Connecting Together Solar Panels Output and AC-DC Rectifier Output??

[emaq]

In post #3, it appears that 230VAC becomes 260VDC RMS is confusing

The inductor and FET on resistance creates a low pass filter and the overall RMS value of full-wave rectified output increases to 260V. Theoretically RMS of full-wave rectifier is 230V x 1.414 x 0.636 = 207V RMS but the filter filters out the high frequency components and the RMS values increases.

 

[c_mitra]

If you ignore the diode drop, the RMS value of the input AC and the (rectified but unfiltered) DC should be same. If you put a capacitor (but no load) it will increase to the peak voltage 325V but it will come down with load.

 

[KlausST]

Hi,

Theoretically RMS of full-wave rectifier is 230V x 1.414 x 0.636 = 207V RMS

This is the formula for average of rectified sine wave. Not RMS of full wave rectifier.

but the filter filters out the high frequency components and the RMS values increases.

RMS does never increase when you filter out any frequency component, it always decreases.
Because RMS = sqrt(V_DC^2 + V_f1^2 + V_fn^2)

Klaus

 

[emaq]

Hi,


This is the formula for average of rectified sine wave. Not RMS of full wave rectifier.


RMS does never increase when you filter out any frequency component, it always decreases.
Because RMS = sqrt(V_DC^2 + V_f1^2 + V_fn^2)

Klaus

You are correct... I meant the average (DC) will increase with the filter.

 

[c_mitra]

You are correct... I meant the average (DC) will increase with the filter.

In the rectified DC (full wave or half wave rectification of an AC waveform), we do not have any negative part. However, if the DC is time-varying, we can consider it to be combination of DC + AC components.

If you remove (filter off) any AC component, the average cannot increase.

 

[dick_freebird]

Or, depending on power level, find a fat isolation transformer
and start removing secondary winding turns until you get the
right answer.

I've got an old 20-pound Variac that's about a foot across.
I bet there are even bigger. How much current you want
from the line side, is the question. These critters can often
be found at surplus. But I don't think you need adjustability
of this sort per se, just to adjust the line conversion one
time.

 

[emaq]

What if the solar panels output is 300V and is directly tied to the rectifier output as shown below...

The 260V RMS was the actual voltage of rectifier output measured with a voltmeter before connecting solar panels.

 

[c_mitra]

The 260V RMS was the actual voltage of rectifier output measured with a voltmeter before connecting solar panels.

1. Measure the AC voltage;
2. Measure the DC voltage at the point labeled 260V;
3. Disconnect the solar panel and repeat step 2;
4. Disconnect the load (with the capacitor also removed) and measure the voltage once more.

Please tell us the actual load (used in the diagram) and the capacitor value. Use the actual load (1.2kW) and report the voltage back.

 

[emaq]

I think with the following configuration it will take most of the power from solar panels. The DC voltage after half-wave rectifier is 140 VDC (not 320x0.318 = 102 V) due to filtering and switching. The solar panel voltage under load is 170 VDC... therefore only for the rectified AC peaks above 170 V it will take power from the AC source while for rest of the duration it will draw power from the solar panels.


Any comments?

 

[KlausST]

Hi,

The DC voltage after half-wave rectifier is 140 VDC

The 140V maybe are the calculated average voltage without capacitor.
But you have a capacitor....therefore you can´t calculate with 140V DC.

I strongly recommend you to use a free simulation tool, like LTspice. Otherwise this will be an endless thread witout result.

With the simulation tool you may adjust all your input voltages, play around with your ideas and immediately see the result.

Klaus

 

[emaq]

Hi,
The 140V maybe are the calculated average voltage without capacitor.

Thanks for recommending simulation method.
With full-wave rectifier I have actually measured the DC voltage of 285 V after the rectifier using a multi-meter.

 

[KlausST]

Hi,

but half wave doesn´t mean half voltage.

With an unloaded capacitor both resulting voltages are the same.
But it´s different with load ... but not that much.


Klaus

 

[emaq]

You mean without load both half- and full-wave rectifier will have approx same voltage?

 

[KlausST]

Hi,

Exactely. But only - as clearely writen - with capacitor.

A 230V AC sine with full wave rectifer:
..gives 325V DC, with unloaded capacitor. (= 325V RMS, 325V average)
..gives 230V AC RMS, without capacitor.
..gives something between 230V RMS and 325V RMS, with loaded capacitor.

A 230V AC sine with half wave rectifer:
..gives 325V DC, with unloaded capacitor. (= 325V RMS, 325V average)
..gives 162V AC RMS, without capacitor.
..gives something between 162V RMS and 325V RMS, with loaded capacitor.

A simulation can show you this.

Klaus