More Diodes Questions...Bypass & Blocking

[luxint]

I did a search on 'diodes' to try and answer my own questions but none of the reply's seemed to address my particular issue.

I've read in a few places that bypass diodes are not needed in a 12v set up. Is that true?

If false how many would I need for a 100w, 5amp panel and are there any instructions on the net about installing them?

I understand that blocking diodes are not necessary as the controller will handle back flow but I should install one in each junction box when putting 3 panels in parallel, correct? I saw a video on YouTube about installing blocking diodes so that was helpful. Wish someone had a similar one about bypass diodes.

Thanks as usual

Lux

[Mike90250]

bypass diodes are not needed on a full sun system (no shade from dawn to dusk)

night time blocker diodes not needed if your controller also does that function.

But panels are made for lowest common denominator.

[luxint]

Hi Mike

Thanks for the response.

The quote I read was something like "bypass diodes are not needed on 12v system, optional on 24v and definitely needed on 48v systems'. So that's just BS then right?

Also I'm not quite sure what you mean by your last sentence.

But panels are made for lowest common denominator.

Thanks

Lux

[Mike90250]

But panels are made for lowest common denominator.

That means they are made to be the most useful, for the most systems.

[luxint]

Sorry Mike I should have been a bit clearer.

I understand the sentence I'm just not sure how it relates to my question regarding diodes.

Thanks

Lux

[Mike90250]

Companies could save $ by not includeing diodes, but then their panels would not work in less then optimun conditions.

So there is a bit of an extra cost, half a volt loss, and a few extra components in each panel.

[MarineLiner]

................
The quote I read was something like "bypass diodes are
not needed on 12v system,
optional on 24v and
definitely needed on 48v systems'.
So that's just BS then right?

[Mike90250]

[QUOTE=MarineLiner;9035]

[luxint]

Just an update on this subject for people that might be interested or when it comes up in a search.

I found this document http://www.scribd.com/doc/6576699/El...r-Power-Wiring that clearly states that bypass diodes are NOT needed on a 12v system. Large systems, 24v and above, however do require them.

Couldn't copy and paste because the document is in Flash format but the relevant section is 1.4

Hope that helps someone.

Lux

[mpan1]

My greetings to everybody in this forum!

I am new here and also i am starting my first panel!

Any tip, help advise would be great!!!!

I also have a question about the bypass diodes!

They are also connected with different polarity or is something more simple?

For example are there standard dimensions to use?How do you estimate the length of the diode?

I saw the images about the connections and my above question came up!

Is there a "guide" for connections?

Thanks to everybody here!

Looking forward in your answers!Pv systems are so interesting....!

[Anttistaatti]

System voltage has nothing to do with the need of bypass diodes. If a leaf happens to stuck on your panel you will lose power if the panel has no bypass diodes no matter if it is a 12V or 48V system.

mpan1 you asked "For example are there standard dimensions to use?How do you estimate the length of the diode?"

What do you mean length of the diode?

[Mike90250]

Diodes are sized by :
Reverse voltage they can withstand
Current (amps) they can transmit (pass)
Generally, your diodes should be rated for 2x (twice) the PV current. Then you look that up in the catalog, and it tells you what size that is.

[mpan1]

Diodes

Hey guys!!!

for starters, thanks for the answers!

About he length; A bypass diode should "cover" almost the 2/3 of a string of cells in order to work and prevent power loss!

In another thread, a guy posted an image (which by the way is very good) about how was his idea of connectin a bypass diode!And it was at least 3 times the width of a cell i think!

That's why i am asking if there are bypass diodes that you can cut any lenth you need and how am i going to ask for!

As older members here how did you solved the problem?

I am trying , even for the first attempt, to make something functional!

Thanks a lot!

[Anttistaatti]

Do you mean fysical length of a diode? You just have to solder some wire to the legs of the diode to get the length you need. Tabbing wire for example. The amp and voltage ratings are othe only specs you have to worry about when selecting a diode. I think you have seen pictures of "panel 2" in my website. I used insulated copper wire(wrapping wire) for that. But wrapping wire is only for low amps.

[Mike90250]

Guys, if you need to learn about diode lead lengths, and where to solder them to, you need a basic electronics class, which is beyond what we're able to do here. You have to know enough to ask the right question, or you are a bushman looking at a empty soda bottle, with no clue as to it's use. (see movie " the Gods must be Crazy")