I am not an electrical engineer and so I could use some help here.
We are a bit concerned about the speed controls pumping too much voltage into our APM2.
It appears our ESC's are outputting nearly 6 volts. Is this too much?
We started looking at some options. A little voltage regulator LM7805C came to mind, but it appears most suck up quite a bit of voltage (drop out voltage) ~ as much as 2 volts ~ so then the board would only get nearly 4 volts. And it sounds like that too could be a problem....yes?
So we found what is called a Low Dropout Regulator (see link). It appears this guy has a drop out voltage of only 0.15 volts at 100mA (did I read that right?) (How many amps do our APM2's need?) see specs at link below
So it sounds like if the ESC's produce anything more then 5.1 volts we could be assured of a safe 5 volts. Of course if the voltage from the ESC's gets down to 5 volts, our board would only get 4.9 volts etc.
I think I would like this little bit of insurance....am I on track or way off the wall ?
Thanks for your input.
Ha, that is funny ...a linear voltage regulator. Where is it on our boards?
But there may be some other item that would blow even before the 6.2 voltage right?
I't would be nice to find out that there is a simple "re settable fuse" type item, that would always be the first thing to go.
Again, I know so little about these things. Is there even such a thing?
Yes, there is, but I forget the name. Self-resetting fuse or something like that. The problem is, I think that they are slower to act than normal fuses.
Most of the passive components on the input could handle the 6.2V 'over condition' fine. The regulator would begin to overheat incrementally as the voltage rises. The extra voltage is rolled off as heat but input current would have to go up also (not the current to the 'protected' components).
At some critical point of heat, the regulator would probably just pop - literally.
The component path is +V(input) ----> [Regulator]------(all the APM2 regulated parts)
Because all the parts are surface mounted, you could probably declare a popped regulator as the death of the entire board. With the right setup, it *might* be possible to pull the blown regulator and replace it with a work-a-like daughter board OR for an experience SMD rework person, replacing the part. It would depend on the amount of collatoral damage to the board and traces.
For a complete obsessive protective mindset, you could put an inline fuse of maybe 0.75A in series with the +V(input). I would want to scope out the max current over a variety of conditions before selecting a fuse value. Surely nothing greater than 1A (1000 mA)
Even that won't stop a serious voltage pulse, i.e. connecting a 24VDC input where the 6.2V is the limit for the APM2 onboard regulator but it could not hurt.
In some cultures, mistakes are seen as a learning experience. In the cult of APM2, a mistake costs just over $200.
And my final comment... I hope (after looking over the entire APM2 schematic)
The APM2 has several components that depend on the +5V input to be just that. The 3.3V regulator is there to throttle +5V down for the devices based on that logic family.
Several parts use +5V. Essentially the APM2 is a mixed family board. This is not uncommon today because some parts are only available in 5V family.
In short, a pre-APM2 regulator for +5VDC would be a good thing. If it were fused or otherwise made to protect the APM2, all the better.
"In short, a pre-APM2 regulator for +5VDC would be a good thing. If it were fused or otherwise made to protect the APM2, all the better."
Yes, I think this is what I was thinking when I started this thread.
So, what do you think? Do some of the suggestions we have seen on this thread fit what you are thinking. Or if not, can you design one....I'll be happy to build a prototype :)
And what do you think of a couple leds.....green if all is good and blinking red if if under voltage or something?
By the way....does under voltage do damage? (Other then the resulting crash) Does the board simply reboot or ?
I have ordered my APM2 just today and plan to push it to an undervoltage situation to find out. I suspect it will either operate erratically or perhaps simply halt machine cycles and maybe freeze. It is unknown...at least to me.
My application is the quadrotor. The 5VDC is sourced from the ESC and piped to the PDB (power distribution board). From there it would feed the APM2.
What is very confusing/funny is what the APM2 documentation states:
Difference between APM 1 and APM 2
The main functional differences between APM 1 and APM 2 is in the sensors. (MAJOR TEXT EDIT - STARWALT)
No on-board power regulator. You must power the board via USB (on the bench) or your regular ESCs (via the ArduCopter power distribution board) in the aircraft, with power coming in through the APM 2 Output pins.
If the schematic is correct, this statement must be incorrect. Then again I would need to look over the APM1 to determine what they really mean by 'No on-board power regulator'.
There is also a section discussing alternate methods of powering the APM2. HERE
Do you mean if I came up with a protected board you would be happy to try it? My initial ideas would be to modify the PDB to incorporate fusing and power on indications or make a new PDB that has some of the features we are looking for.
Let me get my APM2 integrated into the Quadrotor project and make some measurements. I am using the 3DR ESC sold for the Arducopter so maybe their output really is just 5V and not what you started this discussion about.
Up to this point, I have just typed myself smart. Soon enough I can provide some data.
I got with Jordi and the 3DR team and we researched and clarified the power requirements for the APM2.0 and there is new, more detailed information on the power requirements that are approved by the 3DR engineering team. This information is based off the manufacturers data sheets and an understanding of how the board is designed and what the original design targets were. Here is the link: http://code.google.com/p/arducopter/wiki/APM2board
This is now the "official" recommendation and specifications for the APM2.0
Thank you so much, excellent job. You, Jordi and/or the team did indeed answer many questions I once had. I can not think right now of a cleaner, simpler way to word what you all have said.
Do I understand there is a linear voltage regulator on board? And, if so, if one did accidently apply too much voltage, would it be the first thing to blow? It would be neat if they made some form of micro resetable "fuse"?
I guess I have been suspicious of many of the ESC's on the market and the quality of the 5 volt power supply provided by these ESC's. It might appear to be a solid 5 volts on the table, but who knows what happens when the things are flying and all the speeds are increased etc.
I still do not know if my concern is really valid? However, I did end up buying better quality (?) speed controls and a seperate switching voltage regulator BEC for the board. And I have been flying with two batteries with no j1 connector, one for the board and one for the motors. Maybe that is over kill? And maybe as I continue to learn, I will end up feeling comfortable enough to put in the J1 connector and run the board off the one battery with the seperate BEC...
But either way, I really appreciate the time and thought everyone has put into answering and educating me. :)