Float charging, question about ma - Electronic Circuits Projects Diagrams Free

joecool85 · 9th April 2006, 06:55 PM

From what I understand, you can float charge a 12v sealed lead acid battery at 13.6v indefinetly. And, from what I gather, the quickest you can charge float charging is 8 hours or so, I'm ok with that as I'm fine even with 24 hour charging. Here is the question, does it matter how many ma the transformer I'm using is? I was going to use a 300ma and it will be charging a 3.2ah battery, but if I use a larger transformer, would that be a problem? Also, can I use this style of float charging to trickle charge a car battery?

joecool85 · 9th April 2006, 07:19 PM

Also, would it be a good idea to have a switch to go from 13.6v to 14.4v, and then before use charge at 14.4 for a little while (30 min maybe), I read that by charging only via float, the battery will never get a "full" charge.

Hero999 · 9th April 2006, 07:20 PM

You really need a resiustor or voltage regulator with current limit to keep the current to a safe level.

What transformer are you using?

Could you post a schematic?

joecool85 · 9th April 2006, 07:33 PM

Its going to be real basic, a 12.6v transformer (either 300ma or 450ma), into a bridge rectifier, power filter cap, lm317 set to 13.6v, then into the battery.

Here is the schematic:

9th April 2006, 07:40 PM

A lead-acid battery should be charged at 10%-30% of its rated capacity - larger batteries tending to the low end of that range. So, your choice of 300mA is good for your battery. 13.6-14.2 volts for charging. When the current falls to about 40mA it will be fully charged, and a float charge can be applied. 13.5v would be an ideal voltage for "float" charging at 25degrees C. If you use a low voltage (float) to charge from discharge, make sure its FULLY charged before you use it to prevent sulfation of the plates which will decrease its life. A higher current transformer will be no problem. Use current limiting and voltage regulation in any charger you constuct!

Russlk · 9th April 2006, 07:49 PM

You don't need filter caps in the battery charger, pulses are good for the battery. Automotive regulators are set at 13.8 volts and the batteries last for 5 years or more in a severe environment.

joecool85 · 9th April 2006, 08:42 PM

So I wouldn't even need power filter caps?

**edit**
Also, asuming I use the 300ma transformer and set the voltage to 13.5v, if I left it for 24hours, it should be charged right?

Russlk · 10th April 2006, 02:14 AM

correct, you don't need any power filters, except as required by the regulator (see the data sheet). 13.5 volts is not full charge, 13.8 is recommended. Some chargers use a higher voltage but once the battery reaches the high voltage, the charge voltage is reduced to 13.8.

10th April 2006, 03:29 AM

13.8 volts is ideal for charging - NOT a float charge... IF youre going to float, dont go above 13.5 volts.

joecool85 · 10th April 2006, 03:34 AM

Ok, I would like it to float, but I need it to charge, thats possible right? Wouldn't it just take a little longer? From what I understand, you can charge a battery at 13.5v to its full capacity, and its actually good for it. It just takes a while. I was guessing somewhere in the 20-24hour range for charging a 3.2ah battery with a 300ma 13.5v float charger. Please, someone tell me if I'm way off base.

Oznog · 10th April 2006, 03:47 AM

You definitely DO need filter caps. The reg may not be all that stable without it. Also without it, even if it does come out stable, you're only charging a small percentage of the period.

The pulsing thing is not very well defined. There are a lot of pages on it but much of it is pretty questionable hack "reseach". Without a specific pulse shape and amplitude in mind, it's fairly unlikely that such a thing would happen to do something useful by chance.

10th April 2006, 03:59 AM

Youre not off base at all!! Your 3.2 aH battery is tiny - not a car battery, so 300mA at 13.5v is plenty. Anything over 1.5 amps is too much. It should take about 10-24 hours for a FULL charge if the battery is fairly new and the temp is around 25C (77F). It varies a lot depending on the lead alloy used in the plates, its age, temperature, abuse, etc.

joecool85 · 10th April 2006, 12:55 PM

Sweet. So, I'm going to use a 2200uF cap for power supply filtering. And also, you said in 10-24 hours it should be charged, so if I charge it for the 24 hours I was planning on, I should be golden.

**edit**
I was also wondering if I could use this to trickle charge a car battery.

10th April 2006, 03:50 PM

The car battery would be fine - it just may take several days. Its good to apply a short topping charge (14.0 - 14.3v) periodically if float charging is the only way youre going to be charging your battery. This ensures a longer life and a battery that will accept a full charge.

joecool85 · 10th April 2006, 04:13 PM

Ok...now lets say that I use this battery once week and drain it to 50% every time I use it. Would I want to do a 14v topoff charge every time before I use it, or like...once a month or something? Also, how long would I want to leave it at 14v? Maybe an hour or something? I appreciate all the help with this guys!

