Author Topic: Bridge Rectifiers dying  (Read 1069 times)

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windcruiser

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Bridge Rectifiers dying
« on: August 25, 2006, 12:48:41 PM »
I have been using the 35Amps bridge rectifiers and they are continually failing. In many cases they open up and let AC through. Is there a special diode for wind turbines?


Simon

« Last Edit: August 25, 2006, 12:48:41 PM by (unknown) »

Countryboy

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Re: Bridge Rectifiers dying
« Reply #1 on: August 25, 2006, 06:58:34 AM »
Hi Simon,

  Rectifiers fail if you overload their limit.  With a 12V system, 420 watts is the max  you can rectify with 35A rectifiers.


I'm not sure what you mean by saying they open up and let AC thru.  Usually, when rectifiers open up, they don't let anything thru.

« Last Edit: August 25, 2006, 06:58:34 AM by (unknown) »

Flux

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Re: Bridge Rectifiers dying
« Reply #2 on: August 25, 2006, 08:11:11 AM »
Bridges die when you exceed their ratings. The voltage limit is piv not system voltage. Use at least 3 times your system volts.


There is an absolute peak current that depends on time but you will not meet that for your use.


The thing most likely to be causing failure is exceeding the junction temperature.


The current rating depends on the mounting and heat sink but the internal junction temperature needs fairly complicated thermal calculations to predict exactly.


As a rough guide the 35A is not possible in real life with battery loads no matter how big you make the heat sink. The battery looks like a capacitive load and although not often quoted there is a fairly hefty derating.


With very adequate heat sink and mounting a single phase bridge is good for about 25A into a battery.


Three phase ratings are more difficult to establish and are never quoted for single phase bridges. Don't let any mean diode current exceed 25A and don't let case temperature exceed 60 deg C and you should be ok.


There is another factor that is even more difficult to deal with, that is the source of the bridges.


If you stick to IR or General Semiconductor or other genuine brand you know where you stand. There are lots of cheap dodgey brands that may nowhere near approach the supplied data.


Paralleling bridges to increase current rating also implies a further derating so to rectify 100A or greater with these bridges you need lots of them.

Flux

« Last Edit: August 25, 2006, 08:11:11 AM by (unknown) »

ghurd

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Re: Bridge Rectifiers dying
« Reply #3 on: August 25, 2006, 08:16:15 AM »
They need to be kept cool too. Are they on a big heat sink, with heat sink compound?

Heat kills this stuff.

G-

« Last Edit: August 25, 2006, 08:16:15 AM by (unknown) »
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SamoaPower

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Re: Bridge Rectifiers dying
« Reply #4 on: August 25, 2006, 08:18:35 AM »
« Last Edit: August 25, 2006, 08:18:35 AM by (unknown) »

bob golding

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Re: Bridge Rectifiers dying
« Reply #5 on: August 26, 2006, 11:53:19 AM »
hi have a look on ebay. i found a 100 amp 3 phase rectifier for a few dollars.


bob golding

« Last Edit: August 26, 2006, 11:53:19 AM by (unknown) »
if i cant fix it i can fix it so it cant be fixed.

windcruiser

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Re: Bridge Rectifiers dying
« Reply #6 on: August 30, 2006, 05:16:22 AM »
Thanks Guys that was helpful. Flux and the others. I am trying some highly rated diodes and hope to get better results. My source is really not my choice -- they have all kinds here no originals just parts. Kind of lucky sometimes.


Simon

« Last Edit: August 30, 2006, 05:16:22 AM by (unknown) »