Somehow I don't think you'll be able to find anything with a forward voltage of less than 250mV at 300A, a huge Schottky rectifier maybe?

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Hi Sammyb11,

I do not think there are any rectifiers which will meet those requirements.

If i had to meet those requirements, that is a forward resistance of around O.OOO8 ohms
then i would be considering a small sychronous motor running a set of paralleled brushes
on a purpose made commutator.

I personally think that this poster is going about something the wrong way, as Dknguyen
has already mentioned.

Boncuk mentions using power MosFets as surrogate diodes, presumably zero-crossover switching
and driven hard, so as to maximise conductivity.
Boncuk also mentions that this type of arrangement has inherent problems which in his
opinion made it difficult to set up satisfactorily.
However he was referring to a "bridge rectifier assembly", the poster here is looking for
a "single half-wave asembly", such an arrangement may not have the problems that Boncuk
mentioned.
I don't recall what RDSON means, but it may very well not apply to a half wave set up.

Making such an assembly using MosFets, would require at least basic constructor skills
and some understanding of how MosFets work, and how to make and set up the driver circuitry,
and probably use of an oscilloscope when setting up the zero switching.
And it would not be cheap.

Making a sychronous set of brushes is easy to understand, and more could be added to get
the resistance down to an acceptable level.
Most constructors could make such an assembly.

It is dificult to give this poster a reasonable answer which addresses his needs, as he
has only given what he considers to be what he wants for his job.

It is of course possible that Sammyb11 knows exactly what he wants to achieve, and that
a 30 Volt, 300 Ampere, diode with a max forward voltage drop of O.O25 V, is in fact the
most appropriate way to do it.

Best of luck with it, John

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Selenium rectifiers have a serious leakage problem, they are also very bulky.
If you are looking at older tech there was a mercury rectifier which could handle very very large currents, they were used to rectify power for trams.

 

Power Germanium Rectifier? Still probably won't get down to .25V.

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In Victoria there is a cool store called Capital Iron, which has an antiques section in the basement. They have one of these beasts, which together with its mount must be around 2 meter tall. It's a huge glass bulb with various protuberances and some charring from years of use, and they have some documents explaining what it was used for. IIRC this one was used for a subway or tram system like you mentioned.

I'd never even suspected the existence of those things before. That is one impressive bit of kit. I'd *love* to see one powered up. Apparently they are still in use.


Torben

 

Has anyone seen sammyb11 recently? Did we answer your question?

 

the tram museum in Brisbane does have them running, think large electric arc, bottled lightning.
http://www.brisbanetramwaymuseum.org/photom25.html