Access

I thought I'd post some of my more recent discharge curves for LiPo and NIMH batteries I have done.
If nothing else, it's an example of how to categorize battery test data, etc.

http://access.time.angelfire.com/bat...t_data_01.html

The way I took this data was using a test setup (90% the same test setup as before), a digital camera with a movie mode, and an oscilloscope set up to to measure the voltage using a 2-second running average. Recognize that my NIMH aren't exactly the best on the market, the but neither are Venom LiPos the best LiPos available and you can see how they all compare on the free webpage link I posted or the .jpg's uploaded.

The test setup has been reworked a bit to where the first deans go to only one resistor (1/2 ohm) and the second deans goes to the other three resistors (1/6th ohm). Using the parallel connector results in all 4 resistors being used (1/8th ohm). The 33-watt, 9000rpm fan (link below) produces enough airflow (rated at 132CFM) such that the resistors, when checked with a temp tester, never got above 120F in any of the testing.

http://search.digikey.com/scripts/Dk...me=603-1061-ND

savagecommander

very nice article. i think this will give some ppl the hands on difference of lipo and nimh...

FoamyVictim

It really is impressive to see them perform in a car back to back. I have an old XX buggy I dragged out to race. I tried it with both lipo and nimh. With my trusty old matched 3800 IB pack, it performed like it used to, pretty well. I put the 25C lipo in, and the ESC thermaled! lol I actually have to take it easy if I want to run lipo in that old car(still have an ancient Tekin Rebel installed) Good data!

Access

Yeah today I basically have the NIMH for the summit and that's it. Everything else I run is exclusively LiPo.

john01374

Access - Do you have any Zippy's or Turnigy packs to test?

If not i'd be willing to send one. I'd like to see how they compare.

Access

John, it's more the time factor, I probably will eventually get some of those packs to use and test but first I am going to go through and test the remaining ones I have accumulated over the years, time allowing. We don't get many rainy days here. Testing LiPos is especially annoying b'cos the only voltage cutoff is me quickly pulling the plug when the voltage starts to drop below around 6.4V.

john01374

Understood.

FoamyVictim

I was about to ask you that! We have a battery tester that we used to match cells, back in the day. It's been catching dust for a few years now, thought about busting it out to see how they compare.

Access

If anyone needs help in building a good tester I can certainly help with that. I've gone through several iterations even just using these half-ohm power resistors from digi-key.

http://search.digikey.com/scripts/Dk...=FVE300-.50-ND

The latest ones uses copper contacts directly on the resistor, most of the wiring is 10-gauge copper wire and it can run the actual configurations I described above (1, 3, or all 4 resistors run at the same time).

Once you have the tester all you really need is a voltmeter and some kind of timing tool, a stopwatch, digicam with video mode, or something similar. I personally like the digicam method b'cos human errors are easily correctable using the video.

BTW in determining the resistance of a test setup don't rely on a multimeter's resistance measurement feature. I found this just wasn't accurate below 1 ohm or so. I used a power supply with a fixed voltage, measured the current, confirmed that reading with a single-cell NIMH battery (1.2V) and a multimeter that would work up to 10A current.

Some kind of sufficient cooling is very important b'cos otherwise the tester will literally destroy itself (solder will melt, etc.) Those balancing tests were probably done in a matter of seconds while here the objective is to chart a full, continuos discharge of the battery.

rclugnut10

My Feedback: (1)

i'd love to see amp ratings on these runs as well to go along with voltage but tahts still really good data because thats at max draw, so its interesting to see for sure

the lug

Access

Updated the webpage with some new discharge curves form 3s LiPos.

http://access.time.angelfire.com/bat...t_data_01.html

srt10

My Feedback: (20)

during this testing, how many amps are being pulled?
good info here

lee172

very interesting, thanks for sharing [sm=thumbs_up.gif]

MCSRacing

My Feedback: (2)

killer thread

Access

Depends on the setup used, setup #1 is 1/2 ohm load or 2A per volt. Setup #2 is 1/6 ohm load or 6A per volt. Setup #3, which consists of #1 and #2 together, is 1/8th ohm or 8A per volt. So the tests range in current draw from around 14A to 40A. In theory the setup can go up to roughly 88A (a 3s LiPo and Setup #3, or #1 + #2) but this would discharge a 4000mAH LiPo in under 3 minutes, more than 20C, which is rare in practice.

ElectricGuy007

Not killer but kinda cool, the lipos drop off at almost the same point as the nimh, the only difference is
Lipo supplies more voltage and possibly more amps as well.

Access

1) If similar currents are drawn, batteries of the same capacity will discharge in roughly the same time.

2) Batteries, NIMH and LiPo, can perform better when warm (~120F) than cold. You can see this effect in #2, where the discharge voltage actually rises with time for a portion of the discharge.

3) The difference between the best LiPos out there and the worst ones I have (Venom brand) is not huge. 5%, 10%, maybe a little bit more in extreme cases.

4) The difference between LiPo and NIMH seems more significant than (3), but it's hard to say b'cos I never owned or tested a single high-end NIMH.

srt10

My Feedback: (20)

also with lipos they do supply bigger amps for longer times resulting in higher volts for monster trucks and 8th scale buggies that need that extra power..
but for most stock racing Nimh could get the job done well

rebuilder

We would all love to see a test on a Turnigy 5000 2s 20 or 30c!! I know i would. A zippy would be nice too. Lets see how they REALLY stack up!!

srt10

My Feedback: (20)

that would be awesome..

MCSRacing

My Feedback: (2)

the test is cool ... and this is kinda backing up the nimh vs lipo debate .... 5 minute race and a good set of nimh will do the job it seems

srt10

My Feedback: (20)

if you have a motor that pulls alot of amps like in monster truck or 8th scale buggy racing, lipos would be the only choice to stay up front imo

MCSRacing

My Feedback: (2)

also with nimh cells, after a high amp draw it takes a second for the voltage to come back up where as the lipo loses less and comes back faster so ya get a seat of the pants feel of the lipo being stronger than nimh .... atleast that is how it is when i run a 5.5 in my b44.

srt10

My Feedback: (20)

good way to put it..
B44s are awesome

ElectricGuy007

My cars are fast enough with nimh. I still dont have a reason to switch to Lipo just yet.
I just went to 4000 elites for my b44(and will be running these packs in my touring car for dirt oval racing)
And 5000 elite nimh's for my 501x, and it was a lawn dart with these packs and can get close to 15 mins runtime as well.[8D]

Access needs to test some more packs when he gets the chance to. Like the elites vs the promatch packs.
Maxamps vs Thunderpower etc...