Question about powering the OXS

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KAL
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Question about powering the OXS

Post by KAL » Fri Aug 22, 2014 6:12 pm

Hi folks,

up to 3-cell lipos the arduino can be powered directly via the "raw" pin.
With voltages higher than that a VR is recommended (for not loosing the magic smoke of arduino's small VR :mrgreen: ).

Now I want to use a 4-cell lipo and also measure the 4 cells separately (the usual method with 3 dividers).
Unfortunately I have no adequate VR at the moment :o .

Is there any reason not to power the arduino (also via "raw") from the 3rd (~8V) or 4th (~12V) pin of the ballancing port
(apart from the slightly distortion of ballance ;) )?
Or should I use a divider as last resort :? ?

Klaus
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Re: Question about powering the OXS

Post by jhsa » Fri Aug 22, 2014 6:25 pm

I don't think the arduino would cause any unbalance on the lipo cells. It's consumption is minimal.
Don't know how I didn't think about that myself :o
But would like to read other peoples opinions as well..

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Re: Question about powering the OXS

Post by MikeB » Fri Aug 22, 2014 8:56 pm

Another possibility is just to add a resistor in the power line from the 4-cell battery.
Measure the current taken by the OXS, then work out a resistor value that will drop around 4 to 5 volts at that current.

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Re: Question about powering the OXS

Post by jhsa » Fri Aug 22, 2014 9:52 pm

But if the cells could be used safely for powering the arduino and sensors without cause any adverse effect to the whole system, then we could just take the voltage form the first 2 cells for it. The voltage reg on the arduino can handle the 12.6V of the 3 cell LiPo but it does get quite warm to the touch. So if we could use just 2 of them to power the oXs, it wouldn't matter if the pack is 3, 4 or 10 cells :)

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Re: Question about powering the OXS

Post by MikeB » Fri Aug 22, 2014 10:13 pm

Just trying to avoid unballancing the cells.

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Re: Question about powering the OXS

Post by jhsa » Fri Aug 22, 2014 10:22 pm

It's a very small current. Do you think the pack would get that much unbalanced even if you fly for half an hour? How much does a pro mini takes? imagine it is 50mA, I think it is less, How much unbalance that would create when the motor itself takes say 10A average?
A balanced charge would correct the cells's balance, right?

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Re: Question about powering the OXS

Post by offers » Sat Aug 23, 2014 3:22 am

Cool idea!!
I am building 6cell oXs, and just wonder from where i am going to power it.
I will use that trick, i don't care about so small unbalance, the charger will fix it

Another way will be to power it from the receiver voltage.


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Re: Question about powering the OXS

Post by KAL » Sat Aug 23, 2014 7:49 am

I know several guys who power LEDs for night flying through the ballance port
without any problem. As long as we use ballanced charging all should be OK :D .
A single cell doesn't worry about the state of the others, 'cause lack of awareness :mrgreen:

I too thought of powering the OXS from receiver but I want to keep connections
as short as possible (avoid induction voltages ... ).

Klaus
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Re: Question about powering the OXS

Post by MikeB » Sat Aug 23, 2014 9:00 am

Another idea would be to use a zener diode to drop a specific amount of voltage.

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Re: Question about powering the OXS

Post by jhsa » Sat Aug 23, 2014 9:16 am

I did buy some 8V 500mA regulators in D-PAK package. That would allow a 4 cell LiPo and also keep the arduino regulator cooler. But still limited to 4 cells I guess. Will have to make some experiments ;) :)

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Re: Question about powering the OXS

Post by nigelsheffield » Sat Jan 31, 2015 7:12 pm

I am a little confused now as to wiring this up, I thought I read somewhere to use RX volts, one said to raw on nano and another VCC I think?
Now the sensor board , does it need 5v from the arduino or can that be higher?
For now I am just doing the vario but may do cells and current later.
If I just supplied the raw with RX volts at 5v from a bec I also read that the 5v will just be passed through so .........
I will have to play around a bit when I get it delevered.

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Re: Question about powering the OXS

Post by mstrens » Sat Jan 31, 2015 7:56 pm

oXs can be powered by Rx or via a specific voltage regulator.
If oXs is powered by Rx, it is safe to connect the "plus" from Rx to Raw.
When you do so, the internal regulator on the arduino board will regulate the voltage in such a way that the voltage on the microcomputer (which is in fact also the voltage on arduino pin Vcc) will never exceed 5 volt.
It is not a good idea to connect the plus from Rx to arduino pin Vcc because the internal voltage on arduino board is then not used at all and if the voltage on Rx exceeds 5 volts, then arduino board could be damaged.

About connecting the MS5611 sensor:
The MS5611 works at 3.3 volt.
If you use a GY63 board, this board has his own voltage regulator to let the voltage drop down to 3.3 volt.
In principle, you could connect sensor VCC or to arduino Raw or to Arduino Vcc because in both cases, the GY63 board will normally regulate his own voltage .
Personally, I prefer to connect to Arduino VCC (and not arduino Raw) because:
- so, I am sure that the input voltage on GY63 will never exceed his limit (because it will be max 5 volt)
- so, the ripple of voltage on GY63 will probably be less because there are 2 voltage regulators in cascade.

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Re: Question about powering the OXS

Post by nigelsheffield » Mon Feb 02, 2015 5:06 pm

Thanks, I just wondered if connecting the the rx 5v to the arduino raw input would cause a problem, in that the arduino 5v reg might need more then 5v input in order to work but it sounds like it can cope fine with just the 5v RX volts as its input.
I will do it as you say then
5v RX to raw of arduino
5v VCC from arduino to gy63.

I think the volts won't be a problem unless I want to monitor cells etc and done have a good enough bec to maintain a steady 5v is all, but hopefully that won't happen, if it does I will put a better bec in and or power the arduino raw from 2 cells direct.

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Re: Question about powering the OXS

Post by mstrens » Mon Feb 02, 2015 5:43 pm

If Rx get less than 5 Volt (say 4.5 volt) and Rx is connected to Arduino Raw, then the arduino voltage regulator will not really be able to regulate the voltage but it still will work.
The result will be that Arduino Vcc will be Rx voltage minus the drop generated by the voltage regulator. The drop is probably about 0.3 volt (not sure, depend on voltage regulator model).
So Arduino will then be powered by less than 5 volt but it will work as long as voltage on Rx does not go to low (probably it will work at 16 mhz up to a Rx voltage about 4 volt; for exact value, see arduino data sheet).
When arduino Vcc becomes lower than 5 volt, the drawback is that the conversions analog to digital will not provide the expected values anymore if the conversions use arduino Vcc as reference. In order to avoid this issue, it is then better to ask Arduino to perform the conversions based on the internal 1.1 volt reference. Still this requires some calibration because the internal 1.1 voltage reference can have a tolerance of about 10% depending on the arduino device.

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Re: Question about powering the OXS

Post by MikeB » Mon Feb 02, 2015 6:47 pm

3.78 volts is the lowest supply voltage at which the '328 is guaranteed to operate at 16 MHz.

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Re: Question about powering the OXS

Post by mstrens » Mon Feb 02, 2015 7:03 pm

so it means about 4 - 4.1 volt on raw pin.
It is "guaranted" at this voltage but probably most devices will even work at a (little) lower voltage.

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Re: Question about powering the OXS

Post by davx » Mon Feb 02, 2015 9:58 pm

Hi,

@nigelsheffield,

You can find some infos about building an OXS Vario here: https://code.google.com/p/openxsensor/w ... uild_Vario
There is a "Power supply considerations" paragraph ;)

Bye.


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