Bluetti AC200 MAX Want to max solar inputs

Welcome to the forum Jim,

This is sort of the problem with "black box/all in one" systems. We really do not have a good idea of what they exactly do.

In general, MPPT (maximum power point tracking) solar charge controllers will take any input voltage (within spec. range) and efficiently take the higher voltage/lower current from the solar array and down convert to the lower voltage/higher current to charge the battery bank (and run DC loads).

A typical MPPT controller will also automatically limit its output current to is rated maximum--Safely and efficiently. So, for a 145 Vpanel max input--You need to look at the mininum ambient temperature and calculate the voltage rise of the panel (Voc-cold). Pretty safely, unless you are in sub 0F weather, you can use a Vmp-array of around 100-110 Volts maximum.

And you and parallel as many series strings of panels in parallel as you want... Typically the "cost effective" maximum in parallel is around 1/0.77 or 1.33x that maximum current*voltage (Watts) your system can accept.

Now, too much current even on the input of an MPPT solar charge controller--You do run into safety limits--Too much solar panel current could burn out the input wiring of the controller if there is an internal short/failure. So that is one reason that you do not want to exceed the input current maximum rating.

Without knowing more about the actual MPPT controller--We do not know if the maximum input rating is the Max rating of the solar array (no more panels or damage would occur), or if thisd is simply the Max current the MPPT controller will draw...

We can play some math and you can decide if you want to "risk" your very expensive black box or not. But this is how it could be done.

For example, use Vmp~30 volt solar panels (very common voltage). And put 3x of those in series for Vmp-array = 90 Volts.

Your controller has an input rating of 15 amps, so the Pmp rating of the array would be:

• 90 Vmp-array * 15 Imp-array = 1,350 Watt array
• 1,350 Watt array / 3 panel strings = 450 Watts
• 450 Watts of panels / 2 parallel strings = 225 panels

So, if you can find 225 Watt panels (or a bit smaller), with Vmp~30 volts--You would would have an "over sized" solar array that would meet the input voltage and current limits.

I cannot tell you this would be "OK" to do and keep your unit "reliable"--But it could work from a generic approach to how we normally work with MPPT controllers.

The box is rated for something like 1,400 Watt maximum charging power (solar+DC input). The DC input (car charging, etc.) is limited to 8.2 amps... Not sure the input voltage range... Looks a little unusual:

https://www.bluettipower.com/products/ac200max-power-station

Input max: 12-60 VDC, 10 amp max
Output max: 11.5-14.5V; 23-29V, 7.9-8.4A

I would have thought it would be rated to 11.5-29 Volts--Which would be nice with a "12 volt" solar panel (Voc~22 volts, Vmp~18 volts)... But that "dead zone" in the spec--So cannot say if using solar panel would work or not... And is that ~8 amps @ 13 volts and 26 volts or what?

• 8 amps * 13 volts = 104 Watts
• 8 amps * 26 volts = 208 Watts (?)

The D050S DC Charging Enhancer output of 
rthttps://www.bluettipower.com/products/dc-charging-enhanncer-d050s

16-58.8VDC, 8.2 amps Max, 500 Watt Max

• 500 Watt / 8.2 Amps = 61 Volts output(?)
• 8.2 amps * 58.8 amps = 482 Watts max(?)

So the 500 Watt number is pretty close (rounding error).

Problem is that these have pretty narrow and a bit "unbalanced" operating ranges... To get 500 Watts max, you have to run at max input voltage. If you go over max input voltage, one would assume that the converter would be ruined.

And the DC input port to the AC 200 Max would appear to take a wider voltage input than the 12/24 volt input listed--But this depends on which port we are looking at??? Solar vs DC port?

This is one of those situations where you really need to talk with the manufacturer about how to maximize your solar input charging power.

There are a lot of nice videos out there where folks are doing some pretty well documented product reviews (lots more than just the one below):

https://www.youtube.com/watch?v=fwSbuHHbj6A

You have to be really careful here... Normally, we would just attach a MPPT Solar Charger directly to the BlueTTI battery bus. But because these devices have Lithium Ion batteries--And you cannot bypass the BMS (battery management system), and the manual says exactly this (do not charge through battery bus ports). If you bypass the BMS you run the risk of destroying your batteries (and possibly risk of fire) if you over charge them.

