Charge controller and wiring questions

[Kroswind]

So, in a previous thread I asked some questions about how much solar I might actually need (see here in case it helps anyone else out:  https://vanlivingforum.com/Thread-Calculating-solar-capacity)

I went for 2 of the Kyocera 340watt solar panels, for a total of 680 watts.  Here they are for specs and reference:  https://www.solar-electric.com/kyocera-ku340-8bca-solar-panel.html  So now the time has come to pick a proper charge controller, and I wanted to double check if I have this correct or not first, since this may potentially be another large purchase.  I dont want to get something that's overkill if I don't really need it.  There's 3 things I want to try and highlight here and make sure are correct:

1. the charge controller itself
2. wire size
3. fuses

Everywhere I've looked so far, the equation seems to be Total Watts / battery bank voltage + 25%.  So, judging by this, and the size of the battery bank I was recommended in my previous thread, my total amps should be 680/12vdc+25% = ~71 amps total.  So in rounding up (as recommended), I would need an 80 amp charge controller, correct?  Is there any other information I need to take into consideration here?  I was looking around for 80amp charge controllers and the one made by outback seems to be one of the best charge controllers in this range:  https://www.amazon.com/Outback-FM-8...&sr=8-2&keywords=80amp+mppt+charge+controller

Has anyone else used this?  It appears to also contain all the information I might need about the system on the display, which is nice.  I have seen other systems where you need to get a monitor separately and I would rather have everything in 1 if I can.  I believe I watched some videos on this particular model a few weeks ago, and it was highly recommended. 

Now as for the wire size, I purchased a few cables with the correct H4 connectors when I purchased the panels.  They are 10 gauge wire.  I started looking around however, and according to this article, since I plan on putting these 2 panels in parallel, I should go with a gauge between 3-8:  https://www.windynation.com/jzv/inf/choosing-right-wire-size.  If this is the case, what size would you guys recommend I go with?  Could anyone recommend a place to get cables of this size with the appropriate connectors?

For the fuses, do I just use the same size amperage as the charge controller?  I have tried to research what exactly I need, but I'm not sure I totally understand.  I believe what I need to do is fuse between the panels and the charge controller, and between the charge controller and the batteries.  I think I need some kind of combiner box from the solar panels to the charge controller?  I'm kind of in the dark in this area, so any help here is appreciated.

Am I on the right track here?  At this point I know what I'm trying to do, just not exactly what type of hardware I need to do it with.

 

[John61CT]

340 watts max at ~40V = 8.5A, in practice usually much less.

If in parallel, better for partial shading, 40V is plenty high for MPPT, a Victron 75/15 would be perfect at under $100.

The first # is Volts, do NOT exceed, so if serialing need to go up to a more expensive 100/x model.

The second is Amps, OK to exceed by a bit, and nothing lost, since you won't in reality see over 15A from the panels 99.9% of the time anyway.

 

[John61CT]

No need to fuse between panels and SC. Battery should be fused at positive terminal, ideally very close and before any buss, switch etc.

Fuse rated a bit lower than max for the wire, or a bit higher than max amps you intend, wiring is often oversized to reduce voltage drop.

See Blue Sea website calculator, also available as an app.

​genuinedealz.com is the bomb for custom crimped wiring.

MC4 for outside, Anderson PowerPole for indoors.

 

[jonyjoe303]

340/14.4 = 23 amps, which is the most amps the panel will produce on mppt in perfect conditions. I would say you might see a good 20 amps in normal use, if the battery is at 50 percent.  

My 240 watt panel 240/14.4 = 16.6 amps, the most I see is about 15 amps, but once it went as high as 17 amps for a few seconds.  But that is when connected to my lithium battery, with agm I rarely see more than 12 amps even when the battery is below 11.5 volts.

I put a 40 amp circuit breaker on the battery ( the most amps I anticipate I would use), didnt put any fuse between solar panel and controller but I do have a toggle switch between panel and controller to turnoff power when I need to do maintenance.

 

[John61CT]

With Anderson plugs right at the controller, no need to add switches.

Also for high-amp circuit protection, fuses are simpler, more reliable and quicker than breakers.

 

[akrvbob]

The Outback is a great controller! There is an embarrassment of riches in big and superior quality controllers: Outback, Morningstar, and Midnight Solar are all excellent products you'll never regret owning

But, let me think a little out of the box: I'd go with two Blue Sky 3000i controllers, each in their own separate systems. I think you'll find by the time you add a monitor and control module to the others, one of them will cost the same. But the Blue Sky will give you redundancy which I think is very valuable. Like the Seals say, "Two is one, and one is none"

Call Northern AZ Wind and Solar and confirm that the Blue Sky can handle that big panel and then compare prices.

