Something I've been looking at since I undervoltaged one of my LiPo batteries is an auto cut off circuit when it get's below around 6.2v
I think this will do it but could do with some confirmation since this is not my area of expertise so am always concerned. Any comments and suggestions would be extremely appreciated.
If it is OK you can expect to see this replaced with a tutorial
Zener Diode is rated for 6.2V
Mosfet is rated at 85A
I realise a small load may pass through R1 when shut off but I assume it will be so small it will not matter (unless left for a very long period)
Asked
— Edited
I was told Mosfets don't generate anywhere near as much heat as transistors and are extremely efficient, but will take your comments into account and throw on a heatsink at the very least, if it seems to be getting too hot in practical tests I'll also add a small fan too (although reluctant due to noise and power usage but we will see).
Thanks
I have 2 of these running my hottub and home alarm system for a year with no problem
Monitoring is already in place, through the EZ-B. What I am trying to get is extra safety by cutting the power to everything if it drops below a certain level, in this case 6.2V (3.1v per cell, possibly 3.0 & 3.2 if slightly unbalanced).
Sadly, your circuit did not work. In stead of 'snapping' off, the current just went down slightly with the voltage, I had a little talk with Ite, a very experienced EE and he recommended either a comparator or a specialized IC.
I'd also found this circuit, which I will be testing next:
(more info)
I just need to adjust the voltage divider for it to work with 2S Lipo's in stead of 3S.
Edit: we don't currently have the TL431 in stock and a simple cutoff IC would be cheaper
I had assumed that if the voltage was above the rating of the diode it would allow it to pass therefore energising the transistor/mosfet base that allowed current to pass to ground, completing the circuit...
Hopefully we can find a solution, with LiPo batteries becoming more and more popular I'm sure it'll be something a lot of people will want - especially if they do what I did and leave their bot on.
Where did you get with this topic, with your own projects to incorperate a power cut-off circuit/off shelve solution? Was it something you followed up on?
NXP BZX79-C3V3,113 DIODE, ZENER, 3.3V, 500MW, DO-204AH-2
http://uk.farnell.com/nxp/bzx84j-c3v3-115/zener-diode-aec-q101-3-3v-sod/dp/2463537?MER=i-9b10-00002068
DIODES INC. DMG1012UW MOSFET, N CH, W ESD, 20V, 1A, SOT323
http://uk.farnell.com/diodes-inc/dmg1012uw/mosfet-n-ch-w-esd-20v-1a-sot323/dp/2061403
I don't know if this is of any use to you...
LipoShield intelligent lithium cutoff
The basic idea is sound... in fact it is similar to the under-voltage lockout circuit design shown in TI's datasheet for the LM2576.
But it needs some type of Schottky trigger. Otherwise, the battery bouce-back voltage (after the load is removed) will cause the voltage at the Gate to turn it back on. Let, it's my understanding that it will just ripple until it dies.
I haven't found the right solution yet.