Low Voltage/Buzzer Alarm Question

[wbvike]

I recently bought the Lipo Battery Voltage Tester/Low Voltage Buzzer Alarm from Flite Test to use on my Tiny Trainer. I've seen reviews on line that shows how it works and such, but I have a question about the actual beeps and when they go off. If you set the voltage alarm to go off at a certain voltage, shouldn't the alarm continue to go off until the battery is unplugged?

The very first time i used it i didn't change the default setting of 3.30v and flew around for a little bit and the buzzer went off, but only beeped a few times then shut off. I landed and checked the voltage and it said it was still at 3.6v..? Ok, so today I went for another flight, changed the voltage setting to 3.60 and same scenario as above, the alarm went off, but did not continue to sound until it was unplugged. Is this because maybe not all of the cells had hit that low voltage setting yet, and it was letting me know that at least one cell has dropped below the 3.60v? Do all three cells have to be below that low voltage setting in order for it to continuously beep?

Also, what is the minimum voltage most of you will let the battery get to on a flight. I've looked around, different people have different opinions on what the lowest voltage should be allowed to get to before landing the plane? Might have answered my own question there, but just want to see what majority says.

Thanks in advance.

 

[razor02097]

No it will not. Once you hear the buzzer sound you should land.

The phenomenon you experienced is due to a voltage drop by the motor drawing battery power. Once the motor is shut off the voltage will climb to a steady resting voltage again. The more current drawn, the more the voltage will dip. On a LiPo battery as the battery capacity is used the voltage will continue to go down very slowly until it reaches around the 3.6ish mark then it will pretty much plummet. You want to end the flight well before that point.

A lot of people follow the 80% rule. That means to use about 80% of the capacity of the battery before landing. This not only helps extend the life of the battery but gives you some wiggle room in case you did find yourself fighting a headwind to get back or have to circle around again if your approach wasn't quite right. By flying on a critically low battery you risk bringing the voltage low enough to start causing serious issues like the receiver rebooting which results in a temporary loss of control and servo glitches. Even if you are able to work though all of that the battery could be permanently damaged by drawing it too low.


Personally I set my low voltage alarms at 3.7V per cell. Usually because I can land and it comes up to right around storage voltage. On my 250 quad that means I get right around 7 minutes on a 2200 3s.

 

[wbvike]

Ahh....forgot about the voltage climbing once the motor is cut off! When i heard the buzzer, I turned back to my position and cut the motor off and glided towards myself and landed. That would explain why the buzzer stopped. I checked the battery and it was still at 3.7v and overall 11.1, went back up for another flight and made about one circle around and it went off again. I did the same as before, got the plane pointed back at me and shut the motor off and buzzer stopped a few seconds after that. I over shot where I wanted it to land and had enough to give power and make a short turn and land close to me.

I did read a few people do the same as you mentioned, 3.7v so it give you that little extra time to get the plane back, especially if at the other end of the flying field. I think i will stick to the same as you suggested from here on out.

Thanks again for the fast response and explanation.

 

[razor02097]

No problem and happy flying

 

[ZoomNBoom]

I did read a few people do the same as you mentioned, 3.7v so it give you that little extra time to get the plane back, especially if at the other end of the flying field. I think i will stick to the same as you suggested from here on out. .

If you set the buzzer at 3.7, chances are under load, it will sound when the battery is still more than half full. It all depends on how many amps you draw vs the C rating of your battery (x its capacity). The combination of those will determine the voltage sag. The only data point I have is that your alarm went off, and you landed with 3.6v, which is pretty much where it should be, though a tad higher wouldnt hut. So set the alarm at 3.4 or there abouts.

I will say, to me, a lipo alarm is a last line of defense, and I generally fly so it never goes off. I rely on (throttle %) timers and voltage telemetry primarily, the lipo buzzer is there for if something goes wrong. One the problems with a buzzer is that if you fly, say, a powered glider, it will generally buzz much too late while you are gliding (low power draw, so low voltage drop) or way early in a full power climb (high draw, high drop). On a multi rotor you wont have that problem, as near zero amp gliding for more than a few seconds is tricky at best

 

[wbvike]

If you set the buzzer at 3.7, chances are under load, it will sound when the battery is still more than half full. It all depends on how many amps you draw vs the C rating of your battery (x its capacity). The combination of those will determine the voltage sag. The only data point I have is that your alarm went off, and you landed with 3.6v, which is pretty much where it should be, though a tad higher wouldnt hut. So set the alarm at 3.4 or there abouts.

