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I noticed some weirdness when running the AC


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So I noticed this week that when I run the window air conditioner on the inverter I get some weird power fluctuations on the inverter but then if another high power device like the well pump comes on during that time then everything stabilizes. Here is some footage of that happening:

https://drive.google.com/file/d/1mcj2Zbj80Q9uFJ05RRQ1JDZ5plAvsgmW/view?usp=sharing

Well Pump and AC outlet are on opposite legs of the sub panel.  Not really sure what is going on so I am going to keep the AC attached to the grid for the time being.  Here is what the waveform looks like on the inverter when that is happening:

https://drive.google.com/file/d/1meuIILMnuxF7I1haMwSOcuMJXhp58m0F/view?usp=sharing

AC unit is an 8000 BTU 115V 11.2A 1225W window/wall unit from Frigidaire from the 80's so they don't make them like this anymore.

I am working on replacing this unit with a mini-split heat-pump unit at some point but I need to buy a new furnace for the house this year first and as it is, this humble 8000BTU unit cools the entire first floor of the house without issue.

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Thank you for the clues/videos, etc.

Pretty sure this will be addressed in 1.1r3...which as soon as I get it polished up, I plan to release (hopefully within the next few days).  (It will also correct the registered 59Hz back to 60Hz.)

Sean was encountering regulation (flicker) issues similar to this with his regular 3 ton A/C unit.  The root cause has to do with an experimental regulation curve that's too aggressive--so the inverter ends up in an oscillation with itself that it can't purge.  Adding loads results in a change to the math, and it clears up.  For 1.1r3 I dropped the regulation to a much less aggressive curve.

I do notice that you seem to have output frequency droop enabled?  I know I haven't gotten a manual written yet, but that only should be enabled for parallel inverter usage....unless you like it ;-).

 

Looks like you're running AC input to the inverter; we only recently became aware of this, but it's critical to be aware of the possibility of backfeeding power into the inverter if it's connected to a bonded neutral/ground breaker panel that's also connected to AC Mains neutral.  My oversight on the design, the inverter can only disconnect L1...but if there's a bonded neutral/ground connection to AC Mains, that presents 3 input power wires to the inverter...which it can only disconnect 1 of.

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I started noticing the output frequency droop after you had me update from the original firmware I believe since I have one of the early air shipped units.  I didn't realize I could turn that off so I will have to go in and do that at some point. Basically, didn't want to fix what isn't broke and mess something up.

I have the inverter output connected directly to a secondary critical loads panel that is not neutral ground tied.  The main panel is neutral ground bonded but I have all of the circuits in the critical loads panel Line and Neutral isolated from the main except for a 6 gauge ground bonding the ground busbar of the 2 panels.  As well as the 2 panels being physically bonded with conduit.  I am aware of the back feed potential but I am assuming it should be ok with the secondary panel having a non bonded neutral.  Unless power can go in on the ground terminal of the inverter which is bonded to the entire ground system.

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15 minutes ago, kuhrd said:

Just in case you want to see more of my mostly messy setup. https://drive.google.com/drive/folders/1RsulgwRRtCLOekLXwXjWNwo1Q23FZHGZ?usp=sharing

Nice.  Way neater than mine 🤪.

Sounds like you have it set up safely--obviously, or you'd have run into issues right back at the beginning with backfeed.  I'm more than aware of the problem, and it'll be fixed on Rev. C--but in the meantime, we have all these Rev. A.1 and Rev. B inverters in the field.

Frequency droop might not be enabled (should be disabled by default).  Might be a little "oops" on my end with the LCD status line with active AC input (fixed in 1.1r3 to read "InSync".)  You can check it in CFG -> AC Output -> Hz Droop -> should be set to None.

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Nicer than mine too.  My setup started small and simple and fitted nicely into an open frame cabinet (about 1.2m x 0.9m) but as with this sort of stuff it grew a bit.  One day I'll have to take it apart and rebuild it two cabinets high.

Just as a suggestion, check the voltage drop across the outputs of the chargers to the bus bars when they are pushing full current.  It's more of a nicety than a requirement but with lithium's fairly flat charge/discharge curve (except at the ends) you can find that even though you have ample solar and might think that your load is being fully supported by it, you may find that you are shallow cycling your battery more than you would otherwise imagine.

It's very easy to get 60mV of drop across the wire+switch+fuse (and that's just one side of the wiring, the - side has drop too) and 60mV of shift in voltage for a lithium battery represents a fair amount of capacity.  Your chargers will attempt to keep their terminals at the configured voltage and will only supply enough current to do that.  Until the battery discharges down far enough to exceed the total voltage drop from your wiring etc your chargers will never go 'all in'.  Chargers with remote sensing don't have this problem since they see the far end voltage and attempt to hold it at their set voltage compensating for the drop through the wiring etc.

I'm not a micro-cycle nutter that thinks the world will implode if you do it, but you may find that you are pushing your batteries through 15% DOD cycles so it's food for thought.

