On June 18 I asked a question iro generator sizing for Mecer Axpert SOL-I-AX-8M 8kW inverter with utility or generator input.

I asked Mecer the same question & they eventually responded: "The generator must be double the capacity of the inverter. A 12kva and above with a frequency stabiliser should do".

Comments?

You are not giving enough info...

So, you have a 8kW inverter.... ok.... what is this doing? running a small datacenter? does it have batteries connected? solar panels? what is your average and maximum power load on the inverter and why do you want/need a generator?

If you have enough solar, but at times, not quite enough to charge the batteries as well as run whatever hangs off the inverter, then 2 or 4kW extra generation capacity may be good enough, depending on the assumed battery capacity, but the Axpert may not like power coming from a dubious generation source that floats around 50Hz ±5Hzor even worse

So, to recap, not enough info.

Edited August 6, 20223 yr by Kalahari Meerkat

5 hours ago, AMac said:

On June 18 I asked a question iro generator sizing for Mecer Axpert SOL-I-AX-8M 8kW inverter with utility or generator input.

I asked Mecer the same question & they eventually responded: "The generator must be double the capacity of the inverter. A 12kva and above with a frequency stabiliser should do".

Comments?

If that is what you were told by the manufacturer, I would go with it if I were you. The reason why they might have took that long to get back to you, might be because they had to check with their gurus or even test the unit to see what size geny will work well with your inverter. I would trust the information I get from the manufacturer that one I would get from any forum, trust me 😀

5 hours ago, Kalahari Meerkat said:

You are not giving enough info...

So, you have a 8kW inverter.... ok.... what is this doing? running a small datacenter? does it have batteries connected? solar panels? what is your average and maximum power load on the inverter and why do you want/need a generator?

If you have enough solar, but at times, not quite enough to charge the batteries as well as run whatever hangs off the inverter, then 2 or 4kW extra generation capacity may be good enough, depending on the assumed battery capacity, but the Axpert may not like power coming from a dubious generation source that floats around 50Hz ±5Hzor even worse

So, to recap, not enough info.

Nope, I disagree, all the info is there. Mecer Axpert SOL-I-AX-8M 8kW inverter and the responce from Mecer, "The generator must be double the capacity of the inverter. A 12kva and above with a frequency stabiliser should do". Key work in the answer from the manufacurer being MUST, not maybe or check with generator manufacture or all those funny answers that some technical support guys normally give when they are trying to avoid a question

I call BS. You only need a generator the size of your load/draw - A good 4.2kVA generator is fine if you are only trying to charge batteries and keep a 2kVA load running on your Axpert output (ie: home)

When I had my Axpert, I sometimes powered it from my 4.2kVA generator - but the output sine wave needs to be decent. So a cheap clicks/makro/game generator is not sufficient, their AVR's are not normally clean enough. If you can get a proper Sine wave generator without breaking all budgets then go with that. My generator was designed for Server room backups, and although not pure sine wave, it has a decent AVR to provide something decent - cheap generators AVR's give a very bad signal, even many UPS's can't deal.

You can put a cheap generator of 12-15kVA on an Axpert and it will spit at you because it wont recognise the AC signal.

So, my opinion, take your max usage while needing to run on Generator, add 1 to 1.5kVA and use that as baseline. Then approach decent generator suppliers who can prove their sine wave or avr output. Will definately be more expensive, but probably a lot cheaper than the bad 12-15kVA above.

 

PS: AVR/Sine wave is what they mention as a "frequency stabiliser" above - it has to be within range of 48-52Hz, sometimes better, for a good UPS or Axpert to stay stable

Edited August 6, 20223 yr by KLEVA

Although the load is important and each install might have a different need when using a genny to prop up the battery.

No inverter likes it when the speed=frequency is changing. I suggest we read the answer from @Kalahari Meerkat

a second time. Especially those with Axperts. A VSR does not control the speed.......

@Scorp007 - We posted at the same time, so didn't see your post. But exactly...

Thanks everyone!

I asked for comments as I am skeptical of Mecer's "must be double the inverter size or 12kVA would do". Why? Odd comment.

A generator around 6/7kVA would be very adequate for our household- and larger than the 12 x 455W PV panels installed.

Note! I am only considering quality generator sets and established makers with decent support. I am not looking to do this on the cheap!

