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Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 08:01am 08 Feb 2012

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Hi,
I've got few Watt 12V solar panel without diode.

What diode should I put to prevent battery leaking power back to solar panel at night?

I know the simplest is to disconnect it, but when I am not there?

George

Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5111

Posted: 08:13am 08 Feb 2012

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Hi Georgen

Pick a diode with a amp and voltage rating double the panels rated output, just to be safe. If its a 12V 20 watt panel, for example, then a diode rated at 24 volts or more, 3.2 amps ( 20W / 12V * 2 ) or more will do the job. It doesn't hurt to go bigger, diodes are cheap.

For a 12v panel, a diode with a low forward drop voltage would be better too, means a little extra power in low ligh conditions, but not critical.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 12:43pm 08 Feb 2012

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Funny thing about those recommended diodes in solar panels.
I once tried to measure the reverse current with a smallish panel that was placed upside down on a table to block all light out.
The reverse current was very small, so small that I wonder if its worth to bother about it with fitting diodes.

Maybe some solar panels are different, mine was a polycrystalline type.
Has anybody else tried to measure the reverse current.

Klaus

Gizmo

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Posted: 01:03pm 08 Feb 2012

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Hi Tinker

I think it depends on the type, some leak, some dont, but other than that I dont know. I also remember something about diodes across each cell in case some cells are shaded, they can overheat if reverse biased. But again, old brain cells at work here, and this was for a solar car where each cell was wired individually.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 09:38am 09 Feb 2012

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Thank you very much for help.

Just was told that local Dick Smith doesn't keep any components, only selected shops do now.
Looks not many people do things themselves, and shelf space now carries some games.

Will have a look at JayCar.

George

Georgen
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Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 08:41pm 10 Feb 2012

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[quote] depends on the type, some leak, some dont
[/quote]

Measured couple of nights current back to panel and looks it is negligible.
(did not pick up on 0.06 mA scale on my Multimeter)

So as you said, some don't leak

All good then, thanks again for help.

George

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