Author Topic: Store bought rectifier  (Read 5566 times)

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windme

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Store bought rectifier
« on: August 23, 2011, 03:18:53 PM »
Need a rectifier for a new 12' homebrew wind turbine , loading a 48 volt battery bank.
Don't have the knowledge or the time to build one myself. Had a used one but it has seemed to have seen it's last days.
Any idea's on where one might look to find a good one at a fair price?

Thanks in advance for any advice you me give.

zvizdic

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Re: Store bought rectifier
« Reply #1 on: August 23, 2011, 04:38:40 PM »
Any car rectifier.


DanG

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Re: Store bought rectifier
« Reply #2 on: August 23, 2011, 06:03:34 PM »
Usually going industrial surplus is the easiest method to get high voltage - high current rectifiers...

note its also harmonics from multiple coil groups and switching spikes that hammer at a diode junction over time, so going surplus or used gets the higher ratings for a lot less bucks.

A favorite vendor on epay for large bridges,etc. is henhuggers.

mab

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Re: Store bought rectifier
« Reply #3 on: August 23, 2011, 06:09:05 PM »
Any car rectifier.

Are they good for 48v though?  ???

Madscientist267

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Re: Store bought rectifier
« Reply #4 on: August 23, 2011, 09:46:35 PM »
In general, a typical silicon rectifier junction will have a MINIMUM PIV (peak inverse voltage) rating of 50V.

But while this sounds like it would be sufficient, just remember that a 48V nominal system sees voltages well in excess of 50V.

A good rule of thumb is AT LEAST TWICE what you intend to ever see, which helps with reliability. 100V PIV rated diodes would be the lowest I would personally go for a 48V system, but that's just me. Others may have success with closer margins.

A diode won't necessarily catastrophically fail when it's PIV is reached; this would depend on the current that tries to flow in the process. It's still not good practice, because at the very least, the diode is in danger of conducting "backwards" while it's PIV rating is being exceeded, defeating the purpose of having the diode there to start with. Enough current flows during the reverse conduction, and POP! And in my experience, the current capacity when a diode is in avalanche mode (reverse) is nowhere NEAR it's forward rating.

Doesn't do you much good to go too far above the "double" rating, however, either. Just increases cost, and can mean more heat (as the typical Vf (forward conduction voltage drop) is likely to be higher as well, resulting in more power dissipation at the junctions.

I can't say for a 3 phase bridge, but for single phase, calling it closer (ie 50V PIV on a 48V nominal system) might not be an issue, since there are effectively two diodes "in series" all of the time, inherently raising your margins by default.

Others could probably comment on that and clarify a little better than I.

Steve
The size of the project matters not.
How much magic smoke it contains does !

DanG

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Re: Store bought rectifier
« Reply #5 on: August 23, 2011, 10:43:01 PM »
Looks like henhuggers is on vacation - but if you look at last weeks completed sales you'll see what I mean.

Take the part number and google up a spec sheet for it, it will show forward voltage drop and other comparable details. Google will give up educational pages on what the ratings mean if you dig for them...

A cheap diode bridge is just that - there are a lot of design considerations built in higher powered units that don't readily present themselves.

frackers

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Re: Store bought rectifier
« Reply #6 on: August 24, 2011, 04:26:50 AM »
Something like one of these then https://www.ecoinnovation.co.nz/c-44-rectifiers.aspx

I've just fitted this one https://www.ecoinnovation.co.nz/p-167-100-amp-3-phase-rectifier.aspx

Note the 1600 volt rating :)

Robin Down Under (Or Are You Up Over)

joestue

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Re: Store bought rectifier
« Reply #7 on: August 24, 2011, 11:21:22 AM »
there is little reason to use a 600piv or a 1000piv or a 1600 piv diode. all of those have a higher forward voltage drop than a standard 400piv diode.

i'd be willing to bet that 50piv rated diodes are in fact 200piv diodes that failed the leakage test.. they are cheaper for a reason..
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

Bub73

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Re: Store bought rectifier
« Reply #8 on: August 24, 2011, 11:24:42 AM »
Just want to say as DanG mentions above that, I've bought several dozen used rectifier's single and 3ph from henhuggers with no problems.

Bob

Xan

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Re: Store bought rectifier
« Reply #9 on: January 28, 2015, 05:43:46 AM »
I have an 1970's electronic magazine where they built a solar panel up from individual cells. It was pretty small and would not even have produced an amp but they specified a 25 amp diode (I think it might have been for an alternator). The reason for this was at the currents involved it would exhibit a considerably smaller voltage drop than a 1 amp diode like a 1N4001 etc. Seems they didn't have readily available Schottky types.


Flux

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Re: Store bought rectifier
« Reply #10 on: January 28, 2015, 10:59:34 AM »
Surplus branded items are good value. Most of the cheap unbranded stuff is junk.

Car alternator diodes are probably ok for voltage rating but you will probably find no figures.

Diodes with a piv under 200v are basically scrap so as stated 50v ones will actually be 200v or above dies or rubbish.

Watch the current rating and go way bigger than you need even with branded devices, they have lots of de rating for capacitive loads ( which batteries effectively are) . The so called 35A units will be in trouble at 20A and need monstrous heat sinks. Using parallel devices means even more derating. If you want 30A and upwards The big screw terminal modules are better..

Don't go too low on piv, if the battery becomes disconnected a 48v mill can give hundreds of volts.

Flux

joestue

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Re: Store bought rectifier
« Reply #11 on: January 28, 2015, 11:10:04 AM »
@  Xan at a few milliamps forward current, the forward voltage drop for a 30 amp schottky diode will be as low as .2 volts, and at an amp it might be .3 volts. at 30 amps which is what the package is rated for (T0-247 case) you might have .6 to .9 volt forward voltage drop.
so yes using a very large diode is a good thing to do, but the leakage current for large die will be too great for some applications. -when spending 1 dollar a watt for the solar cells.. spending 1 extra dollar to save a few watts in the diode would be worth it i think....

I have used a GM 100 amp alternator diode block as a voltage doubler on a 120v circuit, and i think that's around 340+140 or 480 volts peak reverse voltage. At the time i would not have noticed 2 milliamps of backwards current flow, which would be only 1 watt or something like that.

I don't think backwards current harms the diode in anyway (provided its not thermally significant), so there should be no harm in sending 600 volts through a 100K resistor across the diode to see what voltage shows up across the block.
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.