Low voltage cutout help

[Sunnysky]

next define ideal cut-in /out threshold V and where present chatter occurs.
Rcoil =?

Change Rbe to >>10k. to drive relay On a bit faster (lower Vce)

add R between Vo & Vin+ of 47K or so for hysteresis to prevent chatter.

 

[Sunnysky]

why are you using a 22V coil from 15.4V nom then dropping with a zener.
remove zener.
increase Rbe from 1k to 100 k

if using same Toshiba Relay at 22V it is 1250 Ohm and will not reliably turn on at 14.4V and you should be using worst case V for reliable operation, assuming everything is accurate on your specs.

 

[SimpleJoe]

The ideal cut in/cutout voltage is 14.4v but as stated in previous comments the relay (which i have updated to a 12v, 720Ω coil http://au.rs-online.com/web/p/non-latching-relays/5330895/) is latching on untill much lower voltages (around 12v input) which is what im having problems with. I have found the problem is that the transistor does not completely drop to ground when powered (my comment with the videos) and this is enough to keep the contacts closed but not enough to close them if they start open. The zener was a test to prove that this is the problem (when the transistor was 'off' it was still supplying 6v and 14v when on, the 5.6v zener was used as a constant voltage drop). The chatter started after i added the zener which i fixed with a capacitor as sort of a proof of concept that the transistor was my problem. I am but a simple man and i think i need direct directions (im not sure what Rbe, Vce and many others are)

Thanks so far,
SimpleJoe

 

[Sunnysky]

Rbe is the across BE
Vce is the voltage across CE
Collector
Emitter
ok.?

 

[SimpleJoe]

Even with the changed resistor value and removing the zener setup, the transistor is not pulling completely to ground when there is no output from the lm339 allowing the relay to stay on

 

[Sunnysky]

I've lost track on your complete schematic.
redo for better assistance and include relay coil R value and rated voltage.

Would 3.3k across coil turn it off? 1k?

 

[Mongrel Shark]

I hate to throw a large spanner in the works this late in the piece, but what led to the choice of a relay and op amp set up anyway? Sure its more tunable to those that know how. But an opamp is hardly a beginners component....

I would have gone for a MOSFET with gate on a simple voltage divider. or even a transistor logic gate to a MOSFET. Nice and simple and easy to tune/adjust...
Its basicly a Li-ion protection circuit right? So why not use a standard protection circuit?

 

[SimpleJoe]

I had used a relay op-amp setup in a previous project and it worked perfectly (i found a simple diagram online and went from there) and it used components that i had on hand.

I tried looking into protection circuits but i didnt like the lack of information that i could get on them (i even used this forumn for help). It was mainly towards whether the charge voltage had to be regulated and then i was worried about noise into the amp ( probably wouldnt affect it but didnt want to chance it and have a basically useless system) and whether the circuits balance charged each cell, the better systems i saw that actually looked promising where several time what it would cost to make the 339 option (but apparently much less of a headache)

Finally i wouldnt be completely apposed to switching to a MOSFET solution i would just need a little guidance on how to create one and chosing the right MOSFET for the job (about 3 amps peak and maximum 1.5 amps continous) just with the system i wouldnt have a low battery warning light as i had on the current system (i didnt mention it anywhere in the schematics) unless the is a way to add this also.

TLDR:
What is a good replacement MOSFET setup ( specifying components for a 1.5 amp drain 3 amp peak)
Or a decent li ion battery protection system

Thanks,
SimpleJoe