It is. The primary means of protecting the battery from overcharge, overdischarge, overtemp etc is that the inverter reads the data and stops charging or reduces power if a limit is hit. If that fails, you have to rely on secondary protection (i.e. the battery's BMS.)
Midnite Solar Announced their new 10kw AIO at Intersolar Today
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I think you're right. But, further down you will see the grid to battery charging efficiency listed at 96%. Here again it is same on all 3 models...
Yep, and along with the 48v in series scenario you get a high potential for imbalance between 48v units down the road.....
I see benefits to HV, but I wonder if the benefits outweigh the potential issues and/or risks.
And as far as comparing to high voltage PV, I think a battery is completely different because of the available fault current! Much higher amperage available!
P.S. sorry to everyone for the thread derail here! I'll try to cut it out now.
The way closed loop comms works is the batteries give the target charge voltage to the inverter as well as the max charge and discharge amps. There really isn't much else that closed loop comms does. When comms are lost the inverter continues going off of the target values it received last. Those target values shouldn't be outside of a range that the batteries can tolerate, or you have other issues. (E.g. the battery's closed loop setup is pure junk!)
So no, I respectfully disagree with you. I understand where you are coming from, but temporarily losing closed loop comms shouldn't ever cause a blowup or a fire. I know the BMS will communicate an overtemp issue to the inverter, but if the BMS is worth anything it will shut down long before there is a fire!
Hedges
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What closed loop could do is reduce requested charge current and voltage during balancing, so it doesn't have to disconnect or high cell voltage.
That prevents system shutdown, but no catastrophic failure should occur either way.
Systems often disconnect at high SoC, maybe during load dump.
I think BMS ought to tolerate brief over-voltage.
That prevents system shutdown, but no catastrophic failure should occur either way.
Systems often disconnect at high SoC, maybe during load dump.
I think BMS ought to tolerate brief over-voltage.
Brucey
Solar Wizard
Sounds like a Rosie plus a Barcelona might be a better fit for you.
NC_hydro
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I was considering Rosie or two but was leaning Victron since I know they support comms with Trophy Battery. Plus, I'd prefer an LF inverter, even though I know MNS HF inverters aren't like the other HF junk.
No, hence why the topic has drifted
Honestly I think dual 10kw Quattros can be done cheaper than dual Rosie as well. There’s a lot more retailers with blowout prices from time to time offloading Victron gear
NC_hydro
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Yes, and the Quattro price is pretty close to the Rosie. ($3,609 vs $3,300) But Current Connected has my order when I do pull the trigger.
realpinochet
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I know they are making commercial grade equipment but they are missing a growing market and IMHO the future of residential solar. If they could get packages available for the inverters with a epanel without all the breakers and battery units easy to install they'd be direct competitors for some of the large brands like Schneider. I can't recollect but I believe they had large battery banks available with plug and play liabilities. The only thing Their inverters don't do that I would like is parallel, not so much for more power but for redundancy. I guess you can have a spare. But, a 40kW inverter was like what 9k last year? What was your quote for the battery?
realpinochet
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I'm talking about hardware efficiency, the generation and conversion processes. It's easier to step down than to step up? There used to be a few guys on youtube that used both systems LV vs HV and the points I made is what they found to be true. And, it's cheaper in both materials and ongoing cost.
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ImAnIdiotPleaseBePatient
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128kwh battery for $46k, $360/kwh
Exactly. You have gone from two levels of protection to one. The last level SHOULD work - but I have had BMS FETs fail closed before.
Like I mentioned, the BMS should never give a value (charge, discharge, voltage, etc.) to the inverter that can cause overtemp in the first place. All parameters that the BMS communicates to the inverter should be within range of what the batteries can EASILY handle! There is no reason whatsoever that a temporary loss of comms between battery/inverter should cause a fire! EVER!
Right. And no inverter should ever overcharge a battery, either. But sometimes they do. Which is why BMSes are so important.
Constant communication is another level of protection. Without it, if there are no other failures, everything should still work OK. With it - there's another level of protection. Which is why such systems are safer.
They do? The only times that I have seen an inverter overcharge a battery was when the settings were made incorrectly on install..... That would then be installer error. But maybe I haven't worked with enough bottom of the barrel cheap inverters...??
