How to modify battery charger indicator based on LM393

Thread Starter

luis bustamante

Joined Jul 4, 2018
2
Hi there, new member here. I'm only getting started with electronics and I'm building a 24v battery for a LED lamp. I already have a voltage meter working (based on the LM3914) but I want to add a charger indicator to know when the battery is fully charged. I found the circuit attached online but I haven't been able to modify it to work with 24v at 2.5 amp. Any suggestions?

Thanks for your help.
 

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dl324

Joined Mar 30, 2015
12,668
Welcome to AAC!

What is the battery chemistry, charging voltage, and "charged" current threshold?

Personally, I'd get rid of the schottky diode and just use a smaller current sense resistor.
 

Thread Starter

luis bustamante

Joined Jul 4, 2018
2
It's a Li-ion 6s4p pack using 24 2.5 amp cells. I'm using a BMS like this one. I'm not sure but I suppose the charging voltage is 2.5 amp as that's what the power supply I'm using provides and it seems to charge fine. I have no idea what the charged current threshold is.

Thanks for your help.
 

dl324

Joined Mar 30, 2015
12,668
Li-ion batteries don't tolerate overcharge well.

Here's an article on charging Li-ion batteries:
https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

The charge termination current seems to be 3% of the rated capacity. Set the voltage on the non-inverting input of the comparator to that current times 1 ohm. When the voltage on the inverting input gets below that, the LED will turn on. Where the comparator ground is connected is significant because you don't want it's ground current to go through the current sense resistor.

That circuit is expecting the comparator to sink more then the minimum guaranteed current of 6mA.
 
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