Hello from Maine

On 11/17/2021 at 10:52 PM, Sid Genetry Solar said:

2-stage charging as of right now (though admittedly without an auto-switch-between "bulk" and "float" right now

So how does this play out when charging ones lifepo4 bank...  Is this to say you have to manually watch where the bank voltage is at and then manually switching modes or shutting the charger down? I'm guessing the charger doesn't taper the current down as the voltage rises as the cells approach a full state of charge? Or will the bms just shut the batteries down automatically when they are fully charged to protect them?

Inverter charger is CV (constant voltage) first, CC (constant current) second.  In other words, the charger's goal is to reach the desired charge voltage...but held back by the current limit.

In other words, if the specified charge voltage is reached, the current will taper to zero as the batteries fully charge.  I've tested the charge function on my bench supply...it'll hold the specified voltage at zero current.

I personally don't like the BMS being the "charge gate"--I feel that it should be more of an emergency shutoff in case of rogue equipment.

At the moment, I don't have an "auto-switch to float" programmed in (easy to add via firmware update), I'm just not sure of the best way to handle it.  Thoughts / suggestions?  Once I determine the most useable way to handle this, it's a simple firmware modification.

Thinking maybe the best way would be to have an "absorption timer" (like most MPPTs, etc.), where as soon as the battery voltage reaches the "bulk" setpoint, the inverter will start the "absorption timer" (user configurable duration).  After said timer expires (regardless of the charge current), it could either switch to the "float" voltage setpoint...or maybe have an option for disconnecting entirely (i.e. gen stop / ATS back to battery inverter)??

I'm sure someone will say, "make the inverter watch the battery current until it falls near zero, then switch."  There's one big problem with that: if there are other DC loads on the system, the inverter never will switch to "float" (or "end charge") due to said loads.  Kinda leaves a fixed timer as the best option.

That's a failing of the MakeSkyBlue chargers too.  I looked into the current at which the MSB falls back to float voltage and it was under 1 amp and is not configurable (at least not in V117/8/9 that I can see).  Given the current the MSB can provide it's pretty clear it's intended to support quite hefty batteries so under 1 amp tail current is stupidly low.  The load on the DC system isn't separated by the MSB either, so pretty much one will never see a MSB go to float... at least in my experience.

If the batteries on the GS were lead acid a shunt on the battery bank output would let the GS monitor current in / out, but with lifepo4 there's no real need for that.  Just monitor battery terminal voltage and when it reaches the desired point, hold it there for ... 20 to 60 minutes and the job will be done.  My own lifepo4 battery makes to where the battery current has fallen to zip in about 10 minutes (assuming the charger provides all the current the battery can draw, rainy days are another story).  60 minutes would give plenty of time for the BMS to do any cell balancing that may be needed.

The load on the DC system isn't separated by the MSB either, so pretty much one will never see a MSB go to float... at least in my experience.

My 2 MSB  never go to float  which make the lithium ion  car battery last a long time .  

getting closer here to getting the proverbial waterfowl all lined up nice and neatly.  Looks like a pair of 6k 240s at the moment, so the last thing to do is figure out the generator upgrade, as clearly my trusty little Yamaha is2000ef won't be up to the task of charging a 15kw bank in a timely manner. He's a little long in the tooth these days and I'm sure wouldn't mind being relegated to occasional backup mobile duty.  Considering the preferred charge rate recommended by Kilovault, the 2 HAB units combined, @a .5C would be 100a, so I'm looking for somewhere between 50 and 100.  Unless I've figured this wrong, a 240v 7500 running watts generator @2/3 load, then derated by 40% through the inverter, would net me just around 3kw (61a@48v) of charging power, putting me right in the range I want to be, right? 

And I know you detailed the charging protocols as voltage first, but I'm guessing I can set the maximum current at 61a dc going out (or however you make that adjustment that equals such), which will set the charging duty itself to a 2/3s load on the generator, without factoring in additional household loads that might happen to be occurring. Is this correct?

If this is all correct, does this sound like a solid plan, or is there something I'm forgetting/unaware of?  

And while the inverter is charging, do my house loads take the juice straight from the inverter via the breaker panel, or does it come from the bank ultimately?  I know this sounds like a pretty novice question, but I've always ran external chargers, and the way they were wired, loads always came from the bank while charging, which is probably not the best setup when it comes to avoiding microcycling.

Thereabouts.  Worth noting that a test by another customer (@merner) with a higher voltage battery bank (i.e. a bit harder for the inverter to reach) clocked in at ~70% charge efficiency off of 240v.  This is WITHOUT the to-be-added PFC charge methodology, which should increase the efficiency further.

