need a high amperage, low voltage rectifier...

[Stuart Easson]

Hi All,

I am assembling a 50+ amp test rig for car amps. I have procurred and assembled a nice pair of 12v 35A transformers, a few 100,000uF caps, and some really, really heavy gauge wire.

Problem is I can't find rectifiers with high enough current capacity. I am confident the transformers are more than capable of the current...So far I have destroyed several 35A rectifiers, despite mounting them on a large heatsink and using a variac to give a nice slow start to the caps charging. The car amps I have been playing with are in the 2x100w range, and as such should have average current draw in the 20-25A range, but whatever the peak is, it's obviously too high for the bridges I've been using.

If anyone knows of a good product, please let me know...

Alternatively, does anyone know how to make diodes share the current? I could use 2 or 3 of the bridges I already have.

Stuart

[TwoSpoons]

IRF diodes

There's plenty out there! How much do you want to spend?

You could expect peak currents over 4 x your average current. You need to measure it, then pick suitable diodes.

For parallel operation you could add ballast resistors to each bridge - 0.01 ohms, 10W.

[Stuart Easson]

I havent had any trouble finding specs for high current diodes, I just haven't had any luck finding anyone selling them at sane prices. The trivially available prices are a little prohibitive, the individual 150A diodes at digikey seem to be $20-$25, so I'd really want to know I was getting the right parts, before dropping $160 on the table, hence my question...

I was hoping someone knew of a bridge product, pure laziness on my part, but discrete diodes will of course work perfectly. I don't mind paying for a product which will survive the torture, I only recently did the math, 2x35x0.6 is a lot of watts, I may actually need to fan cool my rectifiers...

The 0.01ohm, 10w resistors aren't a trivial item to find either, digikey have some in the 1-3w range, and they are $2-$3 a pop, I dread to think what a 10w would cost...Perhaps I should be using some sort of resistance wire?

Stuart

[quasi]

You could try stud diodes. The ones used in automotive applications are rated around 100amps or so and are probably the cheapest you'll find.

I have found heaps in junked power supplies (at scrap metal dealers). I can usually pick up something with say 6 or more very high current diodes for a total cost of around $10US. You also get the benefit of a lot of other goodies inside.

Second hand I know...but this usually makes no difference.

Cheers

[Stuart Easson]

Hi,

Sorry if this seems like a dumb question, but which automotive application are you speaking of? I have no problem getting or using second hand auto parts, I just need to know what to look for...heck at the prices we are talking about I can probably use new auto parts...

Stuart

[quasi]

Sorry,

I'm talking about the diodes commonly used in alternators. They often come embedded in a block of 6 or so. These are really press fit styles so I may have misled you with the term "stud"

In junked power supplies I often find stud diodes and half-bridges manufactured by the likes of IRF, semikron, siemens etc.

Cheers

piccy of what to look for;