I have a solar panel whose output is intended for use with a 12V system.
The actual output voltage under light load or no load rises to nearly 20V in bright sunlight.

I wish to obtain suggestions as to how I can regulate the panel's output voltage so that it never rises above 14 V in any circumstances.

Details: I want to use a solar panel to power a 12 VDC input to "mains voltage AC" output inverter in order to operate mains voltage A.C. Fans etc.

I wish to operate the solar panel + inverter without needing to use a low voltage battery.

When the inverter is operated directly from a 12 Volt battery it operates perfectly.
When I attach the solar panel to the inverter without a battery it does not work.

The inverter instructions advise that the inverter will only operate when the input voltage is in the range 10 to 14 VDC. However, when I use a solar panel which is intended for use with a 12 Volt lead acid battery system the open circuit voltage is well above 14 V (almost 20V) and the inverter will not start. Even if the inverter did start with eg the panel loaded temporarily to under 14V, if the temporary load is replaced by a useful load, the input voltage may rise above 14V during operation if the load is decreased and operation would cease.

  • \$\begingroup\$ Please add some informations about the inverter you are using, and i f possible try to be clearer since I find your question quite a mess to understand. \$\endgroup\$ – Vladimir Cravero Jul 7 '14 at 7:45
  • 2
    \$\begingroup\$ @VladimirCravero - the original question was written in English which was slightly different from "'Queen's English" which may help explain the original difficulty that you had understanding it. You may now find it more scrutable. \$\endgroup\$ – Russell McMahon Jul 7 '14 at 11:48
  • \$\begingroup\$ @VladimirCravero Hopefully the above comment did not come across as too rude. New users are extremely easily discouraged and terms like "quite a mess" which seem innocent enough when written can feel fairly brutal when received. Hopefully they will come back and add some extra data BUT the norm is that when a newcomer gets a 'less than encouraging' 1st response they never come back. Some members actually respond harshly on purpose (they have told me) to seek to drive off the more fragile newcomers. Those who survive are deemed more liable to be worthy longer term. \$\endgroup\$ – Russell McMahon Jul 8 '14 at 15:39
  • \$\begingroup\$ @RussellMcMahon Not rude at all, I just did not write back since the question was already answered. I'll try to be more encouraging then, I do not agree at all to the survive of the worthy policy. \$\endgroup\$ – Vladimir Cravero Jul 8 '14 at 15:44

Use a step-up-down buck converter (sometimes referred to as a SEPIC converter). These will give you close to 90% efficiency (or higher). A linear regulator like 78xx will waste a lot of energy, and can only step down the voltage and stop working when your solar panel goes below about 14V. Depending on your amp requirements, you can use an IC like LM2577 or LT1170, or just buy it assembled, buck converter, to get 12V independent of the solar power voltage. Usually buck converters can take high input voltages, LM2577 is rated about 40V, so this will not be a concern for you. Your concern is finding a converter that will supply enough current.

As a side-note, if you are charging batteries, use a trickle charger.


Panels can be loaded with a "dynamic load" that prevents their voltage rising too high.
But you need to know more detail about the system.
It may not start because Vin is too high or because the load is too great for the PV (solar) panel.

What is the panel Watts rating. This should be on a specification plate on the panel.

Approximately what is the panel size = height x width of panel area that faces the sun.

What are the inverter specifications. (Brand , model, datasheet link?, specification?

What load have you operated on it using battery?

More ... ?

Active clamp

Suited only for short periods and modest power. Can be refined when more is known.

Rload =~~ k x (V_panel_max_allowed)^2 / Panel_max_power

<0 < K < 1.
K is a safety loading factor to allow "a bit more load" than needed.
eg 12V 20 Watt system.
Vpanel allowed max = 14V say.
Rload <= k x 4^2 / 14 `= k x 16/14 ~= 1 Ohm Rload = 1 Ohm 20 Watt resistor.

Vloadmax ~ = Vzener + MOSFET Vgth.

enter image description here


Try to use a 7812 voltage regulator IC.

IC 7812 http://4.bp.blogspot.com/-sgAGvfFZI0Y/TteJghNOxeI/AAAAAAAAAgw/TyOOMm5Rpcw/s400/regulator.gif

Source : http://coretankanvasku.blogspot.in/2013/01/membuat-regulator-tegangan.html


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