Ac300 pv parallel settings question

there’s little documentation that I could find on “pv parallel” setting. I am using all 4 of the mc4 connectors into the middle pv charging port. curiously, my wattage seems to go down when I enable parallel charging.
I am assuming there are two separate charge controllers inside, one for each set of mc4 connectors? to get the maximum 2400 pv input I need to be on parallel enabled?
if I have power running into both sets, what happens if I don’t have pv parallel enabled?
maybe I don’t understand this function at all…
thanks for any additional info.

Bluetti has a short explanation on their youtube video https://www.youtube.com/watch?v=IqNXq9arIQQ at about the 9:00 mark. But, you are correct, there are two charge controllers. Each one has a 150Vmax and 12Amax, but total power has 1200W limit. So 8Amax@150v or 12A@100Vmax. The parallel enable does need to be turned on.

My answer here will be slightly different than what Milton stated. It is correct that there are 2 MPPT controllers in the AC300. Each can take 1200 watts of solar, each has a 150 volt limit (use the panel’s open circuit voltage value for this), and will limit current input to 12 amps. You can connect two separate solar banks, one to each MPPT controller, and connect up to the maximum solar input that way. Or, you can have a single solar bank of 2400+ watts, as long as the voltage does not exceed the 150 volt maximum, and connect that with a single MC4 connector pair to the AC300, then turn the PV parallel setting to “ON”. This will allow both MPPT controllers to use the single solar bank.

Note that you can put more than the 1200 watts of solar panels on each MPPT controller, or more than the 2400 watts total combined panels, as long as the 150 volt limit is never exceeded. The MPPT controllers will automatically limit the incoming current so as to not exceed their power capabilities (this is what would be called over paneling).

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that’s useful thanks. my Voc is about 126, so ok there. i have a single (very long) PV cable coming in and i split it into 2 for the two pairs of mc4 inputs. my watts seem to drop when i enable parallel input, but in this situation, using both sides, i don’t need parallel on at all. you are saying that the parallel setting allows the two charge controllers to share one single MC4 input (maybe if over 1200w). since i am using 2 inputs, i will turn parallel off.

That sounds fine for the Voc. I think you can use just a single pair of the MC4 inputs to the AC300, as well as removing the parallel connector from your PV cable. If your potential max input current considerably exceeds the 12 amps allowed on a single MPPT controller you may wish to turn the parallel feature back on (still connecting your panels to just a single MC4 pair from the AC300). I’d love to hear how that works out for you.

i will try that when i get back to the woods in 2 weeks. i have been able to get close to 1700 w input (16 amps) combined into both sides around noon, with parallel on, so i would need parallel on to go into one controller alone, or suffer losses, since i’m over 1200w and 12A. also curious to try parallel off using both controllers to see if things improve a bit. will update after i try this. thanks

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so is it fair to say that i could have a 10kw solar panel hooked up to the AC300 but only need to make sure i don’t go over the 150v i am ok. Some serial and most parallel. The MPPT will on take what it can handle and ignore the rest. I am asking as i already have a 10KW panel installed.

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So I think you’re saying that the single PV input can exceed 12A and you’ll get full PV as long as it doesn’t exceed 24A. Is that correct?

That would be my understanding of the parallel function, yes. The only question I still have personally is whether there is a need to use MC4 parallel cables to supply the input PV connection to both pairs of PV input, or not (ie: does it like all the current coming in through a single PV input pair). The D300S “PV drop down module” accessory (used to lower max PV voltage from large arrays), for example, has dual-pair outputs to go to the AC300, and it also makes use of the parallel mode.

Thanks for that. Good point about the D300S. If we DO have to use separate inputs, that means that there will be separate PV power “clipping” at each 12A-limited input, which would in general mean more wasted power than a single clipping at 24A.

I’ve got an AC300 coming and I’m trying to figure out which wattage panels (with their different Voc’s and Imp’s) in which configuration will maximize the power I can take in. And I’m aware that it’s recommended to stay below 80% of the Voc limit, which constricts the number of series panels further. It’s too bad that there aren’t more AC300’s out there, which would increase our chances of knowing what the actual constraints are.

I’m already editing this. If that separate 12A limit were in effect wouldn’t that mean that the whole purpose of the parallel mode wouldn’t exist. I’ll bet it’s only a 24A limit.

It’s hard to know if splitting the input would have any practical implication. However, speaking of solar panels, what I have done is purchased twelve 250 watt (used) panels. I will make two separate arrays so I can attach each to individual MPPT controllers. I don’t have my array mounts built yet, but I took a set of 6 and laid them out on the ground, slightly tilted, and connected with 3S2P. That gives me a 1500 watt array, of which I can use 1200 watts max (over-paneled). The voltage maxes out at about 113 volts (Voc is 37.6 volts, Vmax is 30.3 volts, Imax is 8.27 amps)). I have seen a maximum input of 1220 watts with this configuration. Once I have the mounting systems complete I should get this from both charge controllers.

