Stupid battery discharging testing questions

[auraslip]

1. "Set you lvc at 3.3/5/6v!" Ok. When you say that. Do you mean discharge until your pack hits that under load, or until the resting voltage is that low? If it's the former, it makes it impossible to test the absolute maximum capacity at real world loads. For example, I want to test from 4.2v down to 3v resting to get the maximum capacity my pack has. Well, under load it'll hit 3v with voltage sag, but once the load is gone it'll rest at 3.6v. Still mostly discharged I know, but I'm trying to find maximum capacity. The only option is to discharge at very load rates, but those are what you will see in real world applications. I'm trying to find max capacity so I know exactly how much headroom I have!

2. Specifically, when a battery sags under load and goes beneath the LVC does that damage the battery. Or is it going beneath the LVC while resting that damages the battery?

3. How important is compression while testing a pack? Bare cells will go up a few milivolts just squeezing them. I haven't tested this yet, but I'll have to try it out.

 

[999zip999]

Love to know. I guess amp. Load and distant and hills. Plus ture c-race of cell and how you wire it up. Now for a legend.

 

[wesnewell]

If lvc is set to 3.5V per cell, Resting voltage will usually be aboiut 3.6V after it cuts out. That's already at the dropoff cliff. If you then baby it for a ways, you can squeez a little mnore distance out of it. At 3.5V resting, you've used up 96% of the capaicity of rc lipo. At ~3.3V resting, you've used up 100% of the capacity. Taking rc lipo down to 3.0V on a regular basis will shorten it's liferspan by ~ 10 times from what I've heard. I couldn'tt say for sure, since I have my lvc set for 3.67V per cell and I'm on my 3rd year and over 8K miles with it. if you need be range. add another parallel group.
Rc lipo states. http://endless-sphere.com/forums/viewtopic.php?f=14&t=47294

 

[dogman dan]

Depending on the load, you may have to adjust your cutoff down even lower to get to 3v resting.

Does it harm your pack? I don't know. I do believe that under a reasonable load, say .5 to 1 c, you can certainly drive a pack below 3.5v, to actually stop someplace close to 3.5v resting. Doing that doesn't seem to have harmed my RC lipos. Doing it under a high load to 3v resting did.

Out on the road, this means when you are flirting with 3.5v under load, you may need to lessen the load to get sag less than 2v.

To discharge deeper though, I think it would be a bad idea to maintain a load that is closer to max continuous c rate once you pass 3.5v. It just seems to me that if you are down that low, hitting it with a higher c rate has to do some damage. At that point, you likely are feeling that pack get hot. Discharging that hot is always to be avoided unless you must. Warm sure, but hot, never.

But I see no reason you couldn't go to 3v resting at a trickle. That won't make the pack hot.

I see it this way, below 3.5v, that battery has a different, much lower c rate.

 

[auraslip]

Glad to know I don't have to feel stupid for asking this :/