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PV array breaker/switch size?

SomebodyInGNV

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Jun 3, 2020
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I'm configuring my Newpowa 180W 12V panels in a 2S2P array for a max 720W of output, connected to an EPEver Triron 4210N SCC.
Panel specs: Vmp 16.77, Imp 11.20, Voc 19.84 and Isc 11.75.​
SCC limits: max Voc 100V, max Isc 40A and max PV array power 1560W @ 12V.​
The SCC manual states that it can handle up to 3x rated charge power (520W) after which damage will ensue.​

The panels will be mounted flat on the roof of my travel trailer and we prefer shaded camp sites. In the interest of mitigating fall risk I plan not to climb on the roof routinely and will not use tilt mounts. The result will be that (I think) I'll usually be under max power, which is why I'm over-paneling.

I'm taking advantage of Black Friday to buy the last small parts for my solar system. One of those parts will be a switch or breaker for the solar panels. Do I even need circuit protection? I think not, but I want at least a switch for convenience. What do you suggest I use for that circuit?
 
How are you combining the strings in parallel? Technically, you do not need a breaker for only 2 strings, but you do need a disconnect. You can use a breaker near the charge controller as both over current protection and a disconnect. 11.75A x 2x 1.56 = 36A, round up to 40A.
 
How about only mounting 2 panels on the roof, and having the other two stowed somewhere, set up with wheels and and easel stand so you could roll out to where there is sunlight? They can still be paralleled with the other two even if those are shaded.
Otherwise, you only get charging while driving in the sun, not while parked in the shade.
 
How are you combining the strings in parallel?
By that, do you mean the physical connection? I'm using a roof gland that I salvaged from the factory-installed solar option. Their intended location was bad and the wiring was inadequate, so I'm repurposing all of it. That roof gland includes MC4 connectors and a 1' stub of 10AWG cable. I'll splice 8AWG to the end for the route to the SCC, using appropriate 10AWG-8AWG reducer crimp connectors.
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As the roof gland already has the MC4 connectors and the panels are prewired with MC4 connectors, I plan to use a pair of MC4 branch connectors between the panels and the roof gland. Whether that will incorporate short extension cables or will be as pictured above, I don't know, because I didn't buy it yet. I know MC4 fuse holders exist but I don't want to deal with a fuse on the roof and don't think a fuse is warranted, anyway.
 
How about only mounting 2 panels on the roof, and having the other two stowed somewhere, set up with wheels and and easel stand so you could roll out to where there is sunlight? They can still be paralleled with the other two even if those are shaded.
Otherwise, you only get charging while driving in the sun, not while parked in the shade.
I won't always be parked in the shade and don't want to deal with portable panels, either storing them or moving them. The panels I already own are way too large to consider that. Most of my camping will be connected to shore power and, in the worst case, I'll have a Honda eu2000i inverter generator with me. I'd rather not use it, though.
 
I know MC4 fuse holders exist but I don't want to deal with a fuse on the roof and don't think a fuse is warranted, anyway.
Correct, not needed for paralleling two strings.

Supposed to be used for more than 2 strings, but I wouldn't worry even with 3. With 4 strings I would want 4 fuses because current from 3 strings into a shorted one would exceed the current it could handle.
 
Where does the 1.56 factor come from? I know there's an allowance for overage but, being 2 decimals, that seems pretty specific?
1 1/4 x 1 1/4 = 1.56

We like to make a breaker 25% oversize to avoid nuisance trips.
Now assume a PV panel can deliver 25% more than Isc because it gets direct sun plus extra reflected/glowing from nearby clouds.
 
1 1/4 x 1 1/4 = 1.56

We like to make a breaker 25% oversize to avoid nuisance trips.
Now assume a PV panel can deliver 25% more than Isc because it gets direct sun plus extra reflected/glowing from nearby clouds.
Thanks for the explanation.
 
I have a disconnect from the panels, outside, for the firemen.
I have a DC breaker by my inverters, so I can turn the panels off whenever I want/need to. So far I have had to "reboot" my inverters twice. They won't reboot themselves if any form of AC or DC input is present. I turn everything off, wait for the capacitors to empty (about 2 minutes sometimes) then turn everything back on.


Saving pennies on breakers is about the last thing you should ever consider. I use these:
 
More breaker/fuse questions. Please critique my plans.

In addition to the 180W panels and 40A SCC described above, I'll have:

2 12V 100A SOK LFP batteries in parallel. They're individually rated for 100A continuous discharge.
A Renogy 2000W PSW inverter. Loads will be modest except occasional use of a microwave oven.
A 6-way fuse block for small accessory items I may add. It supports 30A per circuit and 100A per panel. The likelihood of their being a total load > 30A at any one time is remote. Most of the time it will be 0-5A. (LED lights, USB charger.)

My plans for fuses and breakers:

Location​
Fuse/Breaker​
Between 2S2P panels and SCC40A breaker
Between SCC and batteries50A breaker
Between positive bus and fuse block120A breaker (wire sized accordingly, despite low expected use)
Between battery and positive bus/inverter300A ANL fuse followed by a switch rated for 300A
 
I was going to suggest a charge controller capable of more current, but I see 20A recommended per battery, so 40A is good.
Then I was going to suggest their 200 Ah battery, but I see it has same 100A discharge limit as the 100 Ah.

120A breaker - that's for everything except inverter? Fuse block is rated 100A, maybe technically it should be fused at 100A. Of course it has its own individual fuses, probably doesn't need a fuse on input. But I guess it would help if someone stuck in 6, 20A or 30A fuses.

