Lipos are dying on me!

[spdas]

Aloha, all. My Lipos are loosing charge quickly when driving, (can only get 7 miles when I used to get 12 mile range)

1) 4 x 5000mah 4s = 16s system charging to 4.1 v each = 66.4 see below the actual battery
http://www.ebay.com/itm/2-Turnigy-5000mAh-4S-14-8v-20C-30C-Lipo-Battery-Pack-Losi-HPI-Venom-Redcat-USA-/131473796790?hash=item1e9c72eeb6:g:dPMAAOSwBLlVG0Og
2) I never overcharge past 66.40 v (my charger is constant Voltage and as the batteries become charged, the amperage goes down to .01 A) and max starting amperage is 10amps.
3) My controller shuts my system down @ 54v, so the batteries do not go below 3.37v
4) I charge a full charge 2 times a day plus maybe an "opportunity charge". Has then about 75 cycles on the pack.
5) There is no battery sag past 3.4v and all the cells are Top balanced to 4.10v
6) MY CA shows a current draw of 25amps when I am cruising at 30 mph and 15 amps at 20 mph. When "flooring it to 35-37 mph I draw 35amps (7c max then)
7) batteries are not warm.

Any ideas on what is going on? Should I go up to 10ah Lipo battery but the 5.0ah is good for constant 20c and i am no where near that.

thanks
Francis

 

[wesnewell]

Maybe you're riding faster now or more uphill.

1. 4.1v x16 = 65.6, so I guess your charging to 4.15V per cell average, but since I've never seen a 16s balance charger I'm wondering how you are doing a 16s balance charge.
2. Are you bulk charging to 66.4V?
3. 54V lvc for 16s is too low imo. I'd set it to 56V minimum. At 54V you are running the batteries down to almost 0% soc, and some may be over discharging.
4 I've probably got ~500 cycles on my 4+ yo 10ah 24s pack using the same hardcase packs. But I didn't buy them off ebay. Perhaps you got some old stock that wasn't stored properly to begin with.
5. That doesn't compute with the numbers posted.
6. Those numbers look high for those lower speeds. 35A for 35 mph sounds about right.
7. That's one good thing.
Another 5ah for 10ah total would cut the batteries load in half. I've never run mine at more than 4C, and only rarely at that rate.

 

[mybike]

At 35mph your pack not going to get much distance. Your getting more then I got with my pack, I have been adding more packs on for distance. Your most likely driving has changed or your going up hills more. Personally I would not buy Lipo packs off ebay… Overall have to agree with wesnewell.

 

[fesanand]

What about the wind?
I do the same ride everyday (go and return) and on windy conditions consumption climbs about 20%. Is estrange how wind affects always negatively, considering you have both headwind and afterwards tailwind helping in the return.
On really windy days, 30% extra consumption.

 

[izeman]

...but the 5.0ah is good for constant 20c and i am no where near that.

imho they are NOT. 7c can be too much, especially if you have no BMS to monitor individual cell voltage and discharge to 3.3V. it's almost certain that one or more cells go well below 3V when doing so.
did you measure cell voltages when the battery was empty?
i tend to not exceed 3-4c with my lipo. i would recommend going to 10Ah. this will at least double your range, as the batteries are not stressed that much. but i would not recommend putting the new and old battery in parallel before you can confirm that those old batteries are performing like new ones and the problem is something else but bad cells.

 

[TheBeastie]

Aloha, all. My Lipos are loosing charge quickly when driving, (can only get 7 miles when I used to get 12 mile range)

1) 4 x 5000mah 4s = 16s system charging to 4.1 v each = 66.4 see below the actual battery
http://www.ebay.com/itm/2-Turnigy-5000mAh-4S-14-8v-20C-30C-Lipo-Battery-Pack-Losi-HPI-Venom-Redcat-USA-/131473796790?hash=item1e9c72eeb6:g:dPMAAOSwBLlVG0Og
2) I never overcharge past 66.40 v (my charger is constant Voltage and as the batteries become charged, the amperage goes down to .01 A) and max starting amperage is 10amps.
3) My controller shuts my system down @ 54v, so the batteries do not go below 3.37v
4) I charge a full charge 2 times a day plus maybe an "opportunity charge". Has then about 75 cycles on the pack.
5) There is no battery sag past 3.4v and all the cells are Top balanced to 4.10v
6) MY CA shows a current draw of 25amps when I am cruising at 30 mph and 15 amps at 20 mph. When "flooring it to 35-37 mph I draw 35amps (7c max then)
7) batteries are not warm.