Basically yes 😉.  Charge current is actually measured/regulated on the AC side (as there are no DC-side current sensors in the current run of GS 6k inverters), but as the power out can only come from power in, you can definitely keep the charge current below the necessary limits.  The inverter will try to maintain this set current until the target battery voltage is reached.

Hopefully after a good bit of solid testing/field reports, I should be able to make a "conversion chart" (on the LCD) to roughly estimate the output charge amperage.  (Variables required include the AC input voltage, battery voltage, and possibly a bit of temperature compensation for good measure.)

While the inverter is in charge mode, all loads are directly powered by the generator.  Yes, I've got a lot of stuff to work on, but ideally the charge current will also be subject to the input current limit AND current loads.  In other words, the inverter will need to auto throttle charge down if necessary to avoid overloading the generator.

Actually, once I've written the code (haha, I seem so behind!) the inverter would actually be able to pull power from the batteries to offset a particularly high load draw...that is, if the pass-thru load exceeds the specified input current limit.

I'm trying to get my desk a bit cleared up today, then get back to code work.  Hopefully I can get all these major charge/AC input revamps in 1.1r6 😉.

First inverter just ordered.  Question... for the gen start function, do I need any additional part other than a generator with electric start?

Depends on the generator...if it's got a key-start or something like that, you should be able to adapt the inverter control to it.  My only concern would be the current draw; you might need some beefier external relays to bump up the signal power a bit.

Inverter should (SHOULD!) come with a little 3-pin header with a removable push-release 5.08mm connector on it.  These provide access to 2 separate relays in a "Y" config (i.e. 1 C 2)...however, I won't recommend pulling much over an amp through them.  (Relays are rated 5A, but the wire used on the connector is a bit thinner than I specified...don't want to melt it!)  Relay contacts are electrically isolated from the rest of the inverter, so electrical potentials are not a serious concern here.

I haven't yet purchased the generator, so my options are pretty open if you know of one in the 7-9kw range that plays well with the gs6 right out of the box, or with minimal fuss anyway (gas or dual fuel).

I'm a tad uncertain about the rest. maybe a "buy this relay" and connect it with "x-guage wire" would be in order here... you know the limitations and capabilities of the unit better than anyone, so I'll follow up on your equipment referrals. Are you saying to use an external relay of 1 amp or less? the signal only needs to travel about 8 feet.

Coil load (if an external relay is necessary).  You'd have to run a really big relay to reach 1A coil current 😉.

The GS inverter's generator start electrical capacity is ~1A.  If the generator has push buttons or dedicated controls for genstart, the inverter likely can be adapted to directly control it.

However, if the generator is wired such that the entire current of the starter goes through the start button...you'll need an external relay to handle that load.

I'm not super familiar with generators on the market and how they're designed.

If you have a generator in mind, maybe provide a link and I'll glance over the specs to see if I can determine what will be needed.

ok, I'll figure that out over the next couple days then.  While we are in the subject, what's the highest gauge wire that the ac input accepts?  I'm taking a guess that I'll want 8/3 at a minimum here, right?

45 minutes ago, BlackWaterPark said:

ok, I'll figure that out over the next couple days then.  While we are in the subject, what's the highest gauge wire that the ac input accepts?  I'm taking a guess that I'll want 8/3 at a minimum here, right?

It's 25A max input (=6kw @ 240v)...10AWG or 12AWG should be fine.  Terminal wire holes are roughly 5mm in diameter.

24 minutes ago, Sid Genetry Solar said:

25A max input (=6kw @ 240v)

Does the inverter itself limit the amount of current able to come into the unit then, so as not to overload it as a protection measure?  ie; the charge function cannot exceed a certain threshold?

i think i might have just asked a stupid question, lol. realizing that of course it's rated at 6kw input... it's a 6kw output after all. Don't worry, the questions can only get better from here...

...not right now admittedly (so much code work to do for 1.1r6).  I will implement some sort of hard system protection limit on the input, as well as a user-configurable AC input current limit (with generators in mind).  If the loads exceed the user-set limit, there will be an option to determine what the inverter does (i.e. shut down with error / "hybrid" power by pulling power from the battery, etc.)  Obviously, max battery charge current will be throttled appropriately based on the "headroom" available (and the battery charge current setting.)

I'll be furiously coding away as my schedule allows over the next few days, see how much progress I can make on the AC input stuff 😉