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Simple Battery charging led indicator

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ahsan376

New Member
i want to make a simplest circuit for battery charging indicator(when battery fully charged,low and discharge led indicate like ups) plz help me thanx.
 

MikeMl

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Most Helpful Member
What kind of battery? CHemistry? Voltage? Capacity (AH)?
 
A lot of battery chargers will have an output for an indicator, all you need to do is to make a circuit that can take advantage of this. Combine that with a simple low voltage detector and you have yourself a circuit.
 

Joe G

Member
Look at a data sheet for say a max921-924 comparator, page 13, it might give you an idea :)
 

dr pepper

Well-Known Member
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Joe's idea gives you a way to detect low level using a comparator, if you use 2 more comprators maybe from a quad package you could use them to detect the polarity of the voltage dropped accross a current sense resistor, as the polarity will reverse from charge to dishcharge.
 

MikeMl

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MikeMl

Well-Known Member
Most Helpful Member
it is rechargeable...

Then it is not a "dry battery". Is it lead-acid or NiMh or NiCd or LiPo or ???? Every one of those have different voltage vs state of charge characteristics...
 

audioguru

Well-Known Member
Most Helpful Member
A lead-acid cell is "2V".
A Ni-Cad or Ni-MH cell is "1.2V".
A Li-po cell is "3.7V".

So it must be a 2-cell lead-acid battery. Maybe it has a gel electrolyte that does not spill so it is called "dry".
 

MikeMl

Well-Known Member
Most Helpful Member
If it is a 2-cell Sealed Lead-Acid battery, then it is a bit simpler than other battery chemistries. Unfortunately, building a State-Of-Charge (SOC) indicator for Lead-Acid is still complicated.

**broken link removed** is determined by reading the battery terminal voltage, ideally several hours after no current has flowed into or out of the battery (battery is open-circuited). The SOC is determined by measuring the voltage (to four significant figures), correcting the reading for ambient temperature, and looking up the SOC on a graph.

Various other methods are used:

1. Apply a regulated, constant-current to the battery. Shut off the current when the battery terminal voltage reaches 2.49V to 2.53V per cell (at 20deg C). This would be 5.00V for 2 cells.
The LED indicator would switch on/off when the charging ceases.

2. Same as above, but after the battery reaches the stated cutoff voltage, switch the input supply to a regulated constant-voltage supply that holds the battery terminal voltage at 2.26 to 2.31V per cell (4.55V for two cells, at 20degC). The "floating" voltage can be held indefinitely. The LED indicator would switch or change color as the constant-current phase turns off.

3. Use a current-limited (not necessarily constant-current) regulated constant-voltage power supply, where the voltage is regulated to the voltages mentioned in method 2, above. In this case when the battery is initially discharged, it will pull down the output voltage of the supply. As the battery accumulates charge, it will eventually reach 2.31V per cell, but at that point, the battery is not fully charged, so you cannot use that to light a LED. You must actually watch the charging current flowing into the battery, and when the charging current drops to a small percentage of its initial rate, then that is the "battery is now charged" indication. This method unfortunately takes three to five times longer to fully charge the battery than method 2.

Most of the simplistic LED indicator voltage-reference-comparator schemes published on the web do not really indicate the SOC of a lead-acid battery or terminate the charging at the proper time. It takes a sophisticated microprocessor controlled charger to do it right.
 
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MikeMl

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help me plz...

I quote myself: It takes a sophisticated microprocessor controlled charger to do it right.

Measuring the battery voltage without knowing what the load is doing, or what the charger is doing makes no sense, and does not give any useful indication.
 
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schmitt trigger

Well-Known Member
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Search the Texas Instruments website for "Battery Fuel Gauge".

There are dozens of solutions, depending on battery chemistry and type of communication interface. From your description perhaps the BQ2060A will work.

You still require a microcontroller to issue the proper charging commands.
 
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