fully charged battery

[grapeape605]

How can you connect an LED to a battery that only comes on when the battery is fully charged?

 

[AndrewT]

you could use a comparator to switch on the LED when the battery input comes up to the reference voltage.

But the reference voltage must be temperature compensated to match the "full charge" voltage over a wide range of battery temperatures.

 

[KatieandDad]

Are you trying to turn off something when a re-chargeable battery is fully changed ?

 

[Mooly]

Also, if its a lead acid battery (VRLA gell types) then charging continues long after a current limited supply flips from constant current to constant voltage as the current tapers down.

Every battery type and technology needs a different solution.

 

[grapeape605]

It is a small lead battery. I have it charging off the cigarette lighter in my car/boat through a resistor to keep from damaging the small battery. I just want to know when it is fully charged, I'm really not worried about float or trickle.

 

[AndrewT]

Lead acid is a nominal 2V per cell.
Charge it through a CCS regulator that roughly matches the C/10 rate.
Then after the CCS use a voltage regulator set to ~110% of that 2V per cell.
That 110% is dependent on the cell temperature and the cell acid strength.

 

[Mooly]

You have to worry about float and trickle charge because otherwise your battery will never fully charge and will deteriorate. The battery will stand 13.8 volts 24/7. If the current has tapered off fully and you remove the charger then the battery is not fully charged.

Have a read at the "Yuasa little red book of batteries" downloadable here ,
Norbain SD - Yuasa Little Red Book of Batteries

 

[grapeape605]

This is the battery I am trying to charge but I do not want to pull it out of the box it is in every time I need to charge it.
WKA12-1.3F 12V 1.3Ah Werker Battery with F1 Terminal - 12V - Werker - SLA Sealed Lead Acid Battery - Batteries Plus
I'm going to read the "Little Red Book" and return with more knowledgeable questions. Thanks for the help.

 

[AndrewT]

1.3Ahr will charge well @ 130mA from the CCS.
When the voltage rises above 13.2Vdc then the voltage regulator takes over.

Most lead acid can go to 115% (that 13.8Vdc quoted by Mooly) without harm if this voltage is set with a good tempco.

 

[Mooly]

This is the battery I am trying to charge but I do not want to pull it out of the box it is in every time I need to charge it.
WKA12-1.3F 12V 1.3Ah Werker Battery with F1 Terminal - 12V - Werker - SLA Sealed Lead Acid Battery - Batteries Plus
I'm going to read the "Little Red Book" and return with more knowledgeable questions. Thanks for the help.

If your use of this battery is "cyclic" meaning you use it a bit, charge it and then leave it for some time until needed again, then you really need a dedicated charger that will charge to nearer 15 volts and then taper the voltage down. This type of charger monitors the current and reduces the voltage down toward a "float" charge level as the battery charges. The higher voltage ensures the battery charges in a relatively short time. If your charging it in a car then you haven't the higher voltage available, all you have is the cars alternator voltage will can be anywhere from under 13 volts on a red hot day with a red hot engine to nearer 16 volts (for a few seconds) on an icy cold start. A shottky diode in series with the battery charging lead is probably all you need tbh and just keep it connected to the car lighter socket.

 

[Jsixis]

You have to worry about float and trickle charge because otherwise your battery will never fully charge and will deteriorate. The battery will stand 13.8 volts 24/7. If the current has tapered off fully and you remove the charger then the battery is not fully charged.

Have a read at the "Yuasa little red book of batteries" downloadable here ,
Norbain SD - Yuasa Little Red Book of Batteries

thanks for that awesome link

 

[woody]

If you just want to look at the voltage and value your spare time any you could just
buy a voltage monitor on Ebay for under $ 3.00 including shipping.

 

[Mooly]

thanks for that awesome link

You are welcome

 

[Mooly]

More Yuasa links here. Some really good info and graphs.
Yuasa NP Value Regulated Lead Acid Batteries

 

[dangus]

If you'd like a digital voltmeter, you can get little LED modules on eBay for a couple of bucks (search for LED voltmeter). Wire it up with a switch so it doesn't drain the battery unnecessarily.

 

[Jsixis]

If you'd like a digital voltmeter, you can get little LED modules on eBay for a couple of bucks (search for LED voltmeter). Wire it up with a switch so it doesn't drain the battery unnecessarily.

I bought 2 of those, handle little things for 1 buck.