At this point, I would guess this are a bit "under powered" from a charging point of view...The limits of the charging ports and that you cannot charge via the battery bus--And the limits on charging volts/amps (you only get maximum charging Watts at Max input voltage and current). And there is only one "AC port" (which looks like a 1/2 power rating 1/2 voltage of the "solar" port).

Solar panels have a pretty wide range of output voltage (hot/cold panels, loaded vs open circuit voltage, etc.)... It is difficult to figure out a way to increase charging wattage much more than you are limited to with their accessories.

-Bill

No problem Jim, our forum is small enough that we can pretty much keep up with the posts most of the time.

Your questions:

• I live in northwest Mississippi.  Winter temperature lows above 0F.  Summer can be above 100F.

Solar panels in a wide temperature range will go from (Vmp=30 volts) Vmp-hot=24 volts to Voc-cold~48 volts. (Vmp-hot is voltage maximum power hot==And Voc-cold is voltage open circuit in cold climate/day--As a pretty much "worst case" voltage spread).

We can calculate the voltage spread more precisely... Just need the panel specifications. But for a rough rule of thumb in a very wide range of temperatures (hot desert to cold winter mountains), take Vmp*0.80 for Vmp-hot, and 2x Vmp-hot for Voc-cold. It gets you pretty quickly to narrow down your choices and details of the math.

Pmp = Vmp * Imp (power maximum power = Voltage @ maximum power * Current @ maximum power)

Current is not very temperature sensitive and moves in the "opposet" direction (temperature rises, Imp rises). But since the temperature sensitivity is about 1/5 to 1/10 as much as Voltage--We pretty much ignore current temperature changes.

Vmp-hot needs to be higher than the battery voltage. And Voc-cold needs to be lower than max input voltage (when the controller is drawing zero current). 

• I think I understand most of what you are saying.  Would it make any sense to put a MPPT solar charger between the panels and the Bluetti? 

You most likely cannot use a "Solar" MPPT charge controller... Solar controllers expect to connect directly to the battery bank bus and use that voltage to boot and run their internal electronics. I would guess the BlueTTI does not put battery bus voltage on the "DC charging" pins.

There are DC to DC converters that may work--But this gets into a lot of other issues. Most DC-DC converters are not MPPT type input (maximum power point tracking). If they "over load" the solar array, the DC converter can "collapse" the solar array voltage.

MPPT controllers track the Pmp=Vmp*Imp equation/results. And will only draw enough current to pull Varray to Vmp-array (if that makes sense). The output power from an MPPT controller is therefore based on the Array's power output.

A "standard" DC to DC converter trys to keep the voltage on the output side steady (Pout=Vout*Iout). If the array power is > output power (battery charging) power... All is OK. But if the battery "wants more power", the DC will simply pull more current. And once Iinput > Imp, then Varray will fall. And P=V*I, as V approaches "zero volts", Pout approaches "Zero Watts" (self fulfilling prophecy).

Think of an MPPT controller like a automatic transmission on a car. It matches engine power to wheel power by controlling Engine RPM to Wheel RPM as needed.

• Could an MPPT controller be configured to output only what the Bluetti can take as input in terms of voltage and amps? 

In theory yes--As practiced today--Pretty much now. Solar charge controllers are not "accurate" voltage controllers... They, more or less control charging current to the battery--And the battery bank is what "sets/holds" Vbatt bus voltage.

Yes, the MPPT controllers can have maximum current output programmed for lower levels--But voltage "regulation" is really a longer term average of battery voltage (seconds or more of averaging). 

If you have too large of an array with a large MPPT charge controller and a "small" battery bank, the battery bus voltage can exceed spec'ed limits.

•  I am probably showing my ignorance, but I see where there appears to no leeway in getting the rated input values. 

It is hard to say... Yes, in the "solar world" these max voltage limits are pretty much "hard numbers" based on the transistors/FETs/MOSFETs/etc. used in the switching circuits. If you exceed the input voltage by more than a little, the input silicon can easily be damaged/ruined. And some solar charge controllers will log a "warranty violation" if the Vinput is exceeded.

