opinions about batteries.... - Page 2 - RC-Monster Forums

nativepaul · 06:28 PM

Just this week I dug out 2x turnigy and 1x zippy flightmax 30C 4s 5000mAh packs from storage, where they had sat untouched for 2 seasons due to getting higher capacity packs at the end of '09, the first one gave an error on the charger (too low voltage for the balancer) I put my voltmeter on the pack and it read 8.5V, i tried it without the balancer but it errored again (output low voltage), so I told the charger it was a 3s pack and charged it without the balancer for a few mins, when the voltage reached 12V I stopped it, plugged the balancer back in and finished charging it as a 4s pack as normal, I was holding the pack throughout to monitor for heat or swelling but there was no sign of either, it put over 5000mAh into it as normal, it did take just over 2 hours at 1c though due to a large imbalance on one cell (170mv), although I didn't put the voltmeter on them the other 2 couldn't have self-discharged as far because they charged normally to over 5000mAh straight off, but while not as bad were further out off balance than I would normally expect at 46 and 72mv. I was half expecting them to fall apart under load, but the 2 i have run so far (inc the 8.5v one) seemed to have as much punch as I remember and are still worthy bashing packs.

Rating voltage while simple is not enough, you need temperature in there as well, if capacity and voltage are all that matters you get good performing cells which get hot and only last a few runs, that was the worst thing about NiMh IMO, and are starting to get it again with LiPo boating in boat racing which calls for both high energy and power densities.

zeropointbug · 05.13.2012, 08:24 PM

Nice one, were they stored at storage voltage? Does your charger tell you the iR of the pack as well?

Voltage holding ability or internal resistance (cell iR) of a pack will tell you everything about how a pack will behave actually. The lower the iR, the lower the pack temp will be, simple heating due to voltage drop is how it works. How well the pack handles the temperature increase is due largely from what chemistry it is... ex. A123's LiFe-n-Ph vs. LiPo packs.... A123's can withstand higher temps, without being dangerous.

Bondonutz · 05.13.2012, 09:02 PM

+1 GENS

I sell or give away my year old Gens & Skys and get all new every spring, still cost effective IMO

If I was still serious about racing I'd be looking into the Hyperions myself but as Artct1k said the lipo industry/technology is moving fast so I wouldn't be suprised if the Gens get better better if not cheaper.

zeropointbug · 05.13.2012, 10:10 PM

How much for a 6s 3300mah 45C pack.

nativepaul · 10:12 AM

Yes the packs were stored at 3.8v/cell originally, keeped at room temperature (I know they store better in the fridge but I can't get away with that here) and have not been charged since.

I didn't mark the silly low voltage pack but it was one of the two turnigys, I didn't note the IR when I first charged them but am just recharging the 2 turnigys now and they were 20 and 18milliohnms when it first came up at the start of charge and are now at 12 and 11milliohms nearing the end of their charge, is it usual for the IR to change during charge, or is the first time it comes up a guestimate and it takes a while to work out what is accurately? I've never really paid much attention to it. They are balancing better this time too at 32 and 30mv after 40 mins, hopefully this will continue improving with use.

The IR readings were taken with stock battery wires (6" of 8gauge), then a pair of 6mm bullets, 8" of 12guage charging wires, and 4mm bullets into the charger, charger is a Fusion Emperor L720B Pro.

nativepaul · 05.18.2012, 03:21 PM

little update, the IR of the firs pack kept falling but the second pack shot up right at the end at the end of charge they were 10 and 17milliohms, so I guess i can tell which was the low one now, although both seemed to have plenty of punch again for bashing, (no lap times as these are 3 year old tech budget backs and as such I wouldnt be raceing them even if they were brand new). They were fully balanced by the end of charge (about an hour) this time, so from that viewpoint at least they are improving.

zeropointbug · 05.20.2012, 12:15 PM

Did you take those IR readings through the charge leads, or the balance leads? You will get better results if you go by balance leads, that's how most results are retrieved, but that is cell performance, and not pack performance. Real world results should be read as pack performance as that is all that matters for performance... on the other hand, the lower the actual cell IR, the lower the pack temps will be. That is good, and to be expected from a pack that the IR goes down after some cycles when it hasn't been used in awhile.

