Is this a valid way to charge lead acid - Page 1
Forum section: electronics / beginners

author: Raj
author_rank: Frequent Contributor
timestamp: June 08, 2020, 06:40:12 am
content: So, I have 5v solar which produce power, more than what I use them for ( It keeps the DIY wall clocks and closet lighting running by charging li-poly via chinese circuits).Since the panels are generating enough power to charge that battery many times over, and the clocks don't consume much (being sound reactive [clap to show time]) I was thinking of using a boost converter and current limiter to also slowly charge up a deep cycle lead acid which I won't be using much. (planning it to use it with dill motors and power tools)

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2020, 07:37:33 am
content: https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

author: Raj
author_rank: Frequent Contributor
timestamp: June 08, 2020, 05:14:03 pm
content: Seems to me like it'll do the job... What I'm worried about, would it achieve the downward ramp as it approaches it's end? Or should I replace the current limit (planned on using a lm317) with something else? Btw,I ain't planning on giving it more than 300mA

author: Benta
author_rank: Super Contributor
timestamp: June 08, 2020, 06:03:24 pm
content: Lead-acid batteries need constant voltage charge with current limiting. A simple DC-DC converter will give you this functionality.

author: David Hess
author_rank: Super Contributor
timestamp: June 08, 2020, 11:19:09 pm
content: What you suggest will work fine for either lead-acid or various lithium rechargeable batteries.A slightly more sophisticated lead-acid charger charges to an "equalization" voltage which forces equalization of the cells and then lowers the voltage to the float voltage. The difference could be say charging to 14.2 volts and then reducing to the 13.8 volt float voltage but charging at the float voltage is acceptable also in less critical applications.

author: Raj
author_rank: Frequent Contributor
timestamp: June 09, 2020, 09:32:48 am
content: Quote from: David Hess on June 08, 2020, 11:19:09 pmThanks...I can do that using a micro controller...hcarge it upto 14.2, then slowly discharge it until it reaches 13.8.

author: tunk
author_rank: Super Contributor
timestamp: June 09, 2020, 10:00:37 am
content: You may want to use a (Schottky) diode between thecurrent limiter and battery to avoid discharge whenthe panel cannot provide enough/any power.

author: David Hess
author_rank: Super Contributor
timestamp: June 09, 2020, 07:02:24 pm
content: Quote from: Raj on June 09, 2020, 09:32:48 amWhen I did it last time, I used a comparator to detect the threshold which then tripped an SCR.

author: Raj
author_rank: Frequent Contributor
timestamp: June 10, 2020, 05:10:22 am
content: Quote from: tunk on June 09, 2020, 10:00:37 amYup...that's why I have a diode symbol in my schematic.

author: mikerj
author_rank: Super Contributor
timestamp: June 10, 2020, 09:35:43 am
content: Quote from: Raj on June 10, 2020, 05:10:22 amYour diode is between the panel and converter though. There will undoubtedly be some leakage current from battery into the converter when it's not working, and you need to make sure that the converter is even suitable for this operation i.e. voltage on it's output higher than voltage on it's input may be damaging to some parts.

author: Gyro
author_rank: Super Contributor
timestamp: June 10, 2020, 10:12:55 am
content: If you're in India, 13.8V will probably be too high for float charge. You should looking at something close to 13.60. The optimum float charge voltage is temperature dependant - in fact temperature controlled charging would be a sensible idea for maximum battery life.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 10, 2020, 10:32:51 am
content: Some specs I have saved from various online sources, mostly valid for a car battery. Keep in mind these are generic specs. Always check with the battery manufacturer for the exact specs of your particular model of lead acid battery.Code:Lead Acid generic specs-----------------------At a comfortable temperature of 20°C (68°F), gassing starts at charge voltage of 2.415V/cell.Battery status-40°C (-40°F)-20°C (-4°F)0°C (32°F)25°C (77°F)40°C (104°F)Voltage limit on recharge17.116.215.314.714.1Float voltage at full charge15.314.714.113.813.5or loweror loweror loweror loweror lower

author: Raj
author_rank: Frequent Contributor
timestamp: June 10, 2020, 02:24:44 pm
content: Quote from: mikerj on June 10, 2020, 09:35:43 amNow I get it...thanks for the suggestionQuote from: Gyro on June 10, 2020, 10:12:55 amMan, yup, it's truly quite hot here, specially now

author: tunk
author_rank: Super Contributor
timestamp: June 10, 2020, 02:47:28 pm
content: I don't know if this is a problem or not:Let's say you set the current limit to e.g. 100mA,what will happen when the panel cannot deliver this?

author: Raj
author_rank: Frequent Contributor
timestamp: June 10, 2020, 05:29:59 pm
content: Quote from: tunk on June 10, 2020, 02:47:28 pmWell... Then, the batteries will charge at a slower rate which won't be a big problem since my batteries are larger than what was needed for the application and remain nearly topped up.Plus the panel is huge enough to charge my clock batteries in about 4 hours of winter sunlight.