I notice you are at 98%… in my experience the charge controller throttles back when it gets close to 100 %. your numbers/efficiency are quite good considering you aren’t at the equator ( I presume) . I get about 1700w out of an expected 2800 (3s3p x 320w), but I’m at 39 degree north, and it’s not summer yet.
I have not had a chance to fiddle around with the connections and settings, but I’m happy with using the doubled inputs. I’m not even sure if I have parallel enabled or not. will check it next time

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That’s useful information. Your total Voc is just over 75% of 150V and there’s no problem. And it’s not that warm yet. Good deal!

In the little spreadsheet I was working on to calculate the optimal configurations for panels with various wattages, Voc’s, and Imp’s, I had settled on 3S3P for a 250W panel with Voc of 37.29 and an Imp of 8.21A. That gave me 2192W after a minimal 8% clipping on three panels. Before I set up the spreadsheet I had tried some calculations with higher-wattage panels but that 150V limit (x80%) is a killer, and lower wattages seems to be the way to go.

image

That may not be any kind of global maximum but it sure is creeping close to 2400W.

I’m writing Bluetti tech support about the 12A/24A limit. I should have an answer by Wednesday morning. I’ll post it here.

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I’m also close to 39°N, so we’d have similar solar results. My panels were almost flat to the ground, and that was certainly impeding their performance, but since I’m over paneled they still were able to max out the MPPT controller I had the panels connected to. Regarding getting towards 100% full, I noticed that the AC300 went full-speed-ahead all the way. I would see the charge rate go from 1,200 watts to zero as soon as 100% was reached. Then would go back to 1,200 watts when the system went down to 99% again.

No reply from Bluetti yet on my 12A/24A question but it usually takes a second night in China before I hear back from them.

Hnymann, it occurred to me that you can determine for yourself whether Parallel Enable will take the PV from one input and distribute it to both MPPT’s. You could take three more of your 12 panels and lay out a third parallel string. If you turn on Parallel Enable and it works as we expect, according to my calculations you should get a total PV input (at STC, of course) of 2177 W with just the nine panels.

My spreadsheet screenshot above may have been a little confusing. Since I knew what it was doing I didn’t try to make it explanatory. The “P (no clipping)” is the number of parallel strings if you’re unwilling to have any generated power lost by clipping at 24A. The “max” values are if you want to add another string to max out the 24A and don’t care if you waste some of the PV you’re generating. (All this assuming STC.)

You are correct, I could possibly get away with using the parallel mode also; however, I had decided that I would do two separate arrays instead, and run the needed cables for each back to the house. In my case the solar mounting would be easier to do as 2 arrays, partly because they will be tilt-able mounts so I can adjust seasonally. So each array will be 1500 watts, and each to it’s own MPPT controller.

I didn’t find your spreadsheet confusing, I figured out what you were meaning with the clipping reference. Although this discussion does make me curious about what your understanding is, because, assuming by clipping you mean throttling back the electrical current input from the panels’ max ~16 amps to the 12 amps max for the MPPT, you would still have the clipping with the 6 panels (3S2P).

Yes, that is what I meant by “clipping.” The 1500W for “no clipping” with 3S2P is under the assumption that the parallel mode will distribute the current between the two MPPT’s. No response from Bluetti on that question overnight - perhaps by tomorrow?

Ah, ok, you were referring to both MPPT controllers, that makes sense. I hope they will respond, parallel mode is something that is not well understood at this point.

Just testing the Reply function after a previous problem. Please ignore this.

With the kind of overpanelling I’m thinking about right now, parallel mode wouldn’t matter. Perhaps someone can correct me of I’m off base on this:

Panels in the low-400-Watt range have Impp’s around 10A and Voc’s approaching 50V at STC. Three of those in series would bring you too close the AC300’s 150V tripwire, but a 2S2P configuration would have the potential to produce around 20A at around 100V. Although the AC300 trips for voltages over 150, as I understand it there’s no tripping for a PV source having the capacity to deliver 20A. The AC300 just accepts 12A on a single input and moves on.

So eight 400+W panels in two 2S2P strings would max out the AC300 and provide a decent amount of overpanelling for times of low sunlight - midmorning, midafternoon, cloudiness and winter. Because the two strings are identical there’s nothing to be gained from Parallel Enable, other than the ability to bring in only a single cable pair (which then would have to be heavier gauge.)

Am I getting anything wrong here?