Li-ion power mod

alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Li-ion power mod

Post by alphaseek »

Mathieu wrote:Tnx Rob. I used a 3,3 zener, but the circuit doesn't work. The led should go on under 3,9 volt, but it does not at all.
I double checked the circuit, but cannot find the failure...
You have the 3V zener drop, plus the D2 drop, plus another diode drop across the B/E junction of the transistor - all before any current will flow through the transistor. So I don't know about 3.9V being the threshold.

But what bothers me more is that there's a direct path from the positive battery terminal through D1 and D2 and the B/E junction to ground, with no resistor limiting the current. It seems that setup would draw lots of current if the battery is fully charged, and magic smoke might escape from something.
RobNL
Posts: 122
Joined: Mon Dec 25, 2017 3:11 pm
Location: The Netherlands
Contact:

Re: Li-ion power mod

Post by RobNL »

With a full loaded (4V2) accu, the monitor use 20 mA = 0.08 Watt
For the BC547 it's not a problem, they can handle 0.5 Watt
CU, Rob
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Li-ion power mod

Post by alphaseek »

RobNL wrote:With a full loaded (4V2) accu, the monitor use 20 mA = 0.08 Watt
For the BC547 it's not a problem, they can handle 0.5 Watt
Ok. But here's another way of looking at it, changing the transistor to a PNP. The transistor conducts, and the LED turns on, only when the voltage is low.
Attachments
LowBatteryIndicator.jpg
Mathieu
Posts: 5
Joined: Tue Dec 26, 2017 3:58 pm
Location: Netherlands (Utr.)

Re: Li-ion power mod

Post by Mathieu »

Hi Alphaseek. I build this circuit on my board, but the led stays on until about 1.6 volt.
RobNL
Posts: 122
Joined: Mon Dec 25, 2017 3:11 pm
Location: The Netherlands
Contact:

Re: Li-ion power mod

Post by RobNL »

I change the schematic a little, so there is less current when the batterie is full.....but you have to use a low current LED.

Image
CU, Rob
vcpinto
Posts: 3
Joined: Mon Dec 11, 2017 1:27 am

Re: Li-ion power mod

Post by vcpinto »

MorganFlint wrote:
vcpinto wrote:Hi,

How do you know when the battery is low?
Has anyone made a circuit to show the battery level?
A hardware approach would be to include a specific module (like this one for example), provided there's space for it in the increasingly crowded case (after including also the modules for battery charging, step up converter, serial to USB...).

Possibly, the most elegant way to do it would be a firmware mod to use one of the free AD converters in the MCU to read battery voltage and show a battery level icon on the screen... maybe Jyetech could have this into account for the next FW release; it'd still be better if he included the battery charging and boost circuitry in a future new HW revision! (or, for the cost concerned, include in the PCB the circuitry for battery support and leave it as an option, where you could buy the kit with or without the extra needed components).
I've bought that circuit and some rgb leds before I read your post. I'm waiting for them.
Yes, the most elegant way would be a firmware mod.
RobNL
Posts: 122
Joined: Mon Dec 25, 2017 3:11 pm
Location: The Netherlands
Contact:

Re: Li-ion power mod

Post by RobNL »

The shell is not make for batterie operation, so how will you update the software to detect a low batterie ?
Buy a lowcost powerbank and a USB to 9 Volt adapter from Ebay and you can use the shell for many, many, many houres.
BTW, most powerbank have a low powerbank indication......so you save money and a lot of work.
https://www.ebay.com/itm/USB-Connector- ... 2063831651

Image
CU, Rob
robocog
Posts: 64
Joined: Tue Sep 12, 2017 10:06 am

Re: Li-ion power mod

Post by robocog »

alphaseek wrote:
If you ordered one of the CP2102 modules with the micro-USB socket, be sure you check the voltage at the 3.3V, DTR and TXD outputs before you install it. Some modules are around 4.3V on those outputs, which is not what you want.

The pic below shows what I did with JP1 and JP2. I took over the SWD block, cut the traces going to the middle holes, and connected JP1 and JP2 to them instead. The right-angle pin headers are accessed through yet another hole in the case.
Good catch
CP2102 and the buck boost boards arrived today whilst I was at work , currently got the boards jerry rigged together so I will check the voltages from the cp2102
I know that the 5v > GND on the header is straight USB power (5v measured)

Just measured the 3.3v against GND on the CP2102 board I bought to install internally and indeed it seems to be putting out 4.27v!
Same with txo and rxi pins against ground...doh! -I guess this one is no good then?

What's that all about then?

Just checked the CP2102 board I did the last firmware flash with and that is 3.3v as it should be

Can't thank you enough as I wouldn't have bothered checking and would have blindly believed the pin labelling!

Now to try and recall where I got it from to ask some pertinent questions!

Regards
Rob

Edited to add - just found some references to the issue
(Specifically - https://www.silabs.com/community/interf ... tputi-EaVr )
I got the item from Banggood and have had a whinge
Not sure f I am capable of attempting to cut pin 9 free from the capacitor as suggested...soldering a 4k7 resistor to pin 6 from this cut leg is even less likely!
I may give it a go as not a lot to lose as its only fit for the bin as it stands :(

....and I got out the knife and a magnifying glass and VERY cautiously cut the pin9 trace that goes to the cap....and hey presto I now have 3.4v on the 3.3v line and TX and RX
Good to go?
alphaseek
Posts: 85
Joined: Thu Jan 19, 2017 5:24 pm

Re: Li-ion power mod

Post by alphaseek »

Robocog, it sounds like you're good to go. You don't need to tie pin 9 high. Just leave it floating. I've found that it's floating on all the good modules I've seen.

For those interested in these micro-USB CP2102 modules, be aware that the ones Banggood sells are bad. But I've had good luck so far with ones from this Ebay seller:

https://www.ebay.com/itm/162217753561

This is just a case of screwing up the board design - putting in a trace where there shouldn't be one. But as far as I can tell, once you cut that trace to pin 9, it works fine. Of course it's better to find one that's good in the first place.
robocog
Posts: 64
Joined: Tue Sep 12, 2017 10:06 am

Re: Li-ion power mod

Post by robocog »

Yes all good - had it transmitting data successfully
The lipo fits (1300 mah cell split from a 3s pack), as does the charging board and the 9v boost board along with the cp2102 - and the case still fits and there is room for more if needed...(bluetooth/voltage monitor/dip switch for firmware updates?)

However the small 9v boost board is too noisy and is making the trace all wobbly, tried a few caps on the output but it seemed to make no difference

Have ordered another (but bigger) adjustable boost board that I know does not put out enough noise that the traces are wonky
(quickly swapped one out from another project) - but it does swallow up any extra room for expansion

Not yet discovered how to graph the output from the data from the cp2102 yet, but that is for another thread :D

Thanks once again for such an informative thread (and a massive thanks for the headsup on the rogue voltages on the cp2102 - disaster averted!)

Interesting - on that link you show to the one that is 3v3 - the image also shows the pin 9 trace (wrongly) going to the cap?

Regards
Rob
Post Reply