Hi Guys,
I've ran into some trouble on a project of mine. The issue is I still have some Voltage left on the arduino after triggering the fuse F1 (see schematic)
I can avoid getting a (significant) voltage on the main wire with a simple diode, but the voltage over the arduino remains (roughly 2.6V in my setup)
How can I avoid this?
Any input would be appreciated 
You're building a BMS, and since the circuit is still powered up from the batteries, the voltage dividers will feed voltage into your Arduino.
What voltage is present between positive and negative rail with power from psu, and batteriy?
I can't read the "circuit" you have in front of arduino GND, but if the fuse is after that, you feed full charge voltage to last analog pin.
Yes exactly
You mean while charging?
I'm using 4S Li-Ion Batteries so the voltage between the positive and negative terminal is 16.8Vmax and 12Vmin. I haven't tested what happens if the fuse triggers then, but I assume the charger may just alert and stop charging (it's luckly not a cheap one).
I'm not really sure what you mean. But as far as I know I have a voltage drop over the Arduino ground and the Analog pins of the Arduino, which is undesired when the fuse triggers.
But generally I've only worked on 230V/400V Systems. Is it unusual to have to have a Fuse for battery systems as a way of over-current protection. Is that done electronically?
Generally about the system:
I'm Building a System where I want to send the battery voltages, temperature and Humidity to a Raspberry Pi over I2c. For that I use an Arduino Nano to monitor those values with sensors. I try to avoid to make my own PCB design for a solid BMS due to time and financial constraints. (Also I'm not very well versed with designing PCBs and the challenges that come with it which may lead to further time loss in the future)
Nowadays you have eFuses, but a normal fuse is just simple to use.
I'm thinking that the fuse is placed on the wrong side. Just after incoming positive will keep the Arduino running. Another choice is a couple of DPST relays to cut off the monitoring x4.
That depends.
Do you want the Arduino to be powered or unpowered when the fuse blows?
Yes I see now thank you. That's another design issue indeed!
Fuse is for over current or short circuit protection. Use it if you feel you need it.
I would put it on positive. Just think the practical location since you have two "power supplies" on your circuit.
ps. I don't know your charge system, but doesn't look so safe to me. The charger can get confused because you are powering arduino from it and might not behave like designed for battery protection. Li-ion batteries are dangerous if you f..k up something.
Thank you guys for your feedback. Appreciate it.
If I use a Relais like this:
To switch the voltage dividers:
Would this work? What do you think? See any issues?
Just need to check if we have a Relay rated for 16.8V
PS Because preferably I'd have the whole system powerless when the fuse blows
Do you want the arduino to be powered or unpowered when the fuse blows?
Also unpowered.
As far as I see this would pull my whole system to Ground.
@thorman1999
First, you can't use a 10K/20K voltage divider to power the Nano. If the Nano only drew 1mA (it is actually much more), there would be a 10V drop across the 10K resistor. I would use a 12V voltage regulator.
Second if the Nano is unpowered then everything connected to it must also be unpowered or disconnected, that includes the Rasp PI
Time to re-think the design.
I'm repeating myself, but no fuse or relay protects if li-ion battery explodes.
Battery charger/management is monitoring charge current and stops charging when current is below threshold, for battery protection. If your arduino setup draws constantly current, charger might never stop charging.... Not good!
Yeah I see, that is another Problem of my upper design, although I tested it and it seems to work, But a proper Voltage Regulator would be better.
The Raspberry Pi is powered by the same battery, so It will also be unpowered
This is quite problematic. Luckily I didn't run into any issues so far. Would you recommend I design a proper BMS? Do you have any suggestions and ressources I could use?
I'd have to monitor Battery cell voltage, temperature and humidity and send this data to the raspberry pi (currently I use the I2C bus for this)
