I have an Ac 200 max, AC 300 and a B300. I am wondering since the ac200m and ac300 works like the masters. Can I plug an ac200max into the expansion port of the ac300 and use it like an expansion battery? Or will is mess up the programming?
@AmyC
AC300 only supports connecting to B300/B300K/B300S and does not support connecting to other BLUETTI host with built-in batteries.
I propose to work on this! Many current Bluetti customers have an AC200max or AC200P and want to either pair two units or use those as slave for an AC300. I think it is technicially be possible and needs just to be supported by the firmware. Doing this update is a good way to keep customers. When we cannot reuse our already owned Powerstation in combination with new stuff to increase capacity it means we have to by all components again → making it worth considering swapping to a competitor with more compatible systems. But when we can reuse already owned stuff the chjoice is easy and most likely to upgrade with further Bluetti equipment…
By the way - I have the very similar issue and was hoping to join two AC200max somehoe togehter. You can connect them and the display of the active unit is mirrowed to the other device but only one unit is operational without accessing the extra capacity :-(
Yes that would be a great option. I glad I asked because I assume you could. Hope this can be an option soon!
@BLUETTI
Couldn’t power bank mode be added to the AC200MAX so that it can output from the expansion port using the P090D To MC4 cable at about 500 watts just like the B230 or B300 batteries allow. Even if the AC inverter would have to be disabled while this happened it will still be an amazing feature.
The ideal would be for one AC200MAX to act as a B230 when connected to another AC200MAX though.
BLUETTI P090D External Battery Connection Cable for B230/B300 - BLUETTI UK (bluettipower.co.uk)
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That’s an interesting idea and I dig it! Haha I’ve seen other brands release a sort of “parallel hub” that allow 2 units to work harmoniously kind of like this. I will add this to our “wish list” of items and pass it along for sure. Thanks for sharing your thoughts @Sideeffect 
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You do have me thinking. And an idea would be to have the ac300 as main power with display on app. Hooked into the b300 like normal for expansion battery. Then use the DC charger and have the ac200max having grid charging to both, since they charge in parallel. That would all be able to display on the app. Depending on your output if more than 1000watts discharge then you can also use the solar charge port with the connector. So the ac200max would be a battery bank to charge the ac300 and the expansion battery while you used them. You would have grid and PV charging together at about 900 or so watts I think this would work! Plus since it only calls for charge when below 100% so no risk of overcharging.
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I bought a spare P090D cable recently and was thinking I could keep it attached to the AC200MAX with the locks not engaged. My idea was having the B300 connected with two cables one to the AC300 and one to the AC200MAX so I could engage the locks as needed depending on which unit I wanted to use.
It doesn’t work because when the AC300 is off and the cable is attached to the AC200MAX even with the lock in the off position on both sides the AC300 powers on and an alarm goes off BMS error. It seems that the lock is only for power delivery and that data communication still takes place when the lock is not in place as soon as the cable is connected.
It is not very efficient to charge one battery from another battery using the inverter so I only really do it when it’s excess solar power that would go to waste.
The problem with the AC300 AC input is that it syncs to the grid voltage and enables UPS mode. There is no way to disable the UPS mode and the idle power consumption increases in UPS mode so it ends up using more idle power.
For this reason I use a smart plug and keep the AC300 disconnected from the mains most of the time only turning it on when energy is cheap. I still want it connected to the mains so I can charge it remotely from mains if needed.
To transfer power from the AC200MAX to the AC300 I use the B300 battery. The T500 charger goes into the DC7909 port for 500 watts and I can transfer about 110 watts using the 12V cigarette port on the AC200MAX going into the 200 watt MPPT port of the B300. This allows about 600 watts of power transfer while not engaging the UPS.
I have also transferred power the other way using the 24V output on the AC300 to send 250 watts into the MPPT on the AC200MAX. Currently I have solar panels connected to both units though to take advantage of the extra solar generation.
I hope that when the balcony 2 micro inverter by Bluetti is released that they have some new ways to link to older power stations and batteries.
I see we made the same DIYs for testing…! I investigated the P90D cable some time ago, in fact in this large cable, there are in addition to the 2 large conductors (for power), 8 thin data cables corresponding to the 8 pins that we see on the big connector. These data cables are connected or not to each other in the P90D cable. The switch lock is only used to connect one of the data cable. It’s quite simple. When the P090D is connected to the B300 or B230, which are put into power bank mode, the (good) combination of data cables connected together is tested, and if this corresponds to the expected combination, the B300 or B230 delivers power. On the other hand, the powerbank function is not implemented on the AC200max. When you plug this cable into the AC200max, it detects an error on the communication port (the 8 pins/cables, some of which are connected together in the P90D), it then goes into BMS error and turns off. When you force it to turn back on, you no longer have any useful display information, no SOC, the bluetooth is active but you don’t have useful information anymore, and the solar inputs don’t seem active either. So even if you manage to draw power from the P090D, as the BMS is out and it is he who ensures the safety of the battery (AC200max) it is a little dangerous for your AC200max. Finally, important clarification: the P090D only supports 500W. If you draw more power the cable will heat up dangerously.
It would indeed be a plus to implement a powerbank mode on the AC200max !!
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Thanks @Snips1 that is interesting. I sort of realised the same by connecting the standard P090D to the B300 and trying to enable power bank mode with the other end not connected. It doesn’t work because the pin arrangement must be different.
It is a shame because it might have been nice to cut this spare cable in half and create two power bank cables using lower gauge wire like for example using AWG6 to AWG10 reducer or a fuse block so I can connect to a standard MC4 connector. However if I knew the cable arrangement and which data cables need to be joined together for power bank mode perhaps it would be possible. Do you happen to know? 
“important clarification: the P090D only supports 500W. If you draw more power the cable will heat up dangerously”
Does the B300/B230 not limit the current to 10A in power bank mode? How were you able to draw much more than the 500 watts? The MC4 end of the official P090D to MC4 power bank cable does look particularly thin at the MC4 end. I wonder why such a thin cable was selected and the price is high so no real excuse.
I read on a forum a long time ago someone who wanted to do the same thing as you: take a p90a cable (the expansion cable supplied with the b230 and B300), cut it in two to make two P90D cables. He succeeded, except that he did not sufficiently isolate the two power conductors, an electric arc/short circuit was created and he destroyed his B210 or B300…
It is also very dangerous for yourself because the direct current intensities are very very high.
I will not do it because in addition to the risk above, for me the p90a expansion cable is impossible to buy while the P90D cable is sold online. You will need the p90a cable to connect to an ac200max or ac300, to update the B210 and b300. This is a precious cable, I will not destroy it.
However if you still want to know how the 8 cables/pins are connected, just take your P90D cable, with a multimeter you measure the resistance between 2 pins, trying all possible combinations. You will know which cable/pin is connected to another.
I did it, I don’t remember where I put my notes, but I advise you not to do it but to buy a P90D-mc4 Or xt90… directly!
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Thanks Snips1. I got this second P090D To P090D cable for £15 on eBay from a private seller and it is in good condition so good to keep as a spare as like you say it’s not possible to buy replacements from Bluetti. I will look out for a power bank cable when they go on sale.