Convert a 12v solar panel to 6V

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Wayne Ramsay

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I want to build a solar powered Rc pusher tug. Most panels I've found are 12v, my drive system is 6v. How can I convert a 12v panel to operate a 6v system.
 
Well you can short solar panels without damage, so you could just have a 6 V shunt regulator.

For best efficiency you want a buck regulator, but it isn't that easy when you have a variable load and a variable source.

Can you tell us a bit more about the load? If the load is a motor, you could us a PWM controller, but with no battery in the way it could be difficult in variable light conditions.
 
You really need a battery anyway - so just use a 6V lead acid gel one and use the panel to charge it (presumably your panel isn't 'huge' so no controller would probably be required?).
 
It takes a 12V open-circuit (or higher) panel to charge a 6V battery. It takes a 19V open-circuit (or higher) to charge a 12V battery. Shunt regulator is easy. Series regulator is slightly easier.
 
You can use a buck converter, which is much more efficient than a shunt or series regulator. Here's one for $1, delivered: **broken link removed** Note that the maximum output current of this device is 3A. I guess you can work out if it's enough depending on your solar panel power rating, and on the motor current rating.
 
Running a SMP from a solar panel requires that it have MPPT capability. Otherwise when the SMP wants more current than the panel can supply the voltage drops , which makes the SMP draw more current , which sends the panel voltage toward zero or until the SMP quits working. If you put a 12V battery across the panel then this won't happen. A 12V 1Ah battery is the same size as a 6V 2Ah one.
 

This is why I like shunt regulators for battery charging. While the battery is still accepting charge from the panel, the regulator is totally out of the way, so all of the panel output is utilized by the battery. If the open-circuit voltage of the panel is a few volts above the battery terminal voltage, then the panel is naturally operated near its Max Power Point. The shunt regulator only has to do something (waste power) after the battery has reached full charge. The shunt regulator keeps the panel "loaded", reducing its temperature compared to what would happen with a series regulator, be it switch-mode or linear.
 
 
As long as there is a shunt regulator to hold the charging voltage constant at about 2.4V per cell, then you can parallel the two batteries. The only caveat is that if one of the batteries develops a shorted-cell, that will also kill its neighbor.
 
How if I us a Y from the panel then use one line to the electronic speed control, the other use another Y to charge the batterys
 
The "15-21V" panel is perfect for 12V battery, so if you put two 6V batteries in series, you'll be spot on.
 
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