Just got a data logger

[johnrobholmes]

I picked up an EagleTree V3 logger yesterday, and they should just name it the battery tester. My last logger went on the fritz and started loosing data during big amp spikes.

I have been tooling around with the sidewinder and 4600 motor lately, and decided to give my system a test at 10hz. That is the fastest sampling rate of the V3. First test was a 3 cell 10C polyRC 4 a/h pack. It made the XX buggy haul ass, and I just did some speed runs for a few minutes. Came back in to read the data and the battery did not hang. On one 38amp max burst it sagged to 8.8v. Pack not good enough, and I can't see any signs of swelling. The rating is no longer valid on the pack to me.

Second test was with an old pack of matched gp3700's. Speed wasn't too crazy, and I noticed that it was fading hard. Must be a bad cell in there. Went back to check the data and I had some big amp spikes, the largest was 48.15 amps @ 340W. The voltage sagged down to 7.06v, not good for a 7 cell pack less than a minute into the run. Time to do some voodoo on the pack and bring it back to life I guess. The twin to this pack was doing much better, so I will test it next.

Lesson learned, don't go for so long without a logger again. I want to get the pro version so I can have a higher sample rate. I bet the bursts were actually higher. I got the V3 because it has an LCD screen that can show data live. Perfect for my electric bike I am building.

[sikeston34m]

Originally Posted by johnrobholmes

I picked up an EagleTree V3 logger yesterday, and they should just name it the battery tester. My last logger went on the fritz and started loosing data during big amp spikes.

I have been tooling around with the sidewinder and 4600 motor lately, and decided to give my system a test at 10hz. That is the fastest sampling rate of the V3. First test was a 3 cell 10C polyRC 4 a/h pack. It made the XX buggy haul ass, and I just did some speed runs for a few minutes. Came back in to read the data and the battery did not hang. On one 38amp max burst it sagged to 8.8v. Pack not good enough, and I can't see any signs of swelling. The rating is no longer valid on the pack to me.

Second test was with an old pack of matched gp3700's. Speed wasn't too crazy, and I noticed that it was fading hard. Must be a bad cell in there. Went back to check the data and I had some big amp spikes, the largest was 48.15 amps @ 340W. The voltage sagged down to 7.06v, not good for a 7 cell pack less than a minute into the run. Time to do some voodoo on the pack and bring it back to life I guess. The twin to this pack was doing much better, so I will test it next.

Lesson learned, don't go for so long without a logger again. I want to get the pro version so I can have a higher sample rate. I bet the bursts were actually higher. I got the V3 because it has an LCD screen that can show data live. Perfect for my electric bike I am building.

John, the 8.8 volt sag was probably as far as the Low Voltage Cutout would allow it to sag.

If you had it set at 3.0 volts at least.

[johnrobholmes]

I did have it set to 3v/cell. Im sure the 4600 motor would have tried to flatline the pack otherwise. Good to know this stuff. My better pack just peaked, time to get some more driving.


I also have a logger harness for servo current. I will be able to have a separate graph for my servo system if I want, along with the pulse that I am sending the servo.

[johnrobholmes]

Did another test, this time 3s2p 10C 8000mah [two packs] in the XX buggy. 4600kv motor and sidewinder ESC. Got a max burst of 58amps, low voltage of 9.95. Much better, although some nicer cells would hold voltage better I bet. I might try warming the cells up first to about 120f next time, I think that may help them. Ran for 3.5 minutes before blowing a shock off. Took out 300mah with lots of full speed runs back and forth. By my calculations that is about 80 minutes of runtime with 45mph top speeds. I don't have any more room to drain the pack faster Although I love runtime, I think a higher C pack with less mah would be just fine. Almost an hour and a half of back to back speed runs (on concrete) is just ridiculous.

I did have a few high speed close calls. Twice I got up on two wheels as the XX likes to dig in when it turns. As fast as I was going (over 35mph) it wouldn't have faired well for the old graphite buggy. It was pulling wheelies at half throttle like nobodies business too. Did I mention it has been a while since I have played with fast cars? The pucker factor was high today I noticed a ton more power with the extra pack in parallel.

[johnrobholmes]

I just realized why my nimh seemed crappy. I forgot to turn off the 9v voltage cutoff! Castle needs to hurry that update, I can't be stick programming this thing over and over.