Hi everyone,
I'm building a heavy Octo for aerial photo & video based on the APM2 board + Carbon Core Octocopter1000 with 360 Pano Mount and Mega Radius camera mount.
The power is provided by two Turnigy nano-tech 6000Mah 6C batteries connected to 8 Himodel 40Amp ESCs powering 8 Tiger motor MT3515-15 400Kv motors with Master Airscrew 14x7 3-blade propellers fitted.
The theorical maximum amp draw for each motor is 29Amps making a theorical max Amp draw of 232Amps. I want to measure battery Voltage and current draw but the biggest AttoPilot Current & voltage sensor is rated for 180Amps Max.
I know I'ts impossible or near impossible to go to max Amps with all motors at same time doing AP but given that burning the Attopilot sensor will stop the power feed to the multicopter, and this will result in a more than sure crash, I want to be very conservative and not overload it.
Is there an option to connect two 180Amp sensors to the APM2 board (one on each battery) and get readings?
Two sensors should be capable of handling 360Amps and this would solve my problem.
Other sugestions?
Replies
There are power modules available on eBay that handle up to 8S batteries. I think 3DR might even have them now. People report some quality control issues from time to time but I'm using one rated for 8S with my dual 6S batteries on a hexa and it's working fine. I only monitor one battery as that gives me the correct voltage and I just double the current reading displayed for an approx current draw. But you could probably set the current calculation to do that for you if you want a proper display. Monitoring one battery isn't perfect but it's worked find for me for years now. BTW, if you order a power module off eBay get a longer cable for the connection to the APM/Pixhawk as well. They are cheap and come in very handy. Here's one example of a PM from eBay:
http://www.ebay.com.au/itm/APM2-6-Flight-Control-Board-Pixhawk-Powe...
Same problem for me guys.. I need to use 12S battery connection and 220A current draw at max. Is there no simple alternative to AttoPilot180A ?
I know this thread is a bit old but is there any further info on this? I am also looking for a sensor that will work beyond 180A.
Ecalc tells me my max current will be 217 so not too far over and I probably wont go that high but I don't want to risk it...
Attopilot is difficult to found in Europe, why not use the wire as shunt like this :
wire as shunt
There is a much more straightforward solution: use the 180A attopilot as it measures on a scale of 3.3v and APM measures on a scale of 5.5v, the actual current you can measure is 272Amps!
Hi Jibabio,
The simplest way up to 200A unidirectional or bidirectional for you is to use one of the Allegro's ICs ACS75x - http://www.allegromicro.com/Products/Current-Sensor-ICs/Fifty-To-Tw... .
For higher currents, it's better to use current divider technique - http://www.allegromicro.com/Design-Center/Technical-Documents/Hall-... . In this approach, you sense 1/2...1/5....1/10 of the real current for example where the main current flows through the high current schunt part, while the measurement is made in the measurement part ( the schunt has 2 sections ). Then you have to recalculate the real current.
Also for higher currents you can use a current sensing transformer. The problem with them is that they are not as slim as ICs.
If you decide to use another approach - schunt current sensing - high current schunt with a simple and cheap IC as a current monitor, you can use Diodes current monitors - http://diodes.com/products/catalog/list.php?parent-id=79 with a high current schunts from Isabellenhutte for example - http://www.isabellenhuette.de/en/products/ .
There's another approach of using N current monitors with current or voltage outputs and then make a SUM of them with an OpAmp.
If you have any questions, please just ask me.
Best regards
Nick
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