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Old 11-09-2014, 10:27   #1
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Solar discharge - diode

Hi there,

In an attempt to stop asking 156462 questions in a single thread, I'll make a separate thread about this particular one.

I know solar discharge can be a problem, draining batteries at night. I also know diodes are what you need to stop this process. But fairly little information seems to be at hand about this.

Some sources say the voltage drop in the diode is usually more than the power it saves by preventing discharge at night. I also find it hard to believe that the fancy MPPT controller I got from eco-worthy wouldn't have such a dead-simple thing as a blocking diode in it's systems to control this...

So, long story short: in the typical 1-panel array, do you need a separate blocking diode yes or no?
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Old 11-09-2014, 10:48   #2
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Re: Solar discharge - diode

Most if not all solar controllers have built in blocking diode function, so for single panel array would not need to install a separate blocking diode.

If multiple panels installed in parallel, blocking diodes are required in each parallel path I believe.

Check controller installation manual - likely best source of info on this.
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Old 11-09-2014, 10:50   #3
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Re: Solar discharge - diode

Fairly shitty manual... But your comment confirms what I already thought. Such a smart controller should be able to block it automatically .

Cheers!
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Old 11-09-2014, 14:22   #4
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Re: Solar discharge - diode

You can directly measure the current being consumed by the solar panels (if any). At night disconnect the positive lead from the panels at the controller and insert an amp meter between the panel and the controller. There should be no or very little current flowing.

If the current is greater then 1 amp then a diode might have a net power loss advantage. With a current of less then 0.1 amps a diode would most likely have a higher net power loss. For current flows between 0.1 and 1 amp exact voltage and current measurements would be needed to determine if a diode would be helpful or not.
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Old 11-09-2014, 15:37   #5
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Re: Solar discharge - diode

If you are worried about it, a simple switch in the lead from the panel to the controller that you turn off at night will certainly solve the problem.

Jim
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Old 12-09-2014, 11:04   #6
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Re: Solar discharge - diode

I bet a simple blocking diode is all that is needed. I'll bet if someone took the potting off a "controller" that is what would be found. It isn't nuclear physics.
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Old 12-09-2014, 11:06   #7
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Re: Solar discharge - diode

I'd be very, very surprised if that controller didn't shut the panels off at night.
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Old 12-09-2014, 11:43   #8
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Re: Solar discharge - diode

I notice the $100 controller does not say it has a diode.
20A MPPT Solar Charge Controller Free shipping |Eco-worthy

But the $500 one does...
2*100W 200 Watt Solar Panel Complete Kit with MPPT 20A Charge Controller |Eco-worthy

Bloody horrible when reading specs you have to read for whats not there!
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Old 12-09-2014, 13:54   #9
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Re: Solar discharge - diode

Hey guys, thanks for the extra input.

The MPPT controller in both those sets Mark linked to is the exact same one. They only make one type .

I sent them an email to be sure, I'll let you guys know what they say.
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Old 12-09-2014, 14:13   #10
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Re: Solar discharge - diode

Oh? Ooops! Damn. Reading is tomorrows lesson.

Ahhhh the diodes are in the panels! Look at the photos
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Old 12-09-2014, 14:21   #11
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Re: Solar discharge - diode

Quote:
Originally Posted by MarkJ View Post
Oh? Ooops! Damn. Reading is tomorrows lesson.

Ahhhh the diodes are in the panels! Look at the photos
They are bypass diodes and don't do the same job.

95% of controllers don't need a blocking diode and even without a controller you often loose more than gain by fitting one.

If you are not using a controller it is easy to measure the discharge current for your particular panels and make an estimation of the net gain/ loss of fitting a diode although you need to make some assumptions to keep the maths reasonably simple.

If the result is close it is safer to fit the diode as there can be situations where the panel output drops to zero (say covered in snow) and in this situation the discharge at night can become significant.
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Old 12-09-2014, 20:04   #12
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Re: Solar discharge - diode

I like Jim's work-around...seems to be an easy fix as opposed to searching for a the correct diode.
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Old 13-09-2014, 10:06   #13
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Re: Solar discharge - diode

Rgoing e: Diodes,

If your solar panel is maintenance 5-15W I'm sure someone at a local electrics supply store could set you up the correct diode, not Radio Shack, a real electronics supplier. If your using solar panels to keep appliances going eg. 145W I'd go to NAPA or canalize an auto alternator for the for rectifier diodes. I would use one diode per panel so if one panel goes tits up it wouldn't drag them all down.
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