I've been using my Axpert King 5kW for just over a year without any problems. Yesterday my PV Power started to drop to 0W from time to time. The maximum PV power I get at the moment is about 2700W out of 2380W installed. I didn't change anything in my setup recently. Does anybody know what the cause can be or where I can look for the problem

41 minutes ago, ErickvWyngaard said:

I've been using my Axpert King 5kW for just over a year without any problems. Yesterday my PV Power started to drop to 0W from time to time. The maximum PV power I get at the moment is about 2700W out of 2380W installed. I didn't change anything in my setup recently. Does anybody know what the cause can be or where I can look for the problem

What is the power of the panels and in what configuration are they wired ?

Hi

I think if your pv voltage drops below 60v (MPP Range @ Operating Voltage   60-115VDC ) according to specs you will produce no power if it is overcast.

Edited April 11, 20215 yr by Peter Topp

On 2021/03/30 at 3:15 AM, Coulomb said:

A fridge has a high start-up load compared to its running load, perhaps a little over one kVA for a second or so. That might bother an 800 W inverter if it has other loads on, but will not be any sort of problem for a 5 kW inverter with a decent battery.

Low frequency (50 Hz) designs can tolerate an overload for much longer, of the order of 10-30 minutes (compared with 5 seconds for an Axpert). Their power limitation is generally the temperature of their transformer, which is very large and heavy, and able to absorb a lot of heat for tens of minutes. An Axpert's limit is the temperature of the semiconductors, which are attached to heat-sinks that are only designed for rated load. There is no heavy (tens of kilos) transformer to absorb heat.

Agree with  Coulomb's comment regarding starting current. I have noted startup for our fridge peak at times to 3 KW ! I know it is that appliance as I hear it start up ! Of interest but perhaps for a separate topic - what causes the high initial surge ? I have read that the cause for the high startup current albeit for a very short time is the compressor motor starter capacitor. I suppose it could also be attributable to the initial friction or inertia  of the compressor's pump components ?

If it IS the capacitor then I guess a soft starter would not be of much use to reduce the current as this may prevent the compressor motor starting and this may not be good as it could lead to the motor overheating !

Further to Coulomb's comment about "heavy iron" low frequency transformers, I have a spare unit which is of considerable weight due to the large transformer inside. Yes they can tolerate over-current situations because of the transformer but I have noted that the low-frequency inverters are much more inefficient than the high frequency ones and I would attribute this to the losses (ie heat !) in the large transformer windings and core.  The datasheet claims .>=85% efficiency. 

2 hours ago, Peter Topp said:

Hi

I think if your pv voltage drops below 60v (MPP Range @ Operating Voltage   60-115VDC ) according to specs you will produce no power if it is overcast.

Hi,

There was no sign of clouds. The voltage was about 70V when it happened

Hi ErickvWyngaard

I would like to know what the pv configuration is as GreenMan asked. The graph shown shows a definite problem if there was no clouds. If there are parallel strings I would firstly try to see if any one  of the stings are faulty by removing each string one by one and seeing if you can get the graph to read correctly. Not for max wattage output but to try to eliminate any faulty string by getting an even graph. If you find a faulty string then you can go and check each pv panel of the faulty string. You should also check the surge arrestors if fitted.

Edited April 11, 20215 yr by Peter Topp

Hi ErickvWyngaard

If you are to follow my suggestions please be careful as the pv circuit can be dangerous if not handled properly.(electric shock and arching).

9 hours ago, GreenMan said:

I have noted startup for our fridge peak at times to 3 KW ! I know it is that appliance as I hear it start up ! Of interest but perhaps for a separate topic - what causes the high initial surge ? I have read that the cause for the high startup current albeit for a very short time is the compressor motor starter capacitor.

No, the capacitor adds very little current, and since it's running on AC, the current drawn is continuous; I believe that there is very little surge at start-up that is solely due to the capacitor. [ Edit: the starting capacitor is usually only a few microfarads, compared with a few hundred microfarads you would see in a power supply. So the current is proportionally much smaller. ]

Most of the surge current is from the motor starting speed at 0 rpm, so there is no back EMF to counter the supply voltage. So initially, the only thing limiting the current is the reactance (inductance and resistance added vectorially) of the motor, which is quite low. It doesn't help that the mechanical compressor load is initially high as well.

Edited April 12, 20215 yr by Coulomb

14 hours ago, GreenMan said:

What is the power of the panels and in what configuration are they wired ?

Hi,

 

I have 4 string of 2 x 410W per string. 4 Sets of cables running to a combiner box with 8 fuses and a surge arrestor. 

