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Forum Index : Electronics : Rectification voltage drop
| Author | Message | ||||
South Easter Newbie  Joined: 18/06/2007 Location: Posts: 36 |
Hello. I have done some benchtesting and measured voltage before and after rectifying. This is for a three phase PM generator, rectified at the top of the pole. I found a KBPC3510 rectifier gave DC at 2.4V below the AC voltage. A SB356 gave DC at 1.3V below. I was surprised at that difference! Full details of the tests for those interested are at http://windpower.org.za/benchtests.html I work at 24V, so that kind of drop means there is a lot (ok, some) of the time when the generator could be delivering current but isn't due the voltage drop across the diodes. Is there a way you guys use to lose less volts when rectifying? South Easter http://windpower.org.za |
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| Robb Senior Member  Joined: 01/08/2007 Location: AustraliaPosts: 221 |
Tryed schottky diodes? |
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| South Easter Newbie Joined: 18/06/2007 Location: Posts: 36 |
Hi Robb. Have just stumbled across them on the net. So many types out there... has someone used them successfully to rectify say around 10-20Amps, and if so, can they tell me the part number they used? Thanks! South Easter http://windpower.org.za |
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Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day South Easter, SR2060 Schottky Diodes are used in the Oatley K241 Windmill Shunt Regulator Kit. They are 20 Amp and I suspect 60Volt by the component number. A very successful kit. You could possibly get them from Oatley Electronics, else do the rounds of local and mail order outlets. Local repairers with accounts at WES, Farnells or Radio Spares, to name a few, may assist by ordering off the wholesalers for you, though prices often reflect their effort.  was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| South Easter Newbie Joined: 18/06/2007 Location: Posts: 36 |
Thanks mate! Will have a look around for those. I am in Africa by the way. South Easter http://windpower.org.za |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Africa...! Bloody hell mate, that's a long way to walk to get to my electronics shops. 
Just as an added observation, I see the Oatley designers used two of these SR2060 (twin diode in TO220 case) in parallel for each phase. So that's 4 parallel diodes with same bias per phase on what they rate as 300w or more. Total of 14 x SR2060 to make the 3 phase rectifier. I suppose that grantees reliability, or is it to further reduce voltage drop across the rectifier?????  was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| South Easter Newbie Joined: 18/06/2007 Location: Posts: 36 |
Sure is Gill. I even have a T-shirt which says 'Australia - its a bloody long way!' I have also had a 40CPQ040 suggested as a good option. It seems to have a slightly smaller voltage drop than the SR2060 (0.43V vs 0.55V), and can handle about 40V and 40A. As always, any comments appreciated. South Easter http://windpower.org.za |
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| South Easter Newbie Joined: 18/06/2007 Location: Posts: 36 |
Hi, I have now got some STPS20H100CT Schottky diodes. I can't find this from the datasheets - can someone tell me if the tabs are insulated? I want to use 6 of these to make a 3 phase rectifier, and want to know if they need separate heatsinks, or if all the tabs can be connected. South Easter http://windpower.org.za |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Good chance the tabs are connected to the center pin, they usually are on that package. Googled the code, found http://www.datasheetcatalog.com/datasheets_pdf/S/T/P/S/STPS2 0H100CT.shtml. You can use mica insulating washers under the tab, along with insulated screws. Available from your local Dick Smith store, or junk pile. Dont forget the silica grease. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I have been using some SMD SCHOTTKEY diodes from Jaycar. very cheap in packs of 10. Just parallel them to get require current rating. devices are individually 40V @ 3A using 9 devices, at 15 A I lose 0.3V which is acceptable. cheers Gordon. become more energy aware |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi Gordon, how did you mount the SMD devices, made a special PCB? How big are these diodes anyway? Thanks. Klaus |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
The diodes are not too small. I think 0.2" lead spacing is pretty close. I do make a PCB. Vero board will also do with some linking. The best part is you just parallel them up to keep the power loss to a minimum. Rule of thumb is 1/3 rated amps per diode gives approx 300mV forward voltage drop. You must not of course unload a mill in the wind or you will probably exceed the 40V reverse voltage. The low loss benefit means some form of overvoltage detection has to be used. Good luck, I use them successfully on my mill. cheers, Gordon. become more energy aware |
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