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 John Larkin napisa:

A zener is pretty much a zener. I've never heard of a FAST zener. Use
any similarly-rated (voltage, power) zener.

Other opinions?

I wonder if the circuit actually works, chemistry-wise.

I do not know, but I decided to try. I will also make this:

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

More info here:

http://home.comcast.net/~ddenhardt201263/desulfator/lowpower.htm

 

[Yvan]

Nedavno Jamie napisa:

Mouser has them. Most like you can get them in Axle leads, these are
smt.

I am in Serbia. I'd be paying more for taxes for the part than for the
new car battery :-(

 

[Fred Bartoli]

Yvan a écrit :

Nedavno John Larkin napisa:


Other opinions?

Like John said you, just go for a similar power zener and you'll be OK.

Also, as you app seems to be single pulse, and have a very low duty
ratio, you can slow down the FET turn off quite a bit without any pb.
You could probably reduce the over voltage to the point of not needing
any clamp at all.

Ditto

 

[Jamie]

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?

look for TVS diodes as your replacement.. They can handle some junk.
Look at that one. the 12V version is most likely what you want.
it has a clamp of 22 amps at 27V and only a 5ma of leakage at around
14v or so.

http://www.nxp.com/documents/data_sheet/PESD5V0S1UA_PESD12VS1UA.pdf

Mouser has them. Most like you can get them in Axle leads, these are
smt.

 

[Yvan]

Nedavno John Larkin napisa:

How will you know if they work or not?
The pulsed desulphator sounds bogus to me.

I have two old, unused car bateries. I'll connect desulphator to it, and
wait for a month to see if it works.

 

[Yvan]

Nedavno Jamie napisa:

Well, I don't know who you have there for parts supplier..
Farnell maybe?, Newark? etc...
Digikey? etc.

None of these. We have few parts supplier, I'll check if they have TVS
diodes, thanks.

 

[Jamie]

Nedavno Jamie napisa:





I am in Serbia. I'd be paying more for taxes for the part than for the
new car battery :-(

Well, I don't know who you have there for parts supplier..
Farnell maybe?, Newark? etc...
Digikey? etc.

Just look for TVS diodes.

 

[Martin Riddle]

Nedavno John Larkin napisa:



I have two old, unused car bateries. I'll connect desulphator to it,
and
wait for a month to see if it works.

They actually do work, but may take more than a month and the battery
will have reduced capacity.
Discharging and charging during desulfation seems to help the sulfur to
get reabsorbed back into the electrolyte.

Cheers

 

[Jamie]

How will you know if they work or not?

The pulsed desulphator sounds bogus to me.

John

after looking at the GIF, that is not a zener that he's looking for.
its just a Fast recovery diode of 6 amps with a Vr(rms) of 70v,
Tr(recovery time) of 150nS with 100pf

This is nothing special..

 

[Jamie]

Nedavno John Larkin napisa:





I have two old, unused car bateries. I'll connect desulphator to it, and
wait for a month to see if it works.

If D2 is the diode you are referring too, it's not a zener..
it's fast recovery diode of 6 amps.

I am going by the image of the GIF you posted earlier as you stated
it was the connected to the FET.

 

[Ban]

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 ?s) 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?

Yes put a 3-5W 27V zener.
If diodes use the zener effect, they are always very fast, because no charge
needs to be removed. This is valid for z-diodes above 8V rating.
The circuit discharges the battery, in one year with more than 30Ah,
together with the self discharge rate there will be 0 capacity left after a
year for a normal 45Ah, this is certainly not a good idea and won't prolong
battery life at all. Better to get a trickle charger and keep the battery
fully charged during the storage time.
The article goes back to the seventies BTW and was extensivly discussed and
the circuit was considered pretty much useless.

ciao Ban

 

[Phil Allison]

"Banshee"

The article goes back to the seventies BTW

** The issue date is November 2004.

There were no power MOSFETS in the '70s.

and was extensivly discussed and the circuit was considered pretty much
useless.

** Yep.

Most battery charger / rejuvenator projects are useless scams.


..... Phil

 

[Ban]

"Banshee"




** The issue date is November 2004.

It was then done with some power Darlington AFAIR, and that's where that
zener came from.
BTW IR launched its first power Mosfet in '79

There were no power MOSFETS in the '70s.


** Yep.

Most battery charger / rejuvenator projects are useless scams.


