12v Battery Charger Circuit using LM317 (12v Power Supply) - Page 1
Forum section: electronics / beginners

author: queennikki1972
author_rank: Regular Contributor
timestamp: April 30, 2019, 03:45:02 pm
content: Thinking about building this project.https://circuitdigest.com/microcontroller-projects/12v-battery-charger-circuit-diagram-using-lm317but I need someone to tell me if the circuit is incorrect and also decipher the BOM..Specifically the recommended wattage for all resistors and (Diode- Nn007 (3)) Do they mean 1n4007 for example? They also mention a 0.05R - Shunt Resistor/wire but I dont see on the schematic.I wont be using the Arduino nano or lcd

author: queennikki1972
author_rank: Regular Contributor
timestamp: April 30, 2019, 03:54:31 pm
content: Nevermind on the diodes, i see that it should probably be 1.5 amp diodes

author: woodchips
author_rank: Frequent Contributor
timestamp: April 30, 2019, 03:57:16 pm
content: What a bizarre circuit!Look in any application note for the 117 for a LA battery charger that is far more subtle. It uses a low value, 0.5 ohm or so. series resistor between the out terminal and the voltage divider going to the adjust pin. This automatically adjusts the charge current as the voltage rises, work out how!

author: queennikki1972
author_rank: Regular Contributor
timestamp: April 30, 2019, 04:11:42 pm
content: found it! Very simple circuit instead of this one.http://www.ti.com/lit/ds/symlink/lm117.pdfpage 24

author: Zero999
author_rank: Super Contributor
timestamp: April 30, 2019, 04:23:07 pm
content: Quote from: queennikki1972 on April 30, 2019, 03:45:02 pmConnecting an LM317 current limiter in series with a voltage regulator circuit, like that is a bad idea, because it requires a lot of voltage headroom to work. The LM317 voltage regulator circuit, needs an input voltage of about 3V more than the input. The current regulator circuit needs an additional 1.25V, as that voltage is dropped across the sense resistor: 4.25V. An LM317 voltage and current regulator in series, require an input voltage of around 7.25V more than the output voltage. Then the diode on the output will drop even more voltage.A 12V transformer is much to low for this circuit. It needs an 18V transformer to stand any chance of working properly.Quote from: queennikki1972 on April 30, 2019, 04:11:42 pmYes, that's a better idea. Figure 34, on page 26, is also a good idea, if sensing the current on the negative terminal of the battery, is acceptable.

author: queennikki1972
author_rank: Regular Contributor
timestamp: April 30, 2019, 11:15:27 pm
content: http://www.ti.com/lit/ds/symlink/lm317.pdfpage 13 battery charging circuit "RS" means current sensing resistor? Im sorry for asking such dumb questions

author: MarkF
author_rank: Super Contributor
timestamp: April 30, 2019, 11:36:41 pm
content: Here is a circuit I found online some time ago. There was a description but I didn't save the URL.I have not built it but looks interesting to play around with.

author: queennikki1972
author_rank: Regular Contributor
timestamp: April 30, 2019, 11:46:45 pm
content: MarkF that makes more sense to me. I assume that 1R0 is 1W means 1 WATT resistor.

author: MarkF
author_rank: Super Contributor
timestamp: April 30, 2019, 11:55:45 pm
content: This is not where I initially found the circuit. But here is a write up.https://sites.google.com/site/donutscience/various-projects/the-easiest-diy-lithium-polymer-battery-charger/the-easiest-diy-lithium-polymer-battery-charger---a-bit-moreHere is a link to the first page.https://sites.google.com/site/donutscience/various-projects/the-easiest-diy-lithium-polymer-battery-charger

author: MarkF
author_rank: Super Contributor
timestamp: May 01, 2019, 04:17:36 am
content: Here is the original link:http://www.talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#84B

author: digsys
author_rank: Unknown
timestamp: May 01, 2019, 06:14:20 am
content: Quote from: queennikki1972errr nope. 1R0 = 1.0 ohms (at 1W as stated)Working with V=IR, as current increases, voltage across the resistor also increases following that formula. At near 0.6V ~= 600mA, it will start to conductand start bringing down the Vop. If you need more current,decreasethe resistor value and vice-versaNote: That type circuit is really only for "Trickle charging" at ~ 13.8V, it has no boost capability, as usually ~14.4V. That gets trickier :-)

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2019, 07:41:56 am
content: Quote from: queennikki1972 on April 30, 2019, 11:15:27 pmI thought it meant series resistor, but the naming is arbitrary.Quote from: MarkF on April 30, 2019, 11:36:41 pmIt's probably based around the one on the datasheet I referred to above.http://www.ti.com/lit/ds/symlink/lm117.pdfpage 26.Quote from: digsys on May 01, 2019, 06:14:20 amHe's right. It should be a 1W resistor, to allow some leeway.

author: queennikki1972
author_rank: Regular Contributor
timestamp: May 01, 2019, 02:45:40 pm
content: Typo, 1 Ohm at 1 watt is actually what I meant to say. 1R0 1W = 1 Ohm at 1 watt