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9th April 2006, 06:55 PM	(permalink)
joecool85	Float charging, question about ma From what I understand, you can float charge a 12v sealed lead acid battery at 13.6v indefinetly. And, from what I gather, the quickest you can charge float charging is 8 hours or so, I'm ok with that as I'm fine even with 24 hour charging. Here is the question, does it matter how many ma the transformer I'm using is? I was going to use a 300ma and it will be charging a 3.2ah battery, but if I use a larger transformer, would that be a problem? Also, can I use this style of float charging to trickle charge a car battery? __________________ Life is what you make it.

9th April 2006, 07:19 PM	(permalink)
joecool85	Also, would it be a good idea to have a switch to go from 13.6v to 14.4v, and then before use charge at 14.4 for a little while (30 min maybe), I read that by charging only via float, the battery will never get a "full" charge. __________________ Life is what you make it.

9th April 2006, 07:20 PM	(permalink)
Hero999	You really need a resiustor or voltage regulator with current limit to keep the current to a safe level. What transformer are you using? Could you post a schematic? __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

9th April 2006, 07:33 PM	(permalink)
joecool85	Its going to be real basic, a 12.6v transformer (either 300ma or 450ma), into a bridge rectifier, power filter cap, lm317 set to 13.6v, then into the battery. Here is the schematic: __________________ Life is what you make it.

9th April 2006, 07:40 PM	(permalink)
hyedenny	A lead-acid battery should be charged at 10%-30% of its rated capacity - larger batteries tending to the low end of that range. So, your choice of 300mA is good for your battery. 13.6-14.2 volts for charging. When the current falls to about 40mA it will be fully charged, and a float charge can be applied. 13.5v would be an ideal voltage for "float" charging at 25degrees C. If you use a low voltage (float) to charge from discharge, make sure its FULLY charged before you use it to prevent sulfation of the plates which will decrease its life. A higher current transformer will be no problem. Use current limiting and voltage regulation in any charger you constuct!

9th April 2006, 07:49 PM	(permalink)
Russlk	You don't need filter caps in the battery charger, pulses are good for the battery. Automotive regulators are set at 13.8 volts and the batteries last for 5 years or more in a severe environment. __________________ see my website: www.geocities.com/russlk

9th April 2006, 08:42 PM	(permalink)
joecool85	So I wouldn't even need power filter caps? edit Also, asuming I use the 300ma transformer and set the voltage to 13.5v, if I left it for 24hours, it should be charged right? __________________ Life is what you make it.

10th April 2006, 02:14 AM	(permalink)
Russlk	correct, you don't need any power filters, except as required by the regulator (see the data sheet). 13.5 volts is not full charge, 13.8 is recommended. Some chargers use a higher voltage but once the battery reaches the high voltage, the charge voltage is reduced to 13.8. __________________ see my website: www.geocities.com/russlk

10th April 2006, 03:29 AM	(permalink)
hyedenny	13.8 volts is ideal for charging - NOT a float charge... IF youre going to float, dont go above 13.5 volts.

10th April 2006, 03:34 AM	(permalink)
joecool85	Ok, I would like it to float, but I need it to charge, thats possible right? Wouldn't it just take a little longer? From what I understand, you can charge a battery at 13.5v to its full capacity, and its actually good for it. It just takes a while. I was guessing somewhere in the 20-24hour range for charging a 3.2ah battery with a 300ma 13.5v float charger. Please, someone tell me if I'm way off base. __________________ Life is what you make it.

10th April 2006, 03:47 AM	(permalink)
Oznog	You definitely DO need filter caps. The reg may not be all that stable without it. Also without it, even if it does come out stable, you're only charging a small percentage of the period. The pulsing thing is not very well defined. There are a lot of pages on it but much of it is pretty questionable hack "reseach". Without a specific pulse shape and amplitude in mind, it's fairly unlikely that such a thing would happen to do something useful by chance. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

10th April 2006, 03:59 AM	(permalink)
hyedenny	Youre not off base at all!! Your 3.2 aH battery is tiny - not a car battery, so 300mA at 13.5v is plenty. Anything over 1.5 amps is too much. It should take about 10-24 hours for a FULL charge if the battery is fairly new and the temp is around 25C (77F). It varies a lot depending on the lead alloy used in the plates, its age, temperature, abuse, etc.

10th April 2006, 12:55 PM	(permalink)
joecool85	Sweet. So, I'm going to use a 2200uF cap for power supply filtering. And also, you said in 10-24 hours it should be charged, so if I charge it for the 24 hours I was planning on, I should be golden. edit I was also wondering if I could use this to trickle charge a car battery. __________________ Life is what you make it.

10th April 2006, 03:50 PM	(permalink)
hyedenny	The car battery would be fine - it just may take several days. Its good to apply a short topping charge (14.0 - 14.3v) periodically if float charging is the only way youre going to be charging your battery. This ensures a longer life and a battery that will accept a full charge.

10th April 2006, 04:13 PM	(permalink)
joecool85	Ok...now lets say that I use this battery once week and drain it to 50% every time I use it. Would I want to do a 14v topoff charge every time before I use it, or like...once a month or something? Also, how long would I want to leave it at 14v? Maybe an hour or something? I appreciate all the help with this guys! __________________ Life is what you make it.