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Old Jul 09, 2006, 08:50 AM
Valid8r
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Boston and Belgium
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Low Voltage Cut-off for lipo's

I did a search, but did not find what I was looking for (though some threads seem close). I've overdischarged 3 different Lipo's by leaving the battery connected to my ESC and reciever overnight. There must be a simple, in-line device that can be plugged between the battery and the ESC that will effectively cut the battery to ESC to protect the battery from over discharge.

I know I would pay for one if one were available. Anything like that around?

Thanks,
Jon
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Old Jul 09, 2006, 09:17 AM
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on a boat on the river cam
Joined Jan 2005
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You don't want to do that even at the cost of a battery pack. What if the pack falls below the cut off and the reciever is shut down when you are flying?
You should make it part of your afterflight checks (you do do afterflight checks don't you?) to make sure your battery is disconected, along with all radio conections are OK, all control surfaces are secure. One of the advantages of a slimer is that you have to clean them after every flight, so you check it all out as you clean it. with an electric aircraft the temptation is to fly, switch the tranny off and forget about checking the integrity of the aircraft post flight. Please do before and after flight checks. you may just spot something that could crash your plane.
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Old Jul 09, 2006, 11:43 AM
Valid8r
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Boston and Belgium
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Very true Punkie - and for the most part I do. This particular situation ocurred when I was doing some bench testing work and dinner interrupted my work. You are correct of course about the low voltage cutoff, but I guess what I'm thinking of is something that would cut out at a lower voltage than the ESC's cutoff, or even just something with an audible alarm...

Jon
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Old Jul 09, 2006, 12:06 PM
Pompano Hill Flyers
Miami Mike's Avatar
Miami Lakes, Florida, USA
Joined Mar 2003
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Quote:
Originally Posted by Valid8r
I guess what I'm thinking of is something that would cut out at a lower voltage than the ESC's cutoff...
That might have some value in an electric-powered plane that doesn't glide very well, but I sure wouldn't put one in a sailplane!
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Old Jul 09, 2006, 08:46 PM
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Lindenwold, NJ, USA
Joined Dec 2000
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Quote:
Originally Posted by Punkie
You don't want to do that even at the cost of a battery pack. What if the pack falls below the cut off and the reciever is shut down when you are flying?
You should make it part of your afterflight checks (you do do afterflight checks don't you?) to make sure your battery is disconected, along with all radio conections are OK, all control surfaces are secure. One of the advantages of a slimer is that you have to clean them after every flight, so you check it all out as you clean it. with an electric aircraft the temptation is to fly, switch the tranny off and forget about checking the integrity of the aircraft post flight. Please do before and after flight checks. you may just spot something that could crash your plane.
I've done test of this and the time between the cutoff voltage and the overdicharge voltage is only two or three minutes. What's the difference? you cut it off before it damages the pack and the plane is without power - or you cut it off after it damages the pack and the plane is without power.
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Old Jul 09, 2006, 08:48 PM
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Lindenwold, NJ, USA
Joined Dec 2000
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Quote:
Originally Posted by Punkie
You don't want to do that even at the cost of a battery pack. What if the pack falls below the cut off and the reciever is shut down when you are flying?
You should make it part of your afterflight checks (you do do afterflight checks don't you?) to make sure your battery is disconected, along with all radio conections are OK, all control surfaces are secure. One of the advantages of a slimer is that you have to clean them after every flight, so you check it all out as you clean it. with an electric aircraft the temptation is to fly, switch the tranny off and forget about checking the integrity of the aircraft post flight. Please do before and after flight checks. you may just spot something that could crash your plane.
I've done test of this and the time between the cutoff voltage and the overdischarge voltage is only two or three minutes. What's the difference? you cut it off before it damages the pack and the plane is without power - or you don't cut it off, it damages the pack and the plane is without power.
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Old Jul 09, 2006, 10:30 PM
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Install a lost model alarm on the Rx. When the Tx is turned off, you will end up with a earful to help warn you it's time to remove the flight battery. If you are into DiY projects, then check out the LOMA project at rc-cam.com
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Old Jul 10, 2006, 07:13 AM
Registerd Beaver
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Australia, WA, Warwick
Joined Jul 2003
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My advice to you my friend - make sure your insurance policy is current!

To be honest, forgetting is a poor excuse. your wife/partner will not buy that if you burn the house down.
I also have done this...once...& got away with it.
Frightened the bejeezus outa me. (I am in the electrical game & know better).
Safety is a concept & as such is not a job for machines but for their operators.
But to answer your question - is there a suicide circuit for this? (suicide meaning the unit self-terminates the power to itself at a given preset level) Yes but not suitable to our hobby, they weigh too much. (zener diode & relay)
It could be designed by an Electronic tech but has little commercial market to be truly viable.

Phil
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Old Jul 10, 2006, 02:38 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
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You could also do it with something that plugs into the RX - no signal for 5 minutes = shut off main power. It'd probably be easier to use a microcontroller that has a deep sleep mode with nanoamps of current draw than something that physically disconnects. If you haven't seen an R/C signal for 5 minutes, chances are you're not in the air anymore.
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Old Jul 11, 2006, 11:18 AM
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Ontario, Canada
Joined Nov 2002
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If it is the receiver/servo drain that is the issue (not the ESC itself), then you could easily adapt a cellphone li-ion LVC circuit between the receiver and ESC.

All Li-Ion cellphone (and Laptop) packs come with tiny "smart" SMD boards that offer current control and LVC cutoff.

The LVC cuttoff is usually around 2.5V per cell, so a 2-cell board would at least protect you from disastrous discharge. (2.5V per cell under a tiny load might not hurt the cells...)


A cut-off device between the battery and ESC is probably not practical due to the weigth and resistive losses of a high-power switch.
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Old Jul 13, 2006, 10:57 PM
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Fenton,MO USA
Joined Aug 2005
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I use these little guy's for backup of my esc in my T-38 jet . Light turns on when you hit lvc. I use them in cox-micro warbird with standard esc that has no cut off.

They are at bottom of this link and the next page. For 2S,3S and 4S lipos.
Work for me. Put them on a battery and monitored cutoff. Was right on the money.


http://www.galaxymodels.co.uk/new/re...es%2E&offset=0

and this page:

http://www.galaxymodels.co.uk/new/re...s%2E&offset=10

About $5.50 for the 2S. Good prices.
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Old Jul 13, 2006, 11:10 PM
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Fenton,MO USA
Joined Aug 2005
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Another option is a do it yourself audible alarm from link on RCGroups here:


http://www.rcgroups.com/forums/showthread.php?t=221018

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