do low volt cut offs work with todays high powered batteries

[ozzie-crawl]

just thought i would start a thread on what people thought about this.
i have noticed a lot of guys especially new guys saying they run there boat till lvc cuts in,when they recharge the battery takes say 5200mah but its a 5000 mah.
i see a few thing in this
A,there charger may not be that accurate.
B, a lot of the batteries now have larger capacity than they proclaim (good idea)
C, i think this is the main problem, not just my opinion others say the same
the batteries now can hold there voltage much better than before, a system may be pulling say an average of 60-70 amps but the batteries know can take double that constantly, so under load the voltage does not drop very much at all
this does not allow the lvc to kick in even tho the batteries have used most of there capacity.
maybe cut off voltage needs to be higher or esc,s need to be able to shut down after a certain amount of capacity has been used.
any thoughts ?

[tiqueman]

I got nuthin... but heres what I do have. If I run 3S2P using 2-3s 5000mah packs and run til the LVC kicks in, I put about 3500 to 4000 mah back into the packs... BUT, if I run in the same boat 3S2P using 2-2650mah packs, I put 2600 to 2800 mah back in them.... Why?

[ozzie-crawl]

what c rating are the packs, and what esc,s
this is some thing i wonder if its different with esc,s maybe the cheaper ones the lvc isnt as good, or if the voltage needs to drop for a certain amount of time before it kicks in.
i personally dont run to lvc, i time my runs
but a couple weeks ago i was testing some setups on my tunnel and it doesnt draw a lot of amps so ran it till lvc and puffed to packs, it was a second run so not from a full pack to lvc and only around 2 minute run time
esc/motor were only 100f
it was still going strong till lvc kicked in

[tiqueman]

what c rating are the packs, and what esc,s
this is some thing i wonder if its different with esc,s maybe the cheaper ones the lvc isnt as good, or if the voltage needs to drop for a certain amount of time before it kicks in.
i personally dont run to lvc, i time my runs
but a couple weeks ago i was testing some setups on my tunnel and it doesnt draw a lot of amps so ran it till lvc and puffed to packs, it was a second run so not from a full pack to lvc and only around 2 minute run time
esc/motor were only 100f
it was still going strong till lvc kicked in

All packs are 30C and the ESC I think is a re-branded (no name) Turnigy, SeaKing etc, Id guess 60A. It came in a RTR china set up I got w/ a 2045 36-50ish motor. Ive been running it in my Black Jack since I BBQ'd the ProBoat ESC and I love the set up. On a hard run, the batts wil come in about 115F, but usually just over 100F. I normally do not run to the LVC either, I had just been dong a lot of testing the past couple weeks w/ all the new hardware on the BJ26 and LVC'd it 3 out of 5 runs.

[ozzie-crawl]

well its got me beat, only thing i can think of is the 2650s are holding there volts under load better than the 5000s
would be interesting to know the run times on both sets

[NativePaul]

All of the above.

(A) It's not strictly charger inacuracy but chargers have allways and will allways show a higher capacity than the batteries hold, I remember when i borrowed a friends graupner charger with LCD readouts back in the day that it put about 2400mAh into my 1700SCRC nicads, 400mAh of which was BS on discharge mode they produced 2000Mah, the charger just knows what it puts in and doesn't take into accout the efficiency of turning that electrical energy into chemical energy, although the real figure and charger figures are closer now with LiPo than they where with subCs as there is much less energy lost as heat.

(B) Lots of cells do have a higher capacity than on the label, and there is 2 reasons for this (1) batteries are a global market and there are different laws around the world about how you rate capacity, for instace the 1700SCRCs were sold as 1700s in the UK because you were garenteed to get at least 1700 out of every cell, in germany they were 1900s because that was the average capacity and I believe in some markets they were sold as 2000s because some good cells were, in this day and age where a high proportion of sales are internet sales which may be cross border, I don't think you can do that any more and you would be wise to label all your cells to the lowest cell for the bigest market availability.
(2) There have been cases of companys purposely using the next size up cell from there manufacturer and selling it as a smaller cell to artificialy boost there "C" rating, buy our amazing new 50C hypertechnology 4000mAh pack, but just ignore the fact that its the size and weight of a 5000mAh pack.
(3) I know I said 2 but Although I havent seen it yet, I suspect that there may be a third. Now that is harder shipping LiPo packs above 5400Mah by air I wonder if any of those companys selling 5500 and 5600mAh packs now will be selling 5400mAh packs soon instead.

(C) For sure this is true, the first generation claimed 6C/actually 4C I needed a cutoff of 2.7V, when claimed 10C cells came out I used 2.8V, when real 10C cells came out I needed to up that to 3.0V, 15C I still used 3.0V, 20C I used 3.2v, and now with 30-40C I use 3.4V, I bet if I tried running a 40C pack to the 2.7V cutoff I started with it would get stinking hot and puff the pack on the first run.

[ozzie-crawl]

some good stuff there paul, with pack sizes as you say i had a set of 30c 5000 flight max batts but they were small than my 30c 5000 turnigy and weighed around 30-40 grams less
but you could certainly see the difference of the larger cells on how much more punch they have
and yes it will be interesting to see what happens with battery sizes and the new laws
i suspect as well that some packs will be relabeled.
after think about what i wrote and what you said about lvc needing to be higher with high C rated batteries, i looked at my esc,s cut off voltage that i puffed 2 packs on,as i said i usually never hit lvc but was doing some testing and ran longer than i normally would,turns out my esc lvc is 3.0 volts per cell

[tiqueman]

well its got me beat, only thing i can think of is the 2650s are holding there volts under load better than the 5000s
would be interesting to know the run times on both sets

I will have to time it the next time I run. All I can sa now is the 2650s ran for a little bit, the 5000s ran a long time, but cooler on the batts, a little warmer on the motor and esc, under 125 on any component..

[Flying Scotsman]

Also how accurate are the low voltage cutoff ESC or stand alone devices and remember that most of these devices are looking at the total voltage for all cells and that is why I use as a minimum 3.2v per cell and I would prefer to not drain the battery to that cutoff voltage point under high amperage loads. Unfortunately some ESC designs do not allow programmable cutoff values

Douggie

[electric]

I have one of these on order. It shows you the voltage of each celll while you are running. We will have to see how well it works.
http://www.hobbycity.com/hobbyking/s...try_(1km_Range)

[NativePaul]

There are several companys that sell LiPo shield type devices which plug into the balance lead and work on an individual cell basis, there mostly for 4s max but shultze do an 8s one and a 12s one, also I have seen a chinese ESC that plugs into the ballance tap fore a V/cell cuttoff which I think is a low voltage low ampage unit that is not usefull for me sepcifically right now, but I hope that this is the way of the future and many more ESCs will have this some time soon.

[justintime2w8]

Yea i run a 3v cutoff and get about half the pack's mah used every time. Temps are good so i am not changing it. I like my cutoff, would destroy the packs without it.

[ED66677]

for me, 3.2V LVC on cheap 100A chinese ESC did not kick with new 4900Mah Rhino's from HC, while it used to kick with cheap/lower quality Lipo's, I figure out that, 30min after a run (the time to get back home and measure), the voltage was 3.6V and each pack of Rhino's took almost 90-95% of nominal capacity! got the thing confirmed by a buddy who found out the same!

[ozzie-crawl]

its looking that the lvc are just to low,especialy on esc,s that are only 3 or 3.2 volt
i usally time my runs but a lipo shield with higher voltage cutoff maybe needed to be safe

[ED66677]

Yep! CellShield from Dimensionengineering can be set at 3.5V, I'm afraid this is too low!