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Battery charger advice please? Answered

Could anyone help with advice or plans to build a battery charger where I can regulate the voltage and  amperage seperately to charge a wide range  of batteries please, had thoughts of using a computer ATX power unit for the initial power source, thank you Doc Cox



Best Answer 7 years ago

Get a 0-to-12 volt supply and add this current limit in line to the battery.


nigel cox

7 years ago

Hi Jack thank you for the rsponse, unfortunately I am looking for something a bit simpler, ie. two controls one for amperage and one for voltage, thank you for your time regards Doc Cox

Jack A Lopeznigel cox

Answer 7 years ago

I have a variable benchtop power supply, which looks a lot like this one:

The knobs on the front adjust two limits, one limit for voltage across the load, and a second limit for current through the load.  Essentially the way this kind of power supply works is it drives an increasing current through  the load, but via feedback it stops and holds at the first limit encounters (be it the voltage or current limit).  

The limit it hits first depends on the character of the load.

For example suppose the current limit at 1.0 A, the voltage limit at 5.0 V.

Connecting a 1 ohm resistor as the load, will cause it to hit the current limit first at 1.0 A.  At this point the voltage across the load is 1.0 V, and that's below the voltage limit. Also a little light labeled  CC (for constant current) turns on indicating that it's hitting the current limit.

With the same limits, connecting a 10 ohm resistor as the load will cause it to hit the voltage limit first.  I.e the current rises to 0.5 A, at which point the voltage across the load is 5.0 V.  In this state the little light labeled CV (constant voltage) turns on indicating that it's hitting the voltage limit.

Perhaps you wanted something like that:  simply a current limit and a voltage limit.

When I answered this question before, I sort of assumed something complicated would be necessary, in order to work across a wide range of different battery sizes and types.  I.e. you'd need like a little "program" for each battery size and type.

BTW, a good question to ask, might be: What are the charging programs desired for different types of batteries?  As an answer to that question I found this:
Under the heading, "How to Charge Batteries"  there is a list of about six different charging plans for different battery chemistries.

Anyway, back to the simple current-limited-and-voltage-limited supply, that might work well for charging a Pb-acid battery.  It would supply constant current at first, until the battery voltage climbed up to the voltage limit, after which it would switch into constant voltage mode, at which point there would be some trickle of current that maintains that constant voltage.

It would be almost the  same story for charging a Li-ion battery (i.e constant current, then constant voltage), but the PowerStream page on Li-ion charging specifically warns against trickle charging for that battery type. 
After the current drops to some value it is desired to turn the charger off completely.  So the simple current-limited-and-voltage-limited supply might work, but only if you remember to unplug it.  Forgetting about it, and leaving it connected,  might cook the battery.

Just saying I think there are reasons why universal battery chargers end up being complicated.

nigel coxiceng

Answer 7 years ago

Hi iceng, thank you for the diagram this is just what I was looking for will copy the it and get cracking, have most of the parts in my bits box, many thanks Doc Cox

nigel coxJack A Lopez

Answer 7 years ago

Hi Jack many thanks for the info. battery charging is a bit more complicated than would first seem, many thanks for the reply regards Doc Cox