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Rectifier Question
By Hank, Section Homebrewed Electricity Posted on Mon Dec 08, 2003 at 05:37:39 PM MST
Rectifier help

I purchased several Bridge rectifiers rated at 50 amps 400 volts. They have wire lead outs that appear to be to thin (.040" dia) to carry 50 amps. Can any of you electronic experts out there give me some advice as to whether or not this is accaptable. I plan to use these in my PMA which I guesstimate will be putting out up to 40 amps before it furls.
I would not want to fry these rectifiers and have a run away genny.
All comments appreciated,
Hank

Rectifier Question | 10 comments (10 topical)

Re: Rectifier Question (none / 0) (#1)
by DanB on Mon Dec 08, 2003 at 05:48:02 PM MST

Is it 3 phase?

My only suggestion would be to make sure youve got a very good heat sink, and parallel however many rectifiers it takes so the rating of the whole assembly is at least twice that which you think you'll see. A dead rectifier could mean a wrecked windmill.

Re: Rectifier Question (none / 0) (#2)
by Hank on Mon Dec 08, 2003 at 06:06:17 PM MST

DanB,

No these are not a 3 phase but rather single phase rectifier. I'm currently using 35 amp rectifiers purchased from WonderMagnet which have spade leads and are much larger. I wanted to beef up my system that's why I bought the 50 amp rectifiers. On paper they should be of higher rating but the size of the leads has me concerned.
I always parellel two rectifiers as a safey precaution.

Thanks for the reply,

Hank

Re: Rectifier Question (none / 0) (#3)
by Electric Ed on Mon Dec 08, 2003 at 06:10:41 PM MST

A wire of .040" dia. would be #18 AWG and has a continuous current carrying capacity of about 15 amps if exposed to air, about half that if it's in a cable or conduit.

For 50 amps, a #10 AWG (about .10" dia.) would be recommended if exposed, #6 if in a cable or conduit.

Electric Ed

Re: Rectifier Question (none / 0) (#4)
by Hank on Mon Dec 08, 2003 at 06:37:04 PM MST

Thanks for the response Electric Ed,

It is exactly that that has me concerned. The wire leads coming out of the rectifiers appear to be to small for that rating. I would be using a AWG size of 10 or larger wire, but to me it makes no sense to solder these to the .040 dia. lead wires coming out of the rectifiers.

Just curious why they are reated so high yet have such thin wires.

Hank

[ Parent ]

Re: Rectifier Question (none / 0) (#6)
by Victor on Mon Dec 08, 2003 at 07:17:04 PM MST

Hank,
The "thin wires" are very short ,arn't they. The current capacity of a conducter is very dependant on its heat sinking ability. For example I have a TIG welding torch with a continiuos rating of 150 amps. The torch is water cooled and the lead feeding it is run inside the feed water tube, the tube is 1/4" and the conductor can"t be larger than #10. The designers of the rectifier are relying on the heat sinking of the device, don't forget the 50 amp rating is for a case temp. of 25 deg. C in the fine print . Also if you over size your leads to the device you can disapate a lot of heat into the leads themselves. Rectifiers are relatively cheap and paralleling allows you to spread the heat into your heat sink, when I do this I use equil length wires to parallel diodes to aid in the current sharing.
Make the wind fun!
Victor

[ Parent ]

Re: Rectifier Question (none / 0) (#5)
by kell on Mon Dec 08, 2003 at 07:05:22 PM MST

Are they rated 50 amps continuous? Or surge? Did you get written specs? Look at the power dissipation in watts. A silicon rectifier has a voltage drop of a little less than a volt if it doesn't get too hot. So the watts divided by about 0.7 (nominal) gives you the amps it will conduct and stay within its power rating. Amperage ratings can be very misleading with semiconductors.

Re: Rectifier Question (none / 0) (#7)
by Hank on Mon Dec 08, 2003 at 07:34:59 PM MST

Thanks for all the responses and help,

No wattage specs on these but they are 50 amp continuous with a 400 amp surge ratingand with short wire leads

I'll give them a try on a test stand with a very large heatsink first but from the sounds of it they should work just fine.

Hank

[ Parent ]

Re: Rectifier Question (none / 0) (#8)
by laskey on Tue Dec 09, 2003 at 07:49:33 AM MST

The bridge rectifier you're talking about is designed to be soldered to a PC board, thus the smaller leads. The only reason they'd put bigger lugs on the bridge is to accomodate hooking wire directly to it. You'll notice that those lugs conveniently accept a specific solder-less connector, or in the case of really big bridges, a specific bolt size in the hole.

What you really want to worry about is (as stated above) how hot the bridge itself gets.

Cya,
Chris

[ Parent ]

Re: Rectifier Question (none / 0) (#9)
by jimjjnn on Tue Dec 23, 2003 at 07:12:14 AM MST

Semi-conductors are current devices. Don't exceed their current
ratings by very much unless you heatsink them with large heatsinks.
you can cool them also with a fan on the heatsink too. Voltage ratings
are pretty much the same thing. I hope this helps. Great discussions here !!!!
Jim Nelson
Denver,CO

Re: Rectifier Question (none / 0) (#10)
by Harry Luubovv on Wed Dec 31, 2003 at 01:45:23 PM MST

I can think of three things. One, even the wires are small, but since they each is very very short in length, it does not mean too much difference there. Anything less than a 1/4" is Ok when it is smaller than what you are used to seeing. Two, there are Peak Inverse Voltage rating, there are Forward voltage rating, usually they are wide apart from each other with the same rectifier. Three, if you had a rectifier rated at PIV of 400 Volt and 40 amp, you can safety use it at 50 amp if you only use it in a circuit of say, 12 or 24 volts volts.

Thanks for reading mate.
Luubovv.

[ Parent ]

Rectifier Question | 10 comments (10 topical)

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