So it is my understanding that the MPPT on the Bluetti requires voltage to be in the range of 35V-150V. Anything below 35V, it wont charge and anything above 150V could fry your MPPT(?). Or does it automatically shut down to prevent frying.
Because the specs say it will only take a max of 700W or 12A.
I watched a youtuber “Jehugarcia” charge the Bluetti through the solar PV charge port with a 36V scooter battery. I think he push 432W(36V12A) which makes sense to me. He then put 2 scooter batteries in series(72V) and was able to push like 712W through which meant to me that scooter batteries could have pushed more(72V12A = 864W) but maybe the MPPT regulates it so it cant overcharge(?)
First question is it safe to charge through the Solar PV charge port like this? I’m not sure if the 700W cap on the MPPT means it’s safe bc it only allow 700W to go through even though the scooter batteries could push more. Or are you suppose to keep the charge at a max of 700W? And you may be causing harm by overcharging(?)
Bc if it is safe, my next question is can I run a Sterling Power battery to battery charger which can take 12V input and can output 36V or 48V. The idea is to run the B2B charger through the Bluetti solar PV input. The voltage fits the range. But my concern is that the B2B charger would send too much Amps(?) But I’m thinking that if that is a cap on the MPPT that would prevent an overage so maybe it would be safe to do this? Or is this too much power and could potentially cause a fire hazard or something. Bc the Sterling Product takes a 12v input at up to 70 amps and output is 48v at up to 17amps. I know the 17amps is too much but Sterling allows you to limit to half so you could get 48V at up to 8.5amps which seems to fit the range of what the Bluetti MPPT can take. So charging off the Sterling B2B charger could net you(48V8.5=408W). But if there is a cap protection on the MPPT, I could run at (48V12A=576W). I’m reluctant to try this bc that would mean I would not be limiting the Sterling and would be sending 48V at up to 17amps and hoping that there is some kind of protection on the Bluetti.
Here is the link to the Sterling product:
Your technical advice would be greatly appreciated.
Welcome @Cheeky! First off I love Jehu’s videos and love the expansion options he’s introducing to the ac200. That guys’ VW vans are going to be absolutely incredible too! Haha
Now @Scott-Benson is truly the expert in all this and hopefully will correct me if I’m wrong but I’ll give it a shot… haha
The built in MPPT in the AC200 will regulate the input thru the PV side and you won’t have any issue as long as your VOC is between the 35v-150v range and your line isn’t producing over 12a. The AC200 also has a pretty badass BMS that will protect the unit from over current or short circuits and will throw up an error message before allowing it to harm the unit.
For instance, Dokio makes some 220w panels that are 11.2a/22.5voc that you could technically connect 6 in series to achieve 11.2a/135voc & “1320w”… now of course those panels aren’t sunpower cells like bluettis panels and def aren’t going to yield the same efficiency… but the MPPT in the AC200 will automatically adjust the available wattage to charge the unit. This is what people call “over-paneling”, and the beautiful thing about the MPPT charge controllers.
So as long as your input voltage and amperage is within the requirements, 35v-150v and under 12a, the internal MPPT will take care of the rest. I’d definitely recommend using that feature that allows you to cut the amperage in 1/2, but if your DC-DC charger for some reason is putting out to many amps for the unit to handle, the internal BMS current protections of the AC200 should warn you before doing any damage.
I agree with everything Mikey said except me being an expert. The only thing I am an expert with is foolishly spending money.
But…I recently did exactly what you are referring to in your question above. In my case I used a 24 volt battery (because that is what I had on hand) and a unit that stepped the voltage up to 48 volts at a max 20 amps. The AC200 limited the incoming amps to 11.9 even though the unit was capable of 20 amps. The unit I purchased is much less costly than the stirling you mentioned and it is available in a wide variety of voltage inputs (including 12 v) and voltage outputs. Click on the link below to see my post and see if this is what you are referring to doing with the sterling unit.
Another video (timestamp 9:49) has also demonstrated that the AC200 MPPT input can be fed from a non-solar DC source, and that the MPPT will throttle its input current to 12A.
Like the OP, I am planning to feed the MPPT with a Sterling DC-to-DC charger. In my case, I am choosing the 36V-nominal Sterling product (BB123670), because its configurable range of output voltages (~36.6V to ~46.5V) that can be sent to the MPPT (at 12A) corresponds to a range of alternator loads that I am comfortable with for my vehicle. If I was comfortable with higher alternator loads, the 48V-nominal Sterling product (BB124870) would be great.
Note that when the Sterling BB is feeding a non-battery load, you must configure it for “Power Pack mode”; see the “Force Options” section of the Sterling manual (page 10).
The price of the Sterling BB products is definitely breathtaking (~$500 with shipping).
I would prefer to use a Victron product to feed the AC200P’s MPPT input. However, I cannot find any Victron product that will convert 12V to >35V.
I hope the OP will report how his project turned out.
Good idea, @Scott-Benson. If one does not need any of the common features of a battery-to-battery charger (e.g. “ignition feed” input to switch charger on/off, adjustable output voltage), then a simple DC/DC converter like that Daygreen model would be much less expensive than the Sterling products.