I asked two generator suppliers for their opinion on Mecer's answer to my question. Both were surprised & had not encountered this before. Food for thought!

In any event 16kVA or even 12kVA is not a practical solution; machine size, noise (silent type essential) and then of course the cost.

For the cost of 12 or 16 kVAa machine I could double the size of the solar system - which would solve the problem - at  unjustifiable cost.

 

Suspect Mecer just went with the guaranteed nuclear option,able to provide your entire load + charge at maximum C rating simultaneously - not exactly wrong,but likely overkill

4 hours ago, AMac said:

Thanks everyone!

I asked for comments as I am skeptical of Mecer's "must be double the inverter size or 12kVA would do". Why? Odd comment.

A generator around 6/7kVA would be very adequate for our household- and larger than the 12 x 455W PV panels installed.

Note! I am only considering quality generator sets and established makers with decent support. I am not looking to do this on the cheap!

I asked two generator suppliers for their opinion on Mecer's answer to my question. Both were surprised & had not encountered this before. Food for thought!

In any event 16kVA or even 12kVA is not a practical solution; machine size, noise (silent type essential) and then of course the cost.

For the cost of 12 or 16 kVAa machine I could double the size of the solar system - which would solve the problem - at  unjustifiable cost.

 

Bear in mind if your 5kw PV gives you only 10% peak even a 10kW PV would only give 1kw at peak. This might not see you through and you might wish for even a 3.5kVA genny.

I'll just note that there is an official MPPSolar document about generator requirement, which states that they recommend (not demand) 1.5x (not 2x) the inverter capacity as generator capacity.

Interesting note for King users: they don't recommend using a generator at all! They say you can try, but even inverter-based generators are unlikely to be good enough for the King's exacting requirements. Perhaps the Kings need excellent voltage stability as well as frequency stability. Huh.

Whether the 1.5x recommendation is just to cater for the fact that cheap generators often tend to exaggerate their true output or other reasons, I have no idea. [ Edit: Actually, they state that this is the case. ] Perhaps because most generators aren't all that stable in frequency near full load, as the mechanical system struggles. However, if you have an inverter-based generator as they also recommend, I can't see how that is relevant, as the output frequency should be crystal locked, and hence extremely stable.

Edited August 9, 20223 yr by Coulomb

Thanks again to Coulomb & others. Once again however the definite answer eludes!

I'd suggest it can only come from the inverter maker - having gone through a design, development & testing process. They may not be willing to do this as they don't supply generators so go the safe route saying 2 x or 1.5 times etc. gen output. That said why do they give "utility or generator input" on the inverter? They should give a specification or minimum requirements for power quality input.

I'd avoid cheap generators regardless. Always go for established quality makers where support & spares should not be a problem.

Finally, I wonder if I'm the only person looking for an answer to this question? I doubt it!

1 hour ago, AMac said:

Thanks again to Coulomb & others. Once again however the definite answer eludes!

I'd suggest it can only come from the inverter maker - having gone through a design, development & testing process. They may not be willing to do this as they don't supply generators so go the safe route saying 2 x or 1.5 times etc. gen output. That said why do they give "utility or generator input" on the inverter? They should give a specification or minimum requirements for power quality input.

I'd avoid cheap generators regardless. Always go for established quality makers where support & spares should not be a problem.

Finally, I wonder if I'm the only person looking for an answer to this question? I doubt it!

Axperts and genny don't always like each other.

https://www.bundupower.co.za/inverter_with_generator.php

4 hours ago, AMac said:

Thanks again to Coulomb & others. Once again however the definite answer eludes!

I'd suggest it can only come from the inverter maker - having gone through a design, development & testing process. They may not be willing to do this as they don't supply generators so go the safe route saying 2 x or 1.5 times etc. gen output. That said why do they give "utility or generator input" on the inverter? They should give a specification or minimum requirements for power quality input.

I'd avoid cheap generators regardless. Always go for established quality makers where support & spares should not be a problem.

Finally, I wonder if I'm the only person looking for an answer to this question? I doubt it!

I dont know what battery setup you have, but one could charge lead acids off the generator with a seperate charger. You could also replace your inverter with a Sunsynk where you can limit the generator draw. If the AVR is still not compatible, rectify and push power into a MPPT channel set up for a turbine.