[SOLVED] LM350 voltage/curent regulator!

[leaualorin]

Hello everybody and thank you for existing(you and the internet! ).
I recently been "busy" building voltage regulators using LM338K , LM317T and finally LM350 for charging A123 SYSTEMS LiFePo4 (lithium phosphate) batteries!
The first project was with a LM338K wich "died suddenly" to my GIGANTIC dissapointment...
I never find out the "causes" , although it worked just fine until I hooked up a 55/60W halogen car light bulb wich SHOULD HAVE BEEN in its limits(4,6Amps).
Anyway:
The LM317T is still working but I want to charge these batteries to the specifications that the manufacturer provides (3Amps for normal charging or 10Amps for fast charging).
The circuit with the LM350 caught fire when I hooked up a circuit wich I had no ideea of how much amps draws and it did draw "ABOUT 6,5 AMPS" this being the result for the potentiometer to catch fire and the LM350 to make a "sinister pop"...
I have 4 more LM350 IC and I want to make 1 or 2 chargers and be able to charge the batteries at minimum 3 amps and be able to set the voltage at 3,55 volts on a multimeter before actually charging the batteries!
I gave up the 10 amp charger with 3 LM350 and a LM307 because I simply can't find a LM307 or LM308 IC and the 4,5 volts minimum voltage(I need maximum 3,55 volts for charging these batteries) ...
SO :
I want some advices regarding the well-building of a battery charger with the adjustable voltage and a 3 amp constant and non-variable charging curent!
I searched thoroughly in the datasheet for LM150/LM350A/LM350 and there are 2 schematics that have "drawn my attention":
one is for a 3amp constant curent at page 10/14 in the bottom wich seems preety much "bullet proof" with no potentiometer to "cache fire" :roll: in case of some stupidity from my part and another schematic would be a "combination" betwen the one at the top of the page 6 and the one at top of the page 7 WITH the output capacitors in!
The big dillema is how would I hook these schematic( 3amp curent regulator and the adjustable voltage regulator) without everything ending up in smoke and "strange smell" AGAIN!
Thank you kindly and I hope someone can help me (if it wants) with some good advices regarding this adjustable supply!
Good day!

 

[KerimF]

When you like to charge a battery, think how to regulate (or control) the charging current first.

Applying just one volt above the battery voltage may let the battery sink a high current mainly if the voltage supply is of high power (that is it can deliver high current).

In other words, the charger should act as a controlled current source when the battery is charging. But at the same time the charger (in general) should have a voltage limiter not to be exceeded. So that, at the end of charge, the charger acts as a voltage regulator. Specific chargers for specific types of batteries may have their own algorithm but their current is always regulated so that any voltage difference between the charger and the battery will not produce a current according to their internal resistances only (which are usually of very low value).

 

[leaualorin]

When you like to charge a battery, think how to regulate (or control) the charging current first.

Applying just one volt above the battery voltage may let the battery sink a high current mainly if the voltage supply is of high power (that is it can deliver high current).

In other words, the charger should act as a controlled current source when the battery is charging. But at the same time the charger (in general) should have a voltage limiter not to be exceeded. So that, at the end of charge, the charger acts as a voltage regulator. Specific chargers for specific types of batteries may have their own algorithm but their current is always regulated so that any voltage difference between the charger and the battery will not produce a current according to their internal resistances only (which are usually of very low value).

Hello!
Well , I have been charging these batteries for about a 1 year now(lost the count on charging times) and I followed the manufacturers indications :
"Constant curent , constant voltage" .
The curent I must admit it , at the begining of the charging was high(the highest was 1,23amps ) but the voltage was set by me from the defunct potentiometer and the maximum charging voltage is 3,6 volts (again , following what the manufacturer specifies) but the curent dropped until at the end of the charging(wich took A LOT of time) and it was down to 50 miliamps!
Again, this is exactly what the manufacturer says regarding to the state of charge(50mA coresponds to > "END OF CHARGE / battery full/completely charged").
Now : I want to speed up things "a little" and give it 3 amps from the begining not just "how much the battery is taking in".
That's why I got here on this forum , in an attempt to fix this charging problem wich seems to be over my head and not buying a special charger for this type of cell(I like to do things with my own hands; always have until now , and I'm gonna be 29 in about 2 months.).
If someone has the knowledge regarding my topic PLEASE RESPOND HERE!
Thanks in advance!
:razz:

 

[FvM]

Without a schematic, every word is just a guess. I fear.

 

[leaualorin]

:-D
Here's the schematics, I just thought anyone interested could find the datasheet on the web!

 

[mister_rf]

Try this way:

 

[FvM]

I just thought anyone interested could find the datasheet on the web!

No doubt about. The question was in fact for your actual circuit (including part dimensions, presence of protection diodes) rather than a collection of suggested circuits.

Generally, LM350 (as well as most similar three terminal devices) is said to be fail safe as long as a few requirements are met, e.g. regarding voltage reversal. So if you managed to blow the device, either the said conditions have been exceeded, the device died from permanent thermal stress, or there are additional issues not revealed in the datasheet.

P.S.: I agree with mister_rf, that a dedicated current limit means should be preferred in any case.

 

[leaualorin]

Hello again mister rf!
I have been kind of busy but still,the circuit is made but I have only one more problem :
instead of a 0.22ohm resistor could I use 0.33 ohm?
What would change in the case of using a 0.33 ohm resistor?
I'll wait for your response and not test anything until you reply!
Thanks!

 

[IanP]

5c

Current (roughly) is Ube/R ..
0.66/0.22=> 3A
0.66/0.33=> 2A

:wink:
IanP

 

[leaualorin]

Thank you Ian!
Guess I'll give it a go like that!
I'll keep you all informed regarding the results!

 

[leaualorin]

UPDATE:
it's working just fine!(a bit warm but nothing unusual!
I'm sorry I can't post photos right now but I'll add photos later and a detailed description of the setup!
Right now I have my eyes on the LT1584/1585/1587 regulator family for their fixed voltages that suit my aplication and the high amps ( around 7-8 for the LT1584 , 3.6 fixed voltage).
This topic can be marked as "solved"!
I'll open two more regarding the LT1584/3.6V and one for a DIY voltage regulator and rectifier for a friend's suzuki burgman(permanent magnet generator); maybe someone can help him with a schematic of some kind...
Bye bye!