LVC circuit?

[Drunkskunk]

I've got a few old RC lipo, and a Li-ion Laptop battery as candidates for a headlight for my bike. The only problem is the voltage cutoff.

Rather than re-inventing the wheel, or reverse engineering a BMS, I figured I'd ask.
Anyone have a scematic for a LVC by it's self?

 

[Dee Jay]

Right here Drunkskunk. http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=3035&st=0&sk=t&sd=a&start=75

I was dreaming about making a cell bypass system. It seems I won't need it since A123 cells had been so reliable in celf-equalziation that I had been able to just use my 48v throttle low voltage indicator (yellow LED) to let me know when my 52 volt packs hit 42v = 2.8v/cell

J

 

[Drunkskunk]

Thanks man. I'm not sure I understand how this was being used. was it tripping a relay to bypass a cell if the cell was too low?

 

[Dee Jay]

Thanks man. I'm not sure I understand how this was being used. was it tripping a relay to bypass a cell if the cell was too low?

Sure thing!

The Cell Bypass System was my plan.

But this circuit was created as a simple 2 or 3 cell Lipo LVC LED indicator for an RC http://www.webx.dk/rc/lipoly/low-volt-alarm.htm This guy installed it on the side of his plane so he can see when he's hit LVC .

I thought you might be able change the resistor values and replace an LED with a mini relay to cut your light power at LVC.

J

 

[fechter]

I think Gary made a LVC only circuit at one point with optocoupler outputs.
I can't seem to find a copy of the schematic, but it's similar to this except the LED is the emitter in the optocoupler:

 

[silicium]

Schematic LVC for 4 cells A123:
View attachment BMS décharge schéma.pdf

It's identical for my full BMS 12..15 cells:
View attachment 2

View attachment BMS A123 x15V5complet.pdf

 

[GGoodrum]

Here's the schematic for the latest LVC board I did for my 16s5p a123 pack:

Here's what the completed board looks like:

Basically there are individual cell voltage detectors that trip an opto-coupler if any one cell gets too low. The opto outputs are then all ganged together in parallel, into one logical OR signal. This signal can then be used in many controllers to cut the throttle, via a brake line. For this version, I added the active cutoff circuit that Randomly posted in one of the threads, so when this signal is active, it cuts off the negative power lead that is routed through two 4110 FETs in parallel. As long as the cells are all above the cutoff, this draws very little current, so it is safe to leave it connected all the time. I think if I were going to leave it for a year, I might unplug it, but otherwise, it really isn't an issue.

-- Gary

 

[tostino]

Do you have a list of the parts you used and where to get them? I am interested in building something like that for my Konion pack.

What would have to be changed going from lifepo4 to LiMn?

 

[monster]

whats the LVC on a ping pack. what voltage shouldn't they go below?

 

[swbluto]

I'm subscribing to this.

 

[MitchJi]

Hi,

How about this?:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=9229&start=0

Best damn 6S lithium monitor on the planet for $15

Works for both Lipo and Lifepo4
$15
Reads 6S lipo via 0.100 spacing (perfect for JST-XH balancer plugs)
5mV accuracy - most balancers quit at 20mV
Shows you 8 things in sequence:

Total Pack Voltage
Largest Imbalance
Cell voltages for 1 to 6 (or however many you hook up)

The monitor beeps if you go under 3.0V or over 4.22V
EDIT: I forgot, you can set the LVC to any desired voltage.

Absolutely dead on voltage.
AWESOME product. Works perfectly every time.
I have been running 4 of them for several months on my big Lipo packs and they have saved my ass!

If you plug these into your lipo packs then you will hear a loud BEEP BEEP BEEP any time one of your cells drops below LVC. I think you will be surprised about what happens under load :wink:

The beeper output can drive an optocoupler that can be used to TAP TAP TAP your ebrake when you hit LVC
Does not cut you off, just gives you a warning.