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Custom Low Battery Alarm

Old 03-07-2008, 11:42 AM
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BigTb17
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Default Custom Low Battery Alarm

Hi everyone.

I am currently making a low battery alarm for my planes. I looked at several different hobby shops in the area and none had anything like I wanted.

The idea is that it will turn on an audible buzzer when the voltage gets below approximately 9.1-9.3V (3S LiPo). This will hopefully allow enough time to land under power rather than waiting until the ESC cuts the motor out and having to dead stick it in possibly a bad situation.

I got the last few parts I need in the mail yesterday and am hoping to complete it and do some testing tonight or tomorrow. So far it looks like it will work well, I just need to test the zener diodes I got in the mail to check the exact voltage at which they will turn on the alarm to make sure it is correct.

The system weighs about as much as a micro servo or maybe a little more (that's a guess) and should draw about 30-50 mA of current. I could probably make it lighter if I took the time, but I didn't care about making it too perfect until I know if it works. I made it using about $15 dollars or so worth of parts from Radio Shack and some zener diodes I ordered on-line. The zener diodes brought the total price above $20 because of shipping (the diodes themselves were like $0.30). If it works well I am going to build one for each of my speed controls and one for my flying buddy. I ordered enough zeners to build 5 so I wouldn't have to pay shipping again if it works.

I will post up how well it works, and if anybody is interested I will post up how I built it.
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Old 03-07-2008, 04:07 PM
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Default RE: Custom Low Battery Alarm

Yes, I'm interested in your progress and online plans as well.

Good luck and be well,
Steve S
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Old 03-07-2008, 04:14 PM
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exeter_acres
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Default RE: Custom Low Battery Alarm

You mean one of these?

http://www.heliproz.com/prodinfo.asp?number=335444
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Old 03-07-2008, 10:33 PM
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BigTb17
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Default RE: Custom Low Battery Alarm

Wow, that is almost exactly what I built. I suppose it would be a little bit more expensive to order that, but it would be a lot easier (though less fun, because I like soldering and building things). I didn't really look on-line very much. I just looked at the local hobby shops and then went to Radio Shack to buy the stuff to make one. That really looks surprizingly like what I made. I even have the buzzer on leads like that, and two more leads for the battery. I have never seen that before, but anybody who saw both together would swear I coppied it. Interesting find, thanks for the link.

I did try mine out today and it comes on at almost exactly 9.5V. It is a little higher than I hoped because of the voltage drop across the transister, but it works very well and I am satisfied.

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Old 03-09-2008, 02:34 PM
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DaveFlynn
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Default RE: Custom Low Battery Alarm

Me too. I have PCBs and chips. Normally I use it with an LED, but it works with a buzzer too.
[link=http://www.traincircuits.com/PlaneCircuits/LiPoWatcher.sch.pdf]LiPo Watcher[/link]

I would recommend you set the voltage to the nominal voltage (i.e. 11.1 for a 3 cell).
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