Fast zener diode substitute
in [Design]
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From: Ban on 7 Feb 2010 03:26 "Yvan" <killefitz(a)invalid.invalid> schrieb im Newsbeitrag news:hklqa4$hhp$1(a)news.eternal-september.org... > Nedavno Ban napisa: > >>> 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. > > 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? > > 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.
From: Yvan on 7 Feb 2010 07:08 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? -- ___ ____ /__/ / \ ** Registrovani korisnik Linuksa #291606 ** / / \/ /\ \ ** Registered Linux user #291606 ** /__/\____/--\__\ ** http://counter.li.org/ **
From: Robert Baer on 7 Feb 2010 07:57 John Larkin wrote: > On Sat, 06 Feb 2010 23:35:58 +0100, Yvan <killefitz(a)invalid.invalid> > wrote: > >> 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 > > How will you know if they work or not? > > The pulsed desulphator sounds bogus to me. > > John > To desulphate a lead acid battery, one must cycle it (charge, discharge) and it is wise to do that in such a manner to have a net (or long term average) charge rate at least equal to the trickle charge rate. One needs to force the current without regard to voltage across the battery. One time i took a motorcycle battery that was made for the Army in 1945 that was made dry-charged and zero electrolyte; the idea was that addition of electrolyte would give one a fully usable battery. Well, by the time i bought it (surplus) it was in the 1980s and the battery would not pass more than a milliamp at 6V (its rating); it was "hopelessly" sulphated. I used a 120v/120V isolation transformer, a series current limiting resistor, and a reverse polarity protection diode across the battery and let it run a week; reduced the transformer drive to half and ran another week, etc until i was using a mere 12VAC for a 50mA peak current. Then i could use a standard charger, and cycled it twice to get almost full rating. Lead sulphate is a good insulator, and you need to RIP it apart, but keep the current down to create small lead particles for "re-plating" and thus be able to be a regular part of the charging/discharging chemistry.
From: Bill Sloman on 7 Feb 2010 08:48 On Feb 6, 10:58 pm, Yvan <killef...(a)invalid.invalid> wrote: > I decided to built this: > > http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/Articles/E/e04... > > 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? The BZT03 is a big junction in a small package - it can dissipate 10W continuously, or 600W for a 0.1msec. http://www.vishay.com/docs/85599/85599.pdf I don't recall that it was ever advertised as particularly fast, though Vishay now claims that it can turn on quickly, which may be true, once the first charge-carriers have appeared in the junction. "Zener" diodes with breakdown voltages above about 8V are in fact avalanche diodes, and the avalanche starts with a single charge- carrier pair, which may come from thermal noise or radioactive decay. -- Bill Sloman, Nijmegen
From: legg on 7 Feb 2010 22:20
On Sat, 06 Feb 2010 14:06:09 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 06 Feb 2010 22:58:00 +0100, Yvan <killefitz(a)invalid.invalid> >wrote: > >>I decided to built this: >> >>http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/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? > >A zener is pretty much a zener. I've never heard of a FAST zener. Use >any similarly-rated (voltage, power) zener. > >I wonder if the circuit actually works, chemistry-wise. > >John A 2K2 gate resistor pretty much prevents fast enough switching to cause spikes. The fet swots it out, zener or no. RL |