22.2V li-ion battery level indicator?

Hi there, I am building a portable boombox that runs off of a 22.2v li-ion pack I built.

I would like to be able to know if the batteries are dying/dead in a way other than just hearing my audio suddenly start failing.

I looked up battery level indicator circuits and I've gotten a few mixed messages.

Some such as this suggest using two chips.

I've also learned that Zener Diodes are important and this little kit doesn't suggest using chips at all.

I guess it would be cool if it was a 2 color light and green was good, orange=ok, red=bad, but I would also settle for a light just coming on suggesting "low power"

Also none of the kits I've seen mention working with voltages as high as mine. I figure I could do some shoddy math to adjust it to work for me..

But what would be most awesome is if someone here had a straight answer or suggestion for my case.

Thanks a ton!

 

Awesome! Thanks guys.

I was going to say the same thing about 18v being the low end.


So if I'm not mistaken it will go something like this:

battery + ------ resistor ----- - 18v Zener + -------+ LED - ---------- - battery

I am still not very good at electronics math, so there are 2 values here that I would love some help with.

What should the wattage rating of the Zener be? 500mw, 1w, 5w? I mean my battery bank with safe exaggeration will be 22v X 3A so thats 66W at full draw....I guess the situation here is that the zener and the led wont draw that much... but I'm not exactly sure how that works.

Also the circuit suggests using a resistor to balance the difference between the zener+led voltage drop and the battery max voltage, so as not to blow the led....Or at least thats how I understand it....Any idea what value this resistor should be for me?


The last little thought is that this circuit is designed to light an LED as long as the battery is "good". But I am looking for something that will let me know when it is BAD. Is there some simple way to switch this around, or perhaps work it so when it goes below the zener rating, it switches to a lower voltage, thus producing a different color on a 2 color LED?

Thanks a million

 

Hey thanks Steve.

So the internal transistor in that video which does the gate switching is some sort of chip, and what I understand is that that is not only important but something I have to setup in my circuit. Do you have any idea what transistor that should be? Also are you suggesting this chip come before the pair of BC548's, or are you saying the BC548's are the chips I should use instead of the internal transistor in the video?

So the base would be a runoff from the main power positive, going through an 18v zener and a 10k resistor then going to the transistor(s) then going to the LED(s)? I think I understand that the resistor value would determine the current getting to the LED and yes I would be using a 20ma LED, but then what would be the factor that determines whether the current flows through one transistor-resistor-led vs the other? Also can this be done with a bi-color LED?

Sorry if my ignorance frustrates you. Your help has been truly appreciated

 

THANK YOU SO MUCH! I will start playing right away!....

 

battery #6 in my pack keeps dying

Hey guys, just wanted to once again thank you for all your input. There has been another little puzzle boggling my somewhat novice mind, and it has to do with the battery pack itself, which is why I am sort of addressing you GreenGiant (and all battery pros).

I purchased this 22.2V 6cell PCB from ebay to monitor my 6 cells. I wired everything according to the diagram and general understanding of batteries. Everything was working fine, no sparks, no overheating, and all the voltages across each battery as well as the total pack voltage were fine. That stayed true until several hours of connecting using it to play music on my amp. At this point I noticed somewhat of a lack of power in my unit so I checked the charge of the battery. All the cells were fine except for battery #6 which was totally dead!

I figured it was a bad cell so I switched it with another. Same result! I did this twice!
Then I purchased a new board (same one) and same result!

My last assumption is that there is some fault in the design of this board. But being such a novice I had to just ask if any battery pros have heard of such an issue. If you have I would love to know what you think is going on.

Thanks!

 

Hi Steve, sorry this comes so late, its been a long interesting adventure getting this little level indicator working and I cannot thank you enough for all your help, I am learning a ton.

The good news is that I got the original bicolor 2-lead LED circuit working and it performs just as you described!

Of course just as the initial joy wore off I began to see the downsides of a slowly changing bicolor LED in that at some point the light will be inbetween and will seem off...which would be confusing.

So I ordered some 3-lead common anode LED's and hooked one up the way you described.

I started using a 5v zenner and a 3v supply and it seemed to work, it started red. then I went to 6v and it turned a bit orange. But then when I went to 10v it burned out. I tried again, same thing. Then I realized I burned out one of my little transistors in the last burnout so I changed it. I continued destroying many little components only to find that no matter what, when I went above 6v the system would overheat really fast and blow the LED and or the transistor (the one with the base running to the collector of the other transistor via 10kresistor). I eventually gave up, reset it back to the bicolor 2-lead setup and it worked again with no extra heat. I also went ahead and just used the multimiter as a standin for the bi-color 3-led setup and the voltage seemed to make sense, switching polarity and all, and when I did this nothing heated up at all.

Any ideas why the common anode LED setup is heating up/blowing? Or solutions?

Thanks a million