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Horth

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Joined: 29/05/2008
Location: United States
Posts: 4

Posted: 12:50am 29 May 2008

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I would like to say thanks a lot to start, The Back Shed website has helped me greatly. I'm totaly new to electronics (well all of this really) So sorry if this is stupid. heh I have made a windmill and have a shunt regulator working (picaxe) that i basically copyed from the website. My regulator has 3 dumps 1 batt other 2 just dumps and it works but i would like to put a diode on the batt leg. When may batt is charged and the volts increase load 2 comes on and if volts continue to rise then load 3 comes on. What happens to me though is the battery runs load 2 and 3 but i would like just the windmill power going to those. Anyone know what kind of diode or whatever i could use to isolate the batt from flowing back into the loads. It would have to handle 30 amps into the batt and nothing back out. I tryed 6 amp rectifier diodes from radio shack ( twisted together 5 and ran through them ) but they seem to get pretty hot with only 7 amps going through them. I don't know what any of the stuff on the back means but does Vr: 35V imply that they only run at 6 amp when at least 35v is applied to them? My system is 12 volts.
Thanks for your time.

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 01:49am 29 May 2008

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The problem is the forward voltage drop and the current. Normal silicon diodes can have from 0.6-1.4V across them. Multiply this by the current and you will see that a considerable amount of heat will need to be dissipated. You might consider a shottkey type diode, in a TO-220 or TO3P package. Probably multiple units, on a heatsink, all wired in parallel. For 30A, I would use a total current rating of 60A for devices. I would insulate the devices from the heatsink.

I hope this helps. .. .. Gordon.

become more energy aware

Horth

Newbie

Joined: 29/05/2008
Location: United States
Posts: 4

Posted: 02:24am 29 May 2008

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Thanks a lot Gordon. I have been reading some of the other posts and you guys are great.
From what you just told me I see that i would be wasting power there to though. Is this correct? 1V drop * 30 amp = 30 watts wasted?
Another way i thought of trying was to just turn off the battery leg but i'm reading my volts from there right now. So i would need to add another input leg to read volts on the windmill side. then write the code to make it all work together. Basically is it worth it for me to go back in there and do the above or are the TO-220 / TO3P not really going to waste much power? This was the first electronic device i have ever built and i'm suprised it even worked. I'm kinda scared to tear it a part again lol.

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 02:40am 29 May 2008

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The Shottkey diodes still have a forward voltage drop. Some are as low as 0.3V, but typically they would be 0.4-0.5V at a 50% rating.

The power that is dissipated is proportional to the current. For a 12V system, this would equate to around 4% of power produced. You might consider replacing the bridge rectifiers of the windmill with similar diodes, to compensate for the series diode.

I only use shottkey diodes for my 24V system. Gordon.

PS the TO-220 and TO3P relate to a device type and not a diode type. You might consider a JF SR2060. This is a 20A@60V shottkey diode in a D2PAK. You may find an equvalent in a TO-220 pak. These will all still require some heatsinking of the device.

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Horth

Newbie

Joined: 29/05/2008
Location: United States
Posts: 4

Posted: 03:04am 29 May 2008

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Thanks much. I'm confused but at least i know where to look now.

I was just looking at a DIODE SCHOTTKY 45V 30A TO220AB
but it has 3 legs hanging out of it. (turns on and off like the mosfets i'm using?) I can see i have lots of reading to do Thank you very much for pointing me in the right direction. Mike

Gizmo

Admin Group

Joined: 05/06/2004
Location: Australia
Posts: 5078

Posted: 09:55am 29 May 2008

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Hi Horth.

It sounds like your headed in the right direction, your picking up this electronics stuff very quickly for a novice.

I find Google very handy for this sort of stuff, its knowing what question to ask thats the tricky bit.

A 3 leg diode is usually 2 diodes in one package. The middle leg is the common connection between the diodes. If you know the diode's model number Google should find a datasheet.

Glenn

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

SparWeb

Senior Member

Joined: 17/04/2008
Location: Canada
Posts: 196

Posted: 06:49pm 29 May 2008

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I was just looking at a DIODE SCHOTTKY 45V 30A TO220AB

That sounds like a "barrier" diode. The two diodes point in opposite directions, allowing you to connect two supplies that feed one load, and preventing the supplies from "feeding" each other or interacting in nasty ways.

sort of like:

o--->|---o---|<---o

Connect the load in the middle, and two supplies on the outer ends. The two power supplies (say two separate batteries) cannot talk to each other.

Steven T. Fahey

Horth

Newbie

Joined: 29/05/2008
Location: United States
Posts: 4

Posted: 09:58pm 29 May 2008

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Thanks for the info guys. I finally did find a data sheet for that schottky and saw that. I could just use one leg on those couldn't i? Or go into the outer legs from one power source and run the load off the middle?

sorry my cell phone cam is pretty crappy

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