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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 09-13-2013, 03:58 PM   #1
Pat Masac
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Default Complete Low Voltage Cut Off- Do They Make One?

Okay,

I've got a little project going that I need some of you battery guys to help me with. I'm looking for a low voltage cutoff for a 6s lipo that has no curve or warning but just cuts that battery at a safe voltage not to ruin it. Let me explain why.

I've got a lot of extra FPV equipment that I am not using at the moment and my Dad has 400 acres in TN. What I'd like to do is set up a wireless camera that can be moved from area to area and monitored live (and recorded) back at the house for game (mainly deer). This is a very simple project except for one problem: the battery will eventually discharge below a safe level and ruin an expensive pack. I understand why escs have a curve as I've been flying for some time however this project will never leave the ground! Someone has to make one that plugs into the balance plug or somewhere! All I want is complete cutoff when each cell reaches its respective lowest voltage so I can retrieve the battery, re-charge it and move it wherever. I've had people suggest low voltage alarms but I don't think they understand what I'm trying to do. The battery could be a mile away sending me a video signal so this does me no good. Also, I'd like to just leave it over night or however long and not worry about ruining an expensive battery.

Thanks for the help.
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Old 09-13-2013, 04:49 PM   #2
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You could use a brushed ESC with a servo tester to relace the receiver:
http://www.hobbyking.com/hobbyking/s...USHED_ESC.html
http://www.hobbyking.com/hobbyking/s...vo_Tester.html

The only issue with this set up is that the ESC has a fixed low voltage cut out at 3V per cell, which is lower than you would really want to go. You might be able to find a brushed ESC somewhere that has programmable cut-off voltage.

Or maybe someone clever could design a simple circuit?

EDIT.. Oops.. I see you intend to use a 6s battery, that would be a problem for the ESC I listed because it's 3s max. I dont think you will find a 6s capable brushed ESC.
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Old 09-13-2013, 07:51 PM   #3
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How about one of the stand-alone LVC units used to "upgrade" from NiCd to LiPo without replacing the ESC?

http://www.offshoreelectrics.com/pro...hld-32&cat=136

Dimension Engineering will make one for any current demand you want... if you are willing to pay for it.

or check their regulators...

Or there are solar power system regulators with low voltage cut-off for the load if the battery gets too low. (some are settable as to cut-off voltage)

*********************

May not be any currently made brushed ESCs that can take 6S... Astroflite used to make some that could handle the voltage and more.
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Old 09-14-2013, 04:30 AM   #4
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Default

Thanks for the replies. I hadn't thought of either of them. I'll check and keep you posted on how it goes.

Thanks again.
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Old 09-14-2013, 05:25 AM   #5
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Default

Originally Posted by Pat Masac View Post
Okay,

I've got a little project going that I need some of you battery guys to help me with. I'm looking for a low voltage cutoff for a 6s lipo that has no curve or warning but just cuts that battery at a safe voltage not to ruin it. Let me explain why.

Have you considered a solar charger for your 6S LiPo? A simple adjustable linear regulator circuit would do it.

If not, another option would be a little microcontroller with six analog inputs programmed to monitor each cell, and shut off a relay when any cell drops below a safe minimum. Microchip makes a whole bunch of them. Their Pic18F458 is one I've used many times, and in fact am working on a project with one of them right now.

The microcontroller circuitry would be fairly simple. Unfortunately, the software to run it would not. (I did this awhile back for a different project.)

If you just want to monitor the whole battery voltage as a unit, again, a microcontroller would do the job. Just use one analog input and a relay. The software would be much simpler, like one page. Microcontrollers such as the Pic18F13K50 would do it, along with a 5 volt regulator, a few resistors and capacitors, and a relay. The whole thing could be built on a Radio Shack 276-150 circuit board. The PicChip has a resolution of 1028 steps, so that would be a 30 millivolt resolution.

Just to show how much power these Microcontrollers have, that 20 pin 18F13K50 has a manual that covers 410 Pages!

DennyV
Retired and the days are just too short, busier than ever!
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