| T O P I C R E V I E W |
| BushWhacker |
Posted - 09/09/2007 : 04:54:44
Hi guys (and hopefully gals),
I'm having an electronic idiot moment. I must get at least 1 diode (or a few). I went looking at diodes (on the net) and there seem to be enough types and specs to fill the Encyclopedia Britanica at least twice! I am trying to buy as few as possible, with as much capacity as I will possibly need.
The gen units in question are 2 and 2.5 HP. The one I'm working with right now is the 2.5 HP unit. It's specs are 90 volt, and 23.8 amps TOPS! That's (2.5 x 746) 1865 watts at most (as if I'll ever see that! ). I'm set up with a test rig, with no wind of course, and I forgot to get a diode so the battery doesn't try to turn the turbine in reverse.
How do I spec out a diode, and which of the 37 kinds do I get? If I get a large capacity diode will it still work in light wind? (13volts and fractional amps?) Basically what I'm after is something that won't blow up or burn up in high winds, but adds charge when the gen unit supplies more charge than the battery has.
Is a 1N5401 as good as it gets?
Do I have to run multiple diodes to cover the amperage?
In a word...HELP!
Thanks,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| 15 L A T E S T R E P L I E S (Newest First) |
| BushWhacker |
Posted - 12/09/2007 : 23:07:31
Found it! 85 amp, 1000 volt, 1/4" NFT stud for mounting, "NEVER SAY DIE!"
blocking diode for $31, and it's available locally too.
Surely no one can find fault with this diode, other than price,
but I'll buy it once and forget about it.
Thank you all for your input!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| ghurd |
Posted - 12/09/2007 : 20:28:20
Don't trust a 20A bridge with 20A, let alone 40A, just because the AC terminals are tied together.
That would make it 'more likely' for me to trust it for 15A, or trust it more at 10A.
There are Vf issues even within the same bridge, and duty cycle issues.
Maybe... The $8 85A 800V diode that comes up (for me) in fungus' link?(ebay #140156048619, with the deal killing $10 shipping)
Or something like these? They certainly beat surface mount, under the "I thought life was getting easier" section.
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=11661
A Coke can will move away some heat for smaller devices, but not enough for something near this scale. The more AL the better!
G-
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| BushWhacker |
Posted - 12/09/2007 : 06:42:11
Thanks for the tip Gill. If I screw some aluminum clamps over the metal head/top of those diodes, and screw the works to a heat sink, that should work shouldn't it?
And I thought life was getting easier?
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| Gill |
Posted - 12/09/2007 : 04:50:21
Careful, these are a surface mount component and may be difficult to mount to your heat sink and connect leads to.
On the other hand, the price if fantastic.
Cheers... Gill |
| BushWhacker |
Posted - 10/09/2007 : 19:28:57
AAARRRGGG! I can't believe it! In a city that services about 1.25 million people, the choice of in stock electronic parts is dismal! [/rant]
OK, I'm calmed down now. Anyhow, speaking to a gent with 40 years of electronics behind him, I was told that if you tie the outside legs of a MBR20100C (price $5.30 Can, each) together you double the amperage capacity to 40 amps.
But better yet ( I think?) I found this...
http://tinyurl.com/24zxtp
If I have this right the MBRB20200 will allow me to tie #1 & #3 together for a total of 40 amps and 200 volts capacity, and at a killer price!
If I have to wait anyhow I may as well get a smokin' deal.
Can anyone with some electronics knowledge shoot holes in this plan?
Does it look great to anyone in the know?
Thanks for your patience,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| Del |
Posted - 10/09/2007 : 17:02:35
Hi BW,
If all you need is a small heat sink then use an empty coke can (or any alloy can). I seen these used before as heat sinks for bridge rectifiers and they are certainly cheap and plentiful.
Cheers
Del. |
| ll81 |
Posted - 10/09/2007 : 16:20:52
Work out your dissipation as 0.7x current (worse scenario) . If you expect peaks of 10 amps then expect 7 watts max dissipation. The metal case would get hot under continual loading, just a small rectangle of aluminium is all that is needed. The BR shouldn't cost more than a couple of pounds. 35 amp bR's are about the most common. 200-400v are the most common so hence the cheapest. Just ask what he's got.
There are loads of cheap PM motors for sale on ebay in the states.
They look like these (note how cheap they are) http://cgi.ebay.co.uk/NEW-UNUSED-Bridge-Rectifier-600-Volts-35-amps-5pcs_W0QQitemZ160154079744QQihZ006QQcategoryZ36332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Cheers, Liam
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| BushWhacker |
Posted - 10/09/2007 : 00:17:33
ll81, what about the heat from your BR? Does the metal case dissipate the heat or would it be wise to attach a heat sink as well?
