Maxamps and Neuenergy lipo testing

[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?

[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.

[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.