I have 2nos of 12V,100W,5.8A solar panel (Solar open voltage is (Voc) 20V and Voltage (Vmp) 17V ) and i want to run 24V,3.9A,DC BLDC pump.
So, i connect both panel in series and my out put voltage is 40V (In load 35V). now i want to reduce voltage from 35 to 40V to 24V with 3.9Amp current.
and some time cloudy atmosphere voltage drop up to 9 to 10V and in this condition my pump is stop pumping.
So in this condition this circuit will short-out my problem?
This circuit is drop voltage from 40 to 24V
Also control current 3.9Amp
And if, voltage drop (due to cloudy atmosphere) it will boost voltage up to 24V
You'll need a SEPIC or a buck-boost converter. They are DC-DC converters that can have their input voltage lower or higher than their output.
But it won't work: you can't just expect the solar panels to put out 94W (24V * 3.9A) on a cloudy day. They are only going to be able to provide 100W when there's plenty of sunlight. If you want to run your pump when there's no sun, you'll need batteries (probably SLA's: cheap and easy to charge).
If you want to boost your 9~10V up to 24V @3.9A, you'll draw over 12A (@9V@90% efficiency) which is impossible. You can't just magically get more energy out of a boost converter than you put into it. The solar panels simply don't provide enough power to power the pump when it's cloudy, no matter what voltage you convert it to.
Less light → voltage drops → boost converter kicks in → draws more current → voltage drops even lower → draws even more current, trying to get 24V out → voltage drops lower than before → ...
The converter simply stalls, there is not enough energy to provide 3.9A@24V.
It's called the law of conservation of energy, and physics doesn't like it if you try to break its laws.
P.S: If you find a solution to this problem, don't tell anyone, just give me a call, we can do great business
Indeed, and my calculations are for during normal use only, while it's running.
It'll just stall before starting up, because of the high inrush current.
A BLDC pump may be fairly well behaved for inrush current, especially as 3.9A is the full load
current for 15m of head, and that amount of back pressure won't develop immediately.
But its not possible to be sure without testing it or more data.
Shame the photo of the motor doesn't show the nameplate of the motor legibly which is the only
useful information.
