Voltage protection settings

[Kilby]

Hey gang. I'm just wondering what settings you guys are using in your voltage protection for a 4S battery. As long as I've had this wookong, I've never set this up, so it's still a bit new to me. I'm rebuilding this thing after having a mishap with an under charged battery, so I don't want to take any chances this time.

Thanks in advance.

-Terry

 

[mbsteed]

A full charge is 4.2 V per cell (16.8 V for 4s). Anywhere under 3.0 V per cell and your battery is dead (4s 12V), so you don't want to come close to bottoming out the lipo. Personally I wouldn't go below 3.4V, I would make the second and final safe (3.4*4 = 13.6 V). I would set the first fail safe around 3.6 - 3.7 (3.6*4=14.4V). That is my thinking, others may have different thoughts, my experience is limited. You use 3.8 V per cell for storage (if it will be more than a day or two without using them), you could even use this value as your first failsafe and the bring the bird down and your batteries would be good to store without putting them through the storage routine on your charger.

 

[janoots2]

I used to fly LV values similar to that before my wookong started giving me inaccurate readings. (Went through a whole exercise to confirm). Now I (still) use my timer along with an audible voltage alarm. My warnings were so inconsistent it wasn't worth keeping.

Even though I wish it behaved accurately (for descend only in case of a fly away or some other extreme circumstance...)

To keep better track, I went on a search and found the app called rc logbook. It has a sweet timer and logs your battery performance so you can see how they are trending, and a lot more...

 

[mbsteed]

Right,

We actually have 4 redundant flight battery checks. Of course the WK-m flight controller, we also have a battery voltage monitor onboard that flashes led lights constantly - it changes colour from blue to green to yellow to white with audible alarm at the end (it works very well), and then we set the TX timer and have Spektrum telemetry that gives us real time voltage for flight battery (plus altitude, RX V, temperature of ESC). This might seem like overkill but better to safe than sorry. Oh, we also always use two 4s batteries in parallel for extra redundancy (if one fails we would still have one to get the ship on the ground).

 

[janoots2]

Can you post a link of the onboard alarm with LEDs are you using? Mine gives me the voltage and audio but that's it, would be nice to have LEDs.

Have you found that when you cross reference your other telemetry with the wk, you find the wk alarms to be inaccurate?

 

[mbsteed]

http://www.western-robotics.com/spectrum-LiPo_hp.html

http://www.snhobbies.com/product_info.php?products_id=4387&osCsid=3f414dc1e8a2a20ed03c89783dbb8991

These work really well and I put the buzzer on them as well but the led lights are so bright you can them quite well - until the ship gets way off in the distance.

Today I went out in the cold -10 C and the batteries almost immediately went from blue to red - and my telemetry alarm (vibration and buzzer) went off as well warning me of low flight voltage. I had just balanced charged those so I flew those for just a minute hoping those would warm up but no such luck - those were kind of old batteries but I kept them warm until I put those on but it takes a few minutes to get everything setup - I will have to play with those more, it may be that the batteries are toast (although those have been good before). Had I continued to fly it would have toasted the batteries for sure and probably resulted in a crashed octocopter - thank goodness I have these warning systems.

I haven't compared the WK-m V levels but yes the voltages on the Spektrum telemetry seems to be off. I will have to fine tune the warnings because the actual V and telemetry V differ by about .2 V but there is no way to calibrate to adjust - it may be a matter that I was measuring the batteries at the source and the telemetry is measuring V further inside the wiring system - not sure. This issue has been mentioned by others in the forums. I will have to check the WK-M voltage levels and compare that to the actual and Telemetry V.

 

[PeterLester]

Just a few thoughts.....

The WooKong specs indicate a lower temperature limit of -5 deg C versus -10 deg C for the NAZA.
Pushing the motors towards peak speed draws a lot more current such that the measured load voltage will drop at least momentarily into the "red" zone.
Battery capacity is directly affected by temperature, e.g., for an AGM lead acid battery it's capacity drops 65% @ -50 deg C.......a rather extreme example. Battery capacity/temperature curves also varies with the battery electrochemistry.
A very thin lexan or acrylic dome shield installed over your electronics will allow some of the radiant heat from your VU to help keep the temperatures up in the adjacent electronic components but not the GPS/compass.