Hi guys!

I met the user of PIP 5048MG (high voltage MPPT model) and he's running this inverter without batteries, just on solar panels. That's okay, I know that some high-voltage Axpert models are able to power the loads even when they are running without a battery connected.

But really interesting is, that this user reported that his PIP 5048MG is able to mix Grid + Solar power. Very much like the PIP 5048MK (Axpert King) is able to do.

Till now, I was convinced that Axpert King is the only model capable of "Grid Assist", thanks to it's double conversion architecture.

Is the above really possible? If yes, then where will go the power spikes caused by a large load disconnection? Since Axpert is not hybrid, it can't push the spikes to the grid, so I would assume that without a connected battery, serving as a buffer, each spike is slowly killing some internal caps.

 

Can anybody shed some light on this, please?

3 hours ago, Youda said:

But really interesting is, that this user reported that his PIP 5048MG is able to mix Grid + Solar power. Very much like the PIP 5048MK (Axpert King) is able to do.

... Is the above really possible?

Huh, I've never thought about that, mainly because the unsafe SCC models aren't legal in Australia. But I think that this user is right:

It's not clear to me whether the above blending is still possible with a battery present (surely, even if present, it doesn't have to be used?).

Quote

If yes, then where will go the power spikes caused by a large load disconnection?

A great question. The only place for it is the bus capacitors, at least instantaneously.

The bus capacitors seem to be 2 x 470 μF, call it a millifarad, so that's 1 V per amp.millisecond, from (dV/dt) = I/C so ΔV = (I/C).Δt. If the bus battery protection task operates at 50 Hz (= 20 ms, as it does for other Axpert models), then with a surge of say 3 kW at 400 V, or 7.5 A, then the bus voltage could elevate by ΔV = 7.5 x 20 = 150 V. That would take the bus voltage from 400 V to 550 V, a bit much for comfort. A full 5 kW load coming off would be 12.5 A x 20 ms = 250 V, so 650 V. That could well be too much for the IGBTs.

Maybe there is some hardware on the bus voltage, that generates a high priority interrupt when the bus voltage reaches say 490 V (the bus capacitors are rated at 500 V).

Actually, thinking about this, all Axperts have the same problem. Say you are boiling a 3 kW jug from battery power. The instant that the jug power comes off, there is 7.5 A more than needed coming from the battery DC-DC converter. So this problem you bring up with the GEs (Axpert IIs) and GKs (Axpert Kings) is nothing more than what all Axperts have been dealing with for years. I wonder if that's what the so-called MPPTInterrupt() is all about (all Axperts seem to have this).

Inverter-charger firmware is non-trivial!

Edit: Sigh. The InvInterrupt() and MPPTInterrupt() both happen at 19.231 kHz (every 52 μs, 26 μs apart), and both check the bus voltage. So it's well monitored! Even a 5 kW surge would cause a ΔV of only 12.5 A x 0.026 ms = 0.325 V before the firmware checks it again. So there is plenty of time to react to the surge, and correct it well before there is a problem.

 

Edited May 23, 20197 yr by Coulomb

@Coulomb I love the math!

First timer here.  I'm glad this conversation just started as I'm in the middle or researching and debating on what model inverter (5kW) to purchase.  I don't need grid feed-in but I would very much like a grid assist feature to supplement the load.  If I could start off batteryless, that would be a big money saver to allow me to build up a system over time.  Short of a battery, I don't see how an inverter without grid assist would really work that well under varying load. 

Can anyone verify that the PIP-5048MG will supplement the solar load with grid power?   From all I've read, the PIP series are off-grid and will only do a hard transfer if supply is insufficient.  I've sent this question to MPPSolar, but additional verification would be nice as some  of the their responses I've seen are ambiguous.

Hi @WestTXSolarDude

the user that I've mentioned in my firt post gave me this spreadsheet that he pulled from his PIP 5048MG. Yellow is the solar power, green is the AC out power.
I've added the red column calculating the difference and it's clear that this 5048MG is mixing solar+grid on it's AC output:

The unit was running without any battery.

So, it's confirmed that PIP 5048MK and PIP 5048MG are able to supplement the loads with the grid power.

The only thing left to check is, whether 5048MG does unwanted feed-in or not. 🤨

On 2019/05/26 at 12:08 AM, Youda said:

The only thing left to check is, whether 5048MG does unwanted feed-in or not. 🤨

Hi Youda. Do you have any more info on whether the MG (or GE or GK) is doing its mixing of solar+grid to the AC output in line mode by (a) double-conversion, or (b) undeclared grid-tie?

It is clear that the MK is doing it by double conversion, thanks to Gnome's observation that the AC output voltage does not depend on the AC input voltage when this mixing occurs.

Hi Weber,

I can confirm that mixing solar+grid happens, but the user of PIP5048MG has no way how to check how it's technically done (as his meter does not show a possible grid feed-in). I suggested him to check the voltage between L-in + L-out, when running and mixing. If there's true 0V then it would indicate that terminals are interconnected -> hybrid.

Do you have a better idea?

@weber

so the guy thested the PIP5048MG behaviour and this is the result:

1) With 100W load, there's a voltage 0,27V between the L-in and L-out.

2) When the inverter is set to generate 240V output and is running from the batteries, then this voltage (240V) is being produced on the AC-out terminals. But once you connect the inverter to the Grid (running 230V), then the output voltage drops to 230V.

To me, the above indicates that there's probably a direct L-in to L-out connection rather then DC-DC conversion.

 

Hello,

Can someone who owns a PIP5048MG or MK inverter advice me on the following:   I would like to know if it is normal for the PIP 5048 MG inverter without BATTERIES to operate combined solar and grid and not have the Inverter display show both solar and grid are combining electricity at the same time. On my display the grid always shows the BY PASS mode ON while the solar is functioning. I am confused since in the PIP manual, the BY PASS mode disappears with both solar and the grid are combined . I e-mailed the company in Taiwan and they stated that the manual is wrong. I find this difficult to believe since they should have corrected this error by now.  Someone kindly let me know if they have a similar issue.

 

Thanks,, John