Lithium ion DC FAST CHARGER

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
Hello everyone,
I'm trying to built li-on fast dc battery charger. For this i need high constant current source in my circuit to charge battery in cc mode.
I've searched alot but couldn't find best method to achieve high constant current. The best one i've found is synchronous buck converter but i can't tune the pid for feedback. so if anybody could help me with better way or to tune pid in proteus that would be a great help.
 

Alec_t

Joined Sep 17, 2013
11,744
Welcome to AAC!
How will you terminate the charge? Lithium batteries need a specific charge profile for safety, to avoid a possible fire or explosion.
 

KeithWalker

Joined Jul 10, 2017
1,299
How much current are you planning using to charge the batteries? Are the batteries single or multi-cell? What is the maximum specified charging current and charge termination voltage for the batteries?
Without the above information I can not make any safe suggestions.
There are very many circuits on-line for high current limiter circuits but make sure you understand how to charge the batteries correctly because you could easily cause a fire or explosion.
.
 

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
Welcome to AAC!
How will you terminate the charge? Lithium batteries need a specific charge profile for safety, to avoid a possible fire or explosion.
Yes, I will use BMS for monitoring battery's health temperature , voltage level and will also control full charge.
 

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
How much current are you planning using to charge the batteries? Are the batteries single or multi-cell? What is the maximum specified charging current and charge termination voltage for the batteries?
Without the above information I can not make any safe suggestions.
There are very many circuits on-line for high current limiter circuits but make sure you understand how to charge the batteries correctly because you could easily cause a fire or explosion.
.
Li-on Battery specification :

Nominal voltage : 36 V
Rated capacity : 5.2 Ah
Cell configuration : 10s 2p
Charging rate : 1C for initial state and decreases with increase in SOC

Actually, I'm trying to built fast charging circuit with Multi Stage Constant Current algorithm. So the current varies depending upon State of Charge (SOC) of battery. I've searched alot and found synchronous buck converter to be best choice for providing high constant current however, i couldn't get constant current in proteus. The output current of buck converter varies.
 

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
I suspect buying a ready-made commercial charger will be cheaper and safer than building your own.
Yeah, But i'm trying to built it with Multi stage constant current algorithm for charging. Which has shown promising result for less charging time and better battery cycle life.
 

KeithWalker

Joined Jul 10, 2017
1,299
How are you planning on balancing the charge for each parallel battery? You will need to do that if you want the battery to have the maximum useful life.
 

jtn

Joined Mar 27, 2017
22
You could try to add a current sense resistor on the return path. Send this Voltage sense to a non inverting op-amp with a low gain DC control. The output signal will feed into the inverting op-amp of the IC PWM such UC384 or whichever PWM you are planning to use.
 

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
How are you planning on balancing the charge for each parallel battery? You will need to do that if you want the battery to have the maximum useful life.
hmm yeah that is a problem but first i need high constant current which can be controlled depending upon soc of battery using buck converter. I have step down voltage but i couldn't get constant current.
 
Last edited:

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
You could try to add a current sense resistor on the return path. Send this Voltage sense to a non inverting op-amp with a low gain DC control. The output signal will feed into the inverting op-amp of the IC PWM such UC384 or whichever PWM you are planning to use.
I had used it but for large current there is just too much waste of power in Rsense resistors. Therefore i head for switching regulators like buck converter. But i couldn't got constant current out of buck converter however for high constant current buck converter is used.
 

jtn

Joined Mar 27, 2017
22
I had used it but for large current there is just too much waste of power in Rsense resistors. Therefore i head for switching regulators like buck converter. But i couldn't got constant current out of buck converter however for high constant current buck converter is used.
You could use a 1mili ohm 2W type resistor. Sensing the current at the output and feeding it back to the control loop is the way to get constant current regulator

https://www.ti.com/lit/an/snva829/s...57168&ref_url=https%3A%2F%2Fwww.google.com%2F
 

Thread Starter

SAYAKU

Joined Oct 7, 2020
14
By using LM55117 from Texas Instrument you could eliminate the output current sense resistor
Thnx but i'm trying to built synchronous buck converter on my own thats why i haven't used ic. I'm having problem with feedback path for controlling duty cycle of mosfet.
 
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