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B0B : Battery without BMS ;-)

aeropic

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It took me some time but at the end I get a very simple option to flight any 2S battery , boot the MM directly on this batt and get some basic telemetry (voltage and an estimate of % of charge).
To use it you need to:
- keep the firmware <= 1.0.400
- set the batt type to 0 (firmware 1.0.500 locked this ...)
And that is.
you can see it in action here: B0B on facebook

The total voltage of the pack is displayed in the temperature field and half the value into each cell gauge.
voltage.jpg

basically, very few components are needed:
- microchip PIC12F1840 and its firmware ;-)
- 2 resistors to sense the voltage
- a 3.3V LDO regulator
- some connectors

Here is a first mockup:20200515_142626.jpg
 
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3S will not work? I remember seeing a Mavic Pro on 4s (stock is 3s)
3S should work , with an external battery of course and with the need to connect the "2S-8V" point from the balance connector to B0B while the MM ESC board will be powered in 12V.XT30.png
 
3S should work , with an external battery of course and with the need to connect the "2S-8V" point from the balance connector to B0B while the MM ESC board will be powered in 12V.
That’s somewhat promising, the extra potential thrust to be able to RTH in case of winds, or ability to fly without sinking on a mountain would be good.
 
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That’s somewhat promising, the extra potential thrust to be able to RTH in case of winds, or ability to fly without sinking on a mountain would be good.
Now, it's always risky to power an ESC board in 12V if it has been designed for only 8V... We would have to know the design margins DJI engineers have kept ...
 
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However some long range flyers do fly already in 3S and it seems they never fried their ESC board. We are testing with them the hopefully good behavior of B0B in this configuration. i'll keep you informed ;-)
 
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Why does it say the battery is at 818 degrees C?
Maybe global warming ? ;-)

More seriously, this is the total voltage of the battery: 8,18V
B0B as its name says is a Battery with no BMS. The goal of this board is only to allow a direct boot of the MM and to provide just enough telemetry to enjoy a safe flight.
- there is no way to charge the batt from B0B, an external charger is needed
- there is no cells balancing
- there is no temperature monitoring of the batt

I then decided to display the total voltage in the temp field just because it was easy to do, it has a big font which makes it easy to read.
The cells voltage is just the total voltage divided by 2.
 
Looks like the Facebook group is private, so I can't watch the video. I do know this, though: Watch those voltages like a hawk. If they fall below the cell manufacturer's rating, that cell needs to be taken out of service and disposed of.

Why? Because over discharging a battery and charging it is the fastest way to get you a lithium ion battery fire. How? When lithium ion batteries are discharged too far, it causes dendritic growth between the terminals inside. If the dendrites break through the insulator, there is an internal short circuit.

Source: Mechanism of the entire overdischarge process and overdischarge-induced internal short circuit in lithium-ion batteries
 
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You're fully right over discharging the cells leads to a dead cell and, more dramatic could lead too to a crashed Mini ... This is the reason why I implemented too a king of capacity telemetry. The Mini firmware does not only use the percentage of charge given by the BMS to display the actual remaining capacity. It does some filtering... With B0B I clamp the value to 14% and it still goes down to 11%. This is good enough to trigger the red warning "low batt" under 30%.
My advice is to return to home immediately and land the bird !
Here is the finished version of B0B :
 
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You're fully right over discharging the cells leads to a dead cell and, more dramatic could lead too to a crashed Mini ... This is the reason why I implemented too a king of capacity telemetry. The Mini firmware does not only use the percentage of charge given by the BMS to display the actual remaining capacity. It does some filtering... With B0B I clamp the value to 14% and it still goes down to 11%. This is good enough to trigger the red warning "low batt" under 30%.
My advice is to return to home immediately and land the bird !
Here is the finished version of B0B :
How to use without firmware?
 
I do not intend to publish the firmware for free. But I can sell the ready programmed PIC if you're interested...
 
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Happy to buy if it support 0.500
You can use it with all the benefits of firmware 400 + 500.
Firmware 400 allows to program batt type to 0,2 or 3 (no RTH on low batt).
On top of it you can install the camera module of firmware 500. (This is 'module mixing' method).
But you cannot use B0B, directly with firmware 500...
 
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