Hey All -
Spring is upon us, and that means I get to cut grass.
The battery in my riding mower was cranky this weekend (it's been five months since I last cranked it up!), and after multiple attempts I ended up jumping it off using the battery from my mule. Both use a typical 12V lead-acid battery.
On to the topic, though.
I'd like to build a charger for these 12V batteries. I was thinking of using an application based on the LM 317, but I have a couple of questions...
(1) The LM 317 data sheet provides two schematics for battery charging applications. One involves a 0.2 ohm resistor in series between the LM 317 out and the battery. The other is a 50 mA trickle charger. What's the difference?
(2) I know I need at least 4.5 V more at the input of the LM 317 than the destination battery (12V). Would a 19.5V DC laptop supply (brick-style, I believe it's linear) work for the initial power source? I'm assuming it would (though I need to check the current max to make sure).
(3) Speaking of current, is there a way to maximize current output from the LM 317 (I believe 1 A is the safest bet) to the battery in question, then slowly reduce it as the battery becomes fully charged? Isn't this called a "floating charge?"
(4) Would it be possible to build in some type of indicator (LED?) to tell me when the battery has reached full charge (13.8 V for a 12V battery, correct)? Would I use a typical comparator op-amp for this?
(5) Would I need to house this unit in a metal enclosure? Can I use an ABS box?
(6) I don't trust internet schematics in general, but I trust advice from members here. Does anybody have an existing schematic they care to share so I don't have to start from scratch?
I plan on doing this over the next few weeks, so going slow is OK (and preferable). Most of my past projects have been related to building bench supplies (make-work projects, haha!) and LED/555 toys for my kid. This is my first "real world application" project, so I'd like to do it right.
Spring is upon us, and that means I get to cut grass.
The battery in my riding mower was cranky this weekend (it's been five months since I last cranked it up!), and after multiple attempts I ended up jumping it off using the battery from my mule. Both use a typical 12V lead-acid battery.
On to the topic, though.
I'd like to build a charger for these 12V batteries. I was thinking of using an application based on the LM 317, but I have a couple of questions...
(1) The LM 317 data sheet provides two schematics for battery charging applications. One involves a 0.2 ohm resistor in series between the LM 317 out and the battery. The other is a 50 mA trickle charger. What's the difference?
(2) I know I need at least 4.5 V more at the input of the LM 317 than the destination battery (12V). Would a 19.5V DC laptop supply (brick-style, I believe it's linear) work for the initial power source? I'm assuming it would (though I need to check the current max to make sure).
(3) Speaking of current, is there a way to maximize current output from the LM 317 (I believe 1 A is the safest bet) to the battery in question, then slowly reduce it as the battery becomes fully charged? Isn't this called a "floating charge?"
(4) Would it be possible to build in some type of indicator (LED?) to tell me when the battery has reached full charge (13.8 V for a 12V battery, correct)? Would I use a typical comparator op-amp for this?
(5) Would I need to house this unit in a metal enclosure? Can I use an ABS box?
(6) I don't trust internet schematics in general, but I trust advice from members here. Does anybody have an existing schematic they care to share so I don't have to start from scratch?
I plan on doing this over the next few weeks, so going slow is OK (and preferable). Most of my past projects have been related to building bench supplies (make-work projects, haha!) and LED/555 toys for my kid. This is my first "real world application" project, so I'd like to do it right.