Blocking Diode Question please:

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Hello,
( Heads up, I'm a newbie)

I am installing a solar array:

3s2p , 3 series 2 parallel
  • 330w each panel
  • 10.2A each panel
  • VOC 39.12v each panel.
Each series of 3 panels combined output is: 117v and 10.2A ( with a total array output therefore of: 117v and 20.4A, 1980W)

I have the Victron 150/70 Energy Smartsolar charge controller. ( and no I cant afford a second :oops: one )

I am installing on East West facing.

After watching Will ( truly excellent guy ) I need to install BLOCKING DIODES one on each of the two series. ( because only one of the two parallel series will be in the sun at any given time)

QUESTION: If I need a diode >117v and >10.2 amps, where can I buy one, or do I need to make it myself and put into a combiner box ?

I have looked online and could only find one MC4 type on amazon ( only one I could find on amazon had negative review because it "did not contain a Schottky blocking diode rather a "Schottky rectifier" and the reviewer went on to say "The mic rectifier has a much higher forward voltage drop, 0.750V"...."My 20A Schottky diode that I bought separately from amazon voltage drop of only 0.220V"

Everything is on hold until I figure out:
where / how to get the correct blocking diode ? / MC4 or installer box? / Are my numbers right ? ie: >117v & >10.2A ?

thanks for taking the time to read, all replies gratefully received...

 
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42OhmsPA

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From what I understand the panels already have the diodes.
I'm also trying to find something that will handle high voltage ~360 and ~12 amps, I have 9s S and W arrays I'd like to experiment if the additional diodes actually help. I've struck out everywhere I've looked.


Edit for clarity - panels do not contain blocking diodes, they have bypass diodes.
 
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upnorthandpersonal

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From what I understand the panels already have the diodes.

They have bypass diodes, not blocking diodes.

articles-solar3.gif


I tend to use a Schottky diode from Mouser or some other component store specifically tailored to my needs. Otherwise, for small arrays, just go with the off-the-shelf MC4 ones. You also want to run some tests to see if they make a difference at all.
 

BackTOschool

tellsteve2@gmail.com
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thanks for your responses so far... but both are not relevant to posted question.
Question remains unanswered..
 

BackTOschool

tellsteve2@gmail.com
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thanks for your responses so far... but both are not relevant to posted question.
Question remains unanswered..
I can buy off the shelf, but they do not meet spec.
From what I understand the panels already have the diodes.
I'm also trying to find something that will handle high voltage ~360 and ~12 amps, I have 9s S and W arrays I'd like to experiment if the additional diodes actually help. I've struck out everywhere I've looked.
The panels only contain BYPASS diodes for different purpose I believe, not relevant to question, thanks anyway
 

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They have bypass diodes, not blocking diodes.

articles-solar3.gif


I tend to use a Schottky diode from Mouser or some other component store specifically tailored to my needs. Otherwise, for small arrays, just go with the off-the-shelf MC4 ones. You also want to run some tests to see if they make a difference at all.
off the shelf diodes do not meet the min requirement as described, thanks anyway
 

upnorthandpersonal

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off the shelf diodes do not meet the min requirement as described, thanks anyway

Sure they do, the Amazon one you found. Ignore the 'high' Vf. See if they actually make a difference.

As soon as you go higher voltage, your Schottky diodes will automatically have a higher Vf anyway. For example, this 200V (you have to keep in mind that your Voc is going to go up in cold weather) Schottky diode (20A, 200V):


Vf = 740 mV

If you come to the conclusion that blocking diodes are really needed, you can invest in making a proper PCB etc. Before that, try one of the MC-4 versions and see if they really make a difference.
 

octal_ip

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QUESTION REMAINS.... THANKS
No need to be rude.

I suggest you do an experiment and connect the strings up without any diodes. As long as the strings are made with matching panels and of the same quantity, regardless of the orientation and shading they'll be producing about the same voltage as soon as they're exposed to daylight. This means that the potential for any backfeeding between the parallel strings is minimal, if any at all.
I have a 9S2P east/west array and have done the testing for myself. There is no reverse current to worry about.

I'd only consider blocking diodes if I had mismatched strings or if somehow one of the strings would be in complete darkness while the other was in sunlight.
 

timselectric

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1) any MC4 diode is fine for testing purposes.
I have east and west facing arrays, and tested with and without diodes. No noticeable difference, either way. If the sun is shining, the VOC is enough to keep current flowing the right way. IMO
2) yes, your numbers are correct.
3) politeness, goes a long way.
 

BackTOschool

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No need to be rude.

I suggest you do an experiment and connect the strings up without any diodes. As long as the strings are made with matching panels and of the same quantity, regardless of the orientation and shading they'll be producing about the same voltage as soon as they're exposed to daylight. This means that the potential for any backfeeding between the parallel strings is minimal, if any at all.
I have a 9S2P east/west array and have done the testing for myself. There is no reverse current to worry about.

I'd only consider blocking diodes if I had mismatched strings or if somehow one of the strings would be in complete darkness while the other was in sunlight.
sorry, didn't mean to come across rude, apologies.. problem a little frustration coming out ( sorry )
I would not have even thought of them until I watched one of Wills videos, explaining why you should use them on a east / west roof.
I give way to your testing experience, and if as you say they are not needed, I can save a whole lot of hassle!
Will says that they should be used when east west to avoid feedback as one side is out of the sun and as a result the shaded side will pull current back resulting in reduced output. so now I really don't know! :unsure::unsure:
 

timselectric

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sorry, didn't mean to come across rude, apologies.. problem a little frustration coming out ( sorry )
I would not have even thought of them until I watched one of Wills videos, explaining why you should use them on a east / west roof.
I give way to your testing experience, and if as you say they are not needed, I can save a whole lot of hassle!
Will says that they should be used when east west to avoid feedback as one side is out of the sun and as a result the shaded side will pull current back resulting in reduced output. so now I really don't know! :unsure::unsure:
Will's video is also why I thought that I would need them. And eventually decided that I didn't.
I'm sure that there are situations where they would be beneficial. Just not mine.
 