10 hours ago, Peter Topp said:

Hi ErickvWyngaard

I would like to know what the pv configuration is as GreenMan asked. The graph shown shows a definite problem if there was no clouds. If there are parallel strings I would firstly try to see if any one  of the stings are faulty by removing each string one by one and seeing if you can get the graph to read correctly. Not for max wattage output but to try to eliminate any faulty string by getting an even graph. If you find a faulty string then you can go and check each pv panel of the faulty string. You should also check the surge arrestors if fitted.

Hi Peter,

What is strange, is that the problem seems to be happening only in the afternoon. Thanks, I will see what happen today and then start taking out one string at a time to try and eliminate the fault. 

Hi  ErickvWyngaard

To test if it is the surge arrestor that is causing the fault all you have to do is to remove it and see if the graph comes right.

If it is the fault replace it.

7 hours ago, ErickvWyngaard said:

What is strange, is that the problem seems to be happening only in the afternoon.

That suggests, but by no means proves, that the cause may be temperature.

31 minutes ago, Coulomb said:

That suggests, but by no means proves, that the cause may be temperature.

Coulomb, that was my first thought as well. It is however suppose to be getting colder in South Africa, so I don't understand why it will start doing it now. 

It happened twice today. It seams like it is when there is big power drop. Both time the output power and PV power went from about 2kW to 200W. I'm not sure if it can be the MPPT that is bring the power down to fast and then I goes to 0W

27 minutes ago, ErickvWyngaard said:

 

It happened twice today. It seams like it is when there is big power drop. Both time the output power and PV power went from about 2kW to 200W. I'm not sure if it can be the MPPT that is bring the power down to fast and then I goes to 0W

I'm starting to like @ThatGuy's theory (see another of today's posts; sorry, it's way past my bedtime). Or perhaps a version of it. It looks to me that your battery is getting quite full by 13:00, and the sudden drop in load caused the solar charge controller to over-voltage the battery. Do you have a Pylontech or similar battery? Is your absorb voltage up around 53.2 V, or are you perhaps using the direct cable (so that the BMS itself will be using 53.2 V)? What might be happening is that the temporary over-voltage of the battery is causing the BMS to shut off, which may cause the inverter to go to zero current as it thinks it's time for float stage soon after. The BMS disconnection causes the voltage at the inverter's battery terminals to drop very low, which causes the inverter to go back to bulk stage, but meanwhile the charge current has gone to zero. It might not be the BMS disconnecting, it might just be a really bad PV power undershoot following the sudden load drop. Could we perhaps see the battery voltage as well as solar power on the same graph? If it's too muddled, perhaps two graphs, but of the same data where one or more of these dips has occurred.

3 minutes ago, Coulomb said:

I'm starting to like @ThatGuy's theory (see another of today's posts; sorry, it's way past my bedtime). Or perhaps a version of it. It looks to me that your battery is getting quite full by 13:00, and the sudden drop in load caused the solar charge controller to over-voltage the battery. Do you have a Pylontech or similar battery? Is your absorb voltage up around 53.2 V, or are you perhaps using the direct cable (so that the BMS itself will be using 53.2 V)? What might be happening is that the temporary over-voltage of the battery is causing the BMS to shut off, which may cause the inverter to go to zero current as it thinks it's time for float stage soon after. The BMS disconnection causes the voltage at the inverter's battery terminals to drop very low, which causes the inverter to go back to bulk stage, but meanwhile the charge current has gone to zero. It might not be the BMS disconnecting, it might just be a really bad PV power undershoot following the sudden load drop. Could we perhaps see the battery voltage as well as solar power on the same graph? If it's too muddled, perhaps two graphs, but of the same data where one or more of these dips has occurred.

I have a DIY built LiFePo4 battery with 16 cells. My Bulk Charge Voltage is 54.8V and my Float Charge Voltage is 54.7V with this BMS https://lithiumbatteriessa.co.za/collections/bms/products/copy-of-bms-20a-8s-24v-lifepo4-lithium-ion-phosphate

 

 

On 2021/04/12 at 2:56 AM, Coulomb said:

No, the capacitor adds very little current, and since it's running on AC, the current drawn is continuous; I believe that there is very little surge at start-up that is solely due to the capacitor. [ Edit: the starting capacitor is usually only a few microfarads, compared with a few hundred microfarads you would see in a power supply. So the current is proportionally much smaller. ]

Most of the surge current is from the motor starting speed at 0 rpm, so there is no back EMF to counter the supply voltage. So initially, the only thing limiting the current is the reactance (inductance and resistance added vectorially) of the motor, which is quite low. It doesn't help that the mechanical compressor load is initially high as well.

