Jump to content
Electronics-Lab.com Community

simple question about batt chargers


walid

Recommended Posts

Hi all my friends

When somebody build a batt charger that stop charging when batt full, he
must use a comparator to compare batt voltage to some referance voltage..

when i conect a 3 volt batt to 5v power supply and wat to measure the
woltage across the connection, what would it be?

i ask this question to know at what level of charge i must stop the process

if i have four 1.2v batts (total = 4.8v), now these batts are not fully
charged, its voltage = 4 v or less.
i want to recharge them using 6v power supply. if i connect a voltmeter
across the connection, what would itsreading at thenbegining and at full
charge

i hope that u uderstand me

yours
walid

Link to comment
Share on other sites


Hi.

This is not a simple question. Actually we need more information:

What kind of battery You are using? NiCad/NiMh etc...

For example with NiCad the voltage is not so good indicator, as it stays in 1.2volts but still getting more and more charge. Finally the voltage goes down a little, indicating a fully charge.

Other indicator is that when the battery is full, the battery temperature has gone up to about 40-degrees centigrate.

Others here have answer with other battery-chemistry I believe.

Link to comment
Share on other sites

Hi Walid,
Read the tutorials about rechargable batteries at www.energizer.com . On the 1st page, click on Technical Info near the top, then on the 2nd page select Ni-Cad or Ni-MH type. Then look at the PDFs of charging and discharging.
The voltage changes with chemistry, temperature and the amount of charging current. Tne voltage reaches a peak near full-charge then drops a little. Some battery charger ICs detect the voltage peak or temperature rise to shut-off the charging.
Here is a typical voltage curve for a Ni-MH cell:

post-1706-14279142851815_thumb.png

Link to comment
Share on other sites

audioguru i go to where you point me but nothing

my question is very simple
forget that it is charger
assume that u connect a fully charged 3v batt to a 5v ps and measure the voltage across this connection
what is your reading?

thank you

Link to comment
Share on other sites


my question is very simple
forget that it is charger
assume that u connect a fully charged 3v batt to a 5v ps and measure the voltage across this connection
what is your reading?

You cannot do that!
A Ni-Cad or Ni-MH battery is charged with a current. If you connect a fully charged two-cell battery (about 3.0V) to a 5V power supply then the battery will overcharge with a huge current. The huge current will cause the battery to overheat and vent its chemicals or explode.

I showed a curve of battery voltage vs amount of charge. It is more complicated because the voltage changes with the battery's temperature and its temperature is changed by charging.
Link to comment
Share on other sites

ok ok ok

i want to tell you that i recharge unrechagable batteries for years and reuse them
it is never explode
i have not faced any problem with them and after recharge them the last long time specially in remote control and sound toys

i want that info to stop the charge process whe it must stop
can you help me?

Link to comment
Share on other sites

I'm sorry, lets forget what i said before and start again ....

the emergency neon lamp has a rechargable 6v rectangular batt

if i want to charge it using 7.5 to 9 volt power supply and want to stop the charging process when the batt is fully charged using a voltage comparator

at what voltage i must stop

thank you



Hello Walid!
I think temperature is the most critical criteria to stop charging. If u have lot of experience charging non-rech bats than u can tell us the avg time to charge common cells like AA, AAA or D. It will be usefull



Hi Mr Muhammad Abu Bakar, in fact i want to learn about batt charging and how the designer make a decesion in chossing his components and not to measure temperature and ave time

yours
walid
Link to comment
Share on other sites

Hi Walid,
Rechargable batteries have different chemicals inside and need completely different charging circuits to match the type of chemicals. For some of the batteries, if it is fast-charged then a temperature sensor is recommended instead of a voltage sensor to stop charging, to avoid an explosion or a fire.
Lead-acid?
Ni-Cad?
Ni-MH?
Li-Ion?
Li-Po?

The battery is probably lead-acid. Old lead-acid batteries in cars had a fully charged voltage of 13.8V, so half is 6.9V.
New car batteries have a fully charged  voltage of 14.4V, so half is 7.2V.
Some lead-acid batteries have a liquid electrolyte and others have a gel.
Some have calcium with the lead.
Do you know which type is your battery?

Link to comment
Share on other sites


I have never charged a lead-acid battery. My car does it without my attention.

also my car does it without my attention, but i discuss for theory and then for using this theory as a designer, i told you that i live to learn


To indulis
thank you very much

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
  • Create New...