# two different voltages in parallel?

I have two solar cells. one has an output of about 15-20v depending on the light. The other has an output of about 30-40v depending on the light. what will happen if I connect then in parallel? will the lower voltage one subtract voltage of the higher voltage one leaving me with about 15v? Will the amperage still double with both cells in parallel?

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and also , rectifier diode has a voltage drop of about .5 to .7 volts.

It is possible to connect 2 solar panels of different voltage output in parallel. but first, you need to connect rectifier diode on each output. this will prevent reverse-voltage damage, so that the higher voltage panel will not destroy the lower voltage panel. rectifier diode will connect in forward bias. it has anode (+) and cathode (-) the one marked with single line. if you want to connect diode on (+) positive of your panel, choose the anode (+) of your diode.

in your case, you have 20v max and 40v max. Theoretically in parallel connection, you can get the total voltage output by formula.

total v= sum of voltage / number of voltage source

so you have= 20v+40v / 2

= 60v/2

= 30v max

but your voltmeter analog or digital, will read the 40v of your solar panel mostly. i really dont know why.

if you have a load or battery connected, the voltage will drop. if you have 12vdc battery connected, the total voltage will be 12v. and expect increase of current flowing.

Menirz3 years ago
Take a look at this, it should give you some nice insight into the heretical realm of combining uneven power sources.

http://voltaicsystems.com/blog/combining-non-matched-power-sources/
gmoon8 years ago
Don't connect them in parallel if the voltages are that different!

When solar cells have unbalanced output, some of the cells become reversed biased (current flowing backwards.) The lower voltage cell becomes a load. This can cause the cells to overheat, fail (even explode, according to one source.)

Reverse bias can happen with solar cells fairly easily. One set of cells in the shade, one in full sun, for instance. Good cells usually have "shunt diodes" to prevent the reverse current flow.

If your cells are equipped with shunt diodes, the lower voltage cell probably won't be damaged, but it won't contribute to the output current, either.
carrierpilot1357 (author)  gmoon8 years ago
how about if I use a resistor to lower the voltage of the higher one down to about the same as the lower one? ~18v
8 years ago
Together with shunt diodes that might do the trick. Or a regulator, I guess.

Since one cell is exactly twice the voltage of the other, there are other options:

-- find another 15-20v, connect that in series with the first cell for a 30-40V total, then connect those two parallel to the other cell.

-- see if the 30-40V cell can be split into two separate 15-20V composite cells. You'd then have three of the lower voltage cells that could be used in parallel.
carrierpilot1357 (author)  gmoon8 years ago
what ohms resistor do I use to split voltage in half, what is the difference between a shunt diode and a shunt regulator, and how do I use either one?
8 years ago
A "shunt" is a pathway; essentially they work like a "release valve," or a "drain" if needed. If the term hangs you up, they often called "bypass diodes," too.

A shunt regulator works like a zener diode. It provides a path for current directly to ground when the voltage exceed the set value.

A shunt diode in a solar cell is just a regular diode placed across each cell or group of cells that need protection, creating a current pathway if the cell becomes reverse biased.

Using a resistor alone to drop voltage can be done, but it's fraught with difficulties-- the amount of voltage drop depends not only on the resistor, but also on the load.

I.E., the output voltage will vary greatly depending on the current draw you place on the system.

A regulator is one way around this. The simplest type is a zener diode regulator. Try using a zener regulator calculator to find the values. You still need to know the approx amount of current the panels can supply.
carrierpilot1357 (author)  gmoon8 years ago
the 30-40v cell is glass, so that might be a little hard to split it...
purduecer8 years ago
In parallel circuits, current is additive while voltage remains the same throughout the circuit. Thus, if both cells put out the same current, then the amperage will double. As for the voltage, it will reach an equilibrium point somewhere between 15 and 30 volts.