The post presents a simple Li-ion emergency light circuit with over charge and low battery cut off features. The Circuit was requested by Mr. Saeed Abu and Y0f4N.
Technical Requirement
My requirement is:(1) Circuit is Operated by Nokia standard cell phone charger
(2) Battery nokia 3.7 volt
(3) Auto ac to dc changeover system when ac fail
(4) Battery overcharge protection system(auto battery full charge cutoff) with LED indicator.I have tried many times to develop such type of circuit but i failed. So Please bro help me urgently. Please design it simple.
The Design
The proposed Li-ion emergency light circuit with over charge and low battery cut off features functioning may be understood with the the following points:
Transistor T6 is basically configured to automatically sense and shut off the LED during the presence of mains AC and vice versa. Here a mobile charger is used for powering the T6 circuit.
As long as the mains input is available, the 1 watt LED stays switched OFF due to the presence of a positive potential at the base of T6, T6 starts conducting the moment AC mains fails illuminating the connected LED with the help of the attached Li-ion battery power.
T1 and T2 form the low battery detector stage and does the same when the Li-ion battery voltage falls below a certain predetermined level set by P1.
When this happens, T1 just stops conducting forcing T2, T3 to switch ON hard.
T3 passes the battery voltage to the base of T6 choking its conduction thereby shutting off the LED and inhibiting any further loss of voltage under the situation.
T4 and T5 are configured for the opposite function, that is for detecting the full charge of the li-ion battery.
P2 is appropriately set such that T4 conducts fully at this battery voltage.
With T4 fully ON, the base of T5 is unable to acquire the required negative biasing via R6 and thus is prevented from supplying the charging voltage to the battery, which in turn protects the battery from getting over charged and damaged in due course of time.
The red/green LEDs indicate the relevant states of the battery and the cut off conditions.
The 10 ohm with the negative of the battery may be eliminated, it's not worth with so many existing protections.
For getting a better response from the over-charge cut-off stage, the above circuit could be modified further with an additional transistor stage T5, as shown below:
Referring to the following circuit, we are able to the see a few crucial additions and removals:
IC 7805 has been added, diode at T6 collector is removed, and D1 position changed. These changes ensure that an exact 4.3V is able to develop across the emitter of T6 and ground, irrespective of the input voltage level.
D5 has been removed in order to provide a better illumination for the LED at the collector of T2.
All high value resistors have now been reduced to 1K for an increased current biasing for the BJTs.
As suggested by one of the avid readers of this blog Mr. Syed, the above diagram needed some corrections.
The finalized diagram of the Li-ion emergency light circuit with over charge and low battery cut off featurescan be seen below:
Questions & Answers
Hello Swagatam,
thank you for your fast design.this design more cheap and easy to find for componen at local store.I just modify for LED driver with replacing T6 with BD 139 and adjust R7 with 10 K for 3 Watt. In this design better you remove D1,D2 as T5 already protected the battery. A
P1 is key to prevent battery to drop to deep and P2 to protect battery from overload.
Just suggestion for protection battery , when we set 3.2 volt as cutt off battery and full charge about 4.1 Volt, then we can modify P1 and P2 as fixed resistor. as I see R1,P1 and R5,P2 are voltage devider.may be it's not easy to find match resistor
Thanks & Rgds,
Yofan
Helo Yofan,
You are welcome!
yes, after confirming the exact values, P1/P2 may be appropriately replaced with fixed resistors..it won't be much difficult
Hello Swagatam,
I just want add some detail for your article at first circuit since use variable resistor. For expert will be no issue to adjusting P1 and P2. As your blog mention, we are here for learning an discussion.
To setup P1 as use for protection low batt
– Remove / unplug the input power supply then connect your low battery (can use 3.2 V or 3.0 V) for me prefer 3.2 V.
– Adjust P1 until red LED was glow and main LED was off
To Setup P2 as use for protection overcharge
– Plugin the input with power supply and put batt with full charge. let say about 3.7 V
– Adjust P2 until green LED are glow
hope this can help
Thanks & Rgds,
Yofan
Hello Yofan,
That's perfect. You've made life easier for those who would want to build this.
Thanks very much.
yofan, the full charge threshold of 3.7 li-ion is 4.2V
Hello Swagatam,
agree with you 4.2 V ..it's seem I miss set to 3.7 V
Swagatam,
What modification should I do in this circuit to support 4 rechargeable pencil cells of 1.2 volts each, at 1000mah. thanks this will be tried out soon, what can i use as the equivalent of BC 547 available.
