Fast zener diode substitute

[Yvan]

I decided to built this:

http://notes.ump.edu.my/fkee/e-Magazine/Elektor 2004/Articles/E/e04b020.pdf

It keeps the battery a little bit active, preventing sulphation by
loading the battery with a hefty current (40 A) for a short interval
(50 μs) approximately every two minutes.

But they used a fast zener diode (BZT03 27V) across the FET for
protection, as rather large voltage spikes can occur when the FET
switches off.

I can not find this diode where I am, so can you suggest a substitute? I
guess I can not just put regular 27V zener diode here?

 

[Yvan]

Nedavno ian field napisa:

Have a look at the data sheet for the TL431 adjustable zener, you put
a potential divider (2 resistors or a trimpot) across it with the
tap/wiper to the control input to adjust the zener voltage, if you
need it to be particularly fast just put a few tens of pF capacitance
in parallel with the top leg of the divider.

I am electronics newbie, this sound complicated :-(

 

[Ban]

Not at all, search and download the data sheet - it has application
examples for you to follow, to speed it up you only need add a small
disc-ceramic capacitor from cathode to control pin.

What happens with that small part if up to 10A want to flow thru it?
ban

 

[Yvan]

Nedavno ian field napisa:

Not at all, search and download the data sheet - it has application
examples for you to follow, to speed it up you only need add a small
disc-ceramic capacitor from cathode to control pin.

I've been suggested in another NG to just use any 3-5W 27V zener diode.
What do you think?

 

[Ban]

The best thing to do is study the data sheet;

http://www.ieeta.pt/~alex/docs/DataSheets/BZT03.pdf

It mentions that these zeners are suitable for transient suppressors, that
might be connected to the idea that these are fast zeners, you could
search under transient suppressors and select a substitute from the
results.

The same datasheet states a non repetitive current of 7.9A in transient
suppression, maybe we dont need that much for the application, but certainly
a long lead will give some inductive kick when driven with 40A.

ciao Ban

 

[Yvan]

Nedavno ian field napisa:

BTW: thanks for the URL - backspacing it found some pretty interesting
magazines & e-books.

Yeah, I noticed that too

 

[Yvan]

Nedavno ian field napisa:

This search might be a good starting point;

http://www.google.co.uk/search?sourceid=navclient&ie=UTF-8&rlz=1T4GZAZ_en-GBGB333GB333&q=p6ke


I am electronics newbie, are you suggesting that I can just use 27V P6KE
in place of BZT03 without modifications?

There are uni-polar and bi-polar P6KE, which one should I use?

 

[Yvan]

Nedavno ian field napisa:

I was suggesting you use that search as a starting point, download the
data sheets and compare the spec with the type you want to replace.

Since I do not know what values to compare, that does not help a lot :-(
My knowledge in electronics is limited to finding schematics on the
Internet, drawing a board in eagle, and soldering components to it.

I've had a cursory glance at the schematic you plan to build, and I'm
a little sceptical about "battery revitalisers" that take pulsed
current without incorporating a float charger to replenish the energy
taken - if left and forgotten it will eventually discharge the battery
and cause sulphation.

This circuit is not a battery revitaliser as I understand it this is
sort of sulphation preventer. I am also building battery revitaliser:

http://home.comcast.net/~ddenhardt201263/desulfator/n_channel_schem.gif

It is also possible to do the same job with a much simpler circuit.

If you start with a simple current limiting PSU as a float charger,
you can add a zero-crossing detector to the rectifier section and use
the narrow pulses to switch the MOSFET which then takes pulses of
current from the battery as in the Elektor project.

As I wrote I have (very) limited knowledge in electronics, so unless you
give me a link to the schematics, this does not help. I have a lot to
learn, but very little time for that, unfortunately.

 

[Yvan]

Nedavno ian field napisa:

I suggest you make
the time to stick your nose in a book and learn some of the basics.

OK, thanks.