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Old 22-07-2013, 14:38   #1
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How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

I have two of these panels and I want to run some small 12 volt DC fans and other things. Can someone specifically tell me what I need to buy to do that.

Thanks in advance if you know!

Pmax 280W
Vmpp 31.49V
Impp 8.79A
Voc 38.87V
Isc 9.56A
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Old 22-07-2013, 15:26   #2
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

You're going to need an MPPT charge controller that can handle up to 32V and 20 amps. something like this:

Bz Mppt250 Mppt Charge Controller - Amazon.com
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Old 22-07-2013, 15:28   #3
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You need a solar regulator , that can handle the input voltage , for simple PWM based controller this will be inefficient , but will work, given the high voltage , a power converting mppt one would be best.
you can even conn. the panel directly to the battery as long as you monitor the charge voltage and disconnects It at 14.4 ! ( but I wouldn't reccomend that approach !)

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Old 22-07-2013, 15:29   #4
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

Sounds like house type of panels. I installed 2 panels wired in series for 80v @ 5a into a outback MPPT controller. Used also the mounting hardware intended for roof installation. Recommend these be anodized prior to their use. Fuse & switch the leads from the panel. Also if panels are mounted flat degrade the expected performance by up to 50%.

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Old 23-07-2013, 10:08   #5
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

Have a look at this tutorial, it might help you out:

Boat / RV Solar Tutorial - Understanding the Basics of Solar Power
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Old 23-07-2013, 11:24   #6
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

There are LOTS of threads on solar systems. As the above posts say you will need a charge controller with a max input voltage above the OC voltage of your panels. DO NOT connect the panels directly to your batteries. With that kind of power you will fry your batteries in no time and it could be very dangerous. While an MPPT controller would be best, it is not absolutely necessary. I'm guessing you have those panels because they are the industry standard for installation on houses, and as such are cheaper than some smaller panels. Unless you really need to maximise the efficiency of your panels a standard PWM controller will be fine and save you a great deal of money.

This is one of the best PWM controllers on the market:
Morningstar Corporation TriStar

If you want to go the MPPT route, blue sky will shortly be coming out with a charge controller (the 3000i model) that matches your panel characteristics almost exactly:

Blue Sky Energy Inc. | New - Solar Boost 3000i Available soon

The best controller though (in my opinion!) is the one that is soon to be released by rogue systems:

Rogue Power Technologies

I'll be buying one as soon as they are available.
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Old 23-07-2013, 11:34   #7
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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Unless you really need to maximise the efficiency of your panels a standard PWM controller will be fine and save you a great deal of money.
A PWM regulator will not do any damage. (Providing its input voltage is high enough), but with these high voltage panels you will get only about 50% of the power a MPPT regulator will extract.
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Old 23-07-2013, 11:52   #8
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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A PWM regulator will not do any damage. (Providing its input voltage is high enough), but with these high voltage panels you will get only about 50% of the power a MPPT regulator will extract.
Really, is it that low?............ A good PWM controller is still capable of making the voltage to current conversion efficiently................
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Old 23-07-2013, 11:55   #9
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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Really, is it that low?............ A good PWM controller is still capable of making the voltage to current conversion efficiently................
Only a MPPT regulator can make this voltage conversion.
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Old 23-07-2013, 12:52   #10
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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Only a MPPT regulator can make this voltage conversion.
So the other 50% of available power form the PV array just gets bled of thermally?! Do you have a background in the field? I find this very difficult to believe. A standard DC / DC converter will give greater I on the output if the input voltage is higher. It doesn't just take all that power and dump it......... or have i been sorely misled?!
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Old 23-07-2013, 12:59   #11
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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Originally Posted by DefinitelyMe View Post
So the other 50% of available power form the PV array just gets bled of thermally?! Do you have a background in the field? I find this very difficult to believe. A standard DC / DC converter will give greater I on the output if the input voltage is higher. It doesn't just take all that power and dump it......... or have i been sorely misled?!
A PWM controller will only feed in the current as supplied by the panel. So in the case of this panel, 8 amps. The PWM will just turn off the panel to maintain the batteries at the set voltage. Pulse Width essentially means the amount of time the panels are connected to the battery.
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Old 23-07-2013, 13:05   #12
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

Right, yes i understand the principle behind it. I'm amazed! In that case, i stand corrected! The thermal dump must be huge......... Sorry, i realise this discussion is not particularly relevant to the OP!
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Old 24-07-2013, 06:10   #13
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

Have a look at the wiring in the connection box, some assemblies have two lower power panels wired in series and may be able to rewire them in parallel. The 31 volts sounds a little like the open circuit voltage of a 24 volt panel.
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Old 24-07-2013, 06:20   #14
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Re: How can i Use a 31 Volt, 280W solar panel to run 12 volt DC?

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The 31 volts sounds a little like the open circuit voltage of a 24 volt panel.
This sort of voltage is a common one for larger 60 cell solar panels.

It is NOT suitable for those with a 24v battery system. The voltage is too low. With or without a MPPT controller.

I emphasise this because it is a common pitfall.

Make sure if you have a 24v system any solar panel is 72 cells or more.
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