Lva

[04zrx]

So I bought a Low Voltage Alarm (LVA) I pluge it in while bashing, what a nive feature. It alarms at 3.8v/ cell . Question: Isn't that a little high? I though 3.6 was where it was a safe stopping point? I assume this is for safety so there is a little "cushion" there so you don't harm your batteries??? What do you know??

thanks

[Charlie-III]

Sounds a bit high, I usually use 3.2 - 3.4VPC, but that's me.

Can you adjust the alarm point?

[04zrx]

Originally Posted by Charlie-III

Sounds a bit high, I usually use 3.2 - 3.4VPC, but that's me.

Can you adjust the alarm point?

no adjusting of alarm point but it does display the voltage so I could run it to a lower point, but how low can I safely go (per cell)?

[happymachinist]

I keep a handful of these around. Under $4 off eBay from Hong Kong. Loud as shit, good up to 8S, and adjustable. I set mine at 3.4 by the time I pull the pack it usually rebounds to 3.7 or so at rest.


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[Olle P]

How low you can go depends on how well the cells are matched in capacity.
No individual cell should go below 2.7V, but they drop at different interval and the controller only check the average.

3.0V is for me a good starting point. Older battery and more cells are both indicators that a higher threshold is required.

[Trubble]

I have my trail truck set for 3.5 vpc. If I check it when it dumps to the point where I can't crawl up onto stuff, my voltages are usually 3.6,3.5,3.6. The charger usually registers around 1,250-1,350ish mAh put back in, so I feel pretty confident I've used all I really needed to use out of my packs. Even at 3.8, I think you'll still get plenty out of yours.







.

[happymachinist]

Originally Posted by Olle P

How low you can go depends on how well the cells are matched in capacity.
No individual cell should go below 2.7V, but they drop at different interval and the controller only check the average.

3.0V is for me a good starting point. Older battery and more cells are both indicators that a higher threshold is required.

I disagree with this. I am no battery expert but I have never seen recommendations to discharge a lipo lower than 3.0 volts LET ALONE 2.7. 3.0 volts is the absolute minimum...so why not stop at a higher voltage?

By stopping at 3.4 volts or higher it can greatly increase the longevity and cycles of your pack.

The LVA I referenced above monitors each cell individually and alarms at the first cell that reaches my predesignated voltage level. That way I am not relying on the packs average cell voltage or worrying about an aging packs who's IR cell to cell might effect it's discharge rate cell to cell.

When my first cell hits 3.4 BEEP BEEP BEEP BEEP BEEP BEEP...it's time to stop.

3.0 volts is too low as a cut off IMO let alone 2.7


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[Ryan87zuk]

Happymachinist: I agree with your statement. The higher the voltage cut off the more cycle life you can expect. However if your combo pulls a higher amperage to operate, the cells will sag to a lower voltage in say a bind on a rock. When you let up on the trigger, the cells will recover to well above the preset cutoff. A guy I work with has a lithium-ion powered 1:1 drag car and the cells will sag to about 2.5vpc. After the run it will recover to pretty much full charge. He does this in a regular basis. You can find the car on YouTube it's called "white zombie" runs 10.20s

[04zrx]

my LVA is similar to the one pictured I plug it in and run till it beeps I can't adjust the point at wich it beeps. I'll stop when it beeps then I'll be safe and not harm my batteries.

[Arctic Fire]

Is there a way of programming the one shown in the picture above? I would like to get a few of those.

[Olle P]

Originally Posted by happymachinist

... I have never seen recommendations to discharge a lipo lower than 3.0 volts LET ALONE 2.7... so why not stop at a higher voltage?

Depends on how much of the battery capacity you want/need to use. The cell is "empty" at 2.7V, while some 5% remains at 3.0V.
Lower cutoff allows the use of a smaller and lighter battery, which can be useful!

It's by no means recommended to discharge down to 2.7V. My point is that differences between the actual capacity of individual cells in a battery pack is the main reason for not setting the cutoff extremely low, and hike it up further with more cells and use. (Assuming only the total pack voltage is monitored.)

Originally Posted by happymachinist

By stopping at 3.4 volts or higher it can greatly increase the longevity and cycles of your pack.

True, and if battery longevity is an issue you should also avoid charging it above 4.0V/cell. 4.0V/cell max charge gives up to three times as many cycles out of the battery as charging it to 4.2V/cell.
Running the battery in the span between 20% (lowest charge level) and 80% (maximum charge level) of its capacity is what provides the most cycles at a fair use of the capacity. Requires a battery with twice the nominal capacity of what you actually use though.

Originally Posted by happymachinist

The LVA I referenced above monitors each cell individually ...

Cool! That means one can use a tighter level (provided the LVA is properly calibrated) allowing the use of a smaller and lighter battery.

[happymachinist]

Originally Posted by Arctic Fire

Is there a way of programming the one shown in the picture above? I would like to get a few of those.

Yep, plug it into a battery and there is a button that cycles through what voltage it will cut out at. I have a buddy that on the last run of the day will set his at 3.8 so that when it goes off he's at storage voltage when the pack rebounds a bit. His charger doesn't have a storage feature.

Originally Posted by Olle P

Depends on how much of the battery capacity you want/need to use. The cell is "empty" at 2.7V, while some 5% remains at 3.0V.
Lower cutoff allows the use of a smaller and lighter battery, which can be useful!

It's by no means recommended to discharge down to 2.7V. My point is that differences between the actual capacity of individual cells in a battery pack is the main reason for not setting the cutoff extremely low, and hike it up further with more cells and use. (Assuming only the total pack voltage is monitored.)

True, and if battery longevity is an issue you should also avoid charging it above 4.0V/cell. 4.0V/cell max charge gives up to three times as many cycles out of the battery as charging it to 4.2V/cell.
Running the battery in the span between 20% (lowest charge level) and 80% (maximum charge level) of its capacity is what provides the most cycles at a fair use of the capacity. Requires a battery with twice the nominal capacity of what you actually use though.

Cool! That means one can use a tighter level (provided the LVA is properly calibrated) allowing the use of a smaller and lighter battery.

Sorry if my post came off a little confrontational...was not a good day.

I have always been a firm believer in the 80% rule...that's just me. Just like getting gas at 1/4 tank instead of when the light comes on.

I understand what you're saying. Cutout at 3.0 volts in theory should be ok but I have always had the understanding that your pack will puff and become potentially dangerous much below 3.0 volts...but like I said I'm no expert, that's why I error towards the side of caution.

I set my alarms at 3.4 (higher than some) in case I don't hear it right away and for pack longevity like you said. I also only charge to 4.17 volts. It's not much different than 4.2 but I have been told its a nice happy medium between run time and added cycles to the batteries life.




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