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Not being able to understand simple LM317 lead acid battery charger

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Here is a Schematic for a charger. It also includes a Diode to Prevent Reverse Battery Discharge.
And Formulas to calculate the Output Current and Voltage.

View attachment 95644
this is what ive been looking for but im going to change it up a bit to charge single cell 2vdc lead acid deep cycle cells or make it an adjustable voltage charger...thanks for posting...
 
I am going to make a bench power supply so that current is not fixed.
Then you might want to start a thread about building a bench supply. Start with what voltage and current it has to provide, how many outputs, etc. And BTW: using chips like LM317 is a poor way to build a bench supply. It is not that difficult to build one with adjustable voltage and current using cheap op-amps and transistors.
 
And BTW: using chips like LM317 is a poor way to build a bench supply. It is not that difficult to build one with adjustable voltage and current using cheap op-amps and transistors.
Why do you think it's a poor way? :confused:
Certainly building one with op amps and transistors is significantly more complicated.
An LM317 regulator is cheap, has a built-in reference, current limit, and over-temperature limit -- it's near bullet proof.
The only limitation is that it won't go below 1.2V but not many applications require a voltage below that level.
 
Crutschow, I Agree and if all you need is a Simple Battery Charger, Why get complicated.
 
Why do you think it's a poor way? :confused:
Certainly building one with op amps and transistors is significantly more complicated.
An LM317 regulator is cheap, has a built-in reference, current limit, and over-temperature limit -- it's near bullet proof.
The only limitation is that it won't go below 1.2V but not many applications require a voltage below that level.

1) The LM317 won't adjust down to zero V.

2) It doesn't have easily adjustable current limiting.

It's just a really crappy way to go. For the time it takes to build it, I would do a better design.
 
Crutschow, I Agree and if all you need is a Simple Battery Charger, Why get complicated.
Here is the post I replied to:

Willen said:
I am going to make a bench power supply so that current is not fixed.

My reply to that post:

"LM317 is a poor way to build a bench supply."

and I still say it. I was talking about a bench supply, something you will use a million times in your career. Don't build a piece of junk.
 
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Please see post ten in the thread. Building a lab supply is not that complicated. The design I posted has a lot of features which can be omitted, but the basics of voltage control loop and current control is shown.
What post ten? :confused:
 
chemelec said:
Rather than SIMULATING these Circuits, Why don't you just BUILD THEM?

Your post just made my day.....
...and then, when the circuit doesn't work, you can enter it into the simulator so that it can show you why it doesn't work...
 
It's interesting the number of simulator Luddites on these forums. :rolleyes:
A simulator is just a tool. If you don't want to use one fine, but why act like those who do are somehow wasting time? :confused:
I seems apparent that you simulate a circuit so that you have a good shot that it will work in the real world.
The chances are very high that if the circuit won't work in simulation then it won't work when you build it.
And I've trouble-shot enough circuits to know that finding the problem in a simulator is a lot easier than finding it in a (non) working circuit.
 
And I have found that some circuits that Simulate correctly, don't work in real life.
And Visa Versa.

However I am Fortunate that I already have All the parts, so no need to Buy any for playing.

Crutschow Wrote: And I've trouble-shot enough circuits to know that finding the problem in a simulator is a lot easier than finding it in a (non) working circuit.
This Just Depends on your SKILLS
 
And I have found that some circuits that Simulate correctly, don't work in real life.
And Visa Versa.
-------------------------
Crutschow Wrote: And I've trouble-shot enough circuits to know that finding the problem in a simulator is a lot easier than finding it in a (non) working circuit.
This Just Depends on your SKILLS
Yes some circuits will simulate but not work when built, but it's rare for a circuit to not simulate correctly (other than simulator problems such as convergence issues) but still work in practice.

Of course trouble-shooting depends upon your skills. That's obvious.
But in the simulation you can readily look at all the node voltages and branch currents to see what's happening.
That's not possible in the actual circuit where it's difficult to look at more than two (or perhaps four if you happen to have a 4-channel scope) node voltages, and impossible to easily look at most branch currents.
It's also easy to modify component values to see their effect on circuit operation.

An example: I was given an op amp circuit at work that was exhibiting instabilities and I was asked to trouble-shoot it.
I couldn't determine any obvious problems by probing the circuit so I simulated the circuit.
Initially it worked fine but when I added in the estimated stray capacitance at the op amp input from the coax input line the instability was seen.
So the circuit design was modified, and simulated to optimize the fix before the mod was done to the circuit.
The circuit worked fine after that.
If I hadn't simulated the circuit, it likely would have taken me much longer to determine the cause of the problem as well as what the best fix would be.
 
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