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Old 10-27-2020, 04:49 PM   #1
Mini-Skoolie
 
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Looking for help with my solar system

I already have a 400 watt (4x100w) array on my skoolie from Windy Nation hooked up to a 30amp charge controller which charges a battery bank of 2 100ah agm wired in parallel for a 12v system. (We plan on adding an additional 2 100ah agm batteries eventually).

I have a 30 amp fuse from the panels to the controller and a 30 amp fuse from controller to batteries. 8 gauge wire from controller to batteries and they are less than 3 feet away.

10 gauge wires from the panels which are wired in parallel with MC4 connectors and are not fused individually. approximately 20-30 feet of wire from array to controller

I have two additional 100 watt panels I would like to add to my array that I had laying around (one was cracked from a rock on my van and another was shipped cracked to me and replaced but I got to keep it). I sealed both panels with an epoxy resin specifically made for solar panels.

I plan on adding the two "fixed" panels to my array for a total of 6 100w panels = 600 watts.

I just ordered a 50 amp Victron mppt controller and 60 amp fuses to replace the old controller and fuses.

I was planning on wiring the panels in series of 2 in 3 parallel groups. (That way the two "fixed" panels can be together and if they fail they won't effect the others).

Is the 50 amp mppt controller adequate for my system or will I be exceeding the amps its rated for?

Do I need to fuse each panel individually or can they all be on one? Or do I need to fuse each of the 3 series individually? What size fuses are needed?

Is 10 gauge wire from the panels to the controller adequate?

Is there a better way to arrange my panels to maximize their charging capability?

What other concerns should I have?

Thank you!

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Old 10-27-2020, 05:03 PM   #2
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Using the midnite solar sizing tool I got this info regarding my planned array of 3 parallel series of 2 (6 panels total)


PV Array
Rated PV Array Power: 600 Watts
Anticipated Array Power @ 40C: 560 Watts
Rated PV Array Current: 17.25 Amps
Battery Charging Current @ 14.4 V: 41.7 Amps
VMP (Maximum Power Point Voltage) : 34.8 Volts
VOC (Open Circuit Voltage): 43.2 Volts
VMP @ -30 C: 43.4 Volts
VOC @ -30 C: 51 Volts
Classic, Classic SL & Classic Lite Charge Controller Selection
150 200 250
Max Operating Voltage 150 200 250
Max Non operating VOC (HyperVOC) @ 12V Nominal Battery Voltage 162 212 262
Maximum Number Of Modules In Series 5 7 9
Max Number Of Modules In Series (Using HyperVOC) 6 8 10
Max Allowable Output Current Per Classic
Based On This Current Configuration 96 79 61
Max Allowable Wattage Per Classic
Based On This Current Configuration 1380 1137 878
Present PV Array Wattage Of This Configuration 600 600 600
Design Check
Max VOC OK OK OK
Temperature The Classic Will
Enter HyperVOC -724 C -1075 C -1426 C
Array Power (Wattage) OK OK OK
Classics Required 0.5 0.6 0.7
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Old 10-27-2020, 11:59 PM   #3
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Looks to me like you are safely within the limits of the Victron Smartsolar 100 | 50


If you correctly calculated your Voc (43.2V) and Isc (17.25A)


The Smartsoalr 100 | 50 Can handle a max input voltage of 100 and a max input current of 60A I think (but definitely at least 50A which you are well under)
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Old 10-28-2020, 12:21 PM   #4
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Originally Posted by dzl_ View Post
Looks to me like you are safely within the limits of the Victron Smartsolar 100 | 50


If you correctly calculated your Voc (43.2V) and Isc (17.25A)


