SALE: Tiny Universal LED Battery Monitor (works with SINGLE CELL)

No longer for sale. Please delete thread.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

Photos please, and exact measurements.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

Definitely interested! As Ped said, we need some pictures and measurements. Also, what would the estimated price be?

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

ARGLaser said:

Definitely interested! As Ped said, we need some pictures and measurements. Also, what would the estimated price be?

Click to expand...

OP says about $10


I think these chips are a great idea, make an intro thread w/ pics.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

No pictures yet. Still prototyping, but the circuit works perfect on breadboard. The board in EAGLE currently measures 8.6mm x 12.9mm.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

There is a minor problem that will be for any battery monitor. When the high-power laser is turned on, the battery voltage sags making the reading be below actual.
Is there anyone with a strong electronics background that would know how to compensate for this?
It is an analog circuit which makes this difficult. I could make this with a microcontroller that could compensate for when the laser was turned on but this will greatly increase the price.

Or... I could make a microcontroller one that does many things like I build into the 9mm MagLite Builds that I sell. It would have:

• Battery monitor with sag-compensation
• Alarm when you leave it armed
• Temperature Alarm
• LED that fades in/out when the laser is armed and flashes brightly with the above two alarm conditions

Still just ideas....

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

This may be a dumb idea but what if you only had the battery monitor on when the laser is off. You could do this with a simple spdt switch.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

The sag that your experiencing is common with all sorts of batteries, even awesome ones like a123's. Take a look at pretty much any cell datasheet (like this one) and you can see a voltage vs current graph of some sort.

One issue your going to run into is the battery there can be pretty large ripple voltages when a load is attached to the battery. The change in voltage will depend on the size of the load and the battery itself.

A lot of popular micro-controllers will either run at 5v or 3.3v, both of these options really aren't ideal for a 1s system due to the fact that the lithium batteries can range from 4.2v down to 3.2v depending on the internal chemistry.

I worked at a hobby store as a manager for a while and li-po waring devices were pretty common, but I have never seen one that is good for 1s, they typically are only good for 2s and up. After a bit of googling I did see some diy 1s lipo alarms.

*After re-reading this I realized some of it was written in hobby terms like 1s (1 cell) and I am lazy and don't feel like retyping it.

Hope this helps.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

That would just be impractical as the battery will be drained slowly even when it is stored away. And you couldn't use unprotected cells with it because storing it for a long time may kill the cells. And some protected circuits will not stop very low currents from killing the cells either.

The problem was fine in my MagLite builds as you just look at the battery monitor when the keyswitch (armed) is on but the laser is off.
Its just builds where there isn't a keyswitch or secondary arming system where it may be a problem.

Re: Interested? Tiny Single Cell Li-Ion Battery Monitor

I know why the sag occurs, was just putting word out in case someone with higher electronics knowledge would know how to compensate for the sag in the analog circuit.

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

Nice prototypes! Couldn't you swap out the LM336 for a smaller 3 pin shunt reference and compact it a little more?

Good work :beer:

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

ARGLaser said:

Nice prototypes! Couldn't you swap out the LM336 for a smaller 3 pin shunt reference and compact it a little more?

Good work :beer:

Click to expand...

That would be ideal, but I can't find any other 2.5V references in that package. Do you know of any?

LM336 should come in that package, only 3 pins are used on that SOP-8 after all, a bit retarded.

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

nztdm said:

That would be ideal, but I can't find any other 2.5V references in that package. Do you know of any?

LM336 should come in that package, only 3 pins are used on that SOP-8 after all, a bit retarded.

Click to expand...

I'll poke around a little and see if I can find something in a SOT-23-3 or similar.

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

ARGLaser said:

I'll poke around a little and see if I can find something in a SOT-23-3 or similar.

Click to expand...

Luckily with my PCB design, I created pads underneath the LM336 that will fit a SOT-23.

I originally made the pads so I could solder a TO-92 LM336 in case I ran out of SOP-8 versions. They are a little hard to find.

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

http://www.ti.com/lit/ds/symlink/tl431.pdf

Here you go. c:

Re: Interested? Tiny Universal LED Battery Monitor (works with SINGLE CELL)

Le Quack said:

http://www.ti.com/lit/ds/symlink/tl431.pdf

Here you go. c:

Click to expand...

Looks great. Will have to get some free samples. And they area very easy to find on eBay to compared to the lm336.

+rep