On several posts I read about the warnings for adding solar power in series when the output voltage may be higher than the MPPT rated maximum input. One such post descried a failure caused by over voltage. I recommend Bluetti engineers to add an over voltage circuit to the MPPT inputs of each unit, such that it will shut down to protect itself, and need a power reset to recover.
Basically, such circuit uses a simple comparator to measure a sample of the input voltage through a predetermined resistor divider and compare that to a standard reference voltage (such as a Zener diode). When the input reaches and passes that set voltage, the comparator send a signal to the protection device. Most over voltage circuits use a “crowbar” device (such as a thyristor) to short the circuit power and blow a fuse (as if one tosses a real crowbar against two power terminals!). But instead of that dramatic result, just activate a new relay (rated to the maximum input current) and switch on a power resistor in series to the input to dissipate that excess voltage, lower the power input, and set a visual indicator of that condition or an alarm on the display, so the user must reduce that voltage and do a power down to reset the unit.
If that is possible for future Bluetti units, then I will also recommend designing, assembling, and selling an over voltage protection device as an add-on to existing Bluett units in customer hands. This may be using MC4 connectors or the unique DC charging port connectors depending on the unit. The unit will take power from the same DC input to activate the comparator initially and the over voltage protection itself.
Please reply if my idea is considered for production, so I may buy this add-on for my AC300 units.
I’ve gone overvoltage a few times on my AC200P and it just beeps and throws a fault code, no damage done so there is some protection built in.
@Raymondjram interesting idea man! So it’d be like an external box or device that would sit inline between the panels output and the units input that could be customized to a set “cut-off” point?? Sort of like Victrons Battery Protect modules but with dealing with solar voltages?? Love the idea and would be very useful for people that use panels for multiple devices/applications.
Not sure how it would be able to sync up with each individual units screen but then again, that really wouldn’t be necessary. It’s sole purpose would be to cut off the connection if voltages went beyond the predefined set point.
Genius man! Now get on it and let me know when I can get one!! Haha
In my post I am recommending Bluetti to consider adding it to the next models or producing the add-on because they have great engineers and a large production facility, while I am just a single retired engineer. Ther products may have this protection built in but if they don’t announce it, they might lose customers who buy their products and suffer failures. Anyhow, I am investigating on my own to build one for myself. If it is succesful, I will post about it here.
Hey please help me here.
Seriously. I am pretty ignorant of solar and electricity. In preparation for me buying AC300s and solar panels I bought D300s step down units from Bluetti. I know that if I plug in three of my panels I am about 150 volts. I do not understand what this means in amps. How many amps can I push against the MPPt until it shuts off or blows up.?
From everything I read I’m supposed to be worried about volts going in. Cool. But how does the MPPT controller handle amps?
By adding panels in series, you add volts but take the lowest amps of each panel. Hooking panels in parallel add amps but takes the lowest voltage of each panel. Typically, you want to hook up as many panels in series without exceeding the voltage, lower amp is easier to handle.
3 full sized 60 cell panel typically would add to about 120-130V, so you are within the limit of the AC300’s 150V limit.
The AC300 has 2 solar MPPT input, each can take up to 150V and 12A. You don’t have to worry about exceeding 12A, as any extra will just not be accepted and cause no harm. This is just like how your wall socket can provide 120V at 15A, a iPhone charger won’t blow up even though it only uses 0.01A, it will just not take anymore than it can.
With 3 panel in series, you are unlikely going to exceed 12A anyway. If you need more power, you can use another 3 panel in parallel forming a 3S2P setup, or use the step down and hook up more panels in series.
I found a programmable device on Amazon for $30 that protects against both over voltage and under voltage:
SVR1000 Single Phase Protection Relay Over-Voltage 20V-80V Under-Voltage 0.1V-30V AC/DC(AD48)
Would this suffice for protecting a Bluetti portable power station from overvoltage?
The contactor in that SVR1000 device is only rated for 6A max which may be enough depending on your panel configuration. For my 2s2p setup feeding into my EB150 which draws 8.7A at around 36V this wouldn’t work as I’d be 2.7A over.