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 ?
- Send me a PM here in diydrones, or visit www.mauch-electronic.com and go to the web shop.
Replies
Hi Jim... thanks for the confirmation.
I was already checking all my remaining serial number stickers for any mismatch, but couldn't find one.
Best regards and Happy New Year,
Christian
Nice!! I just burned up my 3dr power module and haven't made my maiden flight yet
Excellent! Been looking for a beefier setup and just found your post. Your 4-14S looks like it should suit the bill.
I found the Drotek post to be quite disrespectful. I am troubled by the fact the no one saw fit to remove it. There was a time on this forum when one was hard pressed to find people being openly rude like that. A time when people were more positive, helpful and encouraging. Now posts like that are becoming all to common on this site, which is why I don't frequent it as much. It is in the nature of DIY and open source to question, or point out a problem or issue, but to do it rudely should not be allowed. Come on people, what happened to civility?
Looking forward to trying out your hardware Christian.
I think it makes more sense, in this instance at least, to leave the disrespectful response in place for everyone to see. Then let the author make their justification if and when they choose.
All parties can then make their own judgement on the quality or otherwise of the product and its manufacturer.
I am too very interested in the power module, because of the accurate measurements, which is critical to squeeze every bit of flying time out of the battery.
By reading the specs I started thinking about the BEC's as stand alone version as well.
I ordered these, but the ripple is so large that I get all kind of problems in the video signal.
http://www.banggood.com/DC-DC-Converter-Step-Down-Module-3A-5V12V-M...
Before I was using these http://www.banggood.com/LED-Driver-Charging-Constant-Current-Voltag... for the 12 volt stepdown from a fully charged 6S, but when I start drawing max current for the engines, the input power is dropping down, not much, but for whatever reason this is then resulting in a drop at the output power.., I.e. 12 volt goes down to 6-7 volt which is way below what the gimbal needs..., so gimbal shuts down, and (low power setting triggers), maybe because it's a constant current version...(it is very clean on the output but I need the stable 12v nomatter what the input voltage is doing)
So if your BEC's with ripple reduction can provide me a way to power the complete video section, including the gimbal from a 6S version, without the power drop at the output, then that would make a big difference.
I do think there is a market for quality products, even if prices are higher, As long as you can justify this by using the quality components.., and that's what everyone can see in your pictures.
Erik
Hi Erik,
I'm right now working on a stand alone version for the HYB-BEC 4-14S. The tests should be finished this weekend and the product might be available at the end of this month. Expected price is $35 for both the 5.3V and 12V version (of cause incl. shipping).
Will post here any updates when available.
Christian
I'm familiar with the ACS Hall sensors, since I use the FrSky FAS-100 module on almost every build I do. And I've unsuccessfully tried to "steal" its readings and feed them to an APM as well as the FrSky telemetry a couple of years ago.
Hi Para, that's actually exactly what I'm doing in my version. I use the 5.35V from the BEC (HYB-BEC) and supply the voltage for the current sensor and offset shifting OP over an ultra-low noise LDO (LP2985-4.0).
Due to this design, I have the full bandwidth of the analog input, means 0V=0.0A and 3.2V=200A, which results in very stable current readings.
When I first saw this post I thought "Well yet another good product but for ten times the cost of the standard one" but my curiosity led me to look at your store. I could not believe it was only U$S 33 for the 200A version and free shipping!
Let´s hope some other vendors start making things going this way: Better than standard but at a reasonable price.
I will but a couple next month.
Keep up the good work!
Very nice! I am planning an experiment which requires current readings from a Pixhawk based vehicle. The idea is to test efficiency under different flight conditions. Christian, do you think this sensor would be more accurate for my purposes than the 3DR power module?
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