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Discussion in 'Cinestar 8' started by Sam Donaghy Bell, Jan 22, 2015.
Yes. i thought it was quite the compliment too.... <evil grin>
I thought as much. That's a mistake on my part! So where should I be connecting it to to get a reading from both lipos? I can't see anywhere that would give me out put from both, just the one.
You will need to connect it to the point where the Y-splitter cable connects to the power distribution board. That's what Steve The Omniscient meant by the "mains."
This may require soldering a connection on to the Power Distribution Board.
With luck and a following wind, your RTF vendor either makes house calls, or is just a few minutes away. Absent luck and following wind, then, if you're not comfortable soldering things, you'll need to find a 12-year old child. They don't actually know how to do this, but nobody has told them it's hard so they give it their best shot. AMHIK.
Failing that, find someone with an electronics background -- the child-like behavior is optional.
The power distribution board might have a spare tap for +/- like the bullet connectors for your ESCs. Do you have a digital multimeter? Are you confident using it? If you power up the copter (maybe use a bench power supply instead of a LiPo) you can easily put a meter on the various connection points on the board and find a good spot to add your wires. But like Andy said, it's not for the faint of heart.
First of all thanks for all your time and help on this it's very much appreciated!
So I bought myself a multimeter but I had no spare power outputs on the board.
I wanted to change my powerpole connectors to EC5 anyway so in the process I joined the cables to the iOSD like the picture shows.
I powered it all up and got picture fine but the battery read out still read 12V!
If I'm being an idiot just tell me but I was sure that would work..
I'm officially stumped...
Is it a Freefly Power Distribution Board?
Yes he has a Freefly PDB.
Sam if you plug a battery into one of the connectors read the voltage on the other pair. What do you show? If it is more than 12V then I would suspect that you have a bad OSD. Or if you have a bench power supply go direct to the OSD and see how it reads.
I think the problem is that Sam needs to power the DJI PMU with full battery voltage. While the iOSD sends the voltage data to the ground station, I don't think it is reading the voltage into the iOSD. DJI uses a PMU (power monitoring unit) to supply power to the other components that are connected to it. I suspect that the FC or PMU is the device sending the iOSD the battery voltage. On the DJI installs I have on a couple Cinestars, we are supplying both the PMU and the iOSD with full battery voltage. If Sam is just supplying the iOSD with full battery voltage but the PMU is still getting 12V I suspect that is why the iSOD is reporting 12V. The iOSD itself can accept the 6S battery voltage to run the device but may get its voltage reading sent through the main DJI bus system.
We also use FF PDBs for the DJI rigs I have and I recall tapping into full battery voltage somewhere on the board and not splitting it off the main battery leads.
Hopefully that helps solve your issue.
By that do you mean plug one battery in and see what the other connector is reading?
Thanks for you input. I'll be honest, you've surpassed my knowledge now. I power the octo with 2x 22.2V 10,000mah lipos. I thought the reason I was getting the 12V reading was because I was originally powering the iOSD off one of the 12V outputs on the copter. Surely though even if my battery wasn't full (it was prob around 75%) I still wouldn't get a 12V reading, esp if there were two batteries plugged in?
Although this is not a perfect example, think of the iOSD as your voltage meter or multimeter tool. A multimeter needs power to operate (AA or AAA batteries probably), but the power that operates it is not what it displays on the screen when you go to check the voltage of something. Your iOSD needs power to operate too (thus the power input wires, etc) but the voltage it is checking is not the voltage used to run it - it is checking the voltage that is powering the rest of your DJI system. The power monitoring unit (picture above) is what you need to make sure you give full battery voltage to and it passes along the current battery voltage to the iOSD which sends it with your camera signal to your video transmitter so you can monitor it from the ground.
Another thing to keep in mind is that you don't need to have an iOSD to operate your DJI flight control system, and without an iOSD you still have the ability to turn on low voltage warnings in your DJI assistant software - which confirms that something other than the iOSD is keeping track of the battery voltage for you.
If you have supplied your PMU with a consistent 12V power supply from your FF power distribution board (the red set of JST plugs in the middle), your FC will only report 12V no matter what your battery voltage is actually at - because that is the voltage it is being provided. To solve this, power your PMU (and also the iOSD while you are at it) from the main battery voltage. There are 2 places to do this on the FF power distribution board. See the attached photo for the + and - indicator on the board - they are full battery voltage solder pads. You could either solder wires (with the connectors of your choice) to both sets of these solder pads (they are on opposite edges of the board) and then solder on the mating connectors to the PMU wires and the iOSD wires - or just use one set and split the power feed to both devices. This should solve your issues and give you the option of setting a low voltage failsafe in your DJI assistant.
Let me know if you need any further clarification at all.
Thank you! Now it makes sense. So I didn't actually have to power the iosd differently at all... that was a massive pain. I'll need to check what the PMU is powered by at the weekend.
If it's powered by the 12V can I move the power of the iOSD back to 12V and move the PMU to the connectors I made?
I've not used the DJI battery warning system. In what way does it warn?
Thanks a million for your help!
You can set multiple levels of battery protection.
1. If you hit a certain voltage, the aircraft can either give you a flashing LED warning or it can initiate the Go Home and Land function
2. You can set a second level in such a manner that if you hit another predetermined battery voltage the aircraft will simply land.
Attached you will see a screen shot for the low voltage alert that is part of the DJI set up assistant.
I'll let you know about whats powering the PMU at the weekend. Thanks again for all your help!
So we got sorted! That's me reading 23V which is great and many thanks for that! That should drop as I fly shouldn't it? Really impressive detective skills there!
Glad you got it all worked out. As you probably know, 23V is not a fully charged battery, but certainly represents 6 cell voltage being displayed properly. A fully charged 6 cell battery will report 25.0 - 25.2 before you start the motors. When you take off if may drop a full volt or close to two depending on the amount of amps you are drawing. The voltage will continue to drop as you fly and you should pick a number you feel is safe for your flight to determine when you need to be heading for home and when you need to be on the ground. Everybody pushes their batteries a little bit differently - and battery age and cell quality are a part of this decision.
Yeah all batteries are sitting in something like a storage voltage right now. Out of curiosity what do you run yourself down to before landing?
Thanks again for all your help!
Yep - makes sense. I head for home somewhere around 21.8V and am on the ground around 21.5. After powering the motors down, the voltage bounces up about 1V or close to it. Many people push their batteries further - and if I need to in a certain scenario I know that I can. There is still a pretty good amount of capacity left when I land and commonly recharge them about 6000 - 7000 mA out of 10,000. I fly them in pairs.
I'm sorry if I led you down the wrong path up there ^^ . Glad you got it working!