When you have "complex" black boxes--It is hard to tell from looking at the paper marketing specifications which are the "hard limits"--We can only guess at them. 

With MPPT Solar Charge controllers, typically the Vpanel input current is the same or somewhat close to the Vouput rated current. For example:

• BlueTTI: 500 Watts @ 59 volts @ 8.2 amps
• Power = 59 volts * 8.2 amps = 484 Watts
• 18 volt array Vmp * 8.2 amps = 148 Watt maximum from "lower voltage" array or other DC source (12 volt car charger, etc.).

A 60 Amp MPPT charge controller will have a rating of 60 amps to battery bank (12/24/48 volt nominal):

https://www.solar-electric.com/motr60ampmps.html

The controller is probably rated max input current of 48-60 Amps (tried to find, but could not!!!!!). Anyway, the input current is near or the same as the output current rating.

So that means the controller will "accept" input voltage from Vbatt+several volts to 145 volts max. Meaning that the controller can output max rated current with any within spec solar input:

• 29 volts charging * 60 amps charging = 1,740 Watts to battery
• 1,740 Watt charging / 30 Volt Vmp-array = 58 amp input Imp array
• 1,740 Watt charging / 90 volt Vmp-array = 19.3 Amp input Imp array

Much more flexible MPPT solar charge controller.

• I know people have said on the Bluetti site that you can go over on amperage, and the Bluetti will only use the spec amps.  No one has indicated a max amp and the the specs indicate that you can not go over.  Since they have a range in input voltages they must be adjusting it to charge the batteries.  There is a lot I do not understand. 

There are a lot of details that need to be understood and accounted for... However, it does seem that there are some definite limits to charging current/power into the battey bank. (I would like to see more charging power).

• I was hoping to run a refrigerator, freezer and a few small items all year long. A lot of clouds and rain in the winter.  The refrigerator and freezer pull about 300 watts together.  I have tested it with 3 of Bluetti 200 watt folding panels and got about 450 watts max in the PV port.  I can not run the 3 Bluetti panels through the D050S in series since that would go over the voltage limitation.  The D050S charge controller goes through the AC port.

Ideally, you measure/define your loads first, then do (typically) few paper designs (and with different hardware) to figure out both what works, and is cost effective for your needs. A too small system, still costs a lot of money and does not do what you need.

AC inverters can be big and fairly cheap. The battery bank--Expensive (or even 2-4x expensive with Li Ion). Most people get a large (or too large) AC inverter and to small of battery bank and too small of solar array. And they need to use a genset to keep up (especially during winter)--And can end up "murdering" their battery banks with over discharging.

I will run through a quick design for you to give you an idea how it is done. But do it in a second post.

• On the confusing gap in the voltages I think they are saying you can charge from a 12 volt or 24 volt battery system in a vehicle.  The input for a vehicle is through the PV port or the D050S charge controller and would be controlled by their voltage ranges.

There are three basic types of DC ot DC converters (switching power supplies):

Buck mode: Drops Input voltage to output voltage (24 volts input to 12 volts output)
Boost mode: Increases input voltage to output voltage (12 volts input to 24 volt output)
Buck/Boost mode: Can take "any" input voltage to output voltage (i.e., 12 to 48 VDC in to 24 volts out)

It sounds like the BlueTTI uses buck/boost converters (probably) in at least some of its power circuitry.

• I forgot to mention that it is also possible to charge the B230 batteries using the D050S. ($150 each)  That would require disconnecting the B230 batteries from the AC200 to charge.  If they are connected the charging is through the AC200.  Would be a pain to do every day when the sun is shining.

Yea... You can get another 500 Watts max charging (1400 Watts total?)--But again not a great "wide input range" for solar panels--So possibly less, or much less than 500 Watts with solar charging (guessing, not really sure).

And feel free to ask more questions. You are jumping into the deep end of the pool trying to learn how to swim (bought hardware first, then trying to configure to meet your needs).

Will go through the "math" in the next post and see if the BlueTTI + various options (battery banks, charging ports) could do what you want.

-Bill