Regards
Gopal
Gopal, No changes would be required, you may use the same configuration.
any general purpose NPN transistor will work in place of BC547
Hello sir,
Just I wana to make a circuit wich work in such a way that when ac supply is off then dc supply automatically on but when ac supply is on then dc supply automatically off.pls reply me sir ….
Trilokee, pls refer to the following article, you can use the transistor stage for your application:
https://www.homemade-circuits.com/2011/12/how-to-make-efficient-led-emergency.html
Swagatam bro hi… maine 3 watt led lagai but transitor hit ho raha h then whai do plz help me
bro use 1 watt led, not 3 watt led, for 3 watt use tip127 as the transistor and a 3.7/2ah batt
Bro thanks for ur developing my requesting circuit and also ur so talent on electronics.If i use 5/6 cell in parallel then this circuit will work properly?What is the alternative transistor of 2N 2907?
my pleasure bro, you can use a TIP127 for 5/6 cells.
but please note that the circuit is not yet tested by me, although i believe it would work
Bro thanks ur reply.Where should i use TIP127 for 5/6 cells(Parallel connection) in above circuit?Also any change is required in Charge section in above circuit for 5/6 cells(Parallel connection) ?
TIP127 should be replaced for the 2N2907 transistor.
no other changes would be required.
what is R4 value?
10k
Bro What is the R3 and R4 value?
bro, both are 10k
Bro what is value of R3 and R4? Is R8 is essential for this circuit?
R8 may be removed
bro is R7=1k is needed and why? Also i can not collect TIP 127 in my locality.So am i use BD 140 or any other NPN Transistor?
Bro R7 is for enabling the transistor to conduct when mains is absent, without it the LED will not glow.
BD140 will do, it's not an NPN, rather a PNP
Bro thanks ur reply.However today i have developed ur circuit as per ur given model and i successfully done auto ac to dc changeover system,battery low voltage cutoff system but i can not success in auto high voltage cutoff(battery over charge protection) system.The problem is here:
1)The green LED is not glow during battery voltage is 4.25 when charger is connected but when charger is disconnected from circuit then green LED is glow but so dim.
2)Then i replace R6 into 1k then green LED is glow normally.
3) I tune P2 very accurately at battery voltage 4.25 but auto high voltage cutoff(battery over charge protection) system is not worked.
4) Only working Battery's self overcharge protection circuit when voltage raised at 4.25v but not ur given over charge protection circuit that's why the green LED is not glowing.
5) I have tested it by connecting a battery without it's self overcharge protection circuit with ur circuit.Ur circuit is continued to give charge that battery and battery voltage is raised up to around 4.75 then i stop to give charge my battery.
So bro it seems to me that in auto high voltage cutoff(battery over charge protection) system there is something wrong.Pls refine it.This circuit is badly needed for me.I have tried to refine it but i failed.
Bro, remove the green LED from the shown position, and connect the collector of T4 to directly to positive.
Now connect the green LED in series with the base of T5, anode to base, cathode to T4 emitter.
When the voltage reaches 4.25V, this LED will shutoff indicating that T5 has been switched OFF and the battery is receiving no charging voltage.
….also reduce R5 to 1K
please try this and let meknow the results.
Bro then what will be the P2 condition it will be removed or not?
everything else will be as before, even the setting of P2
Bro i have tried again as per ur modification guideline but result is not positive.The green LED is not glowing during charging the battery so there is no question of shutoff the green LED When the voltage reaches 4.25V.Also ur developed auto high voltage cutoff circuit (battery over charge protection) system is not working.Only working Battery's self overcharge protection circuit when voltage reaches at 4.25v( I have tested it again by connecting a battery without it's self overcharge protection circuit) .So Bro i think u have to redesign the circuit freshly and upload it again.I am waiting for ur great feedback.
Bro, electronics is not easy, you won't get results even from the easiest of the circuits until you do it by understanding it.
The above circuit is perfect in all respects according to me, however if you can pinpoint the faults in the design then surely we can debate on that.
Alternatively you can try testing the design by checking the voltages at the base of T5 while setting P2. The base voltage should almost become zero at 4.25V.
confirm this by disconnecting the emitter of T4, this should revert the T5 into conducting mode again. once confirmed connect it back in position.
…check it by putting red prod of the meter on the positive line and black on the base.
when conducting, it should show near 0.6V, keep adjusting P2 until it drops to zero at 4.25V.
also replace all 33k resistors with 1k resistors.
