34063 questions...

[zulutime]

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of input
polarity protection is needed?

2) Is an input cap required when running off batteries?

Thanks in advance...

zulutime

 

[jan]

DoNotUse@altavista.com (zulutime) wrote in message news:<33d1a587.0405311712.dccf077@posting.google.com>...

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of input
polarity protection is needed?

2) Is an input cap required when running off batteries?

Thanks in advance...

zulutime

////

Hi zulutime,

You didn't get a response to your problem, looks like you have to find
a smarter NG. Let me know if you do.

Jan

 

[Watson A.Name \"Watt Sun]

jan wrote:

DoNotUse@altavista.com (zulutime) wrote in message news:<33d1a587.0405311712.dccf077@posting.google.com>...

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of input
polarity protection is needed?

Most chips can only take a half volt or less. THe usual way to protect
these is to put a 1N4002 rectifier across the battery leads, with the
cathode to positive. If the battery voltage is reversed, the rectifier
conducts heavily and either drains the battery or...

That's why it's a good idea to have a fuse between the battery and t he
rectidier.

2) Is an input cap required when running off batteries?

For best efficiency you should have a capacitor across the battery,
preferably a low ESR type.

Thanks in advance...

zulutime

 

[onestone]

zulutime wrote:

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of input
polarity protection is needed?

2) Is an input cap required when running off batteries?

Thanks in advance...

zulutime

If there is a strong possibility that a battery may be connected
reverse polarity I use a small bridge rectifier, then polarity becomes
irrelevant. other wise I use blocking diode. I prefer to have akeyed
connector to prevent this.

I always have an input cap when running off batteries.

Al

 

[Winfield Hill]

Watson A.Name \"Watt Sun - the Dark Remover\" wrote...

zulutime wrote ...

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of
input polarity protection is needed?

Most chips can only take a half volt or less. THe usual way to
protect these is to put a 1N4002 rectifier across the battery leads,
with the cathode to positive. If the battery voltage is reversed,
the rectifier conducts heavily and either drains the battery or...

That's why it's a good idea to have a fuse between the battery and
the rectifier.

The forward voltage of a 1n4002 diode is 1.4 volts at 20A, so a
high-current Schottky diode is a better choice for this tough
form of protection. E.g., an axial-lead 1n5822 (Vf = 1V at 20A),
or a TO220 part like an MBR1045 (Vf = 0.8V at 20A) or MBR2545CT
(Vf = 0.75V at 60A with both sections paralleled).

These Schottky diodes have a low enough voltage drop they can be
easily used in series for a more relaxed protection scheme. For
example the 1n5822 only drops 0.4V at 2A.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

 

[zulutime]

Thanks much for the responses and advise.

Some of these converters have a 1N400x reversed across the input, but
without actually blowing one up, it's impossible to be sure how much
reverse voltage they can take. A Schottky is a good idea.

I'm using a 9v snap style connector...keyed, but easy to reverse
momentarily.

Thanks for the help.


DoNotUse@altavista.com (zulutime) wrote in message news:<33d1a587.0405311712.dccf077@posting.google.com>...

Adapting a 34063 based dc-dc cell charger for use as a portable
recharger operating off alkalines, and I could use some expert
advice...

1) How much reverse voltage can a 34063 take? What kind of input
polarity protection is needed?

2) Is an input cap required when running off batteries?

Thanks in advance...

zulutime