After I had a few problems with the standard power module from 3DR and the ones from Hobbyking, like falling off resistors (overheated) and burned out BEC from voltage spikes, I finally designed my own PM modules. The sensor boards are compatible to Pixhawk, APM, Pixhawk lite, AUAV-X2, DroTek und CUAV Pixhack.

These modules are based on a true hall current sensor, so heat is no more an issue !!!

The sensors boards are able for continuous current of 100A for HS-100-V2 and 200A for HS-200-V2 (no time limit), the maximum over current is 1200A@25'C and 800A@85'C for 1 second.

Here some details:

Sensor Board:

  • Current sensor is a “true hall sensor” up to 200A (ACS758-200U) or 100A (ACS758-100U)
  • Ultra-low noise power supply (LP2985-4.0) for current sensor and offset shifting circuit.
  • Microchip MCP601 operational amplifier for offset shifting.
  • LiPo voltage measurement with 1% resistor divider in factor 9:1.
  • 2x10cm / AWG12 cable soldered to current sensor as standard size (Up to AWG8 possible).
  • 6 pol cable connection to Pixhawk / APM (both sides DF-13 connector).
  • 1x 10cm and 1x 20cm / 6 pole cable in the box to select a different cable length if necessary.
  • 18mm x 29mm x 11mm / 7g without cables and shrinking tube.
     

3691258132?profile=original

BEC:

  • Input 2-6S LiPo / max. 28V
  • Output 5.35V / 3A -> +/- 0.05V –> Ripple 10mV (0.2%) at 1.5A output current.
  • Input wrong polarity protection, as well as Panasonic FM 220uF/35V input capacitor to prevent burn out of BEC from voltage spikes.
  • 4 pole cable to sensor board with DF-13 connector.
  • 47mm x 18mm x 11mm / 8g with cables and shrinking tube.

Installation:

The Sensor board is installed only into the positive main battery wire and the BEC should be installed as close as possible to the battery connector.

3691258183?profile=original

Quality control of the finished product:

To post here all the quality control during the production would be a very long story, so all I can say is, that it is carried out and recorded.

The final QC before the boards are shipped, is a setup with an FC (Pixhawk) and connected to MissionPlanner to check the calibration values for current and voltage measurement.
This final test result will be passed to the customer together with the order confirmation and shipment tracking number by e-mail.

REM: Which power module supplier out there actually use the PM to power up a real FC before shipment ?

So I hope everybody understands, that if I say "safety first"... then I mean it.

3691258254?profile=original

FAQ:

Why Hall sensor ?

  • The measurement over a normal shunt resistor is not accurate at lower current (<3.0A). For a Hall sensor the measurement starts at 0.5A with an accuracy of +/-0.5A over the whole range up to 200A !
  • A shunt resistor create heat due to the voltage drop, the hall sensor has only an internal resistance of 100uOhm, so there is no power loss.
  • Due to the heat created by a shunt resistor and the power cable, the measurement of the current is not linear and depends on the temperature. This is not happened to a hall sensor, a temperature change (created by the main LiPo cable) will not influence the measurement.
  • The current flows only through the hall sensor and NOT through the PCB. Most other current measurement boards has the main cable soldered to the PCB and then it goes to the shunt resistor -> these boards can’t handle over 60A constant current ?

 
Why only a few supplier use a true hall sensor for current measurement in an MR ?

  • Hall sensors are very expensive, compared to a normal shunt resistor and not everybody out there wants to spend the money to top up for a good measurement system. So the sales quantity and profit will not be within the target.


Why output voltage to Pixhawk /APM is 5.35V and not 5.0V ?

  • Pixhawk has internally a 3-way power selector over an ideal diode chip. The 3-ways are USB, power connector (6pin) and the Output PWM rail on the back of the FC. So it is possible to power up the FC with either one of this power sources, but how do we know which power source right know is powering up our FC if there is USB, a PM module as well as an backup BEC connected to the output (ESC/Servo) rail ?
    The answer is easy: Whichever voltage is higher by 0.25V to any other power source is selected as the internal power supply, as long as this voltage do not exceed 5.70V !
    The result in practice on the field can be different, as there are many components connected to the FC like, GPS, Servos, opto ESC’s… etc., the power consumed by the system is not stable, which means the supplied voltage is not stable as well. The reason for this is the loss in voltage due to small power supply cables and maybe many connectors.
    To prevent the internal ideal diode to switch too often between different power sources, we choose a bit unusual high voltage (5.35V) as a main power supply. Which means only if any other power supply (USB or PWM rail) is in the small range of 5.35V+0.25V=5.60V and the maximum voltage of 5.70V, then the diode would switch over to the other source.


Why the cable from UBEC to the sensor board is 4 pol ?

  • To reduce the resistance in the power line and increase the safety, or should we ask, why does the DF-13 power input of the Pixhawk has +/+/I/U/-/- ?
    There are also two wires, for positive and negative, used to reduce the risk of failure.


