High frequency inverter for air conditioner unit?

[DanF]

I am building my new off grid system and will be using the MPP 6548 all in one with 16 -280ah battery back-up. Those two points don't really matter as much to me as does whether I should go with 110 or 220 (2) of the units to run the whole house.
So, first of all it appears that the input and output from the mains for these inverters are capable of 60 amps if I am reading the manual correctly.

Two questions will help me figure out the design of my system if someone can help here.

1. When in parallel will these split phase inverters allow for double (amp's for each phase) or are they shared amperage?
2. I only have two 220v appliances the rest is easy enough and figured on the 120v side. Can a high frequency split phase inverter handle the inrush and start an air conditioner? (mine is a 3 ton unit on a 20 circuit) or has anyone tested this? The other is an electric dryer. I have seen where some have managed the dryer as long as you have the capable amperage.

I have tested my sump pump motor and furnace (They work fine).


Thanks for any help on this!
Dan

 

[snoobler]

1. With two you'll be limited to 60A/leg, which means 60A/240V. And other loads on either leg will take away from each leg as well as both legs for anything pull 240VAC.
2. Only if the surge doesn't exceed the continuous rating of the inverter. Surge is typically 3-10X the run. A 14 SEER 3 ton unit has a run power of about 2600W. There are relatively inexpensive clamp meters with inrush function that can answer the question for you.

Something like this could work to reduce surge:

EasyStart™ 364 Soft Starter

EasyStart™ single phase soft starter lets you start your A/C without buying a second or bigger generator or inverter & run 2 air conditioners on a 30-Amp cord.

www.microair.net

 

[DanF]

Snoobler, Thanks for the quick response! The 60amp each phase I should have known! lol..

So, Lets say capacity wise I am good. Then, no motor overload issues.. I will reach overload if I would turn on the dryer and the stove are turned on at the same time (let alone the other amp drains going on at the time).
How are people running big house loads with inverters? May be all in one's are limited that way? All of the inverters that I have researched so far whether high or low frequency seem to have a limitation problem with input and output amperage capacity.

I have to be missing something here..

 

[snoobler]

LF inverters ore more common in higher power installation only in part due to the surge. You still have to size them appropriately. If you want to run every circuit in the house, you must have the power to do so. I have a 200A panel coming into my house. Assuming I actually need all that, I'd need 48kW of inverters to run my house. With my electric bill, my 5 ton A/C, my 4500W water heater, my 3500W oven, my electric dryer, etc... that almost feels right.

Personally, I don't trust the MPP Solar/Growatt for anything beyond "project" stuff. Generally speaking, when powering your home, you're picking the hardware that commonly runs 20+ years based on their track record (Outback, Victron, Midnite Solar, Xantrax, Schneider, etc.), not based on hope.

 

[DanF]

I agree! I would rather overbuild and run things on the 50-75% range on everything I do rather than go cheaper and run hot. I don't mind spending money on better quality at all, but that is kind of the point here. If I cant run say... 100 amp sub panel with the 2 -6548 inverters because of capability, then I'll stay with the 120v circuits and size the solar panels for those loads.

Thanks again Snoob!

 

[DanF]

1. With two you'll be limited to 60A/leg, which means 60A/240V. And other loads on either leg will take away from each leg as well as both legs for anything pull 240VAC.
2. Only if the surge doesn't exceed the continuous rating of the inverter. Surge is typically 3-10X the run. A 14 SEER 3 ton unit has a run power of about 2600W. There are relatively inexpensive clamp meters with inrush function that can answer the question for you.

Something like this could work to reduce surge:

EasyStart™ 364 Soft Starter

EasyStart™ single phase soft starter lets you start your A/C without buying a second or bigger generator or inverter & run 2 air conditioners on a 30-Amp cord.

www.microair.net

I found this information on AC input breaker sizing in the LV-6548 Manual.. Interesting!

 

[the_colorist]

LF inverters ore more common in higher power installation only in part due to the surge. You still have to size them appropriately. If you want to run every circuit in the house, you must have the power to do so. I have a 200A panel coming into my house. Assuming I actually need all that, I'd need 48kW of inverters to run my house. With my electric bill, my 5 ton A/C, my 4500W water heater, my 3500W oven, my electric dryer, etc... that almost feels right.

Personally, I don't trust the MPP Solar/Growatt for anything beyond "project" stuff. Generally speaking, when powering your home, you're picking the hardware that commonly runs 20+ years based on their track record (Outback, Victron, Midnite Solar, Xantrax, Schneider, etc.), not based on hope.

I second @snoobler 's comment about considering another unit if that's in the cards. A recommendation would be to consider a more robust/proven unit(s) from SMA, Victron, Studer, etc. Even a DEYE (based on the feedback of the SOL-ARK units which many consider made by DEYE).

I'm an installer and for me it's not just about the unit's life. That unit is powering everything you own and if it has trouble with starting refrigerators etc it will ruin them/shorten their lifespan in the long run. I've seen it happen. I've even seen more robust units such as the Magnum 4448PAE not even start certain types of equipment/appliances. And it wasn't an issue of surge capacity, it was the signal/waveform/voltage regulation. It wouldn't even start the panel (was a high-end LG washer). IMHO, with some of the HF inverters, the waveform changes based on the load (particularly startup) which shortens the lifespan of the appliance. And even some of the lower-end LF transformer-based models (Magnum) have pretty bad voltage regulation.

This is one of a few things that concern me about the MPP:



Up to 10% distortion for a non-linear load? Ouch. There is no way this could export to the grid IMHO. I suspect that the UL1741 is simply anti-islanding. I doubt it's rated for grid-export and I personally find that if an inverter is not good enough to export to the grid, it's not good enough to run a home for 10+ years. Here is a comparison to a SI6048 (largely considered creme-de-la-creme of battery inverters):

https://files.sma.de/dl/15216/SUNNYIS4548_6048US-DUS161422W.pdf

But that's just my opinion!

Back to your original questions:

1. Parallel/single phase 120A @ 120V. In split-phase 60A @ 240V or 120V.

2: They may start it but I would worry about shortening the lifespan of the motor(s). Adding soft-start should help somewhat. With regards to 120V balance when installed as split-phase, you could add a $300 Auto-Transformer from SolarEdge which would add an extra 25A to either leg making the total capacity per leg close to 60+25=85A BUT that extra 25A comes from the other inverter so it's only there if the other inverter/leg has extra capacity to spare.