. You would better putting it on the load side and make sure you have a swtich to turn it on/off.
You will also find you need to build a little case for it because it will make a lot of noise and that whine will need to be damped a bit or will drive you nuts.
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Old 23-09-2018, 09:07   #8
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Re: Adding PC fans to solar circuit

Donít run off the panels. Do it right, with fuses, switches, etc. or use the proper load output (with fuses!) if your controller has such.

It will make no difference in your charge efficiency either way.
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Old 23-09-2018, 09:45   #9
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Re: Adding PC fans to solar circuit

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Originally Posted by john61ct View Post
Run them off the load output terminals, or batt charge output, not directly off the panels.

Correct. You can wire a terminal strip for them off an existing lighting circuit in that cabin as they are low-draw. You could even rig them to be thermally controlled so they only spin up after X degrees of heat.


I think you are otherwise asking for trouble.
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Old 23-09-2018, 09:56   #10
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Re: Adding PC fans to solar circuit

My pc fan has been running off the batteries for 3 years. Keeps the Natures Head smell flowing out.
Hook it to batteries and let em run. On my house bank it ran 3 months without dropping a half volt without being charged at all.
Seems to work great for me. Im going to put in 5 more fans to have a full cabin air flow, low noise and near zero power. (1 watt)
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Old 23-09-2018, 10:38   #11
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Re: Adding PC fans to solar circuit

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My pc fan has been running off the batteries for 3 years. Keeps the Natures Head smell flowing out.
Hook it to batteries and let em run. On my house bank it ran 3 months without dropping a half volt without being charged at all.
Seems to work great for me. Im going to put in 5 more fans to have a full cabin air flow, low noise and near zero power. (1 watt)
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Old 23-09-2018, 11:18   #12
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Re: Adding PC fans to solar circuit

Get a buck/boast regular board from the Chinese distribution network for less than $20. Some models will input 8V to 48V DC and produce a regulated +12 VDC output. Tee it off from the input to your battery charger module.
The small good quality fans will run for years. The impellers have close tolerances so they need to have a filter on their input side or a regular inspection cycle. Their downside is they can be difficult to mount.

With this setup you could run a bilge hose blower since it would only consume power from the solar panel but will reduce power available to the battery charger.

Good luck with your project.
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Old 23-09-2018, 11:31   #13
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Re: Adding PC fans to solar circuit

Use large pc fans as they run slower but move more air and therefore quieter. 120 mm or larger fans.
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Old 23-09-2018, 11:41   #14
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Re: Adding PC fans to solar circuit

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Originally Posted by mtompson View Post
The panels are wired in parallel, I'll need to check the top end voltage, I guess I may need a DC to DC converter, I'll check the top end allowed on the PC fans as well.
Why not run the fans off of the battery. 12V fans directly from the panel/panels does not make sense.
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Old 23-09-2018, 13:06   #15
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Re: Adding PC fans to solar circuit

I doubt you'll find "maximum" voltage ratings for PC fans. They are pretty much designed and rated for only one voltage, whether that's 5, 12, or mains. And running a 12 volt fan on solar panels that typically are putting out 17 volts, does not seem like a good idea.

As john said, this is what the "load" terminals on a controller are for. The better controllers all give you the option of hooking up a load that is ONLY powered by the panels, not the battery, so there's nothing to lose there.

Now, if you go looking at a catalog from a real fan company, like Rotron, you won't find the "two bucks including postage from Shenzhen" pricing, but you will see an incredible number of variations, each with different airflow, power consumption, noise levels, all listed so you can pick the one that suits you. Online anonymous junk can be a bargain, but then again, you can't really believe any specs it comes with either.
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