If the battery gives a charge target voltage of say 55.6V with a max charge amps of say 150A, (let's call it a 300AH, 48V LFP scenario...) then the battery loses comms with the inverter.... The inverter will keep that target 55.6V charge setpoint until it is told differently! When it hits 55.6V it will throttle back charging and just hold the voltage there! If the batteries will have adverse effects from that, then there are other issues! (Such as the question of why the BMS gave a charge target that it couldn't handle......) The inverter will NOT charge higher than that setpoint if it is a reputable inverter! If you can't depend on that then you need to scrap your inverter and start over! And if your battery has adverse effects because of the inverter charging up to the voltage setpoint, at or below the max charge amps setpoint, then your battery needs to be scrapped and you need to start over!
I have been involved in hundreds of LFP battery/inverter/solar setups over the last number of years, and probably 95% of them did NOT have closed loop comms! And guess what.... those systems have had less call backs and service calls than the closed loop comms ones! Closed loop comms is in NO WAY a miracle fix-all! In fact closed loop comms adds a layer of complexity to a system! If people are not too lazy to do their homework on proper parameters and setpoints, a system can work very well without closed loop comms!
Now I will say that on a high voltage battery (in my opinion anything over 100ish VDC really...) there SHOULD be closed loop comms! That is a whole different animal!
Don't be offended by what I am saying! I am simply spouting what I have learned and/or worked with over the years!
My personal conclusion is this:
Pros of closed loop comms=
- installer doesn't have to set charge volts and amps
- battery could theoretically tell inverter to slow charging on internal high temp (not likely to happen unless there is a loose connection... so this is sort of a moot point really... and furthermore I honestly think most BMSs would just completely shut down on overtemp without ever throttling charging, turning this into a non-elligible "pro"....)
- battery tells inverter the SOC (because some inverter brands can't accurately track SOC these days....) NOTE* this "pro" depends on the BMS to accurately track SOC, which many actually don't!
- Someone tell me more pros.... I can't think of any, really.
- installers are more likely to get lazy and not research the batteries and how they work because they can just "plug and play". This results in systems that don't perform well, or as they should!
- dependent on BMS to work properly, for inverter to work properly. BMS bugs will affect inverter performance and potentially cause power outages, glitches, etc. (I have worked on many systems that power offices, where I'm in trouble if there is a power outage or power glitch!)
- dependent on comms cable connections to not corrode. Sometimes inverter get installed in less than ideal conditions where they may potentially be more subject to corrosion..... Not ideal, but simply a fact of life when it comes to inverters and batteries!
- no universal protocol for closed loop comms, therefore you can't use just any battery with just any inverter. Some may think this is beneficial, I feel this is detrimental to the industry!
- Closed loop comms adds another layer to troubleshoot when there are issues! As someone who has done much troubleshooting over the years, I appreciate when things are done in a simple and easy to figure out way! Some may say, oh but you can hook up a PC to the BMSs and see what's going on... But why do that, when there is an option to not need that? More tech is not always better!
I know for a fact that when you understand how the batteries work and what each parameter in the inverter menu does, you can create an open loop system that has as good or even better capability than closed loop!
You are entitled to your opinion, as am I. I don't know about you, but I have formed my opinion from a number of years of installing and working with batteries and inverters!
One more note.... Just to make sure that you are aware of this.
BMSs are not there to keep inverters from overcharging batteries..... Their whole purpose is to "keep an eye on" the individual cells and shut down the whole battery if there is a cell overvoltage, overtemp, battery overcurrent etc., as well as do top balancing when there is cell imbalance. The purpose is not for comms.... The purpose is for cell and battery protection, in case of failures and issues. Comms just happens to be an additional feature of many BMSs that works out and adds to the useful functions of the BMS... running without a BMS nearly always ends up with cell failures, running without comms doesn't!
I am running open-loop with my skybox right now since I have 3 different types of BMSes but the drawback I can see if and when I switch to a more advanced inverter is the ability for the inverter to get an accurate SOC unless the inverter has a great coulomb counter or shunt. It seems like a lot of advanced features depend on having an accurate SOC. I wish these inverters would just connect to a victron smart shunt to get the current SOC.
HighTechLab
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One of the problems is if you use batteries with internal heaters, external shunts can’t be accurate.
Exactly.
And if that BMS reports that a cell is nearing the top of its voltage range, the communications interface will signal that to the inverter and the inverter will stop charging. If it does NOT stop charging (i.e. the comms interface isn't working or it doesn't have one) then the BMS will be the "last line of defense" and disconnect its charge FET to protect the battery.
Which is why having that comm interface is safer - even if it will usually work without one.
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