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.
     

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.

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.

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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Never got an answer about the I2C... 

and also is there a plan for a 400A sensor?

Guy Tzoler said:

Hi 

I noticed a I2C port on the hub is it working? can I use it instead of the analog ?

Hi Guy... at the moment the I2C port does not support readout of the total current.

I do not plan to develop 400A sensors. But if you need one, then just connect two 200A sensors in parallel. I believe the very low IR of the ACS758 will be enough to ensure a perfect current sharing between the sensors.

To reduce shipping time for the Europe customers, the parts are now also available at AltiGator.

was looking to connect 2x 400A to get 800A :-).... do you plan to add this support? since using 2x 200A gives very low accuracy for current measurement a digital readout would be much better...

I might  be able to do the software part if the HW is ready for it.


Christian Mauch said:

Hi Guy... at the moment the I2C port does not support readout of the total current.

I do not plan to develop 400A sensors. But if you need one, then just connect two 200A sensors in parallel. I believe the very low IR of the ACS758 will be enough to ensure a perfect current sharing between the sensors.

Hi Guy... The hardware is ready for the I2C and the software part is done for my prototype readout display.

I will send you an email, how we can implement the analog value out via I2C.

The new Pixhawk 2 do no more support any backup BEC on the servo rail and can be only powered over the Battery 1 and Battery 2 connector.

Therefore, I've added two new BEC's, one for 2-6S LiPo and one for 4-14S LiPo, with Molex Clik-mate 2.0mm connectors.
Inclusive 2 spare wires (white/yellow) with crimp contact to still use the option of Battery 2 measurement.

Today  had a VERY serious problem with compass after installing the 200A current sensor.

I almost crash since it seems that the current Hal sensor increase A LOT the compass interferences.

As soon as motors are getting  Amperes the EKF Compass rush to the red zone. Is it normal ?

With the previous chinese  current sensor and Ubec from HK : http://www.hobbyking.com/hobbyking/store/__68694__HK_Pilot_Power_VI...

I did non have any issue with compass and the copter was flying perfectly even without compass mot calibration .
I change it because the current sensor was not reading more than 11 A

The 200A bought from Altigator in Belgium arrived without any calibration card, a wrong cable for connecting to Pixhawk 3 ways instead of 5 .
I bought the 50A but after 2 days I paid , told me it was out of stock and sent me the 200A.
Altigator do not answer to e-mails (26 hours without reply)

Compass Mot showed 15A while my data acquisition got 47A

Until now I'm really not happy for this purchase ....

Hi Luc... first of all, the Sensor module does not influence the compass and the source of the interference should be located somewhere else.

Did you calibrate the compass after you installed it in the UAV ?

Are there any high current cables near the FC ?

What BEC are you using and what is the output voltage ?

Furthermore, I guess there went something wrong with your order from altigator.

  • How can it be happen that you order a 50A sensor, but you receive a 200A version ?
  • Each sensor should come with one 10cm long DF13-6p cable... was that not the case ?
  • There should come a small plastic bag with accessories together with the sensor, which also includes a printed version of the final test result (calibration data)... was this scope of delivery ? 

I will contact the guys from altigator to find out what might went wrong. What I can offer from my side is, that you send the 200A sensor directly to me and I send you a HS-050-LV (with all parts) free of charge.

I wrote you an e-mail with attached photos and logs

I trust you when you say that the sensor does not influence the compass but it is hard to believe.

I flew some days with very good compass health , I change the current sensor since the board from HK measure  only up to 11A so I bought your sensor with your ubec from Altigator.
At first I did not calibrate again the compass after I installed your current sensor and at first flight  I got a EKF compass error and almost crash .
Now I have calibrate compass but I'm stuck because I absolute need to run the compass mot since I saw I had a 80° heading variation just starting the motors at low speed.
Compass mot at 90% trhottle gave 15A while my Eagle Tree Elogger4 gave 47A so the calibration datas would be useful but were missing from the package.
The cable I received was a 4 ways instead of 6 ways (I made a mistake in my previous post writing 3 and 5 ways).
After two days I paid I was told by Altigator that the 50A was not in stock and offer to replace with the 200A saying that only the 10AWg wire change , same weight and precision they said.

About compass inluence I sent you the photos of my set up.
What changed is the two ubecs of the HK board that have been replaced , the 5,3 volts by your Ubec , the small one, the 12 volts by a D-sun MP1584 .

I read you email reply about the problem should be in ground loops and not the sensor.
I never heard that  ground loops might affect compass...
I will investigate and try yo find a solution , thanks.

Finally thanks to Christian Mauch suggestions and  support I was able to solve the problem that arise after mounting the Hal current sensor.

I mount the sensor and the Mauch ubec in a non conventionnal manner so normal users will not have the same problem.


Hard to say  what was the reasons of compass perturbance.
I manage a better connection of Ubec grounds to avoid ground loops and move some wire paths .
I repeat several times the compass calibration procedure and finally got a decent EKF compass bar when motors were started.
After I run the compass mot procedure and test flight was  good.

Finally I think that the real point was  that the previous setup with the HK board that had the defective  current sensor because of some very lucky and a bit misterous coincidences has a very very little disturbance factor on the compasses of the Pixhawk.
In fact even without the compass mot calibration (that I could not run properly because of limited measurements to 11A ) I could fly without any compass heading issues or EKF compass warninfs  even if I drawn over 45 A on my hexa.
What bring me to error was that power wiring of Esc and batteries or their location , the part that usually give problems to compass did not change at all.
I might also had an issue with Mission Planner since I notice the the compass , internal and external , were swapped as primary at a certain point when I try to calibrate them at best.

Altigator wake up, replied to my emails and sent me free of charge a replacement cable.

Current readings displayed on Mission Planner Hud varies a lot compared to  traditionnal 3DR current sensor and bec.
Christian explained me that the measurement is more accurate and that behavior is absolutely normal.
I hope that software developpers will apply soon a software filter to current datas displayed on Mission Planner Hud or Mavlink Frsky telemetry, actually it is almost unuseful since @ 14A current, displayed values can varies from 5 to 21A.

Thanks again to Christian for his kind and great support.

For the power modules are now adapter cables available for the HKPilot 32, with Molex / PicoBlade - 6p connectors.
http://www.mauch-electronic.com/apps...s/show/7119616

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