# Bridge rectifier and polarity 'oops'

#### Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

•  Subject
• Author
• Posted on
I plugged into LTSpice the schematic for a bridge rectifier to test if
it could negotiate the change in DC polarity - which it did.

How much wear will the bridge endure before failing?

Along the train tracks, as it is now it is still in development, I have
segments that have reduced voltage and different polarity depending on
the function of the segment.

At this stage, I am only testing over a 3m section of track.

Re: Bridge rectifier and polarity 'oops'

That depends on a lot of factors, all of which you have not told us.
Generally, in a properly designed system with suitable margins, they
won't (or shouldn't) fail.

Your post really doesn't make any sense.
What are you trying to do here?

Dave.

Re: Bridge rectifier and polarity 'oops'

That's modern education for you ! We're producing a generation of clowns,
idiots and know-nothings. And many are functionally quite illiterate and
innumerate too.

Graham

Re: Bridge rectifier and polarity 'oops'

"Wayne Kerr"

**  Will miracles never cease ......

** We might well ask  -  how much can a Koala bear ????

Toooot,   toooot  ...............

.......   phil

Re: Bridge rectifier and polarity 'oops'

If you are talking about a small model train set........

You need to know how much current the train(s) draw - I'd guess a small toy
train would draw < 2A, probably 300mA+ when running. Try something like a
W04 bridge. Be aware that a bridge will lose arount 2 x 0.7V. Your trains
may not run at full speed with the bridge in circuit.

Re: Bridge rectifier and polarity 'oops'

MORON ! 0.7V is a small signal current Vf for typical silcon diodes.

Power bridges are more in the region of 1V per diode at rated If.

Sigh !

Graham

Re: Bridge rectifier and polarity 'oops'

the bridge should be rated for the stall current, when the motor is
running at full speed there will be less drop.

Bye.
Jasen

Re: Bridge rectifier and polarity 'oops'

Well, if the change in polarity is happening across the AC or ~
terminals, and the voltage current ratings are followed, and the
frequency isnt high (you need a fast recovery type if so)  the thing
shouldnt wear out for a long long time - possibly decades even.

Re: Bridge rectifier and polarity 'oops'

Uh ?

How did you understand his 'question' ?

Graham

Re: Bridge rectifier and polarity 'oops'

I didnt really, just made guesses :)

Re: Bridge rectifier and polarity 'oops'

LOL !

Graham

Re: Bridge rectifier and polarity 'oops'

Had a graduate recently apply for a job who could not calculate a
circuit with 1 zener, 1 battery and 1 resistor!

Re: Bridge rectifier and polarity 'oops'

I was helping out my nephew with an op-amp problem a little while back. He
finally got the gain equation right with some prompting but then told me he
needed a calculator. I said "use the one on your PC" but he said he needed an
'expression evaluator calculator' ! For something like A = B + ((C+D)/(E-F)) !

I got the answer accurate to 1 decimal place in my head FFS. <sigh>

Now go to Asia and see if they can answer it !

Graham

Re: Bridge rectifier and polarity 'oops'

LOL !

Graham

Re: Bridge rectifier and polarity 'oops'

Guffaw ! What the heck DO they actually do for those 3 years ?

Graham

Update and clarification: Re: Bridge rectifier and polarity 'oops'

I read through an article using a 6v dolphin battery and an LED.  To
overcome the polarity in the dark, the author used a bridge rectifier.

What I am wondering, can this be relied upon when the train tracks
change polarity through a turn-out loop?

Oh, and no I am not a student.  Just someone who want to do something
fancy with a train set that I am resurrecting after 20 years of sitting
idol.

Re: Update and clarification: Re: Bridge rectifier and polarity 'oops'

Absolutely,

If the voltage on the tracks changes that may cause brightness changes
in the LED, that depends on how your loco is controlled.

Bye.
Jasen

Re: Update and clarification: Re: Bridge rectifier and polarity'oops'

And you don't need effing LTSpice to tell you that !

Graham

Re: Update and clarification: Re: Bridge rectifier and polarity 'oops'

If you want to do something fancy then go with DCC:
http://en.wikipedia.org/wiki/Digital_Command_Control
Just buy the modules and controllers you need.

Dave.

Re: Update and clarification: Re: Bridge rectifier and polarity 'oops'

If my layout was bigger, then DCC is definitely the path I would take.

There was an article in RailBrick e-zine discussing DCC and Lego trains,
plus there is several sites dedicated to or have information about DCC
and similar controls.