# Choosing the right high amperage rectifier

#### RogueRose

Joined Oct 10, 2014
375
I need to have a rectifier setup capable of up to 400A, the voltage will be from 7-75v (higher voltage will have much lower amperage, max power will be about 7200 watts) and the power will not be run for extended periods, maybe a few minutes at a time, with at least equal amount of off time. This setup will be used for various things from welding, electrolysis, resistance heating and a few more things.

I found some rectifiers on ebay that have me a little puzzled as I looked at their voltage & current rating and compared them to surface area and volume, and pricing was a little odd as well.

Code:
Voltage    amp    Cm^2    In^2    Cm^3      In^3    Price    $/ amp 1600v 400 74.8 11.59 254.32 15.52$29.00    $0.073 1600v 300 73.7 11.42 294.8 17.99$28.00    $0.093 1600v 200 71.25 11.04 285 17.39$21.00    $0.105 1600v 150 31.2 4.84 109.2 6.66$8.60     $0.057 1600v 100 31.2 4.84 109.2 6.66$8.60     $0.086 1600v 60 31.2 4.84 109.2 6.66$8.40     $0.140 1000v 50 9 1.395 10.08 0.615$7.89     $0.016 10 pcs What I found odd is the volume of the 300A vs the 400A, as it is larger than the 400A and the 60A, 100A, 150A are all the same size. The 200A is also larger in volume. None of these units have a heat sink but have a smooth metal back on which I thought I would place a computer CPU heat sink. I was really surprised by the price of the 50A units, as they cost about 17% of what a 400A unit would cost. IDK if running 8 of these in parallel would work I don't intend to use them for this high amperage project but will order them for some others. Now if the size of the rectifier makes any difference, I guess the main thing would be heat handling, then placing a CPU heat sink should be sufficient, but I'm thinking that using 2 200A units in parallel along with 2 heat sinks, might be a better option as it has more "cooling" capacity? It would also be possible to use 4 100's and not worry about a fan on the heat sinks, less moving parts, but more connections for rectifiers. All of these units are from the same manufacturer and look basically the same, so I assume they will have virtually identical forward voltage loss, though it isn't stated for all of them, at least all of the same amperage should be the same. #### oz93666 Joined Sep 7, 2010 739 I need to have a rectifier setup capable of up to 400A, the voltage will be from 7-75v (higher voltage will have much lower amperage, max power will be about 7200 watts) and the power will not be run for extended periods, maybe a few minutes at a time, with at least equal amount of off time. This setup will be used for various things from welding, electrolysis, resistance heating and a few more things. . This sort of requirement cries out Li-ion , I'm sure it could be done much more cheaply with these rechargeable batteries rather than buying a 7.2KVA transformer .... I can deliver well over those power levels from the 1,000 18650 cells I have that I salvaged from thrown away laptop batteries (cost$40 from the scrap man) ...you will have to adjust configuration to change voltage... and voltage comes in steps of 3.6V.

If you want to use new batteries ....
this one weighs 600gms and can deliver 800A @ 15V that's 12KW !!

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