Solar Panel with three wires and "cell protector" gizmo

[Ric]

I have just bought a Solara S280M42 Solar Panel. The bumpf claims it has some extra cells that give it better performance blah blah wah. But what surprises me is that it has three wires in the output lead which connect to a little black box called a "Cell Protector" from which there are two output leads.

Does anybody have any idea what the little black box does?

 

[William_H]

Solar panels

The individual cells of a solar panel tend to generate about .4 volt so you need a lot in series to generate enough voltage to charge a battery. How many cells and so open circuit voltage is a compromise question. To charge a battery you need minimum 14 volts. However you need more than that to ensure you get enough volts to charge the battery ie overcome static battery voltage when sun is not at optimum. ie morning or afternoon, winter or cloudy. Most manufacturers opt for 20v open circuit. Some choose less at nearer 17v. Certainly in UK more would be better.
However if you have an MPPT controller it is capable of transforming any voltage to that required by the battery for charging. It both averts wastage of too much voltage and can make the most of not enough voltage.
Regarding 3 wires from the panel. My guess is that the panel is wired in 2 sections either in parallel or series to minimise the effect of shadow on part of the panel. The sections being connected but isolated by diodes.
but I don't really know good luck olewill

 

[alan]

Ric,

I fitted four of these to friens and my own boats; I am less than happy with the reliability of these panels. Three of the four failed for various reasons, so good luck! One is still working after about 6 years but I had to repair this protection device.

On my friends boat this little black box (protection device) got fried and I think it was a lightning storm that caused this. Inside there are a few electronic components and one is FET transistor, this was fried; I managed to find a replacement and replace it. Despite some "burning" of the PC board itself it is still working some 3 or four years on.
I could never figure out what this protection does, as there is an earth wire involved I am thinking that it dumps seriously high voltages to earth through the transistor in cases where no regulator is fitted but as I said guesswork! On older panels from Solara this protection device was encased in a metal tube which was not possible to get inside; on another friends boat some water got into the cable (between panel and protection device) from a joint and caused this protection device inside the tube to fail ... I cut out the tube, replaced the water damaged cable, and it has been OK since.

So, I do not think this protection is essential where a regulator is fitted; I did ask the question of what it was to Solara but they never got back to me.

Alan.

 

[RestlessL]

As William_H says, the panel is in effect 2 panels in series. If one half is in shade the other half would need to drag the current through the dark cells. The protector provides diodes to give an easier path for the current.

Details are here:

http://starboardsun.com/products-page/solar-module-accesories/cell-protector/

J

 

[Ric]

Thanks all makes perfect sense. I had a light-bulb moment last night and figured they were just blocking diodes, but thanks for the confirmation.

 

[noelex]

Bypass diodes, not blocking diodes.
Bypass diodes are sometimes referred too as "cell protection diodes" because their primary function is to prevent individual cells overheating in partial shade conditions. As a secondary benefit the bypass diodes improve the performance of the panel when partially shaded.