Now you can make your own LiPo voltage indicator
the simple circuit below shows how to do it and it will surely cost less than   100

the circuit will activate the buzzer when the voltage (Vin) will drop below the Vz (break down voltage) of the zener diode used so use thezener diode according to your need

PS: the buzzer can be replaced by a LED or a RELAY to activate or deactivate other circuits.

Experts please  comment if you feel there is any problem with the circuit or if you have any doubt or suggestions

Regards

Kartik

Request to administration please change the name of the topic to 'make a LiPo voltage indicator under Rs 100'

Quote from: speedracer on December 24, 2010, 09:54:42 AM
Request to administration please change the name of the topic to 'make a LiPo voltage indicator under Rs 100'

Rather change it to "Low Voltage alarm for Li-Po". It is NOT a voltage indicator.

Its a bit difficult to get exact value Capacitor and transistor ... have you tried any other value... or any other set of values.. for which this circuit works??

You can use any value From 33 to 50 micro farad capacitor
100 ohm resistance can be substituted by any resistance upto 120 ohm but should not be replaced by any less value than 100 ohm.
the transistor 2N4891  can be substituted by any nearby value like 2N4870 or 2N6028 type transistor.


ANOTHER MODIFICATON

In the pic below we can see 2 Coloured lines X and Y there we can use 2 more zener diodes with differnt voltage rating to make a single circuit compatible for 1s, 2s and 3s LiPo.
and the brown dot represents a switch ( a typical on/off switch)
The black dots repesents connection .

For Example if we need to attach it to 1s LiPo we can turn on only the diode with Break down voltage of 3.2 volt (minimum critical voltage for 1s LiPo)
similarly for 2s and 3s LiPo .

The total weight of the circuit if made properly should be around 50 to 80 grams including the battery or mini speaker.

comments are welcome.

Regards

Kartik

pic

Thanks.. will try this tonight.. 

Some More modifications are possible like
on a plane this circuit can be used power the Rx system with 2nd battery when the first one runs out similarly 3rd one i think plane will not be able to carry more battery than that.
OR
checking on Tx when the batterys go weak and you will know when to change them.
OR
while charging a battery it will charge a battey to the break down voltage of the zener diode as that voltage is reached it will stop charging and as the voltage falls down charging starts.
OR
you can combine it with other circuts as per your requirements.

Acronics  you can post your questions/doubts here as there are many Experts here who will be willing to sort out any of your doubts I am just a Novice in front of them

there is many types of lipo alarms on the market for different demands ,

my self using high burst amp drew and a lipo alarm of this kind with the new formula on lipos not work very good unless it indicate on a very moderate voltage , mean u will probably not empty battery enough to be safe or empty to much do voltage drop very quickly when battery is empty do this is average volt and lipo will be out of balance at this point and very big risk 1 or more cells is below 3v.

what u need is something that monitors each cell and warn when the first cell is low and not average volt

like schultze lipodimatic

hope it make sense

just my 2 cent

merry xmas

it can be done if we connect the two terminal leads to each and every call individually (Parallel combination) that way only one zener diode is required with Vz=3 or 3.2v so if voltage of even one cell goes down below the Vz the circuit will be ativated
it has another advantage that it can be then used to moniter multiple cell LiPo like 3s ,4s ,5s,6s or even more.

I am going to put multiple LED's in this circuit.. say.. one LED for every 2 volt drop.. this will keep telling me how much time i am left with before it goes discharged !!

Is this your original design? Have you proved that he circuit is working?

This circuit is a classic relaxation oscillator with an extra zener diode. I have my doubts on how the circuit serves the intended purpose.

-Ismail

I assembled this circuit a few months back and it really worked.

any comments ujjwaana sir ?

Yes. you are right. On a second look I understood what you are trying to achieve. The circuit will work. However, it you need to select the right UJT. I am sure you would have done that. (intrinsic ratio of the UJT should be considered for proper operation).

yup taking that in mind this circut was designed by Mr Forrest M MIMS

Quote from: speedracer on December 24, 2010, 10:28:46 PM
it can be done if we connect the two terminal leads to each and every call individually (Parallel combination) that way only one zener diode is required with Vz=3 or 3.2v so if voltage of even one cell goes down below the Vz the circuit will be ativated
it has another advantage that it can be then used to moniter multiple cell LiPo like 3s ,4s ,5s,6s or even more.

If you connect the terminals the way you have suggested, the cells would - by your own statement - be in parallel! You would no longer get the 2, 3 or more "S" , i.e. series voltage available at the output. A diode in series with each cell to isolate them couold be added  but the highest cell voltage would then be reflected as  the monitoring voltage.

You are right sir.
you just gave me a point to think upon.

hello,

I tried your circuit for my lipo 2S battery but the buzzer was ON even when the i/p voltage was less than 6V. I used the same UJT and used a 6.2V zener. can you please confirm the validity of your circuit again? or is there any other circuit for this?

Thank you

I think the buzzer is supposed to be ON when the voltage is LOW ;P

The buzzer loads the battery itself when it should not be to be on safe side for deep discharge.

The circuit, I designed earlier, is simple. In my diploma project in voltage eleminator circuit I made short circuit alerm where piezo buzzer used for low power requirement and an 1000uF capacitor used for charge storage, to energize buzzer even at short circuit when power supply become zero.
Generally piezo have 3 terminals. One side brass plate, and another side metalized foil conductive area, separated in two part.
If you have 3 end of piezo crystal, you need only one transistor to oscilate as 3rd will give feedback. Else need two transistor astable multivibrator. 3 terminals connects with collector, base and emittor. Collector connected with inductor and base with resistance.
Now another sense transistor works as sensor as well as de-activator of buzzer. It's emittor will connect with fixed voltage sourse (Zener) and base with potential devider. Collector will be biased with the base biasing resistance of buzzer (Minimizing component increases reliability, from talkingelectronics.com). The potential devider at base will have one pot for fine adjustment. The power of buzzer will charge through 1N4007 diode which itself make off when capacitor voltage > supply voltage.

Hope any electronics hobby technician/engineer may design the circuit. I will try to give some ckt drawing and photo if possible.