I ran into the following post at RCGroups which describes a potentially critical error condition with the 3DR power module.
I cannot verify the claims but at least they appear well founded so I'll leave it to the tech guys to comment on that.
Post URL: http://www.rcgroups.com/forums/showpost.php?p=24505558&postcount=2048
Post by jabram:
These folks over at DIY Drones did not mess with the pins
http://diydrones.com/forum/topics/ap...ment%3A1044651
They did experience a spike when disconnecting Lipo while performing ESC calibration of all ESC at once.
How does one assemble a multicopter without messing with pins ? CANT BE DONE -
Disconnect Lipo BEFORE messing with any wiring.
Check, double check, triple check you wiring modifications carefully, VERY CAREFULLY before connecting Lipo
DIY Drones Power Module that you have faith in is a primitive amateur design.
I do not recommend anyone use the DIY Drones Power Module.
The switching regulator chip 3DR use in the simplistic amateur design Power Module is only rated at a Maximum input voltage of 18V, The manufacturer of the chip ONLY recommends it for use with a 12V input supply, hence my "amateur" comment, they did NOT read or did not comprehend the datasheet..
It is extremely easy for a Lipo spike when connecting or disconnecting it to exceed 18V, specially when using a 4S Lipo and can also easily occur with 3S Lipo
Comments
What do you think that would happen in case it fries and i have the APM connected to another power source? I'm not an electric engineer (i would like to become one) but i don't think that nothing will really happen... Worst case you will lose the measurements, but the main flow of current wouldn't be interrupted and the APM would be untouched...
I'm not sure if it's worth to purchase that other equipment and to make the APM work with it...
Isn't 6S also a problem because the voltage divider will output more than 5V, frying the APM? I'm surprised that didn't happen to Wayne yet.
@cedivad: I made the same suggestion that it would be useful to have a solderpad that could be used to disable the power module. Anyway, since that isn't the case you will need to removed the module, which probably quite difficult as it has 5 thick posts soldered on the board. I would recommend buying an ATTOpilot https://www.sparkfun.com/products/10643
I would like to use it with a 6S battery, will it be possible to disable the switching regulator and to provide the energy for the APM from the BESC?
How can i do it? I just want this module to provide me with current/tension readings...
Wayne - dont use it with 6S. How long have you been using it that way, out of interest?
Aurelio, this would be a common thing if this were a brushed DC motor, connected directly to the battery. But a brushless ESC, I think it won't happen. The inducted current would be automatically shorted through the body diodes of the FET's in the ESC.
I wonder if the context where any failures could happen (if in fact they are possible...?) is unplugging a battery *while current is drawn*, that is, while the motors are running. In this case there would be an inductive voltage spike, which the shunt diode is then expected to absorb.
This entire case is about nothing really. If you read the datasheet for the TI PTH08080W design, it has an internal soft-start circuit to prevent output spikes and in-rush current from the input source. The example figure 11. in the datasheet show pretty much exactly the same results as the scope images posted by Arthur.
So I guess the lesson here is, always remember to read the entire datasheet.
Hi Jack,
Yes, mostly it is more expensive to design the PCB from scratch instead of using ready made modules. This approach is widely used all over the world. Especially to RF, Wi-Fi, DC-DC, Video...etc. modules, their manufacturers know how to make the best PCB design for the appropriate ICs. Also buying a large production scale module is cheaper.
Stephan,
What about the above mentioned TI DC-DC Buck module - I think this manufacturer have proven the quality of its products over time. Although this Buck module seems very simple, it has been designed good enough for the purpose. Just should be used within the specified limits.
Also separating the autopilot power supply and the servo/motor power supplies is very clever and recommended ( good explanations could be found here - https://groups.google.com/forum/?hl=bg#!searchin/uavdevboard/the$20best$20way$20of/uavdevboard/5U00XaUUkBc/sK66Qtb3jFEJ ).
Best regards
Nick
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