Rectifier Parts ?

[LowGear]

Aloha,

I've got this dream to rectify around 5KW from a three phase generator to about 300 Volts DC for my SMA Grid Tie Inverter.

I've been watching these three phase units come through Ebay but they're the size of a pack of cigarettes.  I'm sorry but I just don't see these units lasting through the first tank of fuel.  Is this set of SCRs what I should be buying to build a reliable rectifier?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=271286220946&ssPageName=ADME:B:SS:US:3160

Casey

[Tom Reed]

This is rated about 10x more than what you need.

http://www.ebay.com/itm/3-Phase-Diode-Bridge-Rectifier-150A-1200V-SQL150A-New/131002556186?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D163%26meid%3D1589222070854854792%26pid%3D100005%26prg%3D1088%26rk%3D3%26rkt%3D4%26sd%3D271286220946%26

One of these days I'm going to get moving on using a 3 phase motor to do a feed into a charge controller. I bought something similar to do the job.

[Horsepoor]

Some other rectifiers from Central Georgia Generator:

http://www.centralgagenerator.com/rectifier.htm

[Thob]

A little bit about rectifier diodes:

In general, you need a voltage rating of at least 2x the DC output voltage.  In practice, you need a considerable safety margin, something like 25%.  This allows for the voltage to be higher under no load, and for spikes, etc.  So for 300 volt DC output, you would want at least 750 volt diodes.  1000V would be better.

For the current rating, you need it to be at least as much as your average DC current.  Again, a good safety factor is in order.  5KW / 300V = 16.7A, so something like 20A diodes would be the minimum.

Always get two of them - you should have a spare!

Unless you're using some kind of fancy control circuit, you don't want the SCRs in your link.

For 300V DC out, you'll need about 215V AC in.

Somebody better check my math -

[mike90045]

For single phase, you need 4 diodes for a full wave rectifier, unless you have a center tap winding, and then you can use just 2 diodes.

Diodes generate heat, and they have to be kept cool, so figure they drop 1.5V across them at whatever amps, and those are the watts you have to dissipate.   Schottky diodes have less voltage drop, and therefore dissipate less power.  And generally, one lead of the diode is electrically attached to the heat sink.  volts * amps = watts.   1.5V * 7A = 10.5 watts, per diode

Diode Bridge Packs generally isolate the electrical from the heat sink, and you just need 1 bolt to a heat sink to keep all the diodes cool.

[LowGear]

They sure look neat.

Thanks