Lm317 battery charger

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Sorry, I took your question literally. 120 mA would be a reasonable current to charge a 1.2 AH battery. You should find the maximum recommended charging current for the battery on the makers data sheet. If you need to charge the battery quickly you could go up to this current but more gentle charging would extend the battery life.

Les.
 
Hi,

Another visit from the illustrious Miss Steaks. She always seems to show up now and then
Look at Samsung's recent battery compartment design error that cost them 10 billion dollars because of maybe a 0.05 inch shortage of space. Now that's a true mistake.

For this circuit no problem really though, now that we know what the current should be (120ma min) then just change the schematic to reflect that and all is well.
 
baxterdmutt said:
UhOh. My mistake. I'm very sorry. I wrote it wrong the first time.
Click to expand...
This is the life of an engineer.
It is typical for a project to be built and then find out that some of the numbers are not right.
"Oh...The charger is to get its power from USB. ....sorry"
"Look, I can get one from China for $3.95"
"Where is the on/off switch" "What switch." "I just assumed you would have a switch"
Like yesterdays letter: "we ran out of funding" and I spent the money on my personal credit card.
 
I have made some horrific mistakes, that even now make me cringe. In one case I designed an 8 by 8 matrix that was supposed to generate 64 unique codes but, due to a very elementary drop-off, it only produced 16 unique codes. Luckily, it did not matter, as it turned out that 16 unique codes would be sufficient.

One of the funniest was when a proposal was submitted for a system to train pilots, when in fact, the customer had asked for a system to train air traffic controllers.

But one of the most unbelievable goofs, was the Hubble space telescope, which cost 800 million dollars and took 20 years to develop- the mirror had been ground to the wrong profile so, after launch into orbit, the images were blurred.

I bet there was much management and many meaningful, meetings, reports, procedures, and loads of lunches on the project and, while it is very easy to be wise after the event, you would have thought that surely someone would have checked the focus before launch.

spec
 
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spec said:
ut one of the most unbelievable goofs, was the Hubble space telescope, which cost 800 million dollars and took 20 years to develop- the mirror had been ground to the wrong profile so, after launch into orbit, the images were blurred.
Click to expand...
Yes, that was a monumental goof, but fortunately it was precisely ground to the wrong profile, so they could add a correction lens to cancel the error.
 
crutschow said:
Yes, that was a monumental goof, but fortunately it was precisely ground to the wrong profile, so they could add a correction lens to cancel the error.
Click to expand...
Yes, there was a very good program, once again on PBS America, about how they managed to correct the error. The missus was out so I was able to watch the whole program.

spec
 
Hello again,

Dont get me started on the "space program" or should i say the "lack of space program"

Who can forget the mission to mars where Lockheed used English units and NASA used metric units, even though NASA had sent out a paper years earlier stating that metric units would be the standard from then on. The little spacecraft is now either crashed on the surface of Mars or is orbiting the Sun, and the money for that project can now be found down the drain. The REAL funny part is that during tests the error was not detected long before the launch date. So that's TWO mistakes in one which cost a lot of money.

I think there was another Mars crash recently too wasnt there from the European space program's attempt to land on Mars again. That's two swings and two misses for them now too.

I dont even want to talk about the Shuttle program which was a complete bungle on the part of it's management.

In fact, the only good thing i can say about the space program is that it may someday help us deflect an incoming asteroid and if they can do that they will prove their worthiness above and beyond any counter reasoning, but if they fail, they will have proved that man can not defend the planet properly when it's really needed. Going by current knowledge of this phenomenon, they will in fact be needed to perform this kind of defence sometime in the future so i HOPE they are working on this and can get it RIGHT the first time as they probably wont get a second chance.
 

Yes this kind of fundamental and unforced error is all too common.

I expect you are referring to the space shuttle seals, which according to my knowledge, they were warned about but did nothing about it.

I watch a series on UK TV about plane crashes and some of the reasons for the crashes are astonishing: the pilot tried to take off with his foot on the break/ without deploying flaps/ when the aircraft was covered in ice/ without permission to take off/ with insufficient fuel...

But what gets me really going are the procedural gaffs- apparently they do not weigh the aircraft they just estimate the weight and weight distribution. How difficult could it be to have built-in weight sensors with all the technology on-board an aircraft.

I will stop now.

spec
 


Hi,

Oh wow, dont get me started on aircraft now

I saw that program too or a similar one. Just nuts, that's all i can say.