The Smartsoalr 100 | 50 Can handle a max input voltage of 100 and a max input current of 60A I think (but definitely at least 50A which you are well under)
Ok thank you. Is the 10 gauge wire ok to use? Do I need to fuse the series individually? Or will one 60 amp fuse coming in be sufficient?
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Old 10-28-2020, 01:14 PM   #5
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Yes, 10 gauge wire is what I would do for each string of panels. Each string of two panels is 9 amps and 10 gauge is rated for 30 amps so the wire is protected and safe.
I would not use a fuse or breaker for each panel. I would use a fuse or breaker for each string of panels. A 15 amp fuse or breaker should work fine.
Then I would use a 60 amp fuse or breaker on the 6 gauge wire wire from charge controller to batteries. I prefer breakers because they make testing and working on a system convenient. Commonly available Sq. D type QO breakers and sub panels are rated for DC up to 48 volts so you could use them on the input and the output of the charge controller. The enclosures are cheap at the big box hardware store. Ive used a lot of the tiny 2 space enclosures and the 4 space enclosures as combiner boxes and disconnects for the panels and charge controller.
Happy solaring
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Old 10-28-2020, 05:05 PM   #6
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Quote:
Originally Posted by Carlycappy View Post
Ok thank you. Is the 10 gauge wire ok to use?
10 Gauge can definitely handle the current, whether its a good match will depend on the length of the wire run as well.


Quote:
Originally Posted by Carlycappy View Post
Do I need to fuse the series individually? Or will one 60 amp fuse coming in be sufficient?
I suggest doing your own research here, the answer to your question is context specific.

But my rough understanding is that it is generally advisable to fuse each string if you have 3 or more strings in parallel and not necessary in most cases with two or less.

These short articles may shed some light on it:
When to Fuse, When Not to Fuse your Solar Panels
How to Fuse a Solar Panel and why you may not need to
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Old 10-28-2020, 07:32 PM   #7
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Quote:
Originally Posted by dzl_ View Post
10 Gauge can definitely handle the current, whether its a good match will depend on the length of the wire run as well.




I suggest doing your own research here, the answer to your question is context specific.

But my rough understanding is that it is generally advisable to fuse each string if you have 3 or more strings in parallel and not necessary in most cases with two or less.

These short articles may shed some light on it:
When to Fuse, When Not to Fuse your Solar Panels
How to Fuse a Solar Panel and why you may not need to

Could I avoid fusing if I did two strings of 3 in parallel?
(300 watts each)
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Old 10-28-2020, 08:22 PM   #8
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Quote:
Originally Posted by Carlycappy View Post
Could I avoid fusing if I did two strings of 3 in parallel?
(300 watts each)

Usually, yes. At least that is my understanding.


I don't have a full grasp of the concepts or the math, But I believe two rules of thumb for determining fusing for paralleled strings are:
  • 3 or more series strings require fusing, while 2 or less do not
  • for arrays that require string fusing, the fuse should be sized higher than Isc (short circuit current) but lower than the max series fuse rating. Typically about 1.5x Isc. Both of these values can be found on the sticker on your PV panels.
(there is a bit fuller explanation here or here if you want more context)
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Old 11-12-2020, 09:39 AM   #9
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Remember DC and AC aren't the same when it comes to current and wire size. Here is a calculator for wire gauge and length based on DC voltage and current. https://www.wirebarn.com/Wire-Calculator-_ep_41.html
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Old 11-15-2020, 04:29 PM   #10
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Remember DC and AC aren't the same when it comes to current and wire size. Here is a calculator for wire gauge and length based on DC voltage and current. https://www.wirebarn.com/Wire-Calculator-_ep_41.html

One thing to be very aware of with calculators such as that one is that they are only voltage drop calculators, and do not tell you whether a wire is safe to use or not.


For example. If you input 12v, 1 ft, 5% maximum voltage drop and 200A. The calculator says anything above 14AWG is safe. (Obviously it is not safe, if you look at an ampacity table, 14AWG can handle maybe 25 to 35 amps max in moderate temperatures, the national electric code doesn't allow anything above 15A for 14AWG)


Some calculators, like the blue sea circuit wizard will calculate both Voltage Drop and Ampacity (safe current carrying capability of a wire), but most do not. You can cross reference a voltage drop calculator like the one posted above with an ampacity table like this from the national electrical code:


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