Fuse/breaker sizes?

[SomebodyInGNV]

Hello. I'm connecting 4 Newpowa 180W panels(1) in a 2S2P array to an EPEver Triron 4210N MPPT solar charge controller(2). The panels will be mounted flat on an RV roof and frequently shaded by trees. Initially, I will not have an inverter and my battery bank will be the pair of 215A 6V GC2 Duracells I already own. They're in good shape. I'll upgrade to LiFePO4 later and add an inverter at that time.

1. Voc 19.84V, Isc 11.75A​

2. Max Voc 100V, rated PV current 40A, rated PV input power 520W/12V, max PV input power 1560W/12V​

I want a switch between the PVPs and the SCC. Should I use a breaker? I'll have a total of 720W which may result in occasional clipping but won't exceed the max PV power, so a breaker doesn't seem necessary, correct? If a breaker is advisable, can I use an auto-reset breaker so it resets itself when the current drops? I'd use a separate switch as well, in that case.

I also want a switch between the SCC and the battery. Is there any reason for that to be a breaker or fuse? I already have a Blue Sea Systems switch which I can repurpose.

If relevant, the converter charger is the OEM WFCO 8955.

 

[snoobler]

I would use a 15A breaker or whatever size the panel sticker recommends. MidNite Solar sells 150VDC breakers intended for this reason for about $15.

I too use a breaker between SCC and battery.

 

[Hedges]

Isc 11.75A
Fuse not mentioned on data sheet. How about on the label? I hope their spec is at least 20A fuse not 15, because 15A might blow on a day with extra illumination.

I'm thinking either two, 20A breakers (one per string)
or, make your 2S2P connection without fuses or breakers and have a single switch or breaker good for 35 or 40A. Not as protection, just as a switch.

Orient your two strings differently, one for morning and the other for afternoon sun, and you won't have any clipping.

Find what optimum/maximum charge rate is. 2500 Wh battery may want 250W max charge, and even with the two PV strings oriented 90 degrees apart you'll still hit double that in the middle of the day, if SoC is low enough to accept the current.

Unless the charge controller can be programmed for 20A limit, you may get longer battery life with either 2x the battery or 1/2 the PV.

Batteries can probably deliver 4000A into a short, so a fuse with interrupt rating at least that high (and suitable amperage rating for greater of your loads and your 40A SCC) should be used. ANL fuse rated 2700A is marginal but might do some good, considering just 12V.

 

[Zil]

A fuse is not needed between the panel and charge controller. A switch is recommended. Breakers suck for dc circuits.

 

[SomebodyInGNV]

Thanks all for your assistance.

The label makes no reference to fuses. Isc is 11.75A. Being in a 2S2P arrangement, it can't exceed 23.5A, correct? As the SCC is rated for 40A, I won't be anywhere near it. Should I add more in parallel in the future, I'll reconsider then.

 

[Hedges]

A panel can exceed its Isc rating, because it can have full sun plus additional light off nearby clouds. I've measured 15% over.
Of course your SCC will operate closer to Imp than Imp, since it will never pull PV+ to zero.

If you put in a switch (or breaker) rated for 40A DC and the max open circuit voltage of the SCC, that will support current and future configurations (e.g. you might use fuses per string if you add more in parallel.)