Hello all,

Maybe anybody know what wrong. I take two "Dual UBEC Distribution Board VI Sensor 120A 10S for APM Pixhawk PX4"

And try use with Pixhawk. Everything fine but current sensor do not work. Or maybe work but current every time 0.0A

Other power module work fine but with "Dual UBEC Distribution Board VI Sensor 120A 10S for APM Pixhawk PX4" I have this problem. Maybe anybody know how solve and use this board ?

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Hi, I have the same issue .

Guess it is a defective  Ubec board...

On Hobby King I found this message:

Alain 1 points - 8/2/2016

 

Did tests on the board, all was good except their was no current output. Having no schematic of the board, i looked into it. I noticed a INA169 current sensor ic. The output of this ic requires a load resistor on the output. There was one, but of 0.5 ohm(a short). The typical load resistor should be 50Kohm to get a 50x voltage gain in order to to output about 3.0Volts out, compatible with usual ADCs. Conclusion, the board was assembled with the wrong resistor.....i suspect it happened on other boards from that batch, which might explain why it is in backorder......
As far as I know all the boards have 0.5 ohm load resistor just like original Apm 3Dr supplu module.

Alex,

Have you tried entering a value in the measured current box, something like ".3" for 300 milliamps?

Current and voltage sensors will always need to be calibrated.  You may need to give it an initial value to work with, and follow up with a DVM or ammeter to get more accurate results.  I use this power analyzer from HK:  http://www.hobbyking.com/hobbyking/store/__75944__Turnigy_180A_Watt...

but if you have an Frsky Transmitter/Receiver you can also use their voltage/power sensors to calibrate the power module.

I calibrate voltage and current at 50% throttle, since this is close to my normal operating throttle.  The power modules are usually non-linear, so you want your most accurate measurements at close to your normal operating voltage and current.

I think Randy has a good video on calibrating the power module for APM, you may want to take a look at that.

Rich

Low currents are hardly displayed so the current sensor might seems not to work but in fact if you use more Amperes it will work.

The big problem is that the current sensor gives wrong / non linear values.

All readings below 10A are overrated , i.e. real 3A appears 4,8A , around 10A , measurement is ok but after the highest measurement I got was 10.8A, even if Ampere drawn was around 28.

I had the same result on the two boards I own,

The only current sensors I've found accurate are the Mauch Electronics.  If you want a high-quality, reasonably-priced sensor/UBEC, I'd highly recommend them.

Matt,

Thanks fore the heads up on the Mauch boards.  I have had a heck of time finding power modules > 90 amp.  I was going to try a AttoPilot next,  but the Murch board look like a great option.  My heavy lift hexa is capable of drawing > 170 amps.

Rich

Hi Guys, I bought these 120A Ubecs aswell and had the same problems. The current sensors would not output a reading. I then bought some more cause I thought it was just a faulty one but it wasn't they are made/manufactured defective. But good news is read the above and was able to fix it. All you have to do is change the 0.5ohm resistor with a 10kohm one. If you want a pic of where this is I can show you. But you will need a hot air gun to remove it.

Hi, 10K  is 20.000 times more that the original value , it seems to me a very high value for a shunt resistor .

http://www.measurementest.com/2010/08/how-to-measure-current-using-...

Did you measure what is the voltage output  at 10A or 20A ?

If it is to high there is the risk of damage for the flight controller.

Yes, I am not an electronics engineer but I have tested the replaced 0.5ohm resistor with the 10k ohm resistor and at 10A I get a current voltage of about 0.3v. so assuming it is a linear correlation then at 100A it should not exceed around 3v. I did test the previous 0.5ohm original and at 10A I was getting 0.005v which is not really a measurable voltage for the flight controller. I do not know if it has any other collateral effects on anything else but I assume not.

Well, if at 5A you will get 0,15v and at 20A 0,6v , then your solution is good .

Be aware , I got at 10A a precise measure  but  values become non linear (greater) for lower Ampère , from 10,5A to  30A the readings change very little while higher was  11A.

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