Maxamps and Neuenergy lipo testing

[johnrobholmes]

Most factories rate continuous at around 3.3 to 3.4v/cell under load, FYI. The nicer, newer cells do better of course.

example http://www.allerc.com/hp-lvx-lithium.htm


Really you could rate it at X continuous discharge if it didn't hit LVC until the rated capacity had been spent, even if it was at 3.01v the entire time.

[lincpimp]

Originally Posted by johnrobholmes

Really you could rate it at X continuous discharge if it didn't hit LVC until the rated capacity had been spent, even if it was at 3.01v the entire time.

I have a feeling that this is the way certain companies rate their lipos. Problem is that if you do this on a continuous rating, what happen at the surge rating? I would say that it would dip below 3v per cell, kicking in the lvc. So I figure that the cont rating has to be measured higher than 3v per cell, to allow for the momentary surge rating to still be effective.

[johnrobholmes]

Some batteries don't even have a surge rating....


Good point though. The temp of the battery is also very important. I have some 25C lipos that won't put out 25C at 3.35v until I push em hard for a few minutes. Once they warm up the voltage actually bounces up a bit from 3.3 to 3.4v. It is with a prop load, not in cars but you get the idea.

[kulangflow]

I tested 5s2p a123 in my stock 3905 E-maxx. I used a method learned from tiran_rw on the Traxxas forums to manipulate the data like this:

-Sorted the Amps (ascending)
-Dropped the digits after the decimal (forced round down)
-All the voltage points that have the same current get averaged into one sample for that amperage point. (eg anytime 15.00 - 15.99 amps occurred, add all the voltages together, and divided by how many occurrences)

This is what I came up with.

10C - 46A - 14.42V - 0.82V / cell drop
15C - 69A - 13.55 - 0.99V / cell drop
20C - 92A - 13.13V - 1.07V / cell drop
25C - 115A - 12.73V - 1.15V / cell drop

So, what would you say a correct rating for these cells are?

[speedracer1129]

Originally Posted by johnrobholmes

Some batteries don't even have a surge rating....


Good point though. The temp of the battery is also very important. I have some 25C lipos that won't put out 25C at 3.35v until I push em hard for a few minutes. Once they warm up the voltage actually bounces up a bit from 3.3 to 3.4v. It is with a prop load, not in cars but you get the idea.

I agree. I have spoken to FP on several occasions and they state that lipos do there best around 100-110 degrees.

[skellyo]

Originally Posted by kulangflow

I tested 5s2p a123 in my stock 3905 E-maxx. I used a method learned from tiran_rw on the Traxxas forums to manipulate the data like this:

-Sorted the Amps (ascending)
-Dropped the digits after the decimal (forced round down)
-All the voltage points that have the same current get averaged into one sample for that amperage point. (eg anytime 15.00 - 15.99 amps occurred, add all the voltages together, and divided by how many occurrences)

This is what I came up with.

10C - 46A - 14.42V - 0.82V / cell drop
15C - 69A - 13.55 - 0.99V / cell drop
20C - 92A - 13.13V - 1.07V / cell drop
25C - 115A - 12.73V - 1.15V / cell drop

So, what would you say a correct rating for these cells are?

That graph looks pretty unpleasant to me. At 10C, they're already under 3V/cell and at 20C, they're under 2.7V/cell. This would lead me to believe that either you have some bad cells or A123 was smoking crack with their 30C rating. Sure, they may be able to be discharged at 30C, but the voltage drop is horrendous.

[speedracer1129]

Originally Posted by skellyo

That graph looks pretty unpleasant to me. At 10C, they're already under 3V/cell and at 20C, they're under 2.7V/cell. This would lead me to believe that either you have some bad cells or A123 was smoking crack with their 30C rating. Sure, they may be able to be discharged at 30C, but the voltage drop is horrendous.

You have to remember that they are rated at 3.3v per cell.( Anyone correct me if I am wrong here...)

