Hello there!!

I was thinking what this actually mean.Can you please explain the terms in voltage-regulating mode and current-regulating mode. also does it mean that the Led will turn off after full charge??

http://www.electroniq.net/power-sup...y-charger-electronic-project-using-lm317.html

 

Voltage regulating means it senses the output voltage and the feedback works to keep it at a fixed value (commonly called constant voltage mode). In current regulating (constant current) mode the current is sensed and the value is forced to be constant.

IMHO, that circuit is pretty much useless. Using a blocking diode means the circuit can't even read the battery's actual voltage.

 

Since LEDs are current devices I use the LM317 in current regulation mode all the time. The voltage regulator mode needs no explanation.

Most decent variable lab power supplies have both a current regulation and voltage regulation mode.

 

IMHO, that circuit is pretty much useless. Using a blocking diode means the circuit can't even read the battery's actual voltage.

Thanks for answering. So can you please suggest a circuit to charge my nimhs? It will be helpful if you can keep it simple(i.e. not using ICs except LM317s and NE555. It can include transistors). It does not need to be that smart. Just an LED to indicate when the charge is complete will work

 

So can you please suggest a circuit to charge my nimhs? It will be helpful if you can keep it simple(i.e. not using ICs except LM317s and NE555. It can include transistors).

Sounds like your homework assignment.

To actually design a battery charger, you need to define the current rating (battery size), how fast they have to be charged. Charging NI-MH is not trivial. They don't tolerate sustained overcharge and are not easy to detect full charge on.

It would be better if you had more specifics of the application.

 

Thanks for answering!!

It not for my homework. The Ni-mh battery is AA 2700mah and I want to charge it within 20 hours. The time does not matter that much. I have a DUMB charger(costing 1.5 USD) that overcharged my other pair so much that it now has become totally useless. I dont want to destroy my new batteries again. However, when I told that to my parents, they simply told me to leave it and to study. So, I felt that help can be received only from you to save my batteries.

 

Have you read the section about charging in Wikipedia?

 

Yes I have.

 

If you're serious about charging NiMH then read this:
http://www.linear.com/docs/1463
and this:
http://www.linear.com/docs/24954

The LT1510 is available in a PDIP package designed to charge Li-Ion, NiMH, and NiCd batteries.

Note charging batteries of any kind can be dangerous. I suggest using eye and hand protection at the very least when performing initial tests charging Ni batteries.

Do not use a LM317 to charge a battery of any kind.

 

Yes I have.

Well then, you know that charging NiMH batteries isn't a trivial process, and it might involve measuring time, current and/or temperature. What's your plan?

 

Thanks for answering!!

I was thinking of charging it at a slow rate like C/15 so that there is little overcharge. The problem is I dont have anything apart from some transistors, LM317s, SCRs and 555 timers. I now really feel that I should leave trying to make a charger for I dont have the required ICs. Poor me. Poor me...

 

And by the way I have MIP2F2 IC. Can it help in making LI-ion, Ni-cad or Ni-mh charger? I have made my one for lead acid using a LM317. So if there's any circuit that can charge Ni-mhs or ni-cad or li-ion, please inform me. If any other ICs are required, please tell me their names- I will search for them for I have Salvaged a lot many ICs from many circuit-boards.

 

Hey wait!!

I have a thermistor.Cant I use it to detect the temperature increase when NIMH batteries are being charged. For instance, when the temperature will go above "X" volts, then electricity will flow through the gate of the SCR and turn an Led On(or off, OR terminate the charge. No problem for I will keep A CONSTANT eye on the battery and multimeter.). My questions are:

*What is the temperature at which Nimh batteries are fully charged(at C/2)
*I have explained the things the circuit will do(or at least I think I have). Now can you please give me the circuit schematic for it(or is it either possible??). I know it seems like I cant make a Schematic, but the fact is that I lack time. Even when I am typing this, my mother is calling me continuously to study as tomorrow is my exam. So I hope I can get some Help. Thank You.

 

Now you're talking sense. Yes, that's exactly how a charger for NiMH cells might work. Though I think what you'd be looking for would be a rise in temperature over some specific period of time, not just a fixed maximum.

I'm afraid I have some conscience about advising a young person to build something which might be dangerous. If you did this and swore that you'd keep an eye on that over-temp LED, and then you failed in your duty and your house burned down, whose fault would it be? As you say, your mom might drag you off to do homework any time. Of course, "If I turn my back on this battery charger, we'll all die" might be a persuasive reason for her to leave you alone, but then the next day, you could find your computer smashed up in the trash. And Mom might have a few words for the idiot who advised you to build the machine.

Could this be a science fair project? Then you'd have a good excuse to work on it (safely!)

 

Why, was I talking Non-sense so far?

Anyways thanks for answering!!
And I am not THAT irresponsible that I will leave it alone. I am the first boy in my class and I am a responsible one. If in-case I forget to terminate it, I will fit a LDR On the Led and when it will glow, the resistance will decrease and that will turn on another SCR which will in turn feed the electromagnet which will open the contacts on the reel switch. So, I will like you to give me the schematic (not thinking about what will happen if i ignore the Glowing LED).

 

I don't think this can be done without measurement of temperature, time and current, and the ability to control current. I wouldn't try it without a microcontroller, but really it would probably make more sense to buy a special integrated circuit for the job. This is more than you can expect to do with just a regulator and a thermistor.

If you want to investigate further, look at the Wikipedia entry and make some notes. What should this device measure and what should the current be in response?

If your school teaches electronics, ask the teacher about batteries and chargers.

 

Thanks for answering!!

Teachers teaching electronics?? It is kind of my hobby

So, ultimately, I will need an IC to make a NIMH battery charger, right? If thats the case, can you please give me the names of some of the (cheap) Battery charger ICs? It might happen that I find some of those in my salvaged box.

 

I have made a SUPER SIMPLE INEFFICIENT battery charger circuit. If I do This, will this work??

 

So, will I give it a try or is it that it is useless??

 

Nay, it didnt work. Nevermind, I will use an IC for the purpose.