24 volt bridge rectifier

[Blewsage]

Will the the 35A bridge rectifiers be big enough for a 10', 24 volt, Hugh Piggett design with standard dual 12" rotors, 24 magnet, 9 coils 14 AWG @ 66 turns, 3 phase? I'd read where these were probably adequate for 48 volt. I'd rather stay with the standard 3 bridge rectifier design. I see some 70A advertised, should I go with them?

thanks, Russ

[electronbaby]

If you used three of the 35A rectifiers for 48v, you have to remember that the current would be roughly double for a 24v system.

I personally would go with the bigger rectifier because it would have less loss at 24v and be more robust. This means less of a chance of you having a failure. It is a wise investment.

[Flux]

I agree with Roy. The rating of these bridges is difficult at best.

The 35A is mean current with resistive or inductive load for operation in a single phase bridge and to get it you will need an almost infinite heat sink.

You may assume that building a 3 phase bridge and paralleling the halves of the single phase bridge you could double this current. In reality they will not share perfectly so that gives a derating. Additionally you have to transfer the heat to the heat sink and the package thermal resistance plays tricks that are not in your favour. Add to this the fact that the conduction time is very different for 3 phase rectified to a battery compared with single phase resistive loading you come off even worse.

The net result is that I think you are pushing your luck to get 35A dc from 3 of these bridges connected for 3 phase with wind operation even with a large heat sink.

24v 1kW is pushing your luck to the limit and if you get some big gusts that fool the furling you may go over the edge.

Also not all these things are created equal, you can push your luck with some manufacturers a lot more than others and if it was a product of Michael Mouse or some anonymous import it may never even manage 35A in its intended application.

Wise to play safe, probably cheaper than using more 35A units in parallel and a better solution.

Flux

[Blewsage]

Thank you so much for the advice! Is there one manufacture you'd recommend over another?

[Flux]

Unless you buy from a stockist or similar you rarely have any choice.

Top brand names such as International Rectifier or General Semiconductor Ixys etc are fine. Semikron seem much more expensive. Most are of unknown origin with the same part number and the data sheet will be identical. Most work perfectly well but you may not have as much in reserve.

There are a few dreadful ones out there with wrong connections and other manner of problems that turn up as bargains too good to be true.

Flux

[Ungrounded Lightning Rod]

I agree and would go much oversize on rectifiers if possible.

Remember that you can get a BIG excess of current during a wind gust - and it lasts long enough to heat the rectifiers and potentially lead to thermal runaway and dead rectifiers.

Better to go oversize than have to buy replacements later.  B-)

[Blewsage]

Thank you! I guess I'll go with the 70A ones. I could use 6 of the 35A, but I'd like to keep it as simple as possible.