One i remember well is the one where the the tail flaps (if i remember right) adjustment came from a mechanism that worked such that when the pilot pushed the lever forward the flap would turn up so the plane would start to descend, and when the pilot pulled back the flap would turn down so the plane would start to ascend. Well, that original mechanism had a big problem where when it got too cold (as would be typical in jet airliner NORMAL EVERYDAY flight) the action ***REVERSES*** so that then the pilot pushes forward the flaps turn down, and when pulled back the flaps turn up, so the plane does the REVERSE of what the pilot had been doing the whole time he ever flew those planes. Needless to say, it got too cold one day and the pilot pulled back to climb and when he saw the aircraft start to descend he pulled back more, which lead to a faster decent, and so he pulled back more and more, until the plane rolled over and crashed. They didnt find out right away, but another pilot had the same problem and he was able to figure it out and land safely (mucho congrats to him!). The other 200 people were not so lucky, and then finally they figured it out and fixed it.

Sometimes i cant help but think we have little children working on these problems.
 
Well I tried to sort this out on my own but it's not working out. I wanted to use this on a small 1.2Ah 6v lead acid battery so I made some adjustments. The charge voltage and current adjust down to my needs just fine, but I'm unable to get the red led to come on except for a very slight glow. I've tried adjusting the bias resistor but it isn't making enough of a difference, I also tried splitting R2 into an 82R and a 39R and placing the anode of LED1 between (effectively keeping the total for R2 what it was). Help! Please!
 
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Hi BM,

Am I right in saying that the circuit of post #49 is charging your battery OK, but only at a low current and that the only problem is that the LED is glowing dimly.
Assuming that the above is a correct interpretation.
(1) In its present configuration the circuit will only provide around a maximum of 49mA of charging current. The circuit has not been changed to supply 120mA which was a later requirement. I will have a look at increasing the charging current to 120mA.
(2) There will only be about 700 mico amps flowing through the LED so if you are using a standard LED it will be very dull. As I said you need a high efficiency LED. Have you in fact fitted a high efficiency LED?

spec
 
No, sorry, I missed the high efficiency led.
Is it possible to have this work with a standard efficiency led.
I have no problem getting 7.2v or more and a couple hundred ma out of the circuit with the the design as it is.
 
baxterdmutt said:
No, sorry, I missed the high efficiency led.
Is it possible to have this work with a standard efficiency led.
Click to expand...
I did try configuring the circuit for a normal efficiency LED but it got a bit awkward

baxterdmutt said:
I have no problem getting 7.2v or more and a couple hundred ma out of the circuit with the the design as it is.
Click to expand...
Hmm that is odd because the maximum current, with the current control potentiometer adjusted to minimum resistance should be around 49mA.
A lead acid battery charging voltage should be 14.1V, but you mention 7.2V. Are you in fact charging a double cell lithium Ion battery, from a camera for example?

spec
 
Hi BM,

Below is a revised battery charger schematic which provides 120mA charge current and uses a normal LED (afraid I had to add two transistors).

spec

​
 
Spec,
Submitted for your review.

The new 10R resistor is added to get Q2 to turn on slightly after Q4. (about 0.1V across 10R)
Purpose: to pull "ADJ" down as low as possible under high current conditions. Even now it does not handle a short well.
 
Nice Ron- one transistor less.

Did you mean just 10R in the emitter of Q2. That only gives 714uA * 10R = 7.14 mV

What is the problem with the short circuit condition?

spec
 
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Spec,

To the question of 10R: I was shorting to ground the current in 120R. (right/wrong?) I thought 1.25V on 120 ohm.

The idea that Q2 does not function under a short condition is heavy on my mind.
Here I jacked up Q4/Q2 so it takes two diodes drops (1.2V) to get current limit. Something I would not like to do but....
So with 1.2V across 10R then Q4 should turn on and light LED5. Then the LED current appears on 220R and pulls back IC3.
What I was trying to do is to pull "ADJ" to -1.1 volts under a short.
Comments. Thanks.
 

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You probably won't believe this, but I was thinking along similar lines.

I also considered putting an LM358 in to turn the charge LED on, but didn't think that an opamp would be in the spirit of the circuit.

I still cant find an issue with a short across the output terminals of the charger of post #76.

As I see it, under short circuit conditions Q2 will be conducting, the voltage drop across the 1N400x diode will be 0.6V and the voltage across the 4.7R current sensing resistor will thus be, (0.6V [Q3VBE]+ 0.1V[Q2VCEsat])+ 1.25 [LM317 Vref])- 0.6V [1N400x Vf] = 1.35V. This means that the maximum current will be 1.35V/4R7 = 0.28A

Where have I gone wrong?

Of course, with the original circuit, which had the red LED (1.2Vf) in the collector of Q2, the short circuit current would be higher by about 0.6V/10R = 0.06A, giving a total current of 0.34A

spec
 
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