Any ideas on what is going on? Should I go up to 10ah Lipo battery but the 5.0ah is good for constant 20c and i am no where near that.

thanks
Francis

Yeah it seems to me a common theme where (at least in my opinion) folks are a bit delusional of what 1P or 2P etc lithium cell setups are capable of doing simply because they have a high amp rating.. Realistically these high amp ratings should be viewed/based more on the promise that you can use them at high rates and they won't overheat/burst into flames on you rather then giving you a lot of lovely full cycles.. Remember the hoverboard battery fires, your cells should be good for avoiding that but forget about a lot of cycles in 1P lipo (or 2P on 18650 cells)

Sometimes I think cell manufactures are very happy to put really high amp ratings on cells because it helps them get used up and thrown out more quickly so you buy more cells.. The only level they technically have to jump over on their high cell rating is ensuring it doesn't burst into flames and hold a decent voltage under load, easy!

While your cells are 5ah each that's still just 2P in 18650 terms as they average 2.5ah at least..
Similar to what this guy was looking at buying.. a 2P 18650 pack.. it just wont get many cycles before it dies.. just a waste as you try to save money but you end up spending more.. Someone should make a chart to have cell cycle life time over cost to make this stuff more easily absorbable.
https://endless-sphere.com/forums/viewtopic.php?f=3&t=82106#p1206685


It goes both ways of course.. High charging rates kill your total ah output as well, the main difference to note from these 2 cells is one is being charged at half the amps the other one is and gives out almost %20 more total ah.
https://endless-sphere.com/forums/download/file.php?id=187888

Or better look at this brand new expensive cell Panasonic NCR20700A going into the future Tesla packs. The 12amp vs 8amp useful amount of cycles/capacity is going out the window on the 12a discharge rates.. Its the same thing no matter what Lithium cell you use or what the ratings claim for the most part.

http://akkuplus.de/mediafiles/Datenblatt/Panasonic/Panasonic_NCR20650A.pdf

Another way to look at it is why do you think Tesla have such great long lasting battery packs? Its because the amount of cells in parallel is almost as many as there are in series..
Look at how tiny the wires are on a Tesla pack between each cell.. its tiny but drawing a little current from 7000 cells combined adds up and lasts 10 years..

 

[Ykick]

3) My controller shuts my system down @ 54v, so the batteries do not go below 3.37v

You DO NOT know that and it's likely a very wrong assumption. Cells can be all over the place when relying on overall pack voltage for LVC.

Take a look here -


Can you or anyone really "guess" which cell's gonna reach 2.8V/cell under load? I think not...

Also, take that 20C rating with a large grain of salt. 7-10C is more what I've experienced using 4S 20C Turnigy Hardcase.

DC IR test is the best way to know and understand practical RC Lipo C rates.

 

[Drunkskunk]

4) I charge a full charge 2 times a day plus maybe an "opportunity charge". Has then about 75 cycles on the pack.

But how old are they? R/C Lipo die with age, regardless of cycle life. If they get stored in a hot garage, then I would guess your packs are maybe 3 years old?

 

[Paladin]

Maybe you are loosing a cell.
If you can charge and then let the packs sit over night then check the voltage.
If the cells are all over the place and not the same voltage you have a problem.

Have you, spdas, checked the packs individually, like with a celllog or some type of voltmeter?
That would be the first place to check.

Probably be better off with a 10ah. less stress on the discharge.

I have had 1 cell kill/reduce the whole battery.

 

[dogman dan]

Yeah, 5 ah is too small. Even with a moderate use compared to the stated c rate. ( 30-40 amps controller) I have consistently found a 5 ah pack wears out in a year, year and a half, while a 10 ah can last 2-3 years. You definitely don't get many cycles whacking a 5 ah size pack.

What is happening is just one cell is not hanging in there, often the end one that puffs first. Double the capacity and you will have a much better result.