[skellyo]

Originally Posted by speedracer1129

You have to remember that they are rated at 3.3v per cell.( Anyone correct me if I am wrong here...)

Yes, I know that. Quite a few Lipos do >3.4V/cell at 10C easily, so logic would dictate to me that 3.0V/cell shouldn't be unreasonable for the A123's at 10C.

[kulangflow]

If I only count the first 100 mAh and include the fact that the max voltage of the pack at the beginning is 18.1V (as opposed the theoretical 18.5V I used initially), then the numbers look a little better:

10C - 46A - 15.6V - 3.2V / cell
15C - 69A - 15.0V - 3.1V / cell
20C - 92A - 14.0V - 2.9V / cell
25C - 115A - 13.0V - 2.7V / cell

Do they usually factor in the whole run? If you're averaging in the low voltage at the end of a run, it's going to drop everything, right?

[Just go Play]

Most of the charts that I've seen from the mfgrs. have been a constant load measured until LVC or around 3.0 volts per cell or milliamps used over time on constant loads. I have never seen any graphs of real world use in RC cars or MT's, helis and planes sometimes but nothing with the serious current spikes that land vehicles create.

[Finnster]

Originally Posted by speedracer1129

I agree. I have spoken to FP on several occasions and they state that lipos do there best around 100-110 degrees.

This is def true. When I was trying to get my Crt.5 to hit 60 (4S 30C Neu 2500 pack) I had a hard time doing it until the cells got warmed up. It was ~40F outside, so it look most of the packs life in spd runs to get temp up. Consequently the fresh cool pack was only doing ~55, but the hot half-discharged pack got over 60. You could really feel the diff in the punch too.

[Finnster]

Originally Posted by skellyo

That graph looks pretty unpleasant to me. At 10C, they're already under 3V/cell and at 20C, they're under 2.7V/cell. This would lead me to believe that either you have some bad cells or A123 was smoking crack with their 30C rating. Sure, they may be able to be discharged at 30C, but the voltage drop is horrendous.

From alot of my tests, I see ~2.65V @ 50A on a half discharged pack.

They do have a greater V drop than lipos, but they tolerate it better and don't get hot like overstressed lipos, so its not quite apples to apples. A123s are really a whole 'nother beast.

[lincpimp]

Received the 5000 lipo from bdebde today. He said that one cell had puffed, and it certainly had. Check out thepics below.









On a side note, gotta love the copper tab claim, only one tab is copper, the other is al. Plus the tabs are attached to each other in some method, looks like crimping to me. Does not look like resistance welding to me. I easily seperated them with a razor blade, and just popped them apart. No cutting or sawing thru the crimps. I really cannot see how this can transfer much power, and most likely indincates why the shrink melts off the wire end of the pack (happened on most of my maxamps packs too), heat from resistance.

The other 3 cells in the pack look fine, and all of them are in balance. I will try a load on them and see how they do.

[lincpimp]

Ok, pack is fixed, and it is on charge at the moment. I wil leave it fully charged and balanced over the weekend and check it on sunday to see if any of the cells have dropped voltage. Not going to be here tomorrow, small vacation for me!

I have also decided to switch test platforms. I have a HB LS10 that is setup for this size battery. I will put my variety of motors in it and test the batteries. Same size/weight as the crt.5 so it should provide the same results. I also have a pede that can run both of these packs, so that will be used too.

[glassdoctor]

lincpimp... I hope you are not using this maxamps pack as a test pack?

It's not likely that the remaining cells are in 100% condition.

Also, the bottom cell in the pic above actually looks like it might be slightly puffed. A good cell is completely flat... no curve to it.

One of those cells has to be swelled...

I had a pack that had a very slight puff to it... barely noticeable. It lasted a long time like that but eventually did get worse and puffed more. That was a pack that got taken out with an ESC meltdown.

I think the non-copper tab is tin, not aluminum...? Alum is very soft and requires special flux to solder.