Why sensor board and UBEC are separated ?

  • A switching power supply can be a very “noisy” part in the power supply chain and it is very difficult to shield the coils (1.5MHz) from the current measurement board. So it was decided to keep the two away from each other.


 Why is there an additional capacitor installed at the input of the UBEC ?

  • Many people complain that the UBEC seems to be bit big, but fact is that he is only 22mm x 17mm. What makes him BIG are the safety capacitors at the input and output !
    We all had the issues before that any ESC burned out due to the “hammer effect” in the supply lines, but do we consider that the UBEC is sitting on the same voltage source ?
    Does anybody ask himself so far why suddenly his BEC burned out ?
    Why does some people add some capacitors onto the ESC’s to reduce the risk of failure, but in the same time they forget that there is also anywhere an BEC in the supply line which might need some protection too ?
    How good is it if your ESC’s survive a voltage spike, but your BEC didn’t and the MR crashes ?
    If you can answer some of the questions by yourself, then you will also figure out why this UBEC is a bit bigger than others.


 How can I get one of these boards ?

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Replies

  • Hi everybody...today I need help from you guy's.

    Adam started the topic, if it would be possible to monitor 2 LiPo's in parallel to get the combined current reading in MP. Afterwards I design a Sensor Hub PCB (see above posts) which makes that actually possible.

    Then yesterday, I was contacted from one buddy if it would be possible to include an battery protection circuit (like a ideal diode) within the system, what means protection of one LiPo if the other one fails and draining the healthy one... and I start researching a scratching my head... until I finally realized there is no way.

    If we use MOSFED's to switch the battery on and off(ideal diode control), then the parts always have tiny connection pins to the PCB. Furthermore, we are running again the full current over PCB tracks... what we actually want to avoid.

    Yes there are ESC's out there, which can handle easily up to 200A (or more), but they run the current in three phases. That means a duty cycle of 1/3, or an average continues current of 66.6A with a 200A load... and they are big and heavy... we are looking for 200A continues current and we would need a LOT of FED's to carry it... which means we're getting big, heavy and expensive.

    So here comes the question...

    My new sensor hub for 2 Hall current sensors, has already an detection (LED) if one of the sensors is malfunction (so far never happened). So how about we observe if during the flight suddenly one battery stop's to supply current to the system and give out an very strong alarm sound and/or a Power LED) ?
    In that case hopefully the 2nd battery can keep up, at least until we perform an emergency landing... would that be OK ?

    • Christian, you rock!
      Is there any way I could preorder it? I want to support your work.

      I think very strong alarm and Power Led are perfect.
      Power LED should be external, so we could mount it on the frame... (maybe two LEDs so we could put one in the front and one in the back... :-D)
      What color you wanna use? I suggest white because Pixhawk's LED is multicolor...
      Unfortunately white is not emergency color.
      • Hi Adam, I've already decided how the alarm system would be implemented.

        - 1st alarm output: Via relay NO/NC with 5V/1A output for external buzzer or alarm LED (or both)
        - 2nd alarm output: Only relay contacts for external signal to receiver or FC... to trigger RTL or alarm in MP.

        I've already stopped the production of the 2x sensor hub PCB's and hope I can finish the new design within today... will post it here when it is ready.

        Sorry, I don't like preorders as long as a product is only available on paper... but if anybody is interested to get one from the first batch, then send me a PM or post it here... then at least I would have an idea about the quantity of the first batch.

        • Christian,before production of a hub,you should first try to reach some of developers(Randy would be my choice) and ask them what is status of software bcs. in Mission Planner there is already that field(still not functional)...

          • Hi Emin, I design the hub to summarize the current of 2,4,6 or 8 sensors... the not functional voltage reading (BATT2) is actually only interesting for people who use LiPo's in series, like 2x6S=14S

            BTW: My hub will be delayed 2 days... as I include CAN bus at the moment.

        • Hi Christian!  I'm a newbe to this form of education / communication with at least two questions:

          Why not use a 'non-invasive' current 'transformer' - with an appropriately scaled output for pixhawk etc?.  I'm much more comfortable with risking a wire failure (unheard of when properly sized, finely stranded conductors are employed), than I am with inserting a component (hall effect sensor) between my power source and my pride and joy!!

          Have you considered monitoring / alarming on the lowest individual cell voltage?

          • Hi Philip... "current" transformers are too bulky and heavy. If somebody want to install multiple sensors to observe the current of each motor or paralleled LiPo's, then the weight of such system would easily be up to 500g...

            At the moment I do not think about to monitor individual cell voltage... maybe future project. 

  • Will this new Hub be usable with existing Power Modules from you?

    • Yes, of cause... all you would need is a set of cable to connect the sensors to the hub, but these cables will come together with hub.

      • Great stuff!!

        Here in arducopter community we waited for this kind of advanced power module for a long time and now this hub too....Thank you

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