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Pieter Khaki

Axpert inverter not peaking up the generator

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Good day. I got a 5kva Axpert inverter with 3 x Pylontech us2000 plus lithuim battery. I want to connect the generator to the inverter but it dont pick up the generator.

My generator is a Hoffmann petrol generator 6kva en show on the generator total frequency 50hz

What can i do that the generator charhe the batteries? 

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16 hours ago, Pieter Khaki said:

What can i do that the generator charges the batteries? 

It's a common problem. You can try setting 03 = APL, though that's the default. Otherwise, you can try putting a moderate load (~200 W or more, preferably a resistive load like a sandwich maker) on the generator before connecting the AC-in to the generator. Petrol generators without inbuilt inverters don't run all that well on zero load, and the Axpert will be checking the generator output quality at zero load, and rejecting it if the voltage, frequency or other characteristics aren't good enough. Adding the moderate load settles the generator somewhat, and it may be enough to pass the Axpert's test. Once the Axpert starts using generator power, that will settle it down as well, and you can switch off that moderate load.

It won't work with every generator, but I've seen it work with a couple, so it's worth a try. Otherwise, you'll need a generator with an inverter built-in. Voltronic Power recommends a generator with a rating of at least 150% of the expected load; some generators don't work all that well at very high loads, either.

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I've seen that it's the sudden change in the frequency/voltage that the inverter doesn't like (unless the parameters are very bad), some generators I've worked with have been terrible on frequency and voltage but they've been so big that when loaded they don't change frequency and voltage and the inverter is happy. Most small generators react too slowly when suddenly loaded and so what happens is that the inverter tries to connect, the parameters change, the inverter doesn't like it and kicks it out again and the cycle continues. What I've done in installations is connect a bypass switch (changeover switch) that allows the load to be connected to the generator and not through the inverter. The inverter supply is still connected to the generator output so that the generator is loaded and the inverter can still charge the batteries but not supply the load. This reduces the sudden application of a heavy load (i.e. load + inverter charging) and if it's only the inverter charging that switches in it tends not to change the generator parameters as badly and the system will settle and the inverter will charge. The lower your AC charge current the better this works, the maximum I put it on is 10 A. It's not perfect but works most of the time.

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On 2020/03/07 at 10:34 AM, Coulomb said:

It's a common problem. You can try setting 03 = APL, though that's the default. Otherwise, you can try putting a moderate load (~200 W or more, preferably a resistive load like a sandwich maker) on the generator before connecting the AC-in to the generator. Petrol generators without inbuilt inverters don't run all that well on zero load, and the Axpert will be checking the generator output quality at zero load, and rejecting it if the voltage, frequency or other characteristics aren't good enough. Adding the moderate load settles the generator somewhat, and it may be enough to pass the Axpert's test. Once the Axpert starts using generator power, that will settle it down as well, and you can switch off that moderate load.

It won't work with every generator, but I've seen it work with a couple, so it's worth a try. Otherwise, you'll need a generator with an inverter built-in. Voltronic Power recommends a generator with a rating of at least 150% of the expected load; some generators don't work all that well at very high loads, either.

Do you know what the experience is like with the Axpert King?

Since it is double conversion, it could conceivable handle a much wider input range.  I'm just wondering if it'll keep running from the generator or ignore it.

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8 minutes ago, Gnome said:

Do you know what the experience is like with the Axpert King?

No.

8 minutes ago, Gnome said:

Since it is double conversion, it could conceivable handle a much wider input range.

That's certainly possible. There are clues in the firmware that suggest that the AC to DC converter is a "PFC stage" (Power Factor Correcting). That possibly means that a fairly simple chip has to follow the voltage envelope that attempt to make the instantaneous current follow that envelope, while still averaging (with rectification of course) a target current. Such a simple chip might not even have the ability to tell the DSP "help, I can't cope with this messy waveform, make it stop!". The key thing is that nothing has to synchronise with the AC input. If the PFC can't follow the voltage well, the power factor is lower than desirable, but no big deal. If a system has to synchronise with the AC-in and fails, quite serious erroneous power flow can result.

So my guess is: yes, I agree, it may be able to cope with cheap generators much better than other Axperts. On a quick search, I don't see any particular generator requirements for Kings, although the MPPSolar site has the same generator requirement PDF as other models (that may be a cope and paste error on the web pages, though).

