Lm317 battery charger

ronsimpson · Dec 27, 2016

spec said:
with a similar circuit

Yes but yours does not work.

spec · Dec 27, 2016

ronsimpson said:
Yes but yours does not work.

Well Well Well- you are right. Another one of my gross errors.

spec

PS: Well done MrAl.

MrAl · Dec 27, 2016

spec said:
Well Well Well- you are right. Another one of my gross errors.

spec

PS: Well done MrAl.

Hello again,

Hey no problem, just rewire your transistor and you're all set right?
Here's a drawing showing the transistor emitter a little clearer.

Oh but i am not sure if you want that diode in series with the battery for an Li-ion as that messes up the voltage regulation a little. It's up to you though.

ronsimpson · Dec 27, 2016

I like to draw the most positive at the top of the page and the most negative at the bottom of the page.

baxterdmutt · Dec 27, 2016

spec said:
OK BM.

No worries.

spec

Hi again Spec,
As long as 33R is connected I get no output and the red led does not turn on (ever). If I pull 33R then I can adjust the output current (it won't go down low enough without a change. Not able to go below 80ma and my battery only need 12ma. ) and the red led is on when not charging.

spec · Dec 27, 2016

baxterdmutt said:
Hi again Spec,
As long as 33R is connected I get no output and the red led does not turn on (ever). If I pull 33R then I can adjust the output current (it won't go down low enough without a change. Not able to go below 80ma and my battery only need 12ma. ) and the red led is on when not charging.

Hi BM,

As Ron Simpson and MrAl point out, there is a gross error with the circuit of post #8 in the area of the transistor.

I will post a corrected circuit, which I hope will be OK.

Apologies for the inconvenience.

spec

spec · Dec 27, 2016

MrAl said:
... I am not sure if you want that diode in series with the battery for an Li-ion as that messes up the voltage regulation a little.

Hi MrAl,

You are correct about the undesirability of the diode in series with the output but, on balance, it should be OK for a lead acid battery, which is the target application.

But even so, the voltage effect of the diode is not that great.

spec

spec · Dec 27, 2016

ronsimpson said:
I like to draw the most positive at the top of the page and the most negative at the bottom of the page.
View attachment 103293

Thanks again Ron- I have redrawn the circuit in EAGLE and will re-post. Perhaps you would be kind enough to check it for me.

spec

spec · Dec 27, 2016

POST ISSUE 11 of 2016_12_28

Hi again BM,

Below is the corrected circuit for the LM723 battery charger.

spec

NOTES
(1) LED 1 needs to be a very high efficiency type (714uA)
(2) To set the charger up for a 12V, nominal, lead-acid battery, set RV2 (CURRENT) to maximum resistance. Connect a 1K resistor across the charger output terminals (no battery connected) and adjust RV1 (VOLTAGE) for an output voltage of 14.1V
(3) For an output voltage of 14.1V, RV1 (VOLTAGE) will be set to around 1.34K
(4) There will be a standing current of 10.42 mA flowing through the current sense resistors (RV2 + R4) by virtue of the 120 Ohm resistor connected between the LM317 OUTPUT and ADJUST terminals (1.25V). This standing current through the current sense resistors (RV2 + R4) will drop by around 714uA when current limiting is active.
(5) Decoupling capacitors, C1 and C2, should be disc, +-10% disc ceramic types with an X7R dielectric.
(6) C3 should be a high ripple current, low ESR capacitor intended for reservoir applications. The dielectric can be aluminum or polymer.

LINKS
(1) LM317 data sheet: https://www.ti.com/lit/ds/symlink/lm317.pdf
(2) BC54xx data sheet: https://www.fairchildsemi.com/datasheets/BC/BC546.pdf
(3) LED, high efficiency:
https://www.vishay.com/docs/81339/vlms20.pdf
https://www.vishay.com/docs/83293/vlmb40l1.pdf
https://www.vishay.com/docs/83343/tlle4401.pdf

crutschow · Dec 27, 2016

spec said:
Below is the corrected circuit.

The is no "below".

spec · Dec 28, 2016

crutschow said:
The is no "below".

TBC= To Be Completed. The schematic is there now.

spec

MrAl · Dec 28, 2016

Hi,

What kind of lead acid battery takes 5ma to 50ma charge current?
I am used to seeing 200ma, 1 amp, etc., so this must be a very small battery.

spec · Dec 28, 2016

MrAl said:
Hi,

What kind of lead acid battery takes 5ma to 50ma charge current?
I am used to seeing 200ma, 1 amp, etc., so this must be a very small battery.

That is intriguing me too.

spec

MrAl · Dec 28, 2016

spec said:
That is intriguing me too.

spec

Hi,

They arent making 12v lead acid watch batteries now are they ? (har har)

MrAl · Dec 28, 2016

baxterdmutt said:
Hi all,
I have been trying to get this battery charger working. I found the schematic on the web and it all looks good (to me) and others claim it works, but for me I can't get the LEDs to work right. The green is supposed to be on while charging and then when the battery is charged (the Zener in reverse bias) redirects the current to the npn transistor through the red led on the way to ground. This is supposed to turn off the green and turn on the red. For me the red comes on when it's charging and the green is always on. Any ideas?

Hi,

The output current of the original design does not seem to be high enough. Is that really what you need or was there an error?

spec · Dec 28, 2016

ronsimpson said:
I like to draw the most positive at the top of the page and the most negative at the bottom of the page.

Fully agree Ron.That is one of the fundamental tenants of a good schematic, and if I had followed it, the error with the transistor would have stood out like a sore thumb. But that does not mean that I would not still have missed it.

My excuse is incompetence, lack of focus, and complacency- the LM317 charger is such a simple circuit that I dashed it out without really paying attention.

Getting back to schematic layouts, I have been thinking for years about doing a guide, but never seem to get around to it- perhaps, in abridged form, a suitable topic for an ETO article. I broached this subject with Matt about ten months ago: Matt has already done some work on schematic good practice.

On the whole, the schematics on ETO are easy to follow, as are the technical descriptions, and both are well above the average that you see in some areas, although a few newbee posts make me smile because it brings back memories of the days when I could not follow a circuit but would have loved to.

spec

baxterdmutt · Dec 28, 2016

spec said:
That is intriguing me too.

spec

The battery is a 12v SLA rated at 1.2Ah. So what 10% of that?

Les Jones · Dec 28, 2016

Use a calculator if you can't work it out in your head.

Les.

baxterdmutt · Dec 28, 2016

baxterdmutt said:
The battery is a 12v SLA rated at 1.2Ah. So what 10% of that?

Les Jones said:
Use a calculator if you can't work it out in your head.

Les.

That wasn't my point. I was asked what my batteries rating was and I said .12A and others said that seemed small. Is 10% of 1.2Ah no longer .12A???

baxterdmutt · Dec 28, 2016

baxterdmutt said:
That wasn't my point. I was asked what my batteries rating was and I said .12A and others said that seemed small. Is 10% of 1.2Ah no longer .12A???

UhOh. My mistake. I'm very sorry. I wrote it wrong the first time. Apologies to all

Lm317 battery charger

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