i have a problem charging the battery

[naeim golshekan]

I want to charge 12 volt battery by 12 volt charger but when i restrict the current by a resistor, the battery charging  voltage drops.
Can anyone help me?
The picture of circuit is as below

[vern]

it is quite simple.
First of all there is a voltage drop on the diode, about 0.6V
Next you have the voltage drop across the resistor.
Example: Power source 12V, resistor 1 Ohm
Depending on the state of your battery there is a charging current flowing through the diode and the resitor.
If we assume that the current is 1A, there will be the voltage drop across the diode 0.6V, across the resistor 1V, that means you only have 10.4V at your battery.
Since I assume you are just starting with electronics: make yourself familiar with Ohms law, you need it!
You should also be very careful with charging batteries, they can catch fire or explode when not charged properly.
If you have a power battery you can not charge it with the circuit above!

[Sideshow Bob]

MS/LM/TS batteries are all of lithium type most often. Given they are of  lithium type. Your approach is VERY dangerous and irresponsible. Lithium batteries must be charged in a very specific way in order to safe. If not they are just an accident waiting to happen. They will catch fire most probably. A beginner like you, should not play around with homemade lithium charging at all.

[Old_but_Alive]

has he never heard of Ohms law ?

[Sideshow Bob]

has he never heard of Ohms law ?

At least points for clean drawing

[pickit2]

Check for >> Circuit Board Module PCB BMS Charger Li Ion Lipo Lithium Battery And Protections
I bought 100 mixed very cheap, and well worth the money.


Posted on: August 18, 2021, 04:28:09 16:28 - Automerged

thanks
when the battery is fully charged the diod is turned off so the charging operation is stoped and the battery remains safe. isnt true?

No not safe - your fire insurance cliam will be rejected.


https://www.youtube.com/watch?v=ySXtBuawf70

[vern]

The voltage of the battery will rise, the charge current will fall and stop at some point when the battery is charged to almost 12V.
But as me and others here have already pointed out:
it is very dangerous to charge a battery this way! You should use a professional charger!
These chargers have a constant current source that has a voltage limit build in where it shuts off charging when the battery is full.
It's safer!

[pickit2]

Always reminds me when the painters were in the Telephone Exchange, and one put his metal paint pot on the power buss rails.
he had no pot to piss in (english joke) but there was paint every where.

[Gallymimu]

Agree with the others.  This simply isn't wise for a lithium based battery.  The charging method is bad practice and lithium batteries at best don't do well when float charged long term and at worst it is a safety hazard if you are off by a few 10ths of a volt overcharging the cells.

[ero]

If we are talking about the Lithium batteries we have remember the conditions on charging.
Single cell should be charged by 4,2V not more not less. The charging current is very important at the beginning. You should give the current max. 70% of the battery capacity. After about one hour you can give any charhing current but very precision charging voltage which should be 4,2V. Because battery does not pull more current . Later on , when the battery pull around 50-100ma current the charging process can bu stopped automatically or manually.

When the batteries are connected serially the chanrging system is always is same. Only changing thing is the voltage according to how many battry is connected serially.  For instance if you connect three cell you should givee the charging voltage as 12,6V . If you like your batteries do not think there is a tollerance on this voltage it is not.

If you give 12V to that  batteries you can not charge them properly. It is not dangerous also because you give less voltage than normal voltage.
Lets look to the dangerous positions;
- If you give more voltage than 12,6V to the batteries it is dangerous. Because they become very hot there is a possibility of exploding.
- If you give more current on chargng than normal level it is also dangerous and batteries are become very hot again and they can be explode.
- If your batteries become very hot (more than 45 degree celcius) you should terminate the charging. Normally this is not happend but if you do not know your battery specifications and if you give wrong voltage and current to the batteries they can become very hot this is normal.
- Do not attempt to open the batteries. Because there is lithium inside and it can be get fire by the oxygen of the air it is really very dangerous.

Serial connected batteries should be charged also with balance control sysytem. Because one battery which having low inside resistance can consume all the current on charging. If you use balance charging system the current is shared equally to all the batteries and no one can consume all the current by that way.
As a last word use one DC-DC converter which having regulable output voltage and current,  in order to regulate the charging voltage and current one fixed level. Use also balance card. This will be more safety. It is vey easy to reach all these equipments on Internet just look for them.

Do not forget also the lithium batteries can not be discharged until zero volt. Ideal voltage level is around 3V for each cell. By the way the 12,6V batteries can be discharged untill 9V . This can be untill 7,5V but I do not recommend it better 9V.
All these informations are based on my personal experiences.  You can use or not use them. Make your own investigation over internet you can understand and find the right way easily.  I do not take any responsibility.


Ero