Electrical Advice

[KWKloeber]

. Fuses or breakers need to be as close to the power source as possible the panels. Charlie

I'm far from an expert at solar. Actually I know close to zero. But,
Why put a fuse close to the panels? The wiring is sized larger than the greatest amperage  they can produce.  So what fuse would you put there? And if it's larger than the panel output or equal to what the wire can carry, it will never blow. The panels,  like an alternator, is a current-limited device and can put out no more than you size the wiring for.

I don't know how controllers work, but if there's a chance it can backfeed to the panels, the fuse should go there, no?  And the cables at the batteries themselves need a fuse within 7 inches of the battery post.

Am I missing something?

kk

[J_Sail]

I was researching fuse options and looking at the Blue Sea Systems 285-Series Circuit Breakers.
Amongst other projects, I'm in the process of replacing the existing Alternator ... perhaps I should replace the battery fuses with the same series breakers.
Paul

Circuit Breakers are nice for a lot of applications, but would not be appropriate as a replacement for a main battery fuse. One issue is that the 285-series is available only up to 150 amps, a bit low for a battery that powers a starter motor. The other problem is that when a short-circuit occurs on a heavy cable near the battery, the instantaneous short circuit current can be so extreme (thousands of amps) that before the breaker's contacts can open, they weld together. The rating for the peak instantaneous current the breaker can reliably interrupt without failure is called its Ampere Interrupt Capacity (AIC) rating. The breaker you are considering has an AIC of 3,000 amps, which is too low for a multi-battery house bank. The BlueSea MRBF has an AIC of 10,000 amps. See link below for more info:
https://www.bluesea.com/support/articles/Circuit_Protection/98/DC_Circuit_Protection

Jeremy

[J_Sail]

Ken is correct that you do not need to put a fuse between the panels and the controller. The purpose of a fuse is to protect the wiring from overheating, and since the wiring to your solar panels can handle the full short-circuit current of the panel continuously without hazard, there is no need for a fuse.

The reason you need a fuse between the controller and the battery is that the battery can provide more current into a short than the wiring can safely handle. The energy source in that case is the battery, so the fuse goes as close as possible to the battery.

Jeremy

BTW, the controller prevents any backflow from the battery into the panels, but even if it did not, the fuse at the battery would protect.

[J_Sail]

Getting back to your original question of whether two separate MPPT controllers are better than one - I found a thread where MaineSail addressed this specific question:
https://forums.sailboatowners.com/index.php?threads/partial-shading-two-panels-two-controllers.158915/

[J_Sail]

From Victron:
"A single panel producing 17.2V on our MPPT will likely charge very little if at all. The MPPT requires battery voltage +5V from the solar to start charging. If you have bad weather or partial shading it likely will not work. My advice would be to connect them in series (17.2 x 2). This will be much better in terms of voltage production."

I don't know for certain, but I suspect that the Genasuns do not require the panels to output a voltage anywhere near 5 volts above battery voltage to turn-on or operate. I think it's a great question though, and one that Genasun should answer. There is also a chance that MaineSail might know.

I confirmed with Genasun's tech support that their GV-10 only requires that the PV input be at least 1.0v above battery voltage to begin charging, (though it may not provide full output until the PV voltage is 2.0v above battery voltage).  So, if it was my system, I would just go with a separate Genasun GV-10 per panel and not worry about shading, min voltage, etc.

Although Victron's iPhone app feature is cute, after a while you will probably stop using it.


*(updated voltage required by GV-10 on 5/15 due to follow-up email from their tech support)