 

[Kroswind]

Sorry its taken me so long to respond. Works blown up on me.

Thanks for the responses. I'm afraid I'm still confused however. So I don't need to fuse between the panels and the charge controller? I don't want to melt wires or anything here. Everywhere I've seen recommends I fuse everything. I do think a breaker might be the better option as its easier to determine whats been tripped. Someone brought up the point to me that if a fuse blows, it can be harder to troubleshoot depending on how many you have. So I might go that route. I will also look into the anderson connectors mentioned above. My panels use the amphenol H4 connectors however, not the MC4 connectors.

As for the controller, I looked up the Victron 75/15 mentioned above, and the specs say it only supports up to 400watts. Since my panels are a total of 680 watts, I dont think this would work? Dont I need a charge controller capable of handling higher watts and amps with both of these panels together? Or maybe I just don't understand how these are rated and how to determine what they're actually capable of.

What Bob brought up is a great point, however I think if the cost is going to be about the same, I would probably just go with the Outback. I have a generator I can also use to charge the batteries, and I plan on running a line from the alternator as another method, so I have backup systems already in place. But the question remains, is the 80amp Outback overkill? I dont mind spending a lot of money if thats what I need for this system, but I also dont want to end up wasting money on something thats way more than I'll ever actually need. 680 watts is the max I can get on my roof I'm sure, so I cant foresee myself ever having more solar than that, at least in this rig. I will most likely go with the Outback if its an appropriate choice, but I just want to see what the options are and figure out what I truly need before making a decision.

 

[John61CT]

That 440W is at nominal 24V, far lower than your (in theory) 40V max panels.

The key spec is short circuit current, max for that Victron 75/15 is 20A, the highest theoretical per panel is <9A, so you should be OK with two.

Note even better, you could get a separate controller for each panel, good for redundancy.

Then you could go down to the 75/10, at $80 each. This will also optimize handling any partial shade situations. Spec sheet for these panels don't mention any blocking diodes?


Might as well stick to the included connectors and their 10GA, more robust, less voltage loss.

 

[Trebor English]

The Isc, short circuit current, is rated at 8.86 amps.  Two of them in parallel can make only 18 amps.  12 gauge wire is good for 20 amps.  If you wire up the panels with 12 gauge wire they cannot produce enough amps to ignite 12 gauge wire.  A 20 amp fuse won't blow with only 18 amps.  There is no point in having a fuse at the panels.  You probably want 10 gauge or maybe 8 for less voltage drop.  

Similarly, the max charge controller output may be less than the wire capacity making a fuse at the charge controller pointless.  

The battery can feed those wires.  The wires need protection from the huge capacity of the battery.  At the battery you need a fuse to protect the wire from the controller to the battery from being ignited by the battery if the wire shorts.

The controller may be wired to do its magic on the minus side and have the panel plus and the battery plus wired together.  Mine is that way.  The wire from the panel to the controller then needs to be protected by a fuse from the huge current the battery can produce passed through the controller.  That fuse needs to be close to the controller.  It needs to protect the panel wire which is likely smaller than the controller to battery cable.

Breakers have more voltage drop than fuses.  Fuses are available with LED lights in them so they light up when blown.  Fuse boxes are available (even cheap ones) with LED lights.  

One more thing, the fuse between the controller and the battery cannot be allowed blow.  If it does you have the controller hooked up to panels with no battery connected.  That causes some controllers to fry themselves.  If that wire shorts you want the fuse to blow so you don't have a fire.  The solution here is to use a fat cable and a big fuse.  If there is any chance the controller can produce more current, like at the edge of a cloud, the fuse must be big enough to handle it.

 

[Weight]

If you have more than two panels in parallel you should fuse the panel feeds between panels and combiner box, before controller. Otherwise your wire should be heavy enough that a short would be meaningless.

 

[John61CT]

Why would the number of panels be the deciding factor? Six * 50W puts out less than one 340W?

I don't understand any reason to put CP between panels and controller, obviously the wire should be rated properly and PV is happy to be shorted.

 

[Weight]

If more than two panels, that is 3 or more, then a short in one panel could result in the combined current from the remaining panels feeding into the short. There could be more current than the wires can handle. At best, it will shut down the array and cause no charge to batteries. Most experts and solar panel manufactures recommend fuses for each parallel panel.