300A ANL fuse and a switch for inverter - consider also Midnight 250A breaker.
It appears BMS would shut off before these trip

2000W inverter, 12V, 90% efficient. That would draw 185A.

Trying to shoot holes in the plan, but didn't find anything.
 
I was going to suggest a charge controller capable of more current, but I see 20A recommended per battery, so 40A is good.
I aquired the 40A SCC and several accessories used at a very good price. It meets my needs.
Then I was going to suggest their 200 Ah battery, but I see it has same 100A discharge limit as the 100 Ah.
Yes, 1 200A battery has a discharge rate of only 100A but 2 100A in parallel can sustain the discharge rate required by the inverter.
120A breaker - that's for everything except inverter? Fuse block is rated 100A, maybe technically it should be fused at 100A. Of course it has its own individual fuses, probably doesn't need a fuse on input. But I guess it would help if someone stuck in 6, 20A or 30A fuses.
Actually, I ordered a 100A. It will protect the wire to the block should a short occur somehow. The actual load will be far less.
300A ANL fuse and a switch for inverter - consider also Midnight 250A breaker.
It appears BMS would shut off before these trip

2000W inverter, 12V, 90% efficient. That would draw 185A.
According to the respective vendors, the inverter can tolerate a surge of 4000W (no duration given) and the battery can tolerate 370A for 10-15 seconds. Unless a 1000W microwave oven has high starting surges, I'm not going to put loads like that on it. Hence, 300A.

The reason I chose a 2KW inverter is to safely use a 15A single-circuit automatic transfer switch. In addition to the M/W oven, it supplies other 110V convenience outlets like a small TV and a wall fan. We'll use those sparingly.

EDIT: my wife hopes to use our small Keurig coffee maker but we'll see how that goes. We do have a Melitta pour-over coffee pot and a propane stove.
Trying to shoot holes in the plan, but didn't find anything.
Thanks for your help.
 
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my wife hopes to use our small Keurig coffee maker but we'll see how that goes.
I bought the only Keurig Cofee maker under 1000 watts I could find, the Keurig K130, which is 700 watts.

This is a commercial K-Kup rated for continuous use you might find in a hotel. It uses 700 watts. I have not ran it on my trailer yet, but will in a couple of weeks. But I expect it to pull 70 amps on my 12 volt system for a couple of minutes as it heats the water. Total brewing time from room temp is two and a half minutes and one and a half to two minutes of that is heating.

This coffee maker does not have all the options of a 1000 watt or 1500 watt model. It’s missing the reservoir that keeps water pre-heated. Also can not insert the reusable K-Cups. Also only makes 2/3 rds a cup of coffee, since the heating element only holds about that much coffee.

We’regoing to keep this one in the trailer, and get a regular sized one for our house.
 
I bought the only Keurig Cofee maker under 1000 watts I could find, the Keurig K130, which is 700 watts.

This is a commercial K-Kup rated for continuous use you might find in a hotel. It uses 700 watts. I have not ran it on my trailer yet, but will in a couple of weeks. But I expect it to pull 70 amps on my 12 volt system for a couple of minutes as it heats the water. Total brewing time from room temp is two and a half minutes and one and a half to two minutes of that is heating.

This coffee maker does not have all the options of a 1000 watt or 1500 watt model. It’s missing the reservoir that keeps water pre-heated. Also can not insert the reusable K-Cups. Also only makes 2/3 rds a cup of coffee, since the heating element only holds about that much coffee.

We’regoing to keep this one in the trailer, and get a regular sized one for our house.
Ours is a compact medium-size model from Walmart, with a 3-cup reservoir. I haven't looked at the label to determine the wattage. We'll turn it off when not actively making coffee.

We use it only camping as we regard K-cups to be over-priced for the amount we consume at home. We're not picky coffee drinkers. The Keurig is for convenience but we do buy nice coffee for it.
 
Your 2000W inverter and 300A ANL fuse (or the 250A breaker I suggested) will be fine for any appliance plugged into a 15A outlet other than some large motors.
The two batteries and their BMS will deliver less than 200A, 100A each (so long as perfectly balanced wiring).

A "1000W" microwave may draw 1500W to 1800W of AC to deliver 1000W of microwaves.
A coffee maker also will draw no more than 15A, 1800W.

So long as you balance wires to batteries, everything should be fine.
That means the batteries get paralleled with wires, and the busbar/loads and charge controller connect to positive of one battery, negative of other. Not both to the same battery because then other battery sees more resistance, carries less than half the current.
 
... So long as you balance wires to batteries, everything should be fine.
That means the batteries get paralleled with wires, and the busbar/loads and charge controller connect to positive of one battery, negative of other. Not both to the same battery because then other battery sees more resistance, carries less than half the current.
That is my plan. My battery disconnect is actually a Bluesea make/break dual-battery switch. I could wire the positives poles to it symmetrically and use one or the other or both, but really have no reason to. I'll just use one positive conductor on one pole of the switch. The negative conductor will come off the other battery.

EDIT: the above setup will be on a plywood panel for use in a travel trailer. I don't think I can use the Midnight breaker in that scenario.

I may use Durock between the inverter and plywood for fire prevention reasons.
 
... My battery disconnect is actually a Bluesea make/break dual-battery switch. I could wire the positives poles to it symmetrically and use one or the other or both, but really have no reason to. I'll just use one positive conductor on one pole of the switch. The negative conductor will come off the other battery.
Hmm... brainstorm. I don't have a reason to split the batteries to use only one at a time, but I do need separate disconnects between the battery and SCC, and between the battery and 12V charger in the trailer's power center. Maybe I can reverse the use of the switch so the top pole is to the battery positive, with the SCC on one "battery" pole and the converter/charger on the other?
 
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