Shottky Diode! What is it and do I need one.....?

chasroberts

chasroberts

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The replacement Marlec HRDX controller is being ordered as I type. Somebody has told me that I should have a Shottky Diode fitted somewhere in with the Solar panel arrangement. Solar panel is a flexible 32W Uni-Solar.
If I do need one of these diodes can anyone help with sourcing, fitting instructions etc.
Just when I thought it was all sorted as well!!
Grrrrrr....
Many thanks.

Chas
 
To be technical, a Schottky diode is just like an ordinary diode, except that when a reverse voltage is applied across it, it will begin to conduct at some preset level.

Thus a '4V7' Schottky diode conducts in the forward direction, but will also conduct in the reverse direction if a voltage of more than 4.7V is applied.

I can understand an ordinary diode being needed to prevent the battery discharging into the solar cell, but why a Schottky, I've no idea.

They're usually used to give a reference voltage in things like stabilised power supplies.
 
The HRDX is a controller able to combine and regulate the output from a Rutland 503, 913 or 910-3 wind turbine with up to 100watts of solar power, using pulse width modulation, and split the output between two battery banks.

The instructions should tell you all you need to know, but they do not appear to be available on-line. I would think it highly improbable that any additional components are necessary but see this page of the Marlec website if you have more than one solar panel in parallel.
I am sure Marlec will be able to help if you need any further advice.

You will find an explanation of what a Schottky diode is in Wikipedia HERE if you really must know.

For a solar panel on its own the HRDX is a bit of an overkill isn't it.
 
Correction. A diode is required if one is not already included in the solar panel to prevent it taking current from the wind turbine. See This page of the Marlec website. I assumed that everything necessary would be inside the HRDX but i suppose the blocking diode is not to cater for the fact that many solar panels have a blocking diode already built into them.

So then yes fit a diode, Schottky if you wish, between the panel and the HRDX if your panel does not already have a diode fitted or it will take current from the wind turbine.

If your panel is the flexible Uni-Solar FLX-32 then it already incorporates a blocking diode.
 
No CNH you are thinking of a Zener Diode used for voltage regulation.

A Schotky diode is a normal diode in that it conducts only in one direction. It does however recover from blocking to conduction at extemely high speed (of no interest in this case at all but cause for their use in switch mode power supplies eg for computer) but also has a much lower forward voltage drop than normal silicon diode. I think in the region of .2 volt drop in forward direction.

Now in the case of a simple solar panel connected to a battery a diode is connected in the +ve wire to stop leakage when the light falls. Now a silicon diode is fine for this job and is usually supplied fitted to the panel. The forward volt drop of the diode is of no concern becausae the panel produces in excess of 18 volts unregulated. The voltage is simply pulled down to that of the battery ie when the current flows the solar panel voltage falls. So the panle puts the rated current into the battery regardless of charge level.
This is not a problem with small panels.

However if the solar panel has a regulator (charge control) then the voltage of the panel is limited or reduced to 14 volts. This is a suitable voltage whereby when the battery reaches that voltage no more charge current will go in so overcharge can not occur.

If you try to feed 2 batteries via 2 diodes then just as with alternator charging the battery voltage will never rise above the regulated voltage minus the diode forward drop. (.7 volt for silicon diode) If however schotky diodes were used then the smaller volt drop means batteries will still not charge fully but to a much lesser extent.

I suggest that if 2 or more batteries are charged with a solar panel then use diodes (silicon) to feed one regulator for each battery or if the panel is not so big or the batteries are very big just give the batteries full solar power. a factor of charge current less than 5% of amp hour capacity of the battery (all) seems to be a good limit.

Sirry I may have the question misread or not understand the specified controller if so forgive me olewill
 
Silicon power diodes drop normally over 1.1 volt, can be as high as 1.6 volt, it varies from one type to another, can even vary within the same family.
Schottky diodes have a lower forward volt drop, again this varies a lot, it can be 0.3 volt upto 0.92 volt, within the same basic family. The volt drop varies with the working voltage of the device, lower the voltage, lower the volt drop.
Thw volt drop in conjunction with the current produces internal temperature, watts, so the diode needs heatsinking to dissipate this heat and maintain a correct working temp.
Also this wattage come out of your solar panel output, on a dull day may be critical.

Brian
 
[ QUOTE ]
Can I take it then I don't need to do/get anything else

[/ QUOTE ] You can.
I have made the assumption that your panel is a FLX-32, that is Unisolar's flexible 32 watt panel! It says "A blocking diode is included within each potted junction box " on This webpage
They are normally fitted to panels to be used for battery charging to prevent the battery discharging through the panel at night as said on that web page. In your case it is required to prevent the wind turbine output being lost through the panel.
 
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