3 phase bridge recifiers

[bob golding]

hi i have a 3 phase 100 amp rectifier i want to use as single phase. do i assume i will be able to get 66 amps out of it if i just use 2 of the phases? voltage is 1200 so not a problem i only need 30 volts or so. the selenium recifier on the  battery charger is starting to smell. thought it was a dead rabbit the cat had hidden at first. ermm  rotten onions and sulphur

bob

[Ungrounded Lightning Rod]

To a first approximation figure 33 amps, not 66, even though two of the three AC lines are connected.  You're using one phase out of three.

(You can actually go a bit higher because for part of the cycle the currents add in 3 phase and you don't have the added current in single-phase so you can use the full current for one phase rather than splitting it between two.  I don't recall the ratio of the top of my head and I'm busy right now.  Maybe somebody else will tell you.)

I would now IMMEDIATELY throw out the selenium rectifier and vent the shop until you don't smell it any more.  That stuff is REALLY BAD for you.  Stop exposing yourself and your family NOW.  (At this point you should survive but your breath and sweat may smell like garlic for years.)

[bob golding]

thanks for the warning. i will get rid of it right now.

bob

[scottsAI]

Selenium required for good health, yet too much can kill.

http://en.wikipedia.org/wiki/Selenium

Toxicity - "Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis". Much more to Kill.

400 micrograms is quite a bit to get from smelling.

[joestue]

As long as the peak to average current ratio is under 10-20, you do not need to de-rate the diode based on average current. (reason has more to do with the junction temperature oscillating at 120Hz than the I^R loss in the silicon)

However you do need to keep power dissipation under control.

This means you need to estimate the junction temperature.

A litre of water and a thermometer works well for this....

Of course, you also need to verify that the 100 amp rating is not based off a 25C case temperature.

Can you post the part number?

[dnix71]

We use selenium at work to blacken engraved plates that go on award plaques. If you get it on you, your skin will itch and you'll get a stomach ache as a warning. Some people just can't be around it. I can't take Centrum multi-vitamins without getting sick because they contain selenium and I already have enough in me.

[defed]

i found these while browsing around ebay...

http://cgi.ebay.com/75-AMP-THREE-3-PHASE-rectifier-rectifiers-WIND_W0QQitemZ180379901596QQcmdZViewIt
emQQptZLH_DefaultDomain_0?hash=item29ff7ade9c&_trksid=p3286.c0.m14

don't know anything about the seller or the item (still a newbie myself).

is it any good?

same seller also has all sorts of controllers...again, don't know anything about them, but would like to know what the experienced guys here think.

[bob golding]

thanks for the info guys.

i think rather than destroy a perfectly good 3 phase rectifier i will go for stud diodes instead. was looking for a quick fix but could end up with a fried 3 phase rectifier instead. then i would still have to buy the stud diodes anyway. i have ordered one of those coleman wind rectifiers. they look too good to be true. will test one and find out. cheap enough for a experiment.

bob

[defed]

yea, i want to try one too, but like you said, sounds too good...but then again, i don't really know anything about the technical side of these products.

i want to try his diversion controller too.

maybe i will need a new post about his products to get some experts to chime in with their opinion.

[ghurd]

The one controller says "SEA-440".  It also says 'relays'

Might google search the board for "SEA-50"?

If the LEDs showing the battery voltage caught your attention, get a HF $4 alternator / battery tester (#46972) and hang it on the battery.

G-

[bob g]

no wonder the girls didn't like me when i was a kid!!!

i never knew that smoke was bad for me, i used to build high voltage supplies

out of old TV parts, and some of the old ones used selenium rectifiers in lieu

of the 5U4gt double diode rectifier tubes.

i remember one selenium rectifier that really smelled bad after being asked to provide power into a dead short making a crude spot welder.

who knew?

bob g