# Low voltage cutoff for LIPO



## perego (Feb 1, 2017)

I'm about to do my first battery conversion and plan to use a LIPO. For my RC planes the LVC is part of the speed controller. Looking around I find low voltage warning devices but no stand alone LVCs.
Any suggestions?
Thanks, Bob


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## dbodnar (Jan 2, 2008)

Something like this, Bob

http://www.ebay.com/itm/NEW-RC-Lipo...034687?hash=item35fc97353f:g:~V8AAOSwYIhWkUjX

dave


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## Michael Glavin (Jan 2, 2009)

Bob,

Dave linked to a simple method to monitor voltage and provide an audible alarm. These devices can bused Lithium Ion batteries too.

If your LiPo's have balance charge pigtails, I'd suggest a PCM/PCM board much like what is provided by most Li-Ion battery pack assemblers./resellers. This would provide an actual voltage cut-out verses an alarm and monitor individual cells. BUT like with the Li-Ions relying on these devises to protect your battery is haphazard and is employed long after a safe voltage cut-off number should have been noted!

Michael


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## perego (Feb 1, 2017)

Will search for PCM. But, as you note it has to really work. When I use a new ESC in a plane I always bench test running a battery down to test my setting - usually opt for 3.2v/cell.


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## toddalin (Jan 4, 2008)

If you want the voltage to cut off at a certain minimum, you could use a relay that is held closed until the voltage reaches a certain miniumum and run everything through that.

Run the relay coil through a series resistor and calibrate the resistor where the relay opens at/near your desired miniumum voltage.

I do this with my Sierra sound systems using supercaps so that the supercaps are disconnected at a minimum voltage and don't fully discharge.


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## perego (Feb 1, 2017)

Thanks, that is an easy solution if I can't find an off the shelf device.
Keep looking at PCMs but they only mention overdraw and overcharge protection. All the RC plane ones I find wire between the receiver and speed controller - so that when the motor cuts out the servos for control surfaces still work.
Must be missing something because I can't imagine folks running trains off LIPOs without LVC.


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## Michael Glavin (Jan 2, 2009)

I think you'll find Li-Po's aren't popular herein...

I run Li-Po's without LVC (low voltage cutout), I simply pay attention. I use my ESV (expanded scale volt meter with load) and or have tried voltage monitors such as Dave alluded to above. 

I'm heavily vested in Li-Po's for trains, drones and planes. I like to tinker and evaluate different ideas and or offerings. I have a few PCM boards in play, the visual/audible alarm gadgets and have equipped stuff with an LED or two that lights up when the voltage dips to my preselected value. BUT for the most part I run naked.

Michael


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## perego (Feb 1, 2017)

I could be over worrying this - a warning light would probably suffice. But something as simple as Todallin's solution might as well be incorporated.
I did find a device at mcmelectronics but it looks like overkill. Will cut out at 9 to 10v but is over 3" square and requires momemtary voltage on the output to activate its latching relay. I suspect the current capacity is way more than I need.
Will make my own while continuing to search.
No worry about anyone getting hurt from an exploding LIPO. At 71 if I "run naked" there won't be anyone nearby.


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## Michael Glavin (Jan 2, 2009)

Amazon has several doodads that are worth trying, I purchased a couple different low voltage cut-off, detection, monitoring multi-function relays or whatever they call em. In theory they should work as Todd suggested, I haven't gone there yet though.

I'll see if I can't find links for them after lunch.

Michael


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## Michael Glavin (Jan 2, 2009)

This is what I bought to play with, I haven’t experimented with any of these gadgets yet!
https://www.amazon.com/gp/product/B01GJM04GC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B018TW0KN2/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B013PKYILS/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1
Michael


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## toddalin (Jan 4, 2008)

This shows how I use the resistor with the supercaps so that the relay initially sees full voltage to get it to engage. It is a similar situation to what you want to do in that with the resistor you need a dpdt relay and small cap on the relay to come up to voltage and hold it for a moment to get it to fire all the way.

Otherwise, the relay will usually just go into oscillation because the relay looses all power as soon as the armature lifts from the seat..., so the armature falls back to the seat..., where it receives power..., and lifts from the seat, etc., etc., etc. Use a dpdt relay and use the other set of contacts for the shut off. Of course your component values will vary with the relay used, but you get the idea.