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Posted (edited)
6 minutes ago, Coulomb said:

No.

That's certainly possible. There are clues in the firmware that suggest that the AC to DC converter is a "PFC stage" (Power Factor Correcting). That possibly means that a fairly simple chip has to follow the voltage envelope that attempt to make the instantaneous current follow that envelope, while still averaging (with rectification of course) a target current. Such a simple chip might not even have the ability to tell the DSP "help, I can't cope with this messy waveform, make it stop!". The key thing is that nothing has to synchronise with the AC input. If the PFC can't follow the voltage well, the power factor is lower than desirable, but no big deal. If a system has to synchronise with the AC-in and fails, quite serious erroneous power flow can result.

So my guess is: yes, I agree, it may be able to cope with cheap generators much better than other Axperts. On a quick search, I don't see any particular generator requirements for Kings, although the MPPSolar site has the same generator requirement PDF as other models (that may be a cope and paste error on the web pages, though).

Interesting.

I've also noted that although the voltage output of the King is rock solid at 230v (for me) the frequency does follow the AC input.  So my utility is often sitting at 60.1 <-> 59.8 and the output follows the frequency.  The wave form is a perfect sine wave, unlike the utility sine wave which does have some minor THD.

As such there may be some truth to the concern of, how will it deal with crazy frequency shifts.

Curiously if you were able to turn off that PFC and frequency following feature, you'd likely have an inverter that can deal with pretty bad input (all the way up to straight DC power).

Of course the frequency following is very important in the sense that your eco mode & standby switch over can become incredible dangerous without it.  So you'd be in serious trouble if you didn't just turn those off.

Edited by Gnome

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2 minutes ago, Gnome said:

Of course the frequency following is very important in the sense that your eco mode & standby switch over can become incredible dangerous without it.

I did forget about bypass mode, and the desirability of switching between two sources (inverter output and AC-in) that are in sync and roughly similar in voltage. I don't agree with the "incredibly dangerous" part, I'd say more "highly desirable". Given this need for synchronisation, probably the same generator quality restrictions apply.

5 minutes ago, Gnome said:

if you were able to turn off that PFC and frequency following feature,

I think you still want the PFC feature, otherwise the peak currents can get insane. But maybe turning off setting "bypass function" to "forbidden" (setting 23 to ByF) signals to the DSP that you don't care about synchronising to AC-in. Perhaps you could try this for a while, and see if the input and output frequencies differ. This setting has different options and terminology than the equivalent setting on other models (still setting 23, but called "overload bypass" on non-King models).

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Posted (edited)
6 minutes ago, Coulomb said:

I did forget about bypass mode, and the desirability of switching between two sources (inverter output and AC-in) that are in sync and roughly similar in voltage. I don't agree with the "incredibly dangerous" part, I'd say more "highly desirable". Given this need for synchronisation, probably the same generator quality restrictions apply.

Well, correct me if I'm wrong, isn't the switching speed less than a cycle?

If you switch at peak on one cycle then hit peak on the other source because the cycle isn't synchronized, your RMS voltage will be crazy high.

6 minutes ago, Coulomb said:

But maybe turning off setting "bypass function" to "forbidden" (setting 23 to ByF) signals to the DSP that you don't care about synchronising to AC-in. Perhaps you could try this for a while, and see if the input and output frequencies differ. This setting has different options and terminology than the equivalent setting on other models (still setting 23, but called "overload bypass" on non-King models).

Ok I'll do that. Won't take very long to confirm because frankly our power is rarely at exactly 50Hz.

6 minutes ago, Coulomb said:

I think you still want the PFC feature, otherwise the peak currents can get insane

Curiously the Axpert King manual recommends a minimum of 6mm wire for AC input... 

Edited by Gnome

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1 minute ago, Gnome said:

If you switch at peak on one cycle then hit back on the other source, your RMS voltage will be crazy high.

I suppose if you switched from one source at 30° past peak, and switched really quickly to the other source at 30° before peak, you might get a small RMS surge. But switching takes of the order of 10 ms, which is half a cycle, so the above scenario isn't realistic. I'm hazy how the whole synchronisation and relay switching thing happens. I've not been able to make much sense of reading the firmware in this area either.

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