Rectifiers types - What's the difference here

[ozetrade]

I have seen four different types of rectifier setups described on the boards. One is from a auto alternator, another uses diodes and a third use 35A bridge rectifiers.

I'm going to use the 35A bridge rectifiers, but I have seen setups that use 3x 35A and some that only use 2x 35A - What's the difference here?

Greg

[RP]

Electrically all these rectifiers are essentially the same just packaged differently.  The automotive rectifiers come in sets of six diodes for fullwave rectification of 3 phase.  Two bridge rectifiers will have 8 total so two of the diodes are redundant.  Three bridges can be used to rectify each phase separately before wiring in series or parrallel.

[adelaide]

I use 3 but link the 2 ac's on each to take more current.

If i rectifi separately before wiring in series or parallel/star or delta, what are gains? or losses ?over star delta  then rectaifi? is it just more diodes to lose on ?

[Flux]

The normal way to rectify 3 phase ac is with a 6 diode bridge. This can be individual diodes or you can use a 3 phase bridge made for the job or use single phase bridges which contain 4 of the required 6 diodes. You can use 1 & 1/2 bridges and ignore one ac connection or you can use 3 and join the ac connections on each and treat it as a diode pair.

Rectifying phases separately is not standard practice, but if you do so and parallel the outputs the thing behaves the same as a delta connection with a normal 3 phase bridge.

When starting from scratch there is no point in series connecting 3 bridges but if you have an existing winding with too low a voltage you can use the series method to raise the voltage but you need monster capacitors across each bridge to overcome the phase difference problem.

Flux

[bossxero]

Hi All,

Me too is having a hard time with rectification :-)

I appreciate all the comments of the learned one,  indeed we learn lots here but i would like to add something.  I think that it lacks some pictures.  We all know that a picture is worth thousand words :-)

Anyway, I would have like to have more details on the bridging techniques.  I have got the parts from used computer power supplies.  i have got diodes, rectifier diode (flat-pairs) etc.  I would have like to know how to use them to rectify the 4-6vAC coming from my stepper motor.

Thank you all once and again.

Ragards.

[ghurd]

If the link works, the photos show the ~, the one long wire or a cut corner for the positive. Too bad RS can't seem to make a decent loading page.

http://www.radioshack.com/search/index.jsp?kw=bridge&f=Taxonomy%2FRSK%2F2032058&categoryId=2
032058&kwCatId=2032058

G-

[ghurd]

The $1.99 (4A 50PIV) one is good for most steppers.

The $2.49 (4A 400PIV) one is good for the best one I ever had.