The hobby king packs can handle 20c, they just make no claims about how long they last used like that. Discharge them at much much much lower c rates if you want them to last years.

10 ah should do er, for your setup. keep that discharge rate of the starting up spike well below 5c. So 10 ah x 5c is 50 amps. Your 35 now will be ok.

As long as you are replacing them, you might also consider upping the quality. 30 c or so. In fact, a 20c hobby cell is likely just one off the 30c line that tests shitty. So no way are they perfect, not even close. In fact, they are just duds. They still work damn good when in a 20 ah configuration though.

 

[izeman]

i think the main problem here is that the op relied on marketing data. unfortunately this happens very often, and happened to me in the very beginning as well.
afaik C rating is in the following way: you take a fully charged cell and then put some heavy load on it. the c-rating is based on the current it can put out when the voltage hits the nominal voltage. if manufacturers do this and how good this is for the cell life is a totally different story.

 

[999zip999]

5,000mah is small 10ah is a min. A battery pack is only as strong as it's weakest cell.

 

[ulrichw]

[...]Aloha, all. My Lipos are loosing charge quickly when driving, (can only get 7 miles when I used to get 12 mile range)[...]

Aloha, Francis!

It sounds like you have a CA, so instead of using the very inaccurate measure of miles to determine how much energy you're pulling from the battery, don't you have direct access to the real measure - amp-hours? (some reasons for the inaccuracy of miles are illustrated by the posts from wesnewell, mybike, and fesanand).

How many amp-hours does the CA say you're getting from the fully-charged pack?

Other posters' contributions on overly high discharge rate also seem on point.

 

[spdas]

Aloha and thanks for all the responses.

a) the driving conditions have not changed, same route, no wind, same speed
b) I charge by bulk to 66.4 and then check each with a cell-log an all are at 4.14 or 4.15
c) I buy from ebay because no one else will ship to Hawaii. and I get Turnigy from one of the higher volume dealers there and he ships in 2 days. I check before and after several times and all cells seem to be balanced both bottom and top
d) My CA has been acting up a bit so I am only going on my memory as to watts/amps used...but I may have the CA sorted so will try come up with some numbers.
e) I am setting my CA to 55.5 low voltage now.
f) And they are new batteries
g) I always thought that small AH rating (5ah) just means shorter distance, but I see the wisdom in doubling up to 10ah and not run the S--t out of the cells
h) Yes I now have a cell reading low at the end of a ride 3.35v when the rest of the pack is at 3.7v
i) I really like these Turnigy Lipo hard case 5000mah 4s packs as they are cheap and safer and easy to make into a pack, so paralleling 2 to 10ah is a good idea?? (gets more distance AS WELL as pulling less C so batteries my last MUCH longer. what do you think?

francis

 

[mark5]

c) I buy from ebay because no one else will ship to Hawaii

I bought lipos from hobbyking in early 2012 with USPS parcel post shipping. Wouldn't surprise me if things changed since then but they won't ship here any more?

 

[spdas]

c) I buy from ebay because no one else will ship to Hawaii

I bought lipos from hobbyking in early 2012 with USPS parcel post shipping. Wouldn't surprise me if things changed since then but they won't ship here any more?

Hobbyking has some sort of limit like 1500mah 2s. they canceled my order, so went ebay. They explained that airlines are tightening up their rules.

 

[mybike]

Yes… Paralleling 2 to 10ah is a good idea and more Ah in parallel less stress on the packs.
At 10ah your not going to get much distance if your going higher speeds but is far better then 5ah. You can slowly build it up in parallel giving you longer range.

I'v been running Turnigy Lipos (none hard case) for over 3years and bulk charging them everyday and riding 5-6 days a week and there still strong. As long as you look after them they will last you a long time with out issues.

 

[dogman dan]

Getting em to Hawaii is a problem. Since the hoverboards, they can't sneak em on a plane illegal as easy anymore.

Yes, parallel some up to 10 ah when you get them. You can still use your old ones, just stiffen them up with another new pack. Lowering the c rate will help to bring back some of the lost capacity of the older ones.

You can run them as two series connected packs, then parallel them. That way you can still keep an eye on the original pack, in case one cell is failing completely. It sounds like you just have worn them some, and have higher internal resistance now. So far,, nothing I see shows one cell dead.