Temp replacement if FM80 with MX60 - Breaker size

Re: Temp replacement if FM80 with MX60 - Breaker size

Not that I can see...

First, you do not have to disable part of your array... Virtually all (that I know of) MPPT charge controllers will safely limit their output current to rated maximum... No danger or damage.

Second, if I recall correctly, you can program the old MX 60's to a maximum of 72 amps output current.

Third, the wiring is already "sized" for the 80 amp controller--and breakers are there (for the most part) to protect the wiring.

I would not worry at all.

-Bill

Re: Temp replacement if FM80 with MX60 - Breaker size

Technically, there should be a maximum breaker rating for the device too (in the manual)... Obviously, a 1,000-10,000 amp capable battery bank on the output of 60 amp solar charge controller has never been evaluated/tested for failure modes when connected to a huge current source (those types of currents can cause internal wiring to break loose and burn a hole through the case--start a fire, etc.)...

But the difference between a 72 amp output and the 80 amp output is not worth worrying about.

One obscure point... The NEC and various US agencies use a 1.25 safety factor for wiring/fuses vs loads... So, for a circuit designed to carry 80 amps continuously will have wiring/fuses rated for:

• 80 amps * 1.25 = 100 Amp fuse/breaker/wiring rating

A 100 amp breaker carrying 80 amps should never trip. An 80 amp breaker carrying 80 amps can eventually trip (in minutes/hours/etc.).

Outback, as I understand, does their rating differently... The 80 amp rated output FM 80 uses an Outback 80 Amp Rated breaker. However, their rating is for 100% continuous rated load (not the same rating method as the NEC usually uses) (this is my limited understanding--contact NAWS or Outback directly if you have any questions).

-Bill