Three or six rectifier diodes for 3 phase PMA

[Usman]

Here is a set of rectifier diodes, three in line for any PMA. Nicely constructed and fairly priced;

http://www.windbluepower.com/Delco_Rectifier_10si_p/rec-del.htm

What I need to cofnrim is if we need a set of three of these or six for a 3 phase PMA (100 Amps max)? I am told by my technician that we would be needing six, -ve and +ve for each phase, so that's two diodes per phase - although he isn't technically that much qualified.

Secondly, the particular PMA that I am working was 110VAC star configuration, as my battery-pack is 48VDC; I converted it into delta, so another three wires were fetched out from the PMA. Now I intend to put in a manual switch that can switch over from start to delta or vice versa when needed or just to try out the efficiency in both modes, would I still be needing three, or six rectifier diodes? Please illustrate.

Thanks, Usman

[kurt]

look here http://windstuffnow.com/main/Star_Delta_Rectifiers.jpg

http://windstuffnow.com/main/3_phase_basics.htm

[Nando]

It seems that the technician is technically qualified and You are not, because for 3 phases, for full wave rectification, 6 diodes are needed, 3 positive and 3 negative connection and ask the technician if those diodes you have are with the right body polarity.

Those diodes block seem to be car alternator rectifiers.

Nando

[Opera House]

I have concerns when they say

3- 50 Amp Diodes for a total load capacity of 150 Amps.

 This one will handle allot of abuse.

If you parallel diodes the don't load share unless you provide a couple feet of wire lead to each diode.  Automotive alternator diodes are designed for a very high volume of forced air cooling.

     

[Flux]

I can't work out what the thing is anyway. Is it a complete rectifier or is it 3 diodes. If so where are the 3 diodes of the opposite polarity to make a bridge.

The information is just about as useful as the ratings of the alternators on that site.

Flux

[alancorey]

This is only 1 of 2 sets of three, connected for either positive or negative connection.  The other set of three (not listed) is for the opposite polarity.  You'll need a set connected each way.  Whether you can remount one of these for opposite polarity is a good question, but you could always buy a set of 3 different diodes for that part.  Generic diodes are somewhat versatile in how you mount and connect them, these aren't.

And yes, they are meant for forced air cooling and lots of it.

Ah, I see they're also selling permanent magnet alternators for wind use.

  Alan

[billymc]

The rectifier shown in the picture has 6 diodes, 3 attached to the upper heat sink and 3 attached to the lower heat sink. (would assume it is a 3 phase full wave rectifier) I'm not sure I follow the question. Have dealt with automotive rectifers often.  Used one on a conversion.  They work fine if you can work out mounting and connections.  I'm not sure what the PIV is for the automotive rectifier but it wasn't built to work with 48 volt system! Might be OK though.

[scottsAI]

Hello Usman,

Delco Rectifier 10si with 50 Amp Diodes

Made for a vehicle generator. Reverse voltage is NOT high enough for a 48v generator.

Diodes require a reverse voltage rating twice the highest voltage they will see to insure the reverse voltage NEVER exceeds the diode rating. NEVER.

If the reverse rating is exceeded, the diode can act like a zener diode. If acting like a zener it will most likely burn out. Common failure for DIY gen.

Three phase requires 6 diodes in a bridge rectifier.

Vehicle generator diodes are often setup as a zener on purpose. Load dump - the zener turns on at 40v and clamps the generator output to protect the vehicle. Good for a couple sec. (all that is needed to protect for a load dump).

Have fun,

Scott.

[Waterlogged]

That is a General Motors three phase bridge rectifier. You can buy it at almost any auto parts store. It has six diodes in it. The three studs are the three phase input, and the heat sinks (fins) are the output. It is mounted to the alternator case in such a way that only the negative output is grounded. The positive is taken from a stud that only contacts the other heat sink. The stud has a plastic insulator around it and is first mounted in the back of the alternator housing. Then the bridge rectifier is mounted with the stud going through the positive heat sink. It can get hot, therefore it does need cooling air flowing across it.

Rod