Why do I need a blocking diode on the output end of a solar panel?

In some of the instructables dealing with solar panels, the instructions call for a 1N314 blocking diode. Is this really necessary? What happens if you don't put one in? Does the solar panel glow or something? Would a LED be just as useful? Where could I scavenge one if I had to use such a diode?

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Dr.Bill3 years ago
I use a 1N4004 on each of my 20w solar panels. You can get them new from Radio Shack much as I hate to say it. If you don't put the diodes in the batterys will discharge into the panels and you don't want that. You want a nice full battery. To scrounge one you might look in old TV sets or anything else electronic that has been junked.

iceng says:
Some glass diodes and epoxy diodes.

iceing has the right idea. The diode you use has to be able to handle the level of power your panel puts out. This is where you read the labels on the store bought stuff. You have to know your panel's specs so the label in the back of a commercially made panel will give you that info. Little cells found on the garden lights want real small voltage drops in a diode because the cell puts out so little electricity.

For better answers you need to write the size of your panel.
ie; Output Volts, Output Watts and Amps...

dcook123 years ago
I cant find any online can someone help me please
iceng dcook123 years ago
Check newark, digikey, mouser, or any other electronics retailer.
You are looking for a 250ma 25Volt PRV  low forward 0.45 voltage diode
like a 1N5817 diode costing 14¢ at Jameco..

dcook12 dcook123 years ago
http://www.rapidonline.com/Electronic-Components/3A-Ultrafast-rectifier-diodes-29686/?sid=a86d1862-2990-4a3d-a27b-07514b1d4315 would this one be ok?
frollard3 years ago
because silicon is a semiconductor, it conducts...sometimes.

This means, when there is no sun on the panel, instead of it pumping electrons 'forward', it acts like a resistor, draining power from the battery -- essentially, a solar panel with no light is a load instead of a source. The diode acts as a one-way valve, only allowing electrons to flow in one direction out of the solar panel through the completed battery circuit.

Now - LED is a 'diode', this is true. Only problem is most leds are inefficient for 'just' acting as a diode because they have a high voltage drop, 2-4 volts. That voltage drop is used to generate the light as the electrons excite the diode's molecules which then give off light. The amount of current an LED can handle is miniscule compared to most solar panels -- only .02 amps. A 1N314 diode has as small a voltage drop as possible -- and as large a maximum forward current as possible (a few amps if I recall) -- to be as efficient as possible.
javajunkie1976 (author)  frollard3 years ago
So where can I salvage one of these 1N314 blocking diodes? No budget to buy them. Radio Shack and Fry's salespeople are useless...
What do you need a salesperson for? Can't you read the label on a packaged part? The sales staff at RS and other similar stores are there to point you to what they sell, not to TEACH YOU ELECTRONICS.
javajunkie1976 (author)  Re-design3 years ago
I know they're not there to teach me electronics, no need to be nasty. Most of those salespeople aren't even aware what's in the drawers!!
You brought up the salespersons and there was no reason to do that either.

You can find a diode that you can use probably in most computer power supplies.  If you can find one that is un needed search for one there.  There are probably 4 or more if you can find them.  They are usually a small black cylinder with some numbers and a stripe painted on them.
...from a solar panel?

There's not a lot of common applications for that diode - they are quite cheap and readily available online. Check newark, digikey, mouser, or any other electronics retailer.
iceng3 years ago
So you don't want to kick over a solar garden light.....

Always far better then a RS and mostly outdo a Fry's counter types in my
self image, PM me and I will snail mail you some diodes because you
registered in o07 and sound broke :¬)

javajunkie1976 (author)  iceng3 years ago
I have extra solar garden lights, I just don't know what the heck the diodes look like. Got a picture of one?
Some glass diodes and epoxy diodes.