Solar panels and battery banks

[Fred]

I currently have two die hard deep cycle rv/marine batteries each of which is 565 cca (how many amp hours is that?). I have two 270 watt industrial grade solar panels I will eventually mount to the top of the rv. I have a cheap charge controller that says to only hook up one panel to it. I Spent a week in Datil, NM with only one panel pointing south and up. With a 500w inverter I was able to run my omega 8008 juicer, laptop, and a few other low voltage charges on iPads, cameras, etc. and keep a charge on both batteries during the day. At night I ran a small light and watched movies on the laptop.
I was told to not allow the charge in the batteries to fall below 11.9 vdc as it will degrade the life of the batteries.
Everything is hooked in parallel for max efficiency at 12vdc.
Eventually,I want to run everything on dc and be rid of the grid.
One question is will I be able to use the existing a/c wiring to run the dc or do I need to run smaller awg to each location I wish to have dc? Another is about the controller: if I hooked the panels in parallel, would that be to much for the charge controller? It seems to me that if they are Hooked in parallel before the controller it should work.
I do plan on acquiring at least a 3000w inverter eventually as well as better batteries.

[Fred]

[Fred]

[Fred]

I have drawn up a couple schematics for the solar systems. One is the 12vdc which is what I'm using now and the other is for the 24 vdc when I hook up the second panel. I hope you can read them and I appreciate all feedback. I left the fuses empty as I'm not sure of the proper current limits I should use yet. Typically I would go 20 or 30 amp but from your comments, I may need to be higher. 

[Fred]

Thank you all! Lots of good info. Will update when I'm done with whatever I decide to do. I'm also thinking of a disconnect switch for when I'm traveling.

[Jimco_W001]

Hi Fred, I put a fuse on each battery bank.One hundred to two hundred amps depending on the size of the battery bank.This will protect a system from a catastrphic failure.

[Ralph Javins]

Good morning, Fred; 

Why use fuses in a nominal 12 VDC or 24 VDC solar panel system?  For the same reason that you use a fuse in any location; to protect the device and the wiring interconnecting it to the rest of the system. 

A 270 Watt panel is a really big solar panel.  If it is a nominal 17.5 VDC output panel with 36 cells in series, you will have about 17 or 17.5 Amperes current out of it at maximum power.  For that, I would include probably a 20 Ampere fuse in the positive wire side of the panel for each panel output.  Part of the logic on why you would include a fuse in the "output" side of the solar panel is to protect the panel if something else goes bad in the  system, and you may have a high current power source trying to force current through the solar panels themselves.  Then having something to protect the solar panel does make sense.  The main cause of solar panel failure is with the small intercell wiring connecting individual cells or between the strings of cells (usually 4 strings of 9 cells each in series for a "12 VDC" 36 cell panel)  opening up and killing the output of the solar panel.  The 60 Watt portable panels that I use have a nominal output of about 3.5 Amperes each, so I use a 5 Ampere fuse in the output lead feeding each panel into the "combiner" which then goes through a 15 Ampere fuse into the solar panel input of the charge controller, which is basically just a fancy way of saying "Voltage Regulator"  in the solar panel industry. 

With the portable system, I normally have about an 11 Ampere output current from the solar panels going into the charge controller.  Then there is a 20 or 25 Ampere fuse from the charge controller to the battery.  That is to protect the battery and other equipment if there is a major failure in the charge controller, and it also limits the damage there may be in the charge controller so that I might be able to repair it later.  

Then from the battery or batteries there will be a fuse that is selected to be a little over the expected load current for what I am powering.  In the case of my 100 Watt output HF radios, that will be either a 25 or 30 Ampere fuse to handle the expected 21 Ampere load current for the radio at its peak current draw.  At night there may be an additional 1/4 to 1/2 Ampere current draw for the small LED lights that I use when writing down the record of the contacts that I am making at night. 

Why use fuses in the DC circuit wiring?  To protect the devices and the wiring if there is a major malfunction in any of the parts that can provide a high current source that might damage things if they are not protected by a fuse. 

Enjoy;  Ralph, Latte Land, Washington 

[Fred]

Fuses in a 12 or 24 dc solar charged battery bank. I see people going overboard with fuses in their systems. I would like to know if they are even necessary. I've been running my 3 die hard m-2 deep cycle batteries with a cheap harbor freight 500w inverter and charging them with one 270w panel. I have been running for two months now using the renogy charge controller with no fuses. I've had no problems. The batteries charge fully and I'm able to have enough power to charge all my devices and use a rice cooker. I can also use the tv and laptop but that does drain because the inverter is very inefficient. I plan on purchasing another inverter from renogy in order to hook up the second panel and batteries in series for a 24v system. I could for safety put an in line 20a fuse on the positive but before or after the controller is the question. Or should I have a fuse on each battery as I've seen done?

[Fred]

Good morning Ralph,
I was unable to load the photos into this blog so I posted them into "my photos". I don't have a pic of the controller yet, I'll try to get one up later. I'm getting ready for an appointment with my masseuse.
I tried going the individual cell rout and building my own but then the opportunity for me to purchase the two complete panels. Hmmm...the easy way or the hard way? So I took a drive to Sho Lo, AZ and came back with the panels.
At NASA-WSTF I worked mostly with 12vdc input but millivolt and milliamp systems. Basically testing and tearing down thrusters and other parts to rebuild them and test them again.

[Ralph Javins]

Good morning, Fred; 

     OK.  You have my attention. 

     And, I may not be the best guy for you to be near when saying something like " . . . when I was a rocket scientist."  You spoke of perhaps sending a photograph to me of your 270 Watt solar panel.  Maybe one of your solar panel charge controller also.  And, while you are at it, we may need to talk.  We could have a lot more in common than you might think.  An indication:  I used to buy 10mm by 20mm monocrystalline solar cells from Hoffmann Semiconductors for about #11.20 each. 

          Enjoy; 

          Ralph 

          Latte Land, Washington 

[Fred]

I couldn't upload photos to this blog so they are in my photos.