The serious electronics shops will be open in the AM so should I ask for a "35Amp, 200 Volt, Bridge rectifier, in a metal case"?
Price (within reason, say 30 pounds) and fiddling on install are not a concern, so long as I only have to do it once, barring a 100 kph wind storm. I might add I'm still going with a Savonius Turbine so over speed shouldn't be a problem, and certainly not today! :-(
She's been trying to turn but the Gen unit is way to big for the turbine unless I get some 20 or 30 MPH winds. I'm having a heck of a time trying to find a fractional HP motor that doesn't turn about a million RPM, for under about 185 Pounds. Getting a nice Ametek 30 Volt from the states is going to run about 80 or 90 Pounds. I think that's kind of pricey for a used motor with a no return policy.
BTW I still haven't heard back from the Ametek distributor in town.
Thanks yet again,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| ll81 |
Posted - 09/09/2007 : 23:21:15
No AC generation with me. The 0v (earth, -, cathode whatever you know it as) goes straight to the battery, the + output from my genny goes to the AC terminals on a BR then to the battery. The - termianl on the BR is unused.
Br's are cheap and come in a bullet proof square metal cases with big spade terminals on and are easily obtained in 35amp per diode ratings. My BR will take 70 amps of current before it fails and has a reverse voltage (PIV) of 400 volts. Cost about £1.50, easier than fiddly diodes.
Cheers, Liam
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| gotwind |
Posted - 09/09/2007 : 22:10:04
Thanks BushWhacker.
We are all helping each other out here - that's why I created this forum 
The Futures Green - Getwind of it. |
| BushWhacker |
Posted - 09/09/2007 : 21:39:25
WOW! You guys are great! Wonderful input!
Fungus, I think you hit the nail on the head as far as capacity goes.
Is something that "big" available in a Schottky diode?
I also like the idea of a heatsink Ben, reliability = GOOD! I'm sure I have something kicking around I can tear into.
ll81, can I assume you are generating AC power? This rectifier thing seems to creep in from nowhere all the time???
On short notice (remember this is only a test bed and this is being done on a Sunday) I went and picked up 4, 6A05 0610 diodes. They came in a blister pack listed as "Rectifier Diodes" and are rated at 6Amps/50PIV. (With this set up I'll never hit 6 amps or 50 Volts unless there is a tornado!) I'll assume they are intended to be used when making your own rectifier.
I'll be putting one on the positive lead (anode to Gen, cathode to Bat) and see how it goes. I am concerned about the VF of 0.9V, that's a fair amount isn't it?. The IR is 25mAdc, is that a 25 Milliamp leakage?
I imagine I have given some of you a good chuckle with my "Electronically Challenged" position, but between reading up a bit and the great advise you have all shared, I believe I'm starting to "get" some of this. So which one's of you do I call Sensei, Yoda, and His Eminence? ;)
Many thanks!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| ll81 |
Posted - 09/09/2007 : 19:32:31
I just use the AC terminals of a bridge rectifier (on a heatsink) and use the + output to the battery. Two identical diodes will be very similar in current flow. As the current flow is dependent on the forward junction voltage and junction voltage increases with current using two diodes in parallel is commonly done with only minor differences in current. If done though they need to be thermally bonded to eachother.
Cheers, Liam
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| gotwind |
Posted - 09/09/2007 : 18:40:01
To add:
Ensure you do use a heatsink with the stud type diode only one required on the positive wire, a large piece of aluminum will do, but a proper aluminum heatsink ia better.
I got one free from an old amplifier I had.
More here
http://www.gotwind.org/circuit.htm
The Futures Green - Getwind of it. |
| fungus |
Posted - 09/09/2007 : 16:36:19
BushWhacker;
Something like this http://tinyurl.com/2h2elm would be perfect for the job, I much prefer the stud diode packages as they have large mounting areas and bolt directly onto a heatsink. That one was in canada but theres ones available all over the place. |
| BushWhacker |
Posted - 09/09/2007 : 16:17:38
Hi Gill,
As usual your reply was educational, and saved me hours and hours of additional reading. (I am reading up on Schottky diodes) I am a bit confused about the use of rectifiers in this instance. I see I forgot to mention the output from the gen unit is DC. My bad. :(
That being said, could I get away with the use of a single Schottky MBR20100C on the + lead (does it matter which lead?)? Or do I have to run 2 diodes with one on each lead? I like the idea of two diodes for some reason.
I'll mention that I am a big fan of "over kill" when it comes to building things. I'm more than willing to pay a few extra dollars for peace of mind when the wind is up. Reliability is my first concern.
Thanks for you time,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
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