Simple Lipo voltage cut-off

Hi, i need a cut-off for my project and lipos shouldn't go under 3v3.

I got a 3v3 zener diode, when i connect it to my 3.9v lipo it only gives 1.5 which makes my 2n2222 turn on so i can put my load on 2n2222 but it might get high and damage the transistor, so i was thinking of using a MOSFET and it won't turn on. what's problem with my circuit? it's just a simple zener connected to the base of MSOFET and Load is connected to the (-) of MOSFET

is this a good way to do it anyway? i see circuits on net but they all use ICs which i can't buy here. is there anyway i can make a cut-off without using any special ICs?

Lets see a schematic or diagram. And maybe a source for where you got the idea?

Many lipos are sold with that device already attatched.

LIPO CHARGER BOOSTER

kamhagh: what's problem with my circuit? it's just a simple zener connected to the base of MSOFET and Load is connected to the (-) of MOSFET

please, post a schematic of what you've done, a mosfet has no base, and no (-) either ! and I don't understand how you plan to use the zener

This from the same supplier

https://www.sparkfun.com/products/339

Says protection is already built in

Paulcet: Lets see a schematic or diagram. And maybe a source for where you got the idea?

http://www.ez-robot.com/uploads/liposhutoff-635015176764843750.jpg

if this isn't a good idea what other options do i have?

by base i meant gate sorry! just look at the circuit i posted, its similliar, it couldn't work with my 1cell lipo with 3v3 zener but it worked with a transistor !

i couldn't find any lipos with protection circuit in my country.

Where are you ? Is the internet not an option ? Ebay.

Faced with a similar problem last year i found it cheaper to order 3 new lipos with protection rather than get the seperate boards and solder them myself.

FWIW i replaced the batteries on my cordless drill, once i added up the cost of all the required boards and the required space it was cheaper to get batteries with protection

Boardburner2: Where are you ? Is the internet not an option ? Ebay.

Faced with a similar problem last year i found it cheaper to order 3 new lipos with protection rather than get the seperate boards and solder them myself.

FWIW i replaced the batteries on my cordless drill, once i added up the cost of all the required boards and the required space it was cheaper to get batteries with protection

Lets say i basically live in a cave :-\

I can't order from Ebay. I guess i have no other options than :(

Lipo under load shall be cut off at 3v but that is when you draw more amps than its rated for atleast this applies for us with brushless motors in heli, plane, boat, cars or drones and there is no regulator build in those lipo by default.

if this isn't a good idea what other options do i have?

If you have a spare Arduino Analog channel, you can make a voltage divider and monitor the LiPo that way.

Be mindful of the circuits you get on some sites. For instance, the FET circuit you downloaded uses 100K as the Zener load, yet the Zener is spec'd at 41mA test current. The Zener will not exhibit a very sharp "knee" at that reduced current and you will actually get not very repeatable cutoff voltages.

Why not use a REAL comparator? Even an Op-Amp will make a better comparator than that Zener circuit.

That is the weirdest schematic. Why does it have what resembles a JFET symbol for a MOSFET?

That seems like it'll just never turn on. That is a 10V gate MOSFET with about 1V on the gate maximum.

thanks ! i will use my analog pin for determining battery left! I will Stop and make alarm at analogRead = 665! (3.2v)

polymorph: That is the weirdest schematic. Why does it have what resembles a JFET symbol for a MOSFET?

That seems like it'll just never turn on. That is a 10V gate MOSFET with about 1V on the gate maximum.

i already ordered tons of zener diodes :( they were cheap but i have no idea where to put them! :D maybe later i could use them :|

Ok, My analogRead gives 3.99v which is almost exactly right!(code here) analogRead(0) * (5.0 / 1023.0); but when i unplugged my Arduino from pc power and L LEDSs were dimly on and it freaked me out so i unplugged lipo, Is that safe!? I simply connected lipo ground to Arduino's ground and (+) of lipo to A0.

You need a series resistor between your battery+ and the A0 pin of the Arduino. Somewhere around 100k. By connecting it directly, you are powering your Arduino (and everything attached) through the A0 pin which may destroy it.

Never Never Never remove power from any IC while an input still has power. Taking any device's input(s) above or below either supply rail is bad practice.

thanks, i also assume 0.05mA won't hurt :) thanks!

I have an question. I don't understand why the 100k doesn't make a difference in what Arduino reads, yet a potentiality connected to 5v does! And ressitor does not affect voltage, so why does the pot(potentiometer) makes any diffrence in what arduino reads?

Did anybody notice that schematic is for a 2S lipo ? (which has a discharged battery voltage of 7.4Vdc and a charged voltage of 8.4 V dc which would mean the zener needs to be about 3.2 V)

By connecting it directly, you are powering your Arduino (and everything attached) through the A0 pin which may destroy it.

Why ? If the analog input is configured as an INPUT , how could it draw battery current with a an ADC input impedance of about 10 M ohms ?

(and everything attached)

How can "everything else " be powered from the A0 pin ? That is an analog input. It is not connected to the 5V bus .

you have 2n2222’s right…

if you don’t have an opamp, if you’re up to it build a comparator circuit and when the voltage falls the transistor switches off your device…

you’ll also need a couple of pnps but if you’re going to the trouble buy an opamp!

There are diodes internally connected from each pin to Vcc and Ground on the IC. They are there to help protect the inputs from lower amounts of static shock.

That's how this RFID emulator with an AVR ATTiny works: http://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/

Others have done this with a Microchip PIC: http://makecircuits.com/blog/2011-09-26-build-own-rfid-circuit.html

We still need a schematic of what you are doing.

If you simply add 100k between, analogRead may not give you the correct value.