.... Phil

ciao Ban

 

[Yvan]

Nedavno Jamie napisa:

If D2 is the diode you are referring too, it's not a zener..
it's fast recovery diode of 6 amps.

I am going by the image of the GIF you posted earlier as you stated
it was the connected to the FET.

You are looking at the wrong link. Look at my first post, and there is a
link to PDF file, and there in the parts list:

D5 = fast zener diode, e.g., BZT03 24V, 27V or 33V)

 

[Yvan]

Nedavno Ban napisa:

Yes put a 3-5W 27V zener.

Local parts store only has ZY 27 (27V 1,3W), and ZX 27V (27V 10W) which
is to expensive to buy for making something that may not work, just as
a pastime.

If diodes use the zener effect, they are always very fast, because no
charge needs to be removed. This is valid for z-diodes above 8V
rating. The circuit discharges the battery, in one year with more than
30Ah, together with the self discharge rate there will be 0 capacity
left after a year for a normal 45Ah, this is certainly not a good idea
and won't prolong battery life at all.

I wouldn't let it connected for a year. Perhaps a month or two, and then
recharge it. I used to do that, but as soon as the battery is out of
the car, unused, it dies quickly. I tried to connect my charger to a
timer that switched it on for a 20 min three times a week.
Unfortunately timer died while I was away for a three weeks, car
battery got charged all that time, and it died.

Better to get a trickle charger
and keep the battery fully charged during the storage time.

What sort of voltage / current do I need? Do you have any links to a
good proven trickle charger design?

I've found different ones from small ones (like the ones for mobile
phone), to 1A. But isn't 1A (when battery is fully charged) cause
electrolyte to boil?

 

[Ban]

Nedavno Jamie napisa:


You are looking at the wrong link. Look at my first post, and there is a
link to PDF file, and there in the parts list:

D5 = fast zener diode, e.g., BZT03 24V, 27V or 33V)>

I also think this circuit can be dangerous. If there goes something wrong
and that FET keeps conducting...

ciao Ban

 

[Ban]

Nedavno Ban napisa:


Local parts store only has ZY 27 (27V 1,3W), and ZX 27V (27V 10W) which
is to expensive to buy for making something that may not work, just as
a pastime.


I wouldn't let it connected for a year. Perhaps a month or two, and then
recharge it. I used to do that, but as soon as the battery is out of
the car, unused, it dies quickly. I tried to connect my charger to a
timer that switched it on for a 20 min three times a week.
Unfortunately timer died while I was away for a three weeks, car
battery got charged all that time, and it died.




What sort of voltage / current do I need? Do you have any links to a
good proven trickle charger design?

I've found different ones from small ones (like the ones for mobile
phone), to 1A. But isn't 1A (when battery is fully charged) cause
electrolyte to boil?

The batteries have a self discharge rate which is dependent on temperature,
age and condition. If we assume 10%/month we have to replace 4.5Ah which
means a continuous trickle charge of only 6.5mA. You can use any small
supply with higher voltage and calculate the resistor value
(Vout-13.8V)/10mA if you have 15V then use a 120 ohms 1/4W resistor. This
won't hurt the battery.

 

[Yvan]

Nedavno Ban napisa:

The batteries have a self discharge rate which is dependent on
temperature, age and condition. If we assume 10%/month we have to
replace 4.5Ah which means a continuous trickle charge of only 6.5mA.
You can use any small supply with higher voltage and calculate the
resistor value (Vout-13.8V)/10mA if you have 15V then use a 120 ohms
1/4W resistor. This won't hurt the battery.

But how does that work? Surely it is not the same if I connect charger
capable of delivering 10A, and the one capable of delivering only 10mA
with the same voltage.

What determines the current flow, 10mA or 10A or whatever?

And what happenes if, for some reason, battery discharges faster than
the charger can charge? Current flow rises, and charger dies?

When I connest my charger to partially discharged battery it starts
charging at ~5A, and gradually drops down.


I also decided to try this:

http://www.mikroe.com/sr/magazine/p2broj/slike/2b71.gif

It should start charging below 12.5V, and stop at 13.8V (adjustable).

What do you think? Good alternative to trickle charger?

 

[Yvan]

Nedavno Robert Baer napisa:

You will wind up with fully discharged batteries ASS-u-ME-ing they
had any charge in the first place.
You might be able to get them to charge slightly better afterwards
than before treatment.

I will monitor the process, and charge the battery when needed, or
connect a trickle charger (when I find / make one). Perhaps it will not
work, bat as the batteries are written off it can only get better.