VFXR3524A AC out

[provo]

A newbie question I should’ve resolved 16 years ago.

Outback put my system together with a VFX3524, which has since been upgraded to a VFXR3524A, but the situation is the same. OB used a bypass rocker (shown in their schematic below) with the bypass bkr and the normal bkr both 50A.

As it is now, the 50A bypass breaker would be fine running all the loads (or loads plus charging) up to 50AAC, but the normal breaker being 50A could draw much more than the 29AAC (25AAC?) that the inverter is able to supply. The obvious solution would be to drop the normal breaker to 25A.

I’ve never come close to exceeding the inverter’s output rating, but this is starting to bother me. It seems the inverter doesn’t protect itself from excessive loads. Do I have that right?

[raysun]

The circuit breakers are intended to protect the wiring, not the equipment. In the case of this equipment, the inverter has the wherewithal to protect itself. Should loads demand more than the inverter is rated for, it will shut down and raise an "AC Shorted" error.
If the AC Input and Output wiring is capable of safely carrying 50A, the circuit breakers should be OK.

[provo]

The circuit breakers are intended to protect the wiring, not the equipment. In the case of this equipment, the inverter has the wherewithal to protect itself. Should loads demand more than the inverter is rated for, it will shut down and raise an "AC Shorted" error.
If the AC Input and Output wiring is capable of safely carrying 50A, the circuit breakers should be OK.

That's good news, thanks!

There's another note that bothered me about the AC Input breaker, from the VFXR Owner's Manual: "The loads powered by the inverter must not exceed the size of the inverter’s transfer relay. CAUTION: Current draw in excess of the transfer relay rating can damage the transfer relay. This damage is not covered by warranty. Use protective devices of appropriate size."

I also don't want to fry the transfer relay -- is the 50A AC Input breaker a problem when the inverter is in pass-through mode? Does that need to be reduced to 30A? (Or even 25A, since 3500W/128VAC = 27A.)

[JRHill]

"The loads powered by the inverter must not exceed the size of the inverter’s transfer relay. CAUTION: Current draw in excess of the transfer relay rating can damage the transfer relay. This damage is not covered by warranty. Use protective devices of appropriate size."

Here's the way I take that: Its OB's CYA.

"I’ve never come close to exceeding the inverter’s output rating..." If your inverter is shutting down regularly or predictably you definitely need to resolve the source of the overload. I can't imagine the inverter's transfer relay frying under a 'once in a blue moon' occurrence. If it fries in one occurance its not a breaker - its a fancy fuse

"Outback put my system together..." You are saying they spec'ed the design?

Lastly, breakers, switches, etc of quality are going to have a margin of safety. As an example, if your load passes the breaker's rating there might be a slight delay before if opens the circuit. But the inverter should have already errored out and shut down unless it is in pass through or support mode. Frankly I would rather have the inverter shut itself down rather than having a breaker open under an overload.

[raysun]

If the wiring is 6ga, think you're OK.

[provo]

"Outback put my system together..." You are saying they spec'ed the design?

I told them what batteries I was planning to use, what CC (MX60), and what inverter (VFX3524). They put it together (PSAC and PSDC boxes) plus the other components (I had to mount my Trimetric 2020). This was when they shipped a fully assembled and wired massive dark green metal panel -- I just mounted it on the wall and hooked up the batteries and the house subpanel.

Then the Support team and the User Forum fielded my questions for many months...

[provo]

If the wiring is 6ga, think you're OK.

I believe it is, but I'll check today. Thanks for the responses.

[provo]

Here's the way I take that: Its OB's CYA.

Frankly I would rather have the inverter shut itself down rather than having a breaker open under an overload.

Thanks for the assurances -- just checking that it WILL shut itself down before getting damaged

[raysun]

Here's the way I take that: Its OB's CYA.

Frankly I would rather have the inverter shut itself down rather than having a breaker open under an overload.

Thanks for the assurances -- just checking that it WILL shut itself down before getting damaged

I had two instances of "AC Shorted" shutdowns with my older single FX3048T setup, both caused by Microwave/Toaster Oven/Blow Drier simultaneous operation. The disconnects (AC IN and AC OUT) were 30A, IIRC, and the AC OUT didn't trip.

In both cases, the inverter protected itself from overload by shutting down. While I have no desire to test it regularly, I have confidence in the shutdown function.

[raysun]

It's weird. This post does not show up in "Active Topics" for me.
Anyone else seeing that?

[JRHill]

"...which has since been upgraded to a VFXR3524A"

I'm curious: why didn't you go to 48v at that time, other than additional battery expense. Maybe you don't need it?

[JRHill]

It's weird. This post does not show up in "Active Topics" for me.
Anyone else seeing that?

It's because I chimed in.

[provo]

I'm curious: why didn't you go to 48v at that time, other than additional battery expense. Maybe you don't need it?

I actually don't need it, plus it was just a simple swapping out of the MX60 for an FM80, and one inverter with another of the same parameters. Going to 48V would have been more work for not much reward, and even more so once I got hooked into the utility.

I practice the KISS thing like a religion .