Options for shading diodes as alternatives to what was fitted

[Jon Miller]

Hell guys and girls,

I have just been back from fixing a single PV panel system that is running a friend of a friends van that she lives in on a bit of land.

The panel is ~ 170 watt, 72 cell panel, the label has come off, it is wired to a 24 volt battery bank via a PWM charge controller.  Not Ideal but it was putting out 100watts so is working.

Some how, the lady has mullered the shading diodes when she reconnected the panel after moving it.  She doesn't know what she's done with it.

I removed the diodes as they where reading short circuit and where to hot to touch, they still read SC when they where removed.

I cant track down the same diodes on ebay and would like some help finding an alternative that would work.

The number on the panel is SB1240 and a google search lead me to the following data sheet. http://pdf1.alldatasheet.com/datasheet-pdf/view/205321/DIOTEC/SB1240.html

Can anyone recommend an alternative for this that I can get in small quantities, ie three.

Many thanks

Jonathan

[Mary B]

This should work http://uk.farnell.com/semikron/sb15100s/diode-schottky-15a-100v-axial/dp/1772110

[birdhouse]

did you try running the panel without the diodes? 

i've recently set up some 24v laminates without the diodes.  they worked great! 

some folks here swear against diodes in panels in certain situations.  i believe a single 24v panel might well fall under those conditions. 

adam

[bob golding]

certain situations. the far north in the summer maybe?
  i thought the diodes were to stop the panel being back fed at night. this is only true if you are feeding straight into a battery of course. if you are using a controller you wouldnt have this problem as the controller would do the same job.
is what you meant?

[DamonHD]

Let's be clear about the difference between back-feed diodes and bypass diodes: the first to prevent backfeeding and the second to allow the panel to work in the presence of a shaded cell or two.

Rgds

Damon

[Jon Miller]

Some how, the lady has mullered the shading diodes when she reconnected the panel after moving it.  She doesn't know what she's done with it.

I am talking about the by-pass or shading diodes, these diodes stop a string of cells becoming hot spots if they are in shading and the rest of the string of panel(s) is in full sun.  If this happens and there is no by-pass then the cells that are shaded can risk disordering themselves and thus nackering the panel for good.

The setup for my friend, is one panel, no shade what so ever, so not a massive deal that the by-pass diodes are not in parallel currently, but if she moves the panel then there could be a problem.

Thanks

Jonathan

[OperaHouse]

Unless you are operating in the 100V and higher range shading diodes don't do anything.  They are there primarily for higher voltage grid tie systems and higher voltage inverters.  In most systems if you drop 6V from a panel everything stops.

[Jon Miller]

Thats a good point.

My thinking is that the panel might end up with others attached and running on MPPT in the future and bypass diodes will be needed then for sure, for the price of diodes I would rather swap them out on the potential.

Thanks

Jonathan

[dnix71]

That diode is no big deal to get. The 1240 means 12 amps at 40 Vmax reverse.

http://www.ebay.com/itm/20-PCS-15A-45V-Schottky-Diode-SCHOTTKY-BARRIER-RECTIFIER-for-solar-panel-DIY-/261085308808?pt=LH_DefaultDomain_2&hash=item3cc9e5a788

15 amps at 45 volts. $16 for pack of 20.