My G3 packs went from ~15mohm down to whatever i said before... 5mohm? When new 3 years ago they were 3mohm.

nativepaul · 05.20.2012, 03:18 PM

Honestly I have no idea how it is measured, I'm just saying what it says on the charger's display, however it measures it.
I just bought a new Hyperion G3 35c 1800mAh 3s pack for my minihydro this week and that read as 21 milliohms, charged the Turnigy 4s 5800mAh packs I am racing with (still not bought new packs this year) and they were 22 and 26 milliohms.

Is that 3 milliohms per cell or for the whole pack?

zeropointbug · 05.21.2012, 02:18 AM

26 mohm for a 4s pack is alot; so yeah that new G3 (very little) you bought has just as much power on tap as that 5800mah pack, which is 3 times the capacity... if they were rated for the same C rating, the 5800mah pack 'should' have roughly 7mohm.

Are you plugging the balance port in? What charger are you using?

Yes; the displayed IR is for the entire 'pack' level, not for one cell.

nativepaul · 05.21.2012, 06:36 AM

I don't think IR can be the whole story as the 5800s were definatly faster than the 5000s even with the same prop, I have dumped the 5800s in 3 minutes which is 116A 20C, that would be 64C for the little 35C rated hyperions and I doubt they are that underrated.

readings are taken during balance charging with the balance leads pluged in, the 5800s have been stripped with balance leads under an inch long, 10guage power leads about half an inch long soldered directly to the tabs, no PCB. I Used the same charger as above this time too, a Fusion Emperor L720B Pro

zeropointbug · 11:15 AM

Pack IR is actually the only story as far as performance goes... chargers might not be the most accurate when it comes to calculating pack IR to begin with. The Turnigy pack is literally dumping out on you early, which would give a false calculation on the current draw you are using, what kind of temps are you getting? What is your LVC set to?

Also, what are these 5000's you mentioned?

nativepaul · 05.23.2012, 07:31 AM

I believe that amp draw absolutely, it may not be 10% accurate but between 110 and 120A for sure, from the pace that I was lapping the rest of the field (that are pulling an average of around 70A) I knew straight away that I was going to be very short on run time and was surprised that I lasted as long as 3 minutes. I don't ever measure the pack temperatures, even when I run with Eagletree the temp goes on the motor, it was the hottest LiPo i have personally felt though and must have been close to the 60degreec maximum most cell manufacturers advise, and based on that I don't believe the full 30C rating could be sustained for the full discharge without pack damage. I set my LVC to 3.4v for fun and 3.3v for racing, when running 10 secoond laps a few seconds can make a big difference, but from my experience of these cells what is left after 3.3v isn't worth having.

I gave details and figures for the 5000s earlier.

Bondonutz · 09:27 PM

I've recently found (2) Apogee 3s 2500mah Lipos.
I discovered them in the storeroom of my hobbyshop and decided to see if they are salvagable, after ditching the mega old school balance tab for chinese JST's I charged them with 1amp till they read 4.19 each cell. (the storage voltage for all the cells even after 4+yrs was 3.64 each)
At that point the IR/Ohm rate was 67, after a discharge and recharge the number dropped to 24. Both packs has nearly the same results, I have yet to test them but was wondering if these numbers say they are junk and not to even bother ??

zeropointbug · 05.24.2012, 10:33 PM

24 mohm seems like a typical previous gen. lipo IR, IMO. That actually sounds amazing if they perform with decent punch. I am starting to see a trend that older lipo's have a longer 'calender life' but low 'cycle' life, and new packs seem to have not so good calender life but good cycle life.

nativepaul · 05.25.2012, 08:09 AM

I still have a set of Tanic 10C cells in use form around 8 years ago when 10C were just becoming available, and they were the only 10C cells that were actually capable of 10C, it was before balancing was generally available and they dont have balance leads as such although they do have 3x taps on so you could charge each cell individually up to the same voltage, they have never been balance charged except for at the factory (I assume), I bought them for a 6s1p EDF plane but for the last few years I have used them as 3s2p in a boat, they are old cells although have been in constant usage and have never been stored. While the voltage is lower than modern cells at around 3.1v@10C compared to 3.6v@10C for modern cells, after many years and hundreds of cycles they are still rock solid, still have good capacity, and get no warmer than much more recent and higher C rated cells do @10C.