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## 220V Lithium-Ion Battery Bank Charger Circuit

The post narrates a 220V Li-ion Battery Bank charger circuit with an automatic over charge cut-off feature for operating with an electric car. The idea was requested by Mr. George.

The Request

Dear Sir,

I'm George From Australia trying to convert small car into an electric car.

The attached PDF show the configuration of lithium battery modules that make the full pack.

Could be possible for you to suggest what sort of charger or configuration can I use too charge the pack.
I have available 240 Volts or 415 Volts AC.

Kind Regards
George

The Design

The above figure shows the Li-ion battery configuration arranged in series, parallel mode to generate a massive 210V at 80 Amps approximately.

To charge this relatively huge battery set up we need a controller which is able to control current as well as provide the required amount of volts to the pack for charging them efficiently.

The 240V AC source looks more appropriate, so this source could be used as the input for the mentioned purpose.

The next diagram shows the proposed 220V Li-ion Battery Module charger circuit, let's understand its functioning in detail with the following explanation:

The design is quite similar to one of the previous concepts regarding a high voltage battery charger circuit, except the relay part which is replaced with an SCR here, and the inclusion of a high voltage dropping capacitor for an added safety.

The mains high current is suitably dropped by the reactance of the 100uF/400V non-polar capacitor to around 5amps which is applied to the battery bank via the indicated SCR. This current can be increased to higher level by simply increasing the capacitance values of the shown 100uF/400V cap.

The SCR which is used as a switch in this design is held in the switched ON position as long as the associated BC547 at its gate is held switched OFF.

The BC547 base can be seen connected with an opamp output which is configured as a comparator.

As long as the output of the opamp is kept low the BC547 stays switched OFF, keeping the SCR switched ON.

The above situation continuous to be in the activated state as long as the preset voltage level of the sensing input pin#3 of the IC remains below the reference level of the pin#2 of the IC.

Since pin#3 is hooked up to the battery positive (via a resistive network), it implies that the 10K preset at pin#3 is supposed to be adjusted such that at the full charge level of the battery the potential at pin#3 just surpasses the reference fixed potential at pin#2.

As soon as this happens the opamp output pin#6 instantly reverts its output from the initial logic low to a logic high, which consequently switches ON the BC547 and switches OFF the triac.

The battery charging is immediately stopped at this point.

The hysteresis resistor Rx connected across pin#6 and pin#3 of the IC makes sure that the opamp latches ON in this position at least for sometime until the battery voltage has discharged to some predetermined
lower threshold level.

At this unsafe lower level the opamp yet again goes through a changeover and initiates the charging process by triggering a logic low at its output pin#6. The difference between the full charge cut-off voltage and the low charge restoration voltage is proportional to the value of Rx, which could be found with some trial and error. Higher values will result in lower diferences and vice versa

The potential divider network made by the indicated 220K and the 15K resistors ensures the required lower proportionately dropped voltage for the opamp pin#3, which should be not above the operating voltage of the opamp.

The operating supply voltage for the opamp at its pin#7 is acquired through a BJT emitter follower configuration connected across one of the end batteries associated wit the negative line of the battery pack.

For further queries regarding this 220V Li-Ion Battery bank charger circuit please feel free to usdethe comment box below.

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• #### 12 comments:

1. Sir, could you tell me what is the function of 1N4007 diode and 10mf capacitor. And why are you reducing the current using 100mf capacitor. By using high current can't we charge the batteries quickly?

1. Ajay, the 1N4007 and the 10uF are not important and can be removed,...but the 100uF/400V is important otherwise the full AC mains current would try to enter the battery bank and damage the batteries.

2. The battery has a rating of 80Ah,if my aim is to quick charge the battery cant i supply high current till the battery reaches 80% and then reduce the current to 5A for the safe operation of battery.
Also how are you turning the SCR off.The gate of SCR has no control over the SCR once its ON

3. connecting 220V mains directly with the battery is never recommended, you will have to use either a transformer or a capacitive limiter in between.

you can use a transformer, as you have already shown in your email request.

4. The supply to the scr/battery is 100Hz pulsating DC...so SCR will respond to the gate triggers.

2. could you please explain how you are getting a pulsating DC of 100Hz as the input is 250V 50Hz AC.

1. the bridge transforms both the positive and negative half cycles of the AC into full wave positive half cycles causing both the AC halves to appear on the positive side of the bridge supply, and thereby doubling the frequency from 50 to 100Hz.

3. Sir I have 6 Samsung Li - Ion batteries taken from a Power bank.. Each cell is showing a voltage approx. 4.1 V under full charge condition. I need to use these 6 batteries in series to form a 24 V dc power supply which can operate maximum of 48 W load( say each battery can draw max. of 2.5 A ) .. This series combinatiob of the batteries will be fixed and no further alteration is advicable..
I have a suitable 25V power source to charge the battery.. also I have the digital display taken from the power bank which can show the battery charging percentage while charging..

My question is if I am connecting this led display parallel to any one of the batteries in that series combination, will it give an average or approximate charging level indication while charging ?
I want to use this display as the charging indicator. That is why I am asking this question to you.

And if that set up is possible which battery among the series combination will be most suitable to connect with the led display ? The top one, bottom one or the middle one ?

1. Hi RT, if you connect the display circuit with any one of the Li-ion cells, then it will show the charge level of that particular cell, not the average value of the whole series assembly. It's better to connect the display across the whole series end to end, that would provide you with the correct charge level of the unit.

4. The display is capable for voltage less than 5V sir since it has been taken from power bank.. I have asked that question because I need to evaluate the charging of that series combination with that display board.. Since the charging of individual batteries in the series combination takes place simultaneously, there would be a possibility for all the batteries to charge in an uniform way right ? That why i was planning to connect the display to any one of them ?

if my assumption is wrong can you briefly explain how individual batteries get charged while in series config. ?

1. RT, that cannot be guaranteed, all cells might never have the exact same characteristics, and therefore might show slight differences in charge levels, especially when the cells are used ones and not new....you can assume the reading to be approximately equal to the average of the cells, but that cannot be a reliable method of determining the result

2. the charging rate will depend on the instantaneous characteristics of the individual cells, and also their instantaneous discharge levels.

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