Author Topic: Creating a battery cutoff circuit from scratch?  (Read 2249 times)

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Offline vortexnlTopic starter

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Creating a battery cutoff circuit from scratch?
« on: January 12, 2013, 12:23:47 pm »
I'd like to create a battery cutoff circuit for a LiPo battery or maybe even some NiCd cells, but I don't want to search around the internet for an IC (I live in europe and don't like waiting for parts  ;D )

Anyways, I'm not quite sure how to build this from electronic parts, my guess was that I need to compare the voltage from the battery to a known reference voltage, but that takes power, and you probably need to reduce power consumption in order not to drain the battery!  Can anyone give me some ideas on how I could accomplish this? Many thanks, Nick  :-DMM
 

Offline CarlG

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Re: Creating a battery cutoff circuit from scratch?
« Reply #1 on: January 12, 2013, 02:05:36 pm »
If you want to cut off the power you obviously already have some load to cut off, and that load draws some power, right? So what's the problem if you add power for the supervision circuitry? Besides, I guess that the internal battery leakage current is not much less than what a uPower supervisory circuit may draw.

If I understand your problem correct, you first need a power switch (check Dave's blog), combined with the cutoff circuit [i.e. "press button" AND (Uin = OK)] I don't see any way to make a supervision circuit that doesn''t draw power.

Best,
//C
 

Offline vortexnlTopic starter

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Re: Creating a battery cutoff circuit from scratch?
« Reply #2 on: January 12, 2013, 03:36:52 pm »
I made up a little circuit that seems to work, it's kinda like a set/reset latch using one PNP and one NPN transistor. I think I can get it to work using these parts.
 

Offline Things

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Re: Creating a battery cutoff circuit from scratch?
« Reply #3 on: January 14, 2013, 11:38:26 am »
You could use a comparator and a latching soft switch circuit, use the comparator to switch off the softswitch. Means you'll need to re-enable it manually, but not really any other options while having no current draw on the battery.
 

Offline peter.mitchell

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Re: Creating a battery cutoff circuit from scratch?
« Reply #4 on: January 17, 2013, 05:33:23 am »
Have a voltage reference from whatever on hand, compared to a voltage divider, so that the voltage divider is just a tad lower than the reference at the cut off voltage, then, using the comparator, drive a FET to switch everything off/on have all the circuitry on the switched side of the FET, then use a momentary tact switch to manually drive the gate of the FET to turn it back on, also have a resistor to stop the gate from floating.

When the battery goes flat, the comparator will turn the FET off, and the circuit will stay off because the comparator isn't getting any power, nor is the voltage divider, it won't oscillate, then once you recharge the battery, you press the tact switch to turn the FET on, it should power the detection circuitry and keep the FET on until it goes flat again.
 


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