Possible critical error due to a design problem with the 3DR power module

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

May I please double check some wiring with someone, so I don't fry my APM.....
My 180A AttoPilot has arrived and I have soldered on the wires, both the battery and sensor wires, in order to connect it to an APM 2.5. I wanted to clarify the information ArduPilot Voltage setup page. From what I understand it says to connect the current sensor wire to the inner pin on A2, voltage sensor wire to the inner pin on A1, and the ground to the outer pin on A1, is this correct?

After having connected the AttoPilot to the APM 2.5 would the APM be powered or do I still need to connect 5v to it somewhere else?
At present I am using the 3DR power module with 4S batteries, and a UBEC is powering OPTO ESC's on the output rail. Because I'm moving to 6S batteries I have needed to change to the AttoPilot sensor.

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Comments

Cam Donaghey July 22, 2013 at 2:50am

May I please double check some wiring with someone, so I don't fry my APM.....
My 180A AttoPilot has arrived and I have soldered on the wires, both the battery and sensor wires, in order to connect it to an APM 2.5. I wanted to clarify the information ArduPilot Voltage setup page. From what I understand it says to connect the current sensor wire to the inner pin on A2, voltage sensor wire to the inner pin on A1, and the ground to the outer pin on A1, is this correct?

After having connected the AttoPilot to the APM 2.5 would the APM be powered or do I still need to connect 5v to it somewhere else?
At present I am using the 3DR power module with 4S batteries, and a UBEC is powering OPTO ESC's on the output rail. Because I'm moving to 6S batteries I have needed to change to the AttoPilot sensor.
Zoltan Horvath July 4, 2013 at 9:23am

Hi, I would like to ask also something about the current measurement. The power module is rated up to 90A current sensing but what is the effective maximal overload current which could be supported from the chip resistor and the power module? Sure we speak about short spikes on a Octocopter platform which could draw more as rated. Are these values from the Datadheet applicable here?: Datasheet
Cam Donaghey July 1, 2013 at 12:39am

Thank you very much Bill and Wesley for your responses. I will put an order in for an Atto :)
100KM

Wesley Versfeld June 30, 2013 at 11:44pm

@Cam - I'm using the 180A Atto with APM2.5 on 6S and have yet to experience a problem. It reads V's and A's. Just make sure you solder the Atto in the correct direction.
Developer

Bill Bonney June 30, 2013 at 10:55pm

@cam: the atto pilot is scaled to 3.3V, so you can have almost 130A on the sensor and you will not exceed the 5v max. It's all about the max input voltage to the apm's ADCs.
Cam Donaghey June 30, 2013 at 9:47pm

Could someone please confirm that I would be fine to use either the 90A AttoPilot Board or the 180A AttoPilot Board with 6S batteries without damaging the APM 2.5? And if so will the APM 2.5 be able to monitor the voltage correctly from it once setup in mission planner config?

Thanks very much.
cedivad June 30, 2013 at 9:15am

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...
Developer

Arthur Benemann June 30, 2013 at 7:55am

@ Greg Owen

I did test it at a higher sweep speed, but since I just got flat pieces of the waveform I omitted it. But I can't do the 1ns/div test since my scope has a 100MHz bandwidth. I don't think it would reveal much, but if someone care to do the test it would be nice.
Rob_Lefebvre June 30, 2013 at 7:54am

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.
Developer

Bill Bonney June 30, 2013 at 7:40am

@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

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