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One thing I want to add across the main bus at some point is a capacitor bank to help buffer the load and provide temporary buffer storage on sunny days until I eventually buy more batteries. I have several boxes of 250V 6800uF IIRC power filtering capacitors that were taken out of APC UPS units that may be up to the task but I still need to test them.  I have the solar charge controllers set to stop charging at 57VDC and the BMS cuts off at 56.2.  The capacity of the bank right now only measures 150Ah down to around 10% SOC even though the original capacity should be 230Ah.  The loss of capacity is due to the first part of the pack being made of NOS Fullriver cells that have turned out to be a bad investment even though at the time they appeared to be good and the first couple boxes appeared to test near 90% capacity the first couple of cycles.  I have had some of the bank capacity come back as I have cycled the entire battery as it started closer to around 120Ah when I first connected it all.  
Once I have the money to do so I am planning to go the route of the EVE prismatic cells if they continue to prove to be decent.

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1 minute ago, kuhrd said:

Once I have the money to do so I am planning to go the route of the EVE prismatic cells if they continue to prove to be decent.

We are seriously considering importing several pallets of EVE prismatic cells if like you said, they continue to prove to be decent.  If business scales up like we are hoping, a shipping container is a flat rate (albeit a quickly rising one!) whether it's empty or fully loaded.  Earliest on this might be towards 2022 though.

 

2 minutes ago, kuhrd said:

One thing I want to add across the main bus at some point is a capacitor bank to help buffer the load and provide temporary buffer storage on sunny days until I eventually buy more batteries. I have several boxes of 250V 6800uF IIRC power filtering capacitors that were taken out of APC UPS units that may be up to the task but I still need to test them.

I'm assuming these go across the battery bank, not the AC output of the inverter?  FWIW the inverter itself has 40,000uF of DC filter caps on it.

 

5 minutes ago, kuhrd said:

I have the solar charge controllers set to stop charging at 57VDC and the BMS cuts off at 56.2.

Could you explain the reasoning for this?  I would think you'd want the BMS shutoff to be an emergency shutoff only, not an everyday cycle thing?

For LiFePo4 cells, I have heard that high float voltages gradually damage the batteries--and as such, my system peaks at 56.5 for absorption ("equalize") and holds float at 56.0.  There really isn't much added capacity to speak of beyond the battery "holding" at 53v--just equalization IMO.  (Li-Ion is different though.)

 

6 minutes ago, kuhrd said:

The capacity of the bank right now only measures 150Ah down to around 10% SOC even though the original capacity should be 230Ah.  The loss of capacity is due to the first part of the pack being made of NOS Fullriver cells that have turned out to be a bad investment even though at the time they appeared to be good and the first couple boxes appeared to test near 90% capacity the first couple of cycles.

Aha, did you buy those on eBay from "dougdeals"?  My 12kwh bank is a DIY build of NOS LiFePo4 32650s from "dougdeals"...though I liked the more solid-sounding "Tenergy" brand, and bought those instead.  Nary an issue with them, and the 2 times I nearly ran out of power (before getting more solar last year!) it was pretty much a full 12kwh on the MPPT before they reached full charge.

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I would normally want the BMS to disconnect as a last resort but I have found that at least with the MSB charge controllers I would end up in a short cycling situation as TheButcher is describing and with a MOSFET based BMS like I am using that is not much of an issue as it is only disconnecting in the charge direction but the BMS is still connected in the discharge direction.  If the MOSFETs in the BMS fail short the solar charge controller will disconnect charging.

The capacitors would go on the DC side if I decide to go that route.

I originally ordered the Fullriver cells from "athomemarket" which I am pretty sure is "dougdeals" and  "CDN Systems LLC"

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2 hours ago, Sid Genetry Solar said:

We'll get to that after you get the master back 😉.  I didn't put the "hold Enter for SoftAP" in yet...

Oh, so the master going to have to be redone to connect to my network again and I'm guessing the serial change since having to replace the main board?

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10 minutes ago, The Blind Wolf said:

Oh, so the master going to have to be redone to connect to my network again and I'm guessing the serial change since having to replace the main board?

Nope, both are stored in the WiFi board.  Just the setup will be need to be redone (voltages, etc.)

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1 hour ago, Sid Genetry Solar said:

Nope, both are stored in the WiFi board.  Just the setup will be need to be redone (voltages, etc.)

cool.  Cause right now my friend that help me installed to the main, ended up with the china virus last friday and I've not been able to get any word on how he is doing since monday.  Which sucks cause he lives like a 5 min walk from my house to his, and he is also my grocery getter and stuff geesh. sucks.

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Installed the release 1.1r3 and it seems to have mostly taken care of the instability that was there when running the AC.  I can still see a bit of flicker that is not present when the unit is off but is almost not noticeable anymore.  I will have to take a look at the waveform when I get a chance but this update seems to have mostly fixed the issue I was having with the AC.

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17 minutes ago, kuhrd said:

I can still see a bit of flicker that is not present when the unit is off but is almost not noticeable anymore. 

Always glad to hear a good report.

When the A/C is off and there's a smidge of flicker in the LED lights, could you go OUT -> Diag (past the 'scopes, 4th menu item) -> scroll all the way down to the bottom and watch the "Throttle" line?  If it's constantly changing, the flickering is being caused by the inverter regulation...if it's rock-solid, the flickering probably is caused by other appliances down the line on the system.

When the A/C is running, is the "BattVolt" Diagnostic line holding fairly steady? (+/-2 counts max.)

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