Dear Sir,
I request you to kindly suggest me a simple circuit to cut off power supply to a 4V-4Ah lead acid battery on full charge (over charging protection) from a 5V mobile charger.
Dear Vidyarthi,
you can use the following design
https://www.homemade-circuits.com/2013/12/make-this-usb-li-ion-37v-battery.html
sorry here's the correct link:
https://www.homemade-circuits.com/2013/12/usb-automatic-li-ion-battery-charger.html
Dear bro, I have tried again as per ur latest direction but i am again failure.here the problems are:
1)The voltages at the base of T5 cannot make zero from 0.6v by setting up P2.
2) The green LED keep glow gently at 4.25v of the battery.
3)Also ur developed auto high voltage cutoff circuit (battery over charge protection) system is not working.Only working Battery's self overcharge protection circuit when voltage reaches at 4.25v( I have tested it again by connecting a battery without it's self overcharge protection circuit).
4)But ur other system low battery cutoff and ac to dc change over system is ok.
So bro what can i do now to over come above problem.Please do something.I think u should practically make this circuit then u can easily find out the problem.
Dear Bro, I have modified the diagram with an additional stage, please do it as per the new diagram and check the response.
Dear bro i have tried again ur new circuit as per ur direction but no positive result.The problem is here:
1) The charging green LED is glowing during charging but no so much glow.
2)The yellow LED is not glow during battery voltage is 4.25 also i can not glow that by adjusting the P2. At 4.25v the voltage remain in yellow LED is approx. 0.65v.
3)Also ur developed auto high voltage cutoff circuit (battery over charge protection) system is not working.Only working Battery's self overcharge protection circuit when voltage reaches at 4.25v( I have tested it again by connecting a battery without it's self overcharge protection circuit, it getting charged 4.40v then i disconnect the charger).
4)But ur other system low battery cutoff and ac to dc change over system is ok.
Bro what will be the solution of this.I think u have to develop this circuit practically to find out the solution of this.
Dear bro, the second circuit is perfect in every way.
again I'll say if you do without understanding, you will keep getting problems.
if T4 and the yellow led are not conducting it means either one of them is faulty or the connections are wrong in your circuit.
make R5 = 1k (I had suggested this before also)… and check.
as soon as T4 conducts, T5 will switch OFF and the green LED will also switch OFF
you can try making the series resistor of green LED to 1k for increasing its current and brightness.
practical making won't be required because I am sure this circuit is OK.
…bro, i think got the culprit.
the yellow led should not be placed at the emitter of T4. connect the emitter of T4 directly with ground
put it at the base of T4….and check.
the emitter position is not allowing T5 to stop conducting completely.
I'll correct the diagram soon.
Pls bro correct the diagram ASAP.I am waiting for this.Also i need true over charge cut off system i mean battery will be over charge cut off by ur circuit not his(battery) self over charge circuit.
Thanks bro I'll wait for ur corrected diagram also i need true over charge cut off circuit which only worked by ur developed circuit not by the battery's self over charge protection circuit.Pls bro update ur circuit ASAP.
Thanks bro, I updated it yesterday itself….please check it out.
Dear bro, i have tried again ur revised circuit but problem is still exist, these r:
1)Ur developed Over charge cut off system is not worked only work in case of battery with self over charge protection circuit which i have told u before.
2)During low cut off and Over charge cut off stage the charging Green LED is glowing gently (when i disconnect the charger.)
3)During over charge cut off stage the full charge indicator Yellow LED is glowing gently.If i adjust the P2 to increase the brightness of Yellow LED then Green LED glow gently and vice versa.
So i am hoping a nice solution of it from u.
Sorry Bro, that looks impossible…
If the blue LEd in the last diagram illuminates it means T4 is conducting.
If T4 is conducting it would ground the base of T5, stopping it from conducting.
When T5 is stopped from conducting how will the green LEd glow???
Because as long as T5 is conducting the green LED is getting its ground through the collector/emitter of T5, once T5 stops conducting this passage is blocked and the green LED also has to stop glowing, resulting in shutting off the 2N2907 transistor completely.
Check the voltage at the base of T5 when the BLUE LED is glowing. It should be zero and the green LED must stop glowing.
Please do the above, we'll troubleshoot it right here…..
1 watt led glow dim can i remove 10 ohm and how to check battery charging or not
yes you can remove the 10ohm resistor.
the green LED indicates battery is charging.
When charger connect green led not glowing