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
Not directly related to this problem but the cable that came together with my power module had it's crimped connections stick out of the plug and made contact to another which resulted in a little puff of smoke and a dead power module, luckily it happended on the ground.
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
Just had a look at the datasheet in full. If they are using a 117 ohm resistor as per the eagle diagram above, then the output is set to 5.5V (not 5.4 or 5.3V as some are stating). Therefore the only issue I have is with regard to the 10W max power output of the module. At 5.5V that would make it a 1.82 Amp maximum output, not the advertised 2.25 Amp rating. That's probably splitting hairs a bit, but if we are going 100% by the datasheet, then it is what it is..... Never the less, I will be very confident powering my 20Kg plane with this device running APM2.5, and I will trust the power supply more than the APM for sure. TI makes some great parts, and they tend to under-spec their parts.
It is another example of 3D Robotics's annoying habit of whacking a 3rd party board on another board & calling it a new product instead of just designing all the parts on 1 board.
Why? How expensive would it be to design a single board & mount the parts yourself instead of mounting a 3rd party board that someone else mounted the parts on? They both have to be tested. It would be more compact. There would be fewer connections.
TVS diode can eliminate voltage spike, it's necessary for high current power line.
this kind of diode acts like zener diode but it's much faster.
it's widely used in external port protection.
also, for AD input, a RC low pass filter follow a zener diode can greatly reduce the risk of MCU damage
Once had back EMF from motors burn out a regulator that was rated for 5V. The back EMF created 6V spikes on a 4.2V battery lead. Just a matter of how much resistance is between the regulator & battery, how close the battery is to the limit, the battery's resistance, how much back EMF the motor generates, whether it's for flying over people, desire for fame. 18V is probably enough for obeying the FAA rules, but most people fly over 400ft, over property, & beyond line of sight which makes you want at least double the battery voltage.
I've had a discussion with Joe about this before. It's good to remember that data sheets are also pieces of best guesses and error prone. Brian makes a good point that the datasheet says its' good for 12V applications, but it does not preclude it form higher voltages like 16.8V (4S) levels. And Dany and Wayne make excellent points, real world data say there isn't any real Field Failure Rates to talk about.
Electrical engineering is best guestimates and testing. If there is any reason for power failures with the PM it's probably more likely worn out connectors from being pugged in and out a lot. They don't have the same lifetime like a electrical plug for your house ;-)
An actual problem with the PM is not even the PM, it's the fuse/diode that protects the APM by limiting the power the APM to 500mA. People connect 'specliaized' Radio Transceivers (ie. LRS ones like the RDF900 or UHF ones for FPV) that draw more current than 500mA and this has been causing an issue fro some, hence the change to the new 1.1A fuse.
As Monroe Lee King Jr. requested here are some measurements:
The setup:
Signals:
On a power on I got this:
On power off:
At this test at least I didn't see anything that looks like a problem. Any I can't see why the inrush current of the cap. (the spike) can damage anything else than the cap. or the connectors.
There is no problem with this module, that is a fine and reliable regulator and works very reliably up to its rated 18 volts.
There simply is no issue here and no context for the claim of either amateurishness or inadequacy.
Much Ado about Nothing!
Monroe, no I didn't run it at 32v but I have been running at 24v with it powering The apm, gps, osd, and 3dr radio. No problems but obviously not recommended.
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