3 Phase bridge rectifier, made from 3 single phase rectifiers.

[BobEdge]

Hi,

I need a 3 phase bridge rectifier that can handle around 15A / Phase.
The limit for fairly inexpensive ones seems to be 35A, higher than this and the price is just not viable for the product.
I know paralleling diodes is not a good idea since one diode will usually take most of the current.
My idea is to use 3 35A single phase rectifiers, with each rectifier having it's AC inputs tied together, which works out cheaper even than the one 3 phase 35A unit.
They will of course be bolted to the chassis of the machine, and have thermal grease, and the duty cycle is less than 10%

Can anyone think of a reason why this is a bad idea?

Regards
Bob.

[amgen]

actually, you only need 2 full-wave bridges to rectify 3 phase.
2 legs to AC inputs on 1 bridge and use 1/2 of the second bridge.
7119
don

[Dave]

That is true, But with the third bridge, and paralleling the inputs you can double the current capability of the 3 phase bridge.

[BobEdge]

Thanks for the replies.
Good to know paralleling the inputs is not a problem.
We buy the 35A rectifiers in bulk for less than £1 each, so using 3 is no problem.
Very relieved to know There is no need to pay £60 or more when we can do the same job for less than £3
Have a good day guys.

Regards
Bob.

[amgen]

Well maybe, because you don't know if the parallel diodes share the current equally .
But definatly paralleling would raise the current capabilities.
All that stuff has to do with the temperature/resistance relationships. Some devices like FET's resistance goes up with temp so they tend to balance the current when in parallel, but with silicon diodes, the hotter it gets, the lower the voltage drop gets, so the more current that diode will take.
don

[Archangel]

Parallel circuits usually use series resistors on the diodes to balance the current.