Homebrew Low-Voltage-Detector for my Helis

[Daniel Wee]

I've gone through several incarnations of (8211 based) LVD's for my several helis. The initial few were crude and detection voltage was set at 9.1V or so, which turned out to be too low to be really useful. Furthermore, it was large, heavy and wasn't as slick as I would like it to be. I finally decided to do it right and this is what I've come up with.

http://www.tsebi.com/reviews/RC/VIDEO_015.avi (300k)
http://www.tsebi.com/reviews/RC/VIDEO_013.avi (867k)

The video quality is pretty bad as it came off my handphone but you can see the bright blinking blue LED and hear the beeper going off on the Hornet X3D. I made a bunch of these and am pretty happy with it so far. I made several modifications to the circuit floating around, mainly to deal with the noise in the power supply and to add more hysteresis to the detector, as well as adding the blinker and beeper which needed an additional drive since it was drawing more than the 7ma that the 8211 was capable of.

Daniel

[Daniel Wee]

I forgot to add that the unit weighs about 6-7 grams depending on the wire length, thickness, and connector so it's pretty insignifcant in terms of additional weight.

Daniel

[Daniel Wee]

Here's what the previous design looked like - at 10 grams, with dual LED's but non-blinking and non-beeping piezo sounder. It was louder though. Unfortunately I had the threshold set at 9.1V to 9.2V based on conventional wisdom, which was a little too low for my liking. The new designs trigger at 9.7V to 9.8V thereabouts.

Daniel

[jerahteo]

This will be very practical for those who do not have a ESC with low batt protector.

I removed my so call low voltage sensor after I realised that my Align ESC actually come with the battery protection function. No longer required for my Trex, only contribute to extra weight.

The external sensor will be good for Heli like Honey Bee where the Electronic are 3 in 1 or 4 in 1 type.

Good job

[Super-Hornet]

Nicely done LVC circuit u have there. Keep it up.

For those who using Futaba 9CHP or most better quality TX, u can use timer also. I use timer to alarm me when I expected the the battery is going weak. Take example, I set timer to buss me when it is 9Minutes of total of flight time.

Super-Hornet

[Daniel Wee]

You can't really depend on the ESC's cutoff because by that time the battery is already in pretty bad shape. I selected the cutoff to give me early warning so that I don't discharge my battery over the "knee" in the discharge curve. This will prevent the battery from getting excessively hot and prevent bloating and extend battery life. I would not recommend flying until the ESC cutoff point.

Secondly, the ESC cutoff for Align is better than others in that it has a "soft cutoff" feature. Even so, this will affect your flight characteristics. Personally I don't like surprises so a higher cutoff warning actually allows me to know in advance that I am nearing the end of the battery power.

Daniel

[Daniel Wee]

I use a timer too but because I frequently land and inspect the heli or just to cool off the motor, I sometimes find that the timer is still not accurate enough. This allows me to know exactly when the battery is reaching a low point. Usually you can tell from the reduced power that it's time to quit, but I found that this "reduced power" point is after you go over the "knee" in the discharge curve and is actually prety bad for the battery. The lipo discharge characteristics is that the voltage drops off steeply after this point and may not give you enough time to recover properly. Furthermore, this results in overheated battery and shortened life.

Daniel

[Super-Hornet]

Daniel, plz don't get me wrong, your LVC is good. What I'm saying is what we normally been doing to walk around it.

Last time I fly my TRex with ETec 1700mAH 3S1P, at the end of the flight, the battery normally very hot and sometime get bloated but will strink back when cool down. Then tried using 5S1P on the same battery and it is better. Not as hot as before and seldom got bloated. Then I recently purchase ETec 1900mAH 4S1P, each time I flew finish the battery only warm.

As for the timing, I set my timing only start when throttle stick is in the position the motor start turning and pause when throttle stick in position where motor stop spinning. Like that, it is more accurate a bit.

As for Low Voltage Cut off for ESC, I not sure about Align ESC but I can say Castle Creation Auto Voltage sensing and LVC is much better than Quark. PHX-xx (Castle Creations product) allow u to set LVC to go hard cut off or soft cut off. When it reaches soft cut off, you can really see the heli is like slowly loosing power and u got time to land properly. For Quark, the LVC is somewhat like hard cut off where when battery weak, it goes hard pulsating. Difficult to land properly when u are in that state.

Super-Hornet

[MicroHeli-Nut]

Minority REport

Hmmmm...
Daniel, would there be a case where the battery is discharged intermittently to below 9.8V because of stressful manuvuers and the LVC goes to work? (On account that some of the poorer batteries are not able to hold their voltage that efficiently.)

You think I can get one of those LVCs from you?

[Daniel Wee]

Hi Super Hornet, no worries - no misunderstanding. I do personally use the timer too but I guess I can be rather perfectionist (or retentive) about these things, lol. I try not to discharge the battery anywhere near enough for the ESC to cutout for the very reason you mentioned, that the battery gets hot and bloated.

I've not really tested the Quark cutout characteristics but I hope I won't have to experience it in flight!

I am also thinking about 4S because the higher voltage results in lower current and exponentially lower heat dissipation since heat is (I * I * R). However, I'm not totally prepared to go 4S right now. Still have some hopes for 3S.

MicroHeli-Nut, yes there will be times when a full punch out on a moderately discharged battery may bring the voltage below 9.8 volts for a while but if this happens, ie. voltage sags badly, it is usually an indication that your battery may not be up to the current demands of the application. Nevertheless my LVD has some guard against intermittent voltage sags. The alarm doesn't really come on unless the sag last for more than about 500ms and if the voltage is near the threshold, it will beep and flash the LED in short beeps. If the voltage goes considerably below the threshold you will get long flashes of the LED accompanied by long beeps. This way you can know a bit more about the state of the battery.

I think I can make one extra and lend it to you to test if you like I just made five of these and have enough parts to just make one more on hand. Until I can make another trip to Sim Lim, that's all the extra parts I have. Let me know.

Daniel

[Daniel Wee]

Super-Hornet, just a quick question here. Am I to understand that the Futaba 9CHP has a feature that will automatically start/stop the timer based on the stick position? That would be so cool. The JR timer leaves something to be desired. I wish they would set the stop-watch/timer to be triggerable based on throttle stick position.

Daniel

[dareaper]

hi daniel, i dun suppose you would want to make these and sell them do u? if so, i would be interested in one.

[Daniel Wee]

Maybe for small numbers, I would not mind making it as a service. It's certainly not profitable since it takes me about 30 minutes to put one together nicely and test it.

Daniel

[Yeek]

Me too!

Hi Daniel,

I'm afraid this is gonna become a "me too" thread.

Me too! I want one if you have the time and parts.

Been searching for one that does not cost 2 bombs.

Thanks!

Yeek

[Daniel Wee]

Hehe, I had a feeling it might get this way. I think maybe I will make a batch of say 5 of them? Maybe about $20 each? Is that reasonable?

These will be for 3S and nominally will activate around 9.7V to 9.8V or so, giving you early warning. If you want red for the LED color you have to let me know. You will have to solder your own connectors as I will just put in the wires without connectors. Does this sound like something you guys could use?

Daniel