Noted Coulomb,  which leads me to the next thought that a soft-starter then may assist in lowering the starting surge current ?

18 hours ago, ErickvWyngaard said:

I have a DIY built LiFePo4 battery with 16 cells. My Bulk Charge Voltage is 54.8V and my Float Charge Voltage is 54.7V with this BMS https://lithiumbatteriessa.co.za/collections/bms/products/copy-of-bms-20a-8s-24v-lifepo4-lithium-ion-phosphate

Oh. Unless your BMS is misbehaving badly, I can't see how this fits with the theory. Your absorb voltage setting is nowhere near the point where the BMS should be disconnecting due to overcharging.

What is the capacity of your cells? Are they "energy" or "power" cells?

Thanks for the graphs, but I really would prefer a graph of battery voltage, rather than battery power, if that's possible.

4 hours ago, GreenMan said:

which leads me to the next thought that a soft-starter then may assist in lowering the starting surge current ?

Well, yes. Soft starters are intended to reduce starting current surges. By ramping up the voltage relatively slowly (over a second or few), there is never a huge difference between back-emf and applied voltage, so there isn't ever a huge current drawn. I imagine that the current might still be 20-50% higher than steady state, but that's much easier to handle than a 700% increase.

46 minutes ago, Coulomb said:

Oh. Unless your BMS is misbehaving badly, I can't see how this fits with the theory. Your absorb voltage setting is nowhere near the point where the BMS should be disconnecting due to overcharging.

What is the capacity of your cells? Are they "energy" or "power" cells?

Thanks for the graphs, but I really would prefer a graph of battery voltage, rather than battery power, if that's possible.

I have 2 x 16 of 120Ah cells. I'm not sure if they are energy or power cells. What is the difference between a power cell and and energy cell?

I've attached the battery voltage for the same period

8 minutes ago, ErickvWyngaard said:

I have 2 x 16 of 120Ah cells.

That should be plenty, unless they are really rubbish.

8 minutes ago, ErickvWyngaard said:

What is the difference between a power cell and and energy cell?

It only matters if you have a relatively small capacity battery. They can somehow add or subtract secret sauces to make the battery store more energy in a given volume, or put out more power without sagging. A123 cells are usually power cells, for example. What you'd find in a bus is probably an energy cell; they need as much range as possible, and make enough peak power available by having many strings of cells in parallel.

I'm out of ideas for now.

Hello everybody,

my first post, so first I want to thank all of you for all the valuable information and advice you share on this forum.

I have recently started running an offgrid system with Axpert King I and I would need some advice, I do not want to create a separate thread so I am posting my questions here as it seem a general thread about this model. At the moment I would appreciate your advice on the two issues below:

1. I accidentally shorted the battery +/- terminals on my spare Axpert King I shorty after it was turned off and the battery was disconnected. As the capacitors were charged, there was a popping noise and a spark/arc for a brief moment, as the capacitors discharged. I connected the battery again (through a bulb to avoid too high a current) and the inverted started up and seemed working normally. Could I cause any damage by shorting the terminals?

2. Strange intermittent static noise/clicks coming from the inverter at random intervals, usually once in a few minutes, it is similar to the sound of static discharge or relay clicking - but it is at stable load, no system mode changes, so it is not a relay, the inverter is new and working normally. Have any of you had a similar experience? Is it normal or something to worry about? I have come across a few people reporting this on another forum, but generally it is not something frequently reported. I found that somebody posted the same issue on Youtube, you could hear the noise here 

 

Thanks for your help in advance!

 

 

4 hours ago, Jumajazu said:

I accidentally shorted the battery +/- terminals on my spare Axpert King I shorty after it was turned off

That's not a problem unless you do it regularly. It is most unlikely to have caused any damage. 

4 hours ago, Jumajazu said:

Strange intermittent static noise/clicks coming from the inverter at random intervals,

I don't know what it is, but I don't think it's anything to worry about. 

Thanks a lot for your answer, Coulomb

I've been reading this thread and was thinking about upgrading my existing RCT 5kva inverters (x3) with the King version.

The specs are about the same, but I understand that the King is actually Grid-Tie where my current setup is not.

I'm not too concerned about the actual time being 0ms vs 20ms but more to be able to feed back to the grid once this is allowed and formalized.

 

I've got 3x RCT 4000VA/5000W models with different MPPT strings which works quote well, just want to know if there will be other real benefits (except for above) by upgrading to the King versions?

 

The only reason why I'm considering this is as I've seen 3x kings available on marketplace.

Any advice / inputs here?  

 

ok it seems that the King is not really Grid-tied, but are there any good reasons to upgrade?