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Charger for 2-3Ah 12v SLA

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joecool85

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I saw this: https://www.aaroncake.net/circuits/charger1.htm But I wouldn't mind something a little simpler. I don't need it to be a "smart" charger. I'm fine with having to check the voltage or the battery or something to see if it's charging. I guess what I'm asking for is a circuit that can just charge for like...8 hours or something and charge a 2.2Ah 12v battery and then I unplug it. Can I just use a lm317 and regulate to 14v and run it to the battery?
 
I did a little research and it seems that at room temp (70F) I should be able to charge it at 15v @ 500ma for 5 hours for a full charge. But, I could be wrong.
 
Never mind, it seems that my research was right. I'm going to buy a 400ma 15v regulated adapter and use that to charge the battery. It should take about 7 hours.
 
It would be wise to monitor the voltage across the battery terminals as if the battery voltage reaches 14.7 volts and the charge current drops to 0.03A you should remove the charger or reduce the charge voltage to between 13.5 and 13.8 volts, otherwise you could easily overcharge the battery.

As an alternative, if the charger is set to between 13.5 and 13.8 volts you can leave the charger on indefinately.
 
Oh wow, in spanish.

Judging by the schematics though, it looks like I'm on the right track. Now, if I was to set up a charger using a 300ma transformer, and then regulating voltage to 13.8v, how long would it take me to charge a 2.3ah SLA? Is it any different than charging at 15v?
 
It will take a little longer to recharge the battery at the lower charge voltage because generally the higher the charge voltage the greater the current the battery will accept. But it is difficult to say as it also depends on the depth of the discharge. The advantage of using the float charge level is that you don't have monitor the battery and reduce the charge voltage or disconnect the charger at the specified point.
As a side note most manufactures of SLA batteries recommend on the size of battery we are talking about that the initial charge current be limited to 0.2C or for a 3Ah battery 3 x 0.2 = 0.6 amps.
So which ever transformer mentioned using should be just fine.
If you go to this web site **broken link removed**
scroll down to Power-Sonic technical handbook and down load the PDF you will have lots of info.
 
Ok, so I read through most of that PDF, good read btw. But, it didn't answer what I was wondering.

Here are my two options I have been thinking of:
13.8v
15v

Either one would use a lm317 to adjust the voltage, and a 300ma transformer.

So it would go, transformer, rectifier, lm317 circuit, battery. I know the idea is that you charge to 120%. So if you had a 1ah battery, to charge it with 200ma, it would take 6 hours (or 200ma x 6hr = 1200mah). But, doesn't the math change when you are charging with different voltages?

**edit**
Would I be right in saying that you can figure it out in watt hours? IE - to charge a 2ah battery with 10v @ 100ma, it would take 24 hours, or to charge the same battery with 20v @ 100a, it would take 12 hours?

**edit again**
Or would it be that since a 2.3ah charges with 15v @400ma, it take twice as long at 13.8v because the difference between full (12.6v) and charge voltage is halved?
 
It seems that is about right since I found that normally charging an SLA at float charge levels (using 13.5v), it takes about 16 hours, this is according to a PDF found at jaycar electronics. The cool thing about float charge is that if I was to charge a battery at 13.5v, I can leave it hooked up indefinetly like that, which is great! So I think I will do that. I'm fine with leaving it hooked up for 24 hours or so. The batteries are going to be used for a bike light setup (2x2.3ah) and I'm going to leave them in parallel for use and for charging now that I know more about it. I'll build a quick little regulated 13.5v setup and just plug them in for 24hr and I should be golden. Think a 300ma transformer will be enough or should I up it to a 450ma if I'm going to be charing essentially a 4.6ah battery?
 
hi joecool85, i build this charger and im happy with the results **broken link removed** for me its ideal i did a 12.7v 2ah battery (i must admit the battery is about 4 years old, 10v - 13.85v in 25 hrs. i know it seems long but i think its the age of the battery. im busy running down a new 10a 12v battery then i will check its time.
 
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