I will say, to me, a lipo alarm is a last line of defense, and I generally fly so it never goes off. I rely on (throttle %) timers and voltage telemetry primarily, the lipo buzzer is there for if something goes wrong. One the problems with a buzzer is that if you fly, say, a powered glider, it will generally buzz much too late while you are gliding (low power draw, so low voltage drop) or way early in a full power climb (high draw, high drop). On a multi rotor you wont have that problem, as near zero amp gliding for more than a few seconds is tricky at best

Before i had the buzzer/alarm, I would fly until there was not enough power to keep it airborne. I had no idea of time frame it would fly because it was different each time, as it was dependent on how i was flying. I'm not an aggressive flyer because I'm still learning and basically go up and practice turns and will do a couple loops with it as well. I currently use a Turnigy Nano-tech 460mAh 11.1v 3cell lipo. I recorded a couple flights and then used my stopwatch to time the flight from watching the video. On two different flights i was able to fly for 7mins and 11mins. I believe that when i recharged the battery it was at 3.29 in the cells and i don't remember the over all voltage. I'll give the 3.4 a try and see how it goes. That might give me an extra min or so of flight. I just want to be able to hear the alarm and have enough juice to get back to where i'm standing to land and a possible go around should i have to do it again.

Thanks again for the input, very much appreciated.

 

[ZoomNBoom]

time frame it would fly because it was different each time, as it was dependent on how i was flying. .

Thats why I use throttle % timer. Its a timer that counts down proportionally to the throttle position. So at 100% throttle it will go twice as fast as at 50%, and at idle, it wont count down at all. I could even put a curve on it, so the relationship is not linear (power draw tends to increase more than linearly with throttle position), but as it is, its accurate to about 10% on most of my planes even with very different flying styles.

 

[Timmy P]

My story goes.... I set my buzzer to go off at 3.2 and that gives me time to swing around and land before my ESC goes into low cut mode.. I've never damaged a battery and I only use cheap Turnigy's. A lipo can go as low as 2.5-2.7 before it is damaged so I feel anything above 3.5 is just to high.. Yeah your charge times will be faster.. But I would rather get a full cycle out of the battery before re-charging... But thats just my opinion. But then again "better safe than sorry".. But really....... how fun is "safe"?
3 volts per cell is the lowest you want to go.. Because some chargers wont charge a lipo thats below 3. But there is a tiny bit of wiggle room if you drop below 3 volts per cell..

 

[razor02097]

But really....... how fun is "safe"?

Being safe is super fun. More fun than going down in a 50' tall tree because the battery had insufficient capacity to clear it. Or even more fun than flight times being cut in half because all of the polymers have been converted to methane gas in your battery.

When I flew NiCad I did exactly what you describe. Fly until I couldn't anymore. But NiCad batteries have a gradual discharge curve. You could tell when the battery is getting low. With LiPo you fly and fly until all of a sudden the battery simply says "nope". Voltage drops like a rock. Maybe you could get away with flying on a low LiPo battery if you have something with a glide slope and turn off LVCO. But most quadrotors will fall out of the sky well above a 3 volt resting voltage because they draw so much power.

It's okay. They are your batteries bought with your money. You can do what you want. A properly cared for LiPo lasts a long time. One that isn't cared for doesn't last at all. Please do not advise people to over fly their LiPo batteries.

 

[Timmy P]

It's okay. They are your batteries bought with your money. You can do what you want. A properly cared for LiPo lasts a long time. One that isn't cared for doesn't last at all. Please do not advise people to over fly their LiPo batteries.

Hey now.. I didnt mean to do any of that. I was implying that I set my buzzer to go off before my my esc, that has the stock Turnigy settings with what I would assume is proper for use with their batteries.. And I added that even though you might bring a pack to low by maybe leaving it plugged into your plane too long.. It can go slightly below 3 volts with out doing any damage. In the 4 years Ive been using lipo in trucks and planes.. The only one I killed was stuck in a tree over night.. Also never puffed a battery..

Ill add that I store all my batteries in Lipo pouches that I put in a strong ammo box for 40mm Machine guns lol.. Storage and charging safety are also important when using Lipos. Get some bags!!!