DC fuse caught fire! Help ?

[EliteSolar]

I don't know, but I have an assumption about this that it definitely won't back feed and here it goes:
Let's assume the AC IN has just two ways to go into the system: Through the bypass relay and through the battery charger (which is actually just an AC/DC converter to a DC rail plus the battery charger which feeds from this rail).

Now there are three cases for running without a battery:

1. load is below what PV can provide
2. load is above that but below AIO power rating and
3. load is above AIO inverter power rating (in your case the 3.6kW).

This would have the AIO do the following:

1. If load is below what PV can provide, the inverter runs on PV only - that's the easy part.
2. If load is above PV but below AIO inverter power rating, the AC IN provides the power difference needed via the AC/DC converter in addition to the PV power - not the most efficient way, but it would work.
3. If load is above the AIO inverter power rating (or PV is off), the system switches to Bypass mode.

Now for the question how to test this:
IMHO the only way to test my hypothesis is to run your system with a load above PV power but within AIO inverter power rating (case 2). Using a power meter in front of the AIO should give you a slightly higher power draw as if you'd connect the load directly to grid AC (as the AC/DC converter loss will be missing).
I guess, a hair dryer running as load on a partly cloudy day will do ...

Now this is a wild speculation, but could answer your question. If there is no difference in power draw, the AC IN would directly feed the AC OUT instead of running AC->DC->AC. And then there might be a chance, the system potentially could back feed ...

That's correct.

I mean that's how I understand the system to work.

When it mixes/blends ( power below the 3.6KW ), the AC IN feeds on the AC->DC-AC ( because in this mode, without battery, it shows it NOT to be in bypass mode in the manual ). (With battery it shows in bypass mode, someone explain this has to do with the ac charger. Even more confusing. )

( so running PV with batteries it would be in AC bypass mode to mix/blend power , running without batteries wouldn't ) ?

So in my setup , without batteries , up to 3.6kw , when blending power, my inverter theoritically doesn't go into bypass mode. Only when it exceeds that it will completely switch to BYPASS mode.

When in bypass mode, AC IN directly goes to the AC OUT, according to a guy that opened and examined an MPP Solar unit similar to mine, like this :

" when the AC bypass mode is enabled, the AC input and AC outputs lines are bridged together via relay switches, the inverter feeds the energy created from the solar panels on to the bridged AC input/output lines by raising the AC voltage via internal semiconductor power switches (IGBTs), in the same way that a normal grid-tied feed-in tariff inverter does. The only difference is that this inverter can never feed energy back into the grid. This must be limited in the software, even though in hardware it is possible to do. "

This is so confusing

Sure there are. But I was thinking more about instantaneous power flow or very small amounts of energy. Very small amount of net kW-Hours more like kW-seconds.

Do some meters use their data over power line or wireless signaling to inform the utility of some certain level of sell-back ?

boB

My meter is a new smart digital meter and according to a post by "robby" in the forum , it could "let the power company know that something is going on and they will send someone to investigate. If your not legally grid tied they may cut your power on the spot until you get the Inspection work done."

 

[SpongeboB Sinewave]

My meter is a new smart digital meter and according to a post by "robby" in the forum , it could "let the power company know that something is going on and they will send someone to investigate. If your not legally grid tied they may cut your power on the spot until you get the Inspection work done."

My question is, how much energy, real watt-seconds or watt-hours, does it take for that to happen ? Or how many multiples of how many watt-hours does it take to alert and how does it alert the utility ? Wireless radio ? Power line communications ?

And some meters will just not spin backwards but will increase your bill if you sell back energy to the grid. THAT I could handle without a complaint if no net metering agreement with the utility. That might be the situation you have if not the alert.

boB

 

[EliteSolar]

Good questions , I guess it depends on the meters used by the electric companies and how they were implemented and the rules of the electric company. I can check my meter model online and see if I find any data on that.

But my question really is how I make sure it never backfeeds, not if and how much it takes to alert the electric company, although these are good questions too.

 

[SpongeboB Sinewave]

Good questions , I guess it depends on the meters used by the electric companies and how they were implemented and the rules of the electric company. I can check my meter model online and see if I find any data on that.

But my question really is how I make sure it never backfeeds, not if and how much it takes to alert the electric company, although these are good questions too.

I think you just have to trust it or make sure the external CTs going into the utility power panel coming into the house are set up correctly with the inverter. Or make sure the inverter is operating properly.

But passing through to loads without grid-support happening won't sell back through its input unless the charger has a problem at low power levels.

There could be external hardware to make power unidirectional but I don't think that anyone makes it.

So, you can detect backfeeding but I think the only thing you can do about it is to have the inverter disconnect before it does it any more. Even a relay can take a couple of milliseconds to turn off.

But then again, I am not familiar with your particular inverter so that might all be fake news !
boB

 

[KaFun]

So in my setup , without batteries , up to 3.6kw , when blending power, my inverter theoritically doesn't go into bypass mode. Only when it exceeds that it will completely switch to BYPASS mode.

Have you tried to do that? As you wrote "theoretically" I assume, you did not try this yet. But this test could set your mind at rest! The way I understand this system is that there is no connection between AC IN and AC OUT except in "Bypass Mode". Only then the relay switches the AC OUT connector from internal inverter output to AC IN.
I expect the manual is somewhat misleading in their picture drawings. I assume, they skipped the relay drawing altogether for clarity.

Now if I'm right and you test this with your system, you will hear the relay clicking when exceeding the 3.6kW power limit of your internal inverter. This is independent from you having extensive PV power or just a little sun on your modules. Because the system will try to add DC power (converted from AC IN via the battery charge circuitry) as this is much easier to add (AKA to blend PV with grid power) than on the AC side (which would require a phase control of your inverter AKA a grid tied inverter).

And if I'm right, then there is no way that your inverter can back feed anything into the grid as under no circumstances will your inverter output be connected to AC IN. The relay will select one of the two AC sources: either the internal inverter (when feeding from PV or PV plus grid but below 3.6kW) or from AC IN (if your load requires more power than 3.6kW or there is no PV power at all).

 

[SniperX]

So I posted a question on a Do-It-Yourself forum…

I am sorry because this is a serious discussion/older thread, but I got a good laugh at this. Thanks!