Bypass Diodes

[Mike90250]

Holy Crapola.......look at these.....'Smart' Bypass Diodes: http://www.mouser.com/new/Texas-Inst...-bypass-diode/

z

Those look like a winner !

[Zardiw]

Holy Crapola.......look at these.....'Smart' Bypass Diodes: http://www.mouser.com/new/Texas-Inst...-bypass-diode/

z

[Zardiw]

What about these.......would they work on a 60 cell (6"x6") Panel?
http://www.futureelectronics.com/en/...-TAP.aspx?IM=0

Edit. Found out those won't work. Too weak.

[Zardiw]

So where can you buy them.......do they make thin ones?

z

[Mike90250]

Those diodes should work OK. For the diodes you expect to be "active" when shaded, you should heatsink them - don't forget their case is electrically live.. With .63V @ 7.5A, you will be dissipating about 5 watts per diode, so chose a heatsink accordingly, strive to keep junction temp below 90C, sure their spec is 150C, but they won't last long that hot.

[Solmark]

Mike,
I was planning on using some bypass diodes, the gif will hopefully explain, that said, schoolboy error on that drawing - all diodes placed the wrong way round!

Regarding Schottky Diodes, these seem to be freely available for about $0.75, how do their specs look to you? Array Max output 20v, 7.5A

Manufacturer: MULTICOMP
RoHS : Yes
Description : DIODE, SCHOTTKY, 16A, 45V
Diode Type:Schottky
Repetitive Reverse Voltage Vrrm Max:45V
Forward Current If(AV):16A
Forward Voltage VF Max:630mV
Forward Surge Current Ifsm Max:150A
Operating Temperature Range:-65

[Mike90250]

...is this thinking totally silly? Mark

No. As long as you have thought it out, and are happy with the tradeoff's you mention.

The .GIF did not come out real clear on my work computer, I'll look at it tonight, I'm not sure how you will bypass the lower 5 cells, will they have their own diode ?

No way you are able to orient the panels to avoid the shade ? Bummer.

Also, have you thought how you will prevent moisture buildup in the array ?

[Solmark]

bypass diodes

Mike, Thanks for such a rapid response, (non dragon gif of said pdf here by the way) pv schematic.GIFnot to mention the heads up regarding ply and plastic, not that I was going down that route.

If I may expand a little on my thinking... (charge controllers were next on my list to investigate and may well deserve some searching on here before I put my foot in it there too)

proposed output of panel was to be, in an ideal sunny cool situation would be 20volts @7.5 amps.
each of the 8 strings of 5 cells contributing 2.5 volts at said current

During the 3 darkest months of the year, when the sun is shining, (rare but appreciated in my part of the world) the lowest 5 cells would be in shadow - not a good thing)

If however they were bypassed I would, or at least could hope for 17.5 volts from the remainder of the panel, enough for a deep cycle recharge.

However, on cloudy days where all cells are getting a diffuse light, the extra cells may help the overall supply to the charger.

Now I appreciate that in high summer I'll be loosing some valuable voltage, but to be frank the power demands on my outbuilding will also be lower, ie less lighting and longer daylight hours to compensate as well.

is this thinking totally silly?
Mark

[Mike90250]

1) I don't open PDF's from new posters, sorry, too easy to have a dragon lurking in there. I'd open it a week from now, when new AV updates are out.

2) design for shade, will fail. If you over-voltage the panel to allow for loosing 3,6 or 9 volts in shade conditions, then when in full sun, your charge controller will waste the extra voltage, and watts are lost. If you DON't comnpensate by over-voltageing your panel, then when the shade occurs, the 3 volts bypasses, your 17V panel is now 14V and too low to charge a 12V battery (12V deep cycle battery needs 16V to fully recharge, it's not a car battery with brief discharges from starting)

Best is to mount smaller panels, in parallel, so when shade happens, you only loose wattage off your array. PanelDiodes.gif PanelFire.jpg
Click on the thumbnails, and observe the results of plastic & plywood DIY panels.

Panel diodes need to pass the full array amps, so if you plan a 3A array, you need 6 amp diodes. They should be Schotkky Diodes, which have lower Vf and waste less power. You need to research this in an electronics class, as to why, and how, that's beyond the scope of free advice, just enough to get you in real trouble.

Read the earlier posts in this thread, some of which have links to background info on diode applications.

[Solmark]

specify diodes

My thought too, I'd put them in every 3 volts, that way, if shaded, losses are lower.

Many DIY have no idea how diodes work, how to orient them, and how to conservatively rate them to work with out heatsinks.

I'm in the process of designing my first panel.

The panel is to be somewhat experimental in design and have decided to include bypass diodes principally due to winter shading of the lower 15% of the panel. Unavoidable thanks to location.

Each panel designed to give a notional 150 watts
using 6"x6" polycrystalline cells 3.5w 7.5a 0.5v (0.6v full sun) each
40 cells total - 5 across, 8 high .

I want to provide a bypass for each of the 8 horizontal strings of 5 panels - running bus bars to a box on an end of the panel where diodes can carry a heatsink if needed, be acessed, either for maintenance in the future or/and to remove them from the circuit for evaluation purposes.

Can someone explain how to assess the rating needed for these diodes, or better still recommend some to me, I do however need to understand the how and why.

I do bricks better than electronics.

Schematic below

[Mike90250]

My thought too, I'd put them in every 3 volts, that way, if shaded, losses are lower.

Many DIY have no idea how diodes work, how to orient them, and how to conservatively rate them to work with out heatsinks.

[solarrules]

Thanks Mike. That's what I thought but I needed confirmation.

Other than a small cost increase and a small complexity increase, I don't see any reason why a DIYer shouldn't be fairly generous with bypass diodes.

[Mike90250]

Does a bypass diode subtract from panel performance during times of full light?

Generally, no.

[solarrules]

bypass diodes in full light

Does a bypass diode subtract from panel performance during times of full light?

[Anttistaatti]

My new panel with bypass diodes is finished and it works great. I used 8 diodes for 36 cells. You can see it here http://sites.google.com/site/diysola...i/solarpanel-2