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## Dave Ottney (Jan 2, 2008)

You could also try this product
https://www.dimensionengineering.com/products/liposhield

I've used it in one of planes that has a non-lipo aware ESC so I don't over discharge a pack. Its a good company.
Dave


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## Greg Elmassian (Jan 3, 2008)

Nice gadget, although you need a "signal" from the ESC.

Can you just hook this to one of the motor outputs on the ESC?

A little pricey and 4 week delivery.

Greg


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## perego (Feb 1, 2017)

I did as Toddalin suggested and it is an easy solution. Haven't put a cap in yet so with both the cut out and latch resistors hooked up to either side of the DPDT relay it does oscillate. Didn't have specs for the relay I bought so just took some fiddling to discover the minimum latch and hold voltages and then calculating the resistance worked out first try.
Thanks for the help.
Bob


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## toddalin (Jan 4, 2008)

My pleasure. Glad it worked out for you.

Actually, thanks for posting this. I've been wrestling with a relay circuit, with only some success, and this gives me a whole 'nother perspective to accomplish the goal.

I want to use a momentary pulse of 12 volts to latch, then unlatch, then latch, ... a common dpdt relay. While this is a cinch using two switches, trying to do it with just one switch greatly complicates the matter and I've not been able to get it to work consistantly.

Looking this over, I thought of yet another way to "skin the cat."

Thanks


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## perego (Feb 1, 2017)

Well, I wound up using a momentary contact switch to fire the relay because I figured a cap wouldn't have time to charge. No big deal - when I connect the battery I just press the "start" button.
I powered the "hold" part of the circuit off the relay contacts so if I accidentally leave the battery hooked up, when it automatically disconnects I don't have the small coil draw from the "hold" voltage.
Interestingly it is more accurate than an LVC buzzer I tried. My device shuts down at 9.6 volts and the buzzer goes off at 10 volts.
Parts: relay, 2 resistors(to get the required voltage drop), momentary contact switch, and a fuse and fuse holder.
For anyone like me with a minimal electronics background, to size the required resistors, I found the relay disconnect voltage by using a DC transformer with one meter watching the voltage and another watching the contacts. I then slowly lowered the voltage until the relay disconnected hence giving me the drop out voltage to calculate the resistance needed. 
Will post a pic of the circuit(overstatement to even call this a circuit) if anyone is interested.
Bob


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## toddalin (Jan 4, 2008)

Did you see this?

I was about to give up when you posted, the light bulb came on, and I came up with another approach based on what we do here.

http://largescalecentral.com/forums...atched-contact-amp-back-a/view/post_id/337126


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## Avel (May 4, 2017)

toddalin, perego, good ideas.
Now my opinion on the LVC. 10v cutoff for a 3 cell lipo isn't bad. That's 3.33v per cell. In my RC vehicles I have my lipo cutoff set at 3.5 per cell. Everything I've read says that this will prolong the battery life, but by then new/better batteries will be out. So maybe there really isn't any point to lowering the LVC point.
Some people run them down to 3 volts per cell, and from what I've been reading, these trains don't require as much current as Radio Controlled airplanes, helicopters, quadcopters, etc. My point being that the batteries aren't abused to start with. 
Sorry for rambling, need to break that habit.


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## Batsco (Mar 30, 2011)

Bit late maybe but;
These are what I use in my locos audible alarm when battery cells reach a pre set level. Monitors the cells and when one reaches the level the alarm sounds this reduces the chance of discharging one cell to low.
Similar to what Dave suggested but just another source.

https://hobbyking.com/en_us/hobbykingtm-lipo-voltage-checker-2s-8s.html?___store=en_us
https://hobbyking.com/en_us/hobbykingtm-lipoly-low-voltage-alarm-2s-6s.html?___store=en_us

For my motor control I use Pololu simple controllers (18V7 or 18V15) that have a programmable battery level function.


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## Greg Elmassian (Jan 3, 2008)

yeah, good price and adjustable.... thanks!

Greg


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## Del Tapparo (Jan 4, 2008)

FYI - The RailBoss 4 Plus controller has had built-in low battery warning and cutoff for Li-Ion and Li-Po's for years now. Works great, no additional hardware needed. www.GScaleGraphics.net


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