Quark 125 - cutoff settings....
 

Hey everyone -

On a Quark 125, there is a battery selection, and a LiPo cutoff selection, which is next in line when programming.

Unless you choose Manual for the battery selection, there is no need to choose a LiPo cutoff voltage (manual says this).

If I choose LiPo Normal for my battery selection, is it using 2.7v for the cutoff by default, since it isn't necessary to set it? Same question for LiPo High, does it default to 2.7v cutoff? Is the 2.7v a safe level to cutoff at, to avoid damange to the packs?

If I set the battery selection to Manual, and set the cutoff to 2.7v (or whatever is a safe level), is it using a profile similar to LiPo Normal, or LiPo High?

Darn manuals..... Darn over-thinking......

10k

i'd set it to 3.0volt per cell.

not lower.

dont have a quark tough, so cant give you any quark info.

You need to program battery selection twice. Do manual the first time and select your voltage. This setting will now stay untill you change it again no matter what battery you choose.(I'm not sure what mode it runs in at this point, im thinking whatever setting was set last)

Then start programming all over and sellect your battery choice.

I switched back to 2.7, but I balance my packs often. (and i take a few risks :) )

I was just told by Jhautz that in pm, so thats the right thing

BLipoRacer - when you say you balance your packs often, you mean while charging correct?

Aren't you supposed to balance them all the time during charging, or is it not necessary?

Sounds good with setting the voltage cutoff, I will give it a go.

Yes, when you set the cut-off voltage, you do that first, then go into programing again and select Li-Po 'normal' or 'high'.

Also, you should use at least 2.8v cut-off for lipo's minimum. I have A123's, I use 2.2 volts cut-off, A123's dump very quickly, hold there voltage right up to the last few seconds.

When you say "at least 2.8v" for cutoff, do you mean 2.8v is the highest it should be set at, and i can set it to say 2.5v safely, or that is the lowest it should be set, meaning if I set it at 3.0v it'd be better?

If I set it wrong, meaning higher than it should be, the pack will just not give me total runtime, but if I go too low, then I can damage the cells (right?)......

Yes, preferably 2.8v or above. usually 3.0v is best, if you have good batteries then 3.0 no prob, but some batts might just 'droop' down past 3.0v/cell before they are supposed to dump.

And yes, the higher the cut-off the longer they will last, exponentially so.

Actually, if possible, I set the LVC voltage so that the pack voltage drifts back up to ~3.6v/cell after sitting for about 20 minutes.

What exactly do you mean by that?

When a pack reaches 3v/cell (or whatever value you set) under load, the ESC cuts off. Once you disconnect the pack, the voltage will come back up. Some of that is because the pack is no longer under load, some is just the cells drifting back up. So, after 20 minutes or so, the pack will actually have a higher voltage.

That said, the LVC setting really depends on the load. For high pulse loads (like in cars), you can get away with a slightly lower LVC setting because the average current is much less. Plus, you wouldn't want the LVC to kick in falsely as it dips for the few ms the load pulse lasts. For a constant load, you'd set a higher cutoff because of the constant high drain. You also have to take battery quality into consideration because the good cells will drop less under load.

So, instead of trying to consider all this, I just start with a 3v/cell cutoff. If the pack voltage (after a 20 min rest) is over 3.7v/cell, I drop it a little to 2.9v. Or, if the pack voltage is under 3.5v/cell, I increase the LVC until the pack is right around 3.5-3.6v/cell after rest.

Oh IC. How much more runtime can you get out of it though really? I think just throwing it on the charger again would be a better choice, IMO.

Aaah, the day will come when we have dismal voltage drop, and super flat discharge curve for a more enjoyable R/C experience.

That is entirely possible now, and has been for the last 50 years or more; just get a long extension cord! ;)

And, you probably meant "minimal", not "dismal", right? Dismal means "bad". I don't think we want a bad voltage drop. :)

I either balance my packs while charging, or right after. (if after, I repeak them again.)(I dont do this EVERY time, but MOST of the time.)

2.7 is safe for individual cells, but in multi cell packs, your cells dont drain the same, so 1 cell is always lower then the rest. (especially if you dont balance out your cells, that 1 cell will get a LOT lower over time)(and then ignite)
So the better you keep your cells in check, the harder you can be on them.

The Quark has a 'soft' cutoff, it will start back up when the pack regains some juice, and I noticed that at 3.0 cutoff, the battery comes back up to over 3.2, (and still has a bit of pep to it) so I dropped down to 2.7 and now dont cutoff untill after I 'dump'

If I do catch on fire, I would fully expect there to be more spectators at my next race. :005:

I believe that the voltage cutoff table that the Quark uses really shows the Quark's age. A 3v cutoff was appropriate with the older 10C lipo packs, but the newer packs that hold their voltage better really need a cutoff of 3.2v or higher to protect the pack.

It really is a shame that after all of this time, S&T is working on a new controller and it's just another 1/10 controller.

I set the LVC to 3.0, but I also try to follow the airplane guys over at RCgroups and never discharge more than 80% of the capacity.

I'm cheap and want every last cycle from my lipos ;).

You're not cheap... you're just caring for your stuff.

And if you REALLY want your batts to last long, you discharge them as little as possible, and top them back up again. They would last exponentially longer, simply using half of your capacity would grant you much longer lasting batts than if you used them up.

I never wait for the lvc to kick in. I set my watch when I start to run on the track. For the 8Ah pack, I go for 30 minutes and on the 4800 packs, I go for 20 minutes. This usually results in less than 90% discharge. I also change my battery when I take a break and top it off.

I too like to take care of my batteries, but by the time they no longer have the capacity they had when new, there will most likely have better cells out. Call it forced upgrade. :) If you get the "good cells", I can see wanting to take better care of them. In my book, as long as they are discharged under their max rating (I usually shoot for a constant C rating about 25% higher than I plan to run), don't get over 120*F, and don't puff, I'm happy.

Wow, guess I'm hard on my packs. I use a 2.7v cuttoff, run my packs up to around 170*f, repeak them after balancing, and ding them or bow them a bit from makeshift straps. (Flew them into the ground at 80mph)

I have never lost a cell. I have every cell I ever bought and they all work. They just get replaced with better cells. At the rate of improvement, most of my retired cells probably have half of thier cycles left. This is Airplane, Helicopter, and 1/10 scale-1/8 scale off road.

I am very carefull to charge, and store my packs, and I keep tabs on packs and their performance. I keep tabs on balancing. I read stories to them about fast cars, and tuck them in at night. But once they are plugged in, I work them hard, till they dump. (my 1/10 scale doesnt even have a v. cut-off)

Havn't heard about the 3.2v cutoff for higher draw packs yet, I'm having good luck at 2.7v so far. (and Im not going for longevity at this point)