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DC-to-DC Converter


The output voltage of solar panels goes up and down all day. This fluctuation depends on the brightness of the sun, or if there is cloud cover. An Inverter (DC to AC) cannot take this varying voltage as input. A Converter (see the picture) takes the variable Voltage coming from solar panels, and outputs constant voltage for the inverter.

SUMMARY: The voltage output from solar panels varies, based on how bright the sun is. This fluctuating voltage is a problem, since an inverter requires specific voltage range to operate. This is why we need a DC-to-DC Converter. It takes voltage from solar panels, and outputs a constant voltage for the inverter.

SOLAR PANELS (unstable voltage) —› DC-to-DC Converter (constant voltage) —› Inverter


PURPOSE: A DC-DC converter can be put to many uses. Here we want to use it to run solar in the daytime without batteries. Solar panels can be connected directly to an inverter and used without battery.

For an inverter to work, it requires a minimum input voltage, e.g. 12V, 24V, 48V, etc.
An inverter also requires a maximum input voltage, which must not be exceeded.

If you have a 24V inverter, and your solar panels can only supply 12V, the inverter won't work with the 12V.
If you have a 24V inverter, and your solar panels supply 24V, the inverter would work as expected.
Likewise, if you have a 24V inverter, and your solar panels supply 48V, the high voltage would shutdown the inverter, or could even damage it.

So, that means your inverter must be supplied with the correct voltage that it needs.

Your 24V solar panels only supply 24V when the sun is shinning brightly. So when the sun is not bright, or there is a temporary cloud cover, the solar panels would output less than 24V. So let's say the panels are outputting 10V, then your 24V inverter won't work.

At the point when your inverter isn't working because of low input voltage, the output from the inverter would be zero.
Normally, to deal with this voltage fluctuation, we use batteries. The batteries store charge for us to use, until the sun begins to shine again.

So what happens when you don't have batteries in your setup? How can you keep the inverter working under low voltage?
That is where the DC-to-DC Converter comes in. It takes voltage (low or high) from solar panels, and it steps it up or down to output a constant voltage that the inverter needs.

For example, let's say under bright sun, your panels output 36V. Your DC-to-DC converter would step it down to 24V, before feeding it to the inverter.
Conversely, on a cloudy day, let's say the panels put out only 9V. Again the DC-to-DC Converter would step up the 9V to the 24V that the inverter needs.

So as long as the panels are putting out some amount of voltage, the converter would boost or buck the voltage to what the inverter requires.

The output voltage from the DC-to-DC converter can be configured to match the input voltage for the inverter.

Look at the diagram below to see how the output voltage can be adjusted.

Connections


--------------   ----------------   ----------------
SOLAR PANELS |---| SOLAR PANELS |---| SOLAR PANELS |
--------------   ----------------   ----------------
 \
  \
   DC-to-DC converter
   (output = 24V DC)
   /
  /
  Inverter
  (output = 240V AC)



Voltage Adjustment

Basically, you connect solar panels to the DC-DC converter.
Next, connect a Voltmeter to the +/- output terminals of the converter.
Then use a screwdriver to turn the "Voltage Adjustment", until the voltmeter reads 24V, or whatever voltage your inverter requires.
Finally, remove the voltmeter, and connect the inverter to the DC-DC converter's output terminal.

With this setup, on a cloudy day, the Inverter will always get 24 volts input, and be able to output AC power. A set up like this can be used to run Water pump, Air condition, etc without batteries. Imagine running AC all afternoon without electricity bill.