BackTOschool

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That's helpful to know, thanks.
seems a consensus they have minimal impact at best. So I'm now leaning towards not include them.
Can I ask your opinion ( on the comments ) made by another purchaser on Amazon re MC4 30A 1000V blocking diodes.
"..... do not contain a Schottky blocking diode rather a "Schottky rectifier" and the reviewer went on to say "The mic rectifier has a much higher forward voltage drop, 0.750V"...."My 20A Schottky diode that I bought separately from amazon voltage drop of only 0.220V"

If I did choose to use them ( I have already purchased ) Do the comments above mean they are not suitable because they will use more power?
is it negligible impact overall, or does he have a valid point and they should not be used?
thank you.
 

octal_ip

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Will's videos are a good starting point, but there are many variables involved and some design decisions really come down to testing theory vs reality.
I'm a big fan of The Off Grid Garage channel, because Andy starts with the theory but methodically tests everything, often with surprising results. I encourage everyone to do the same. It takes a bit of extra time, but you'll develop a proper understanding of your system and you'll have confidence it's working as it should.
Good testing will also help you disregard the things that may be true in theory, but have no significant real world effect (there are many long threads on this forum discussing these kinds of topics).
 

BackTOschool

tellsteve2@gmail.com
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Will's videos are a good starting point, but there are many variables involved and some design decisions really come down to testing theory vs reality.
I'm a big fan of The Off Grid Garage channel, because Andy starts with the theory but methodically tests everything, often with surprising results. I encourage everyone to do the same. It takes a bit of extra time, but you'll develop a proper understanding of your system and you'll have confidence it's working as it should.
Good testing will also help you disregard the things that may be true in theory, but have no significant real world effect (there are many long threads on this forum discussing these kinds of topics).
thanks useful tip I will follow up
 

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Will's video is also why I thought that I would need them. And eventually decided that I didn't.
I'm sure that there are situations where they would be beneficial. Just not mine.
That's helpful to know, thanks.
seems a consensus they have minimal impact at best. So I'm now leaning towards not include them.
Can I ask your opinion ( on the comments ) made by another purchaser on Amazon re MC4 30A 1000V blocking diodes.
"..... do not contain a Schottky blocking diode rather a "Schottky rectifier" and the reviewer went on to say "The mic rectifier has a much higher forward voltage drop, 0.750V"...."My 20A Schottky diode that I bought separately from amazon voltage drop of only 0.220V"

If I did choose to use them ( I have already purchased ) Do the comments above mean they are not suitable because they will use more power?
is it negligible impact overall, or does he have a valid point and they should not be used?
thank you.
 

timselectric

If I can do it, you can do it.
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That's helpful to know, thanks.
seems a consensus they have minimal impact at best. So I'm now leaning towards not include them.
Can I ask your opinion ( on the comments ) made by another purchaser on Amazon re MC4 30A 1000V blocking diodes.
"..... do not contain a Schottky blocking diode rather a "Schottky rectifier" and the reviewer went on to say "The mic rectifier has a much higher forward voltage drop, 0.750V"...."My 20A Schottky diode that I bought separately from amazon voltage drop of only 0.220V"

If I did choose to use them ( I have already purchased ) Do the comments above mean they are not suitable because they will use more power?
is it negligible impact overall, or does he have a valid point and they should not be used?
thank you.
These variables are minimal impact.
Those are the ones that many here have used/ tested with.
If you do decide to use diodes, keep them where they are easily accessible. They are known to be a failure point. And might need to replace them.
 

octal_ip

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That's helpful to know, thanks.
seems a consensus they have minimal impact at best. So I'm now leaning towards not include them.
Can I ask your opinion ( on the comments ) made by another purchaser on Amazon re MC4 30A 1000V blocking diodes.
"..... do not contain a Schottky blocking diode rather a "Schottky rectifier" and the reviewer went on to say "The mic rectifier has a much higher forward voltage drop, 0.750V"...."My 20A Schottky diode that I bought separately from amazon voltage drop of only 0.220V"

If I did choose to use them ( I have already purchased ) Do the comments above mean they are not suitable because they will use more power?
is it negligible impact overall, or does he have a valid point and they should not be used?
thank you.
They'd be fine, they'll just produce a bit more heat.

0.75v @ 10.2A = 7.65W heat/wasted energy.
0.22v @ 10.2A = 2.24W heat/wasted energy.

Worst case it's a 0.4% difference in the total maximum output of your array. Not worth worrying about.
 

BackTOschool

tellsteve2@gmail.com
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Thank you so much for your reply and advice, clearly I've been over cooking this ( personality trait )
 

BackTOschool

tellsteve2@gmail.com
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These variables are minimal impact.
Those are the ones that many here have used/ tested with.
If you do decide to use diodes, keep them where they are easily accessible. They are known to be a failure point. And might need to replace them.
Thank you for your advice, I don't think after speaking to you that i want to put another variable in the system that might fail. and it sounds as though the net benefit is negligible at best.
thanks.
 
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