Voltage between the charge controller and the PV panel?

**Mike90250** · 09-23-2014, 08:39 PM

Whoa ! Some of those numbers you typed in, are nonsense.
Don't know what wp is, along with others.

But you have a 7amp panel, and a 10 amp controller, so it should be fine. The controller takes the panel voltage and regulates it to charge the battery.

**inetdog** · 09-23-2014, 09:32 PM

And the way that a PWM charge controller (CC) does its job is by alternating between shorting the panel to the battery and opening the panel circuit completely.
A PWM CC set up for 12V batteries will have a Vmp of about 18V and a Voc of about 22.5 volts. That means that the CC can handle an input of 25V or more without damage, and that the load when the PWM switch is turned on will draw the panel output down to within a volt or two, so that the CC does not have to handle a lot of power.
An MPPT CC set up for 12V batteries may take and input anywhere between about 15V and 30V for inexpensive to hundreds of volts for something like the Midnite Solar Classic models. That gives you the freedom to use less expensive high voltage panels, or strings of panels in series.
As Sunking always says, with MPPT Power In = Power Out, so and input of 10A at 28V can produce an output close to 20A at 14V to charge a battery.

PS: In going from the per-cell data to the panel data you seem to have lost the distinction between the open circuit voltage (Voc) and the operating voltage (Vmp) and between the short circuit current (Isc) and the operating current (Imp).
One example: If your individual cells have an Imp of ~6.28A, the the Imp of the panels will also be 6.28A, not 7.57A.

**Mike90250** · 09-23-2014, 09:42 PM

since i see you have individual cell data, can I assume that you are building your own panel ? Building one for the fun of it is great, but if you are spending your grocery money on your own home-built panel, I have to warn you - don't. Too many things to go wrong soldering cells together and trying to seal it all. And the cells are basically, rejects being sold by unscrupulous vendors.

**inetdog** · 09-23-2014, 09:47 PM

Whatever else you may or may not do, be sure to test each and every cell for Voc and Isc before you assemble it into your panel.
If you see a range of values, toss out the really low current cells and try to match the cells in each panel to be close together in current value.
Having a difference in current from panel to panel is not a problem as long as you put them in parallel. But having a low current cell in a panel will effectively reduce the power output from that panel to correspond to that minimum current. (Bypass diodes will not help you when you are going to put panels in parallel.)

**sermormo** · 09-26-2014, 03:28 PM

First, let me introduce myself, I am young software engineer from Costa Rica, trying to learn slowly about solar systems, so that I can place an small system at home. I am planning to build an small solar system based on the solar cells described before, I know that solar systems has its own science so I am trying to learn the basics first on a small system so that I can move forward to bigger challenges. As you can see, I don’t have strong skills on electricity stuff so I will appreciate your help to learn about it.

inetdog

“A PWM CC set up for 12V batteries will have a Vmp of about 18V and a Voc of about 22.5 volts. That means that the CC can handle an input of 25V or more without damage, and that the load when the PWM switch is turned on will draw the panel output down to within a volt or two, so that the CC does not have to handle a lot of power. “

Thanks for your explanation about CC’s setups and max and min inputs, I am planning to use 12v battery PWM set up so assuming that if I correct my numbers I will be save.

“ In going from the per-cell data to the panel data you seem to have lost the distinction between the open circuit voltage (Voc) and the operating voltage (Vmp) and between the short circuit current (Isc) and the operating current (Imp).

The true is that I am not an Electric Engineer as I commented early, could you please help me to understand all those concepts (Voc, Vmp, Isc, Imp) in practical way so that I can understand and correct my numbers.

One example: If your individual cells have an Imp of ~6.28A, the the Imp of the panels will also be 6.28A, not 7.57A.”

How do you get to ~6.28A number?

“Whatever else you may or may not do, be sure to test each and every cell for Voc and Isc before you assemble it into your panel.”

How can I test Voc and Isc cells? I already bought Amprobe Multimeter at Amazon..
Mike90250

“Building one for the fun of it is great, but if you are spending your grocery money on your own home-built panel, I have to warn you - don't.”

I am building this panel for education purposes. So, I am okey to spent some money in order to learn… It will not heard me.. thank for the advice anyways..

Again thank you,
Sergio

**inetdog** · 09-26-2014, 04:18 PM

"Operating current: 6.12 amp -6.44 amp" That would be the Imp value for the cell.

Voc is the open circuit voltage. No load on the panel, just measure with a voltmeter from one lead to the other.
Isc is the short circuit current. Just connect a DC ammeter from one lead to the other, putting essentially a zero ohm load on the cell or panel. For a panel, make and break the connections with the panel covered to avoid sparks and damage.
Both open circuit and short circuit produce no usable power, since the power is volts times amps.

In between these two zero power points there is a combination of voltage and current which will pull the maximum possible power from the panel (for full light conditions).
This voltage and current are Vmp and Imp.

Voltage between the charge controller and the PV panel?

Voltage between the charge controller and the PV panel?

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