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Old 06-03-2013, 16:55   #1
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Change 12v Solar Config to 24v?

I have 6 - 100w panels. That are currently in 12v configuration.

I was watching my charge controller the other evening and noticed it was only putting in around 10-13v since the sun was going down.

So I was wondering if I had the panels in a 24v configuration would I be putting in a higher voltage in the evenings that my controller could squeeze the juice out of for a little longer.

I have an Outback FM60 controller and it can step down from higher voltages to my 12v battery bank.

Thanks.
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Old 06-03-2013, 17:08   #2
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If I'm not wrong it's not the voltage you should look at but the amperage

With 600w and 12 volt you should have 50 Amps available for use or charge.
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Old 06-03-2013, 17:16   #3
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Re: Change 12v Solar Config to 24v?

Hum I have never seen 50amps before I think most I have ever seen was somewhere around 35amps.

What I am asking though is if I have it in a 24v configuration will I be able to get more volts / amps what ever at earlier or later times of the day then in the 12v configuration?

Thanks
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Old 06-03-2013, 17:29   #4
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In 12v 'configuration' they should be putting out about 18v when not connected to the batteries. When they are connected, the measured voltage will start at whatever you batteries were at (10-12v I'm guessing) and then gradually tick up to about 13.5v when fully charged. I assume you're using some kind of charge controller? If so, it will flick over to trickle after that.

Don't put them into 24v config unless you want to destroy your batteries... Or unless your charge controller is set up to take that and step it down.

Depending on he much sun you're getting, you should expect about 5-7 amps per 100w, so your 35a sounds about right if your batteries were already 2/3 charged when you started.
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Old 06-03-2013, 18:31   #5
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Re: Change 12v Solar Config to 24v?

Yes, you will be able to charge your batteries longer if you configure your panels for 24 volts. They'll go over the minimum threshold controller voltage earlier in the morning and will provide usable charging voltage longer into the sunset. It's one of the advantages of at least partially serial configuration (i.e., higher voltage) over straight parallel.
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Old 06-03-2013, 18:34   #6
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Re: Change 12v Solar Config to 24v?

Adamante: Thanks for the confirmation that was the answer I was looking for.

thanks again.
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Old 06-03-2013, 22:04   #7
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Re: Change 12v Solar Config to 24v?

I'm also going to experiment with doing this with the six 80 watt panels we are using...



Endeavour 37 Electrical Mods Index

...and try them as six 12 volt panels and as 3 sets of two panels (24 volts each set),

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Old 06-03-2013, 22:20   #8
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Re: Change 12v Solar Config to 24v?

If you run the panels in series you'll be able to charge earlier in the morning and later in the afternoon, by a little bit (you're at the end of the light range by then, so it won't be a lot). You'll also have lower wiring losses. If you already have a controller that is capable of the voltage conversion then you are probably already paying the price for that conversion - it is not 100% efficient. So put them in series (if they are identical panels, and will be shaded similarly). If you were going to have to change to a voltage-conversion capable controller then you would not see the same increase, as you would have to pay the price of the conversion during the middle of the day when the bulk of your power is generated.
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Old 07-03-2013, 03:30   #9
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Re: Change 12v Solar Config to 24v?

I came across a series parllel knife switch. You may be able to incorporate it into your solar panel wiring so you can choose which mode to operate in. You can find and example here:

Knife Switch: Double 2-Way 12/24-volt Heavy Equipment Switch | Northern Auto Parts

I made a diagram for using the switch too but the file is too big to post. It is a pdf that I can email to someone who knows how to make it smaller or maybe someone can suggest how to shrink it.
Attached Files
File Type: pdf Series parallel knife switch.pdf (102.0 KB, 32 views)
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Old 07-03-2013, 04:11   #10
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Do you have a controller capable of taking the 24v input and charging 12v?
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Old 07-03-2013, 05:34   #11
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Re: Change 12v Solar Config to 24v?

The
Outback FM60 Flexmax Charge Controller - FM60-150VDC

....which the OP said he already had


....is a very capable, programmable MPPT controller capable of handling 60A and inputs up to 150VDC.


Yes, by all means wire your panels in series. You're losing a lot of charging (and $$$) by not putting this excellent controller to it's intended use.


Bill
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Old 07-03-2013, 07:58   #12
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Re: Change 12v Solar Config to 24v?

Quote:
Originally Posted by Tomm0 View Post
Do you have a controller capable of taking the 24v input and charging 12v?
I believe that all of us that are considering this do have MPPT controllers,

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Old 07-03-2013, 08:14   #13
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Re: Change 12v Solar Config to 24v?

Putting the panels in series will make very little difference to the charging early in the morning, or late in the day.
By the time the panel voltage has dropped below the battery voltage the amount of current the panels can deliver is very small.
Have a look this output. Very late in the day when the panels are only capable of 0.6A the MPP (Vmp) voltage is still 15.0 v ( the maximimium voltage the panels could produce would be higher again)
In the second photo the controller has actually shut down because the energy from the solar panels is less than the energy the controler needs to run.
Notice the voltage is still high (Voc) at 18v despite the very low light. These results are typical. It's not low voltage that shuts the output down if there is no shading.

The difference between series and parallel shows up with shading there is almost no difference to the low light performance.
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Old 07-03-2013, 08:23   #14
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Re: Change 12v Solar Config to 24v?

Quote:
Originally Posted by noelex 77 View Post
Putting the panels in series will make very little difference to the charging early in the morning, or late in the day.
By the time the panel voltage has dropped below the battery voltage the amount of current the panels can deliver is very small.
Have a look this output. Very late in the day when the panels are only capable of 0.6A the MPP (Vmp) voltage is still 15.0 v ( the maximimium voltage the panels could produce would be higher again)
In the second photo the controller has actually shut down because the energy the solar panels is less than the energy the controler needs to run.
Notice the voltage is still high (Voc) at 18v despite the very low light. These results are typical. It's not low voltage that shuts the output down if there is no shading.

The difference between series and parallel shows up with shading there is almost no difference to the low light performance.
Still, this might be just one panel with the rest partially shaded. What you show here is what I typically see with the same controller and 6x110W panels all in parallel. Others who had exactly that have reported a 25% improvement after going to some sort of series connection. I'm prepping to change to series and to parallel/series combinations to see what difference it makes. I'm pretty sure all panels in series will be the winning setup. Folks connecting in series must take care of voltage: anything over 48V can be lethal so treat it as you would outlets etc. My setup will be able to go up to 130V ...

cheers,
Nick.
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Old 09-03-2013, 07:18   #15
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Just be sure you don't go too high on the voltage. It's surprising how much hight the peak voltage can be vs nominal. With a controller rated up to 150v which I think is the outback rating, you need to keep the peak panel voltage below that. I found that meant no more than 48v nominal.

Peak voltage is the panels max rated open circuit voltage. But you need to calculate it at min ambient temp, not the rated temp on the nameplate. And you need to further jack it up for cloud edge lighting which through some magic of optics is brighter than full sun. I don't recall the adjustment factor, but it's in the 15 to 25% range. Then on top of all that I'm pretty sure there is a further NEC de-ratng of 15%. It all adds up surprisingly fast.
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