Would it be better to just have the charge terminate at 13.6 volts if it's going to drop the voltage down to that after it gets to 14.4 volts anyway?

 

Would it be better to just have the charge terminate at 13.6 volts if it's going to drop the voltage down to that after it gets to 14.4 volts anyway?

No, As I previously noted, 13.6V is not sufficient to fully charge a lead-acid battery.
That's why the typical charge voltage is about 14.5V.
You only drop to 13.6V to maintain the charge.

 

Is it ok for me to substitute another resistor for R9? 26.7 kilo ohms is a bit of an odd value. Could I substitute 33 kilo ohms or 22 kilo ohms?

 

Is it ok for me to substitute another resistor for R9? 26.7 kilo ohms is a bit of an odd value. Could I substitute 33 kilo ohms or 22 kilo ohms?

Why do you say it's odd? It's a standard 1% value.
That resistor determines the trickle charge voltage so it can't be changed without adversely affecting that voltage.

R2, R3, and R9 should all be 1% resistors.

 

I don't think I have any 1% resistors that are 26.7 kilo ohms. I do have some 1% resistors (pretty sure they are the ones that are small, blue, and have no bands on them), but they are 48.7 kilo ohms. Since R9 being 26.7 kilo ohms is a necessity, do you think I should just use the circuit you posted in post #30? If so, am I correct in assuming that it can't be left on the charger when full and should be disconnected when the battery reaches 14.5 volts? I will keep searching for some 26.7 kilo ohm 1% resistors, but I'm not sure if I will be able to find any.

 

am I correct in assuming that it can't be left on the charger when full and should be disconnected when the battery reaches 14.5 volts?

You could leave it at that voltage for a few hours to top off the charge.

I will keep searching for some 26.7 kilo ohm 1% resistors, but I'm not sure if I will be able to find any.

They can be purchased at any electronics supply outlet.
Where do you get your electronic parts?

 

I buy parts off ebay usually, but I get most of my components by de soldering broken circuit boards. If I need a specific part, I can order it online (but it usually takes a while to ship), but I usually have the components required on hand. Unfortunately, I haven't had a need to order any high precision resistors, so I don't have any right now.

 

I will try and find some on ebay or amazon.

 

Suppliers, such as Mouser, Jameco, and Digikey also sell them.

 

Just got some 1/4 watt 26.7k ohm resistors on ebay.
Edit: While running the circuit, one of my parts cases slid onto the circuit and caused it to short out. The 1 ohm resistor got fried, but everything else is fine. I can't find another 1 ohm but I have loads of 1.1 ohms. Could I substitute a 1.1 ohm resistor in the 1 ohm's place or should I order a new 1 ohm?

 

Could I substitute a 1.1 ohm resistor in the 1 ohm's place or should I order a new 1 ohm?

You can use the 1.1Ω, but it determines the charge current so that current will be about 10% less or ≈600mA.

 

That's ok. The battery isn't used very frequently, so the charge current can be slow.

 

I've been testing the charger from post 30 and I noticed something that seemed odd. When I un plugged the battery it was at about 13.5 volts. A few minutes later, the voltage had dropped to around 13.2 volts. Is this just because the charger was at 13.5 volts, or does the voltage of SLA batteries drop like this when they stop charging?

 

does the voltage of SLA batteries drop like this when they stop charging?

Yes, the open-circuit voltage of lead-acid batteries drops after charging and will eventually (may take a day) go to about 12.7V for a fully charged battery.

 

The resistors arrived and I will start working on the circuit tomorrow.

 

The resistors arrived and I will start working on the circuit tomorrow.

Excellent.
Keep us posted.

 

Got the circuit soldered up and it looks like it's going to work. I just have to make a casing to hold the perf board. I will post some pictures of the board when I get a chance.

 

Circuit works great! Thanks a ton for all the help!

 

Circuit works great! Thanks a ton for all the help!

Great to know it works.

 

I have a 12 volt 17.5 amp hour gel cell SLA battery and the charger I was using died on me. I want to get it charged asap to minimize the amount that the battery sulfates. I remember seeing this schematic online and many others that are similar to it and I thought it may just be easier to assemble this one since I have the parts lying around. Since there is a lot of conflicting information online on how to charge batteries, I just wanted to make sure that this circuit is ok for me to use for an SLA that is occasionally subject to shallow cycles and very rarely to deeper cycles. I was also thinking about charging the battery at less than 0.1C. Maybe 0.05C. Since I don't use the battery often, it is ok for it to charge slowly as long as that doesn't damage the battery.
Here's a link to the page the circuit is from.
http://www.circuitstoday.com/lead-acid-battery-charger
Thanks in advance for the help!

I've seen *MUCH* worse. Yuasa published various technical booklets that are worth reading, probably worth checking other manufacturers for data libraries.

In days of old - the L200 (ST AFAICR) was most peoples first choice for SLA work.