Advanced Lipo Voltage question
06-10-2015 | 04:12 PM
#46
My question is if you have a meter. What voltage drops are you seeing at the different amps? Maybe you just have a bad battery or "weak" one. If you have nothing wrong with your truck and have a friend do the exact same test with his battery. You should get a similar voltage drop. If your is much higher your battery just needs to be replaced. IR under load is also a good way to test. There are all sorts of videos of computing IR under a load. If your IR has doubled under load on those batteries they may not be good for truggy. Move them to another life. Keep the newest in truggy. A new set of batteries is cheap once a year compared to Nitro fuel.
What seems to be hell on my batteries. Time, Overdischarge, Overcharging, Improper storage. You can easily fix 3 of them. Never charge completely to 4.2 per cell. try 4.18 or something where if the charger is a bit off you are not overcharging. LVC between 3.2 and 3.5 per cell. Store them half charged.
I am not Ryan so I don't miss a little of the top and the bottom. When I get that good I will get free batteries. lol
What seems to be hell on my batteries. Time, Overdischarge, Overcharging, Improper storage. You can easily fix 3 of them. Never charge completely to 4.2 per cell. try 4.18 or something where if the charger is a bit off you are not overcharging. LVC between 3.2 and 3.5 per cell. Store them half charged.
I am not Ryan so I don't miss a little of the top and the bottom. When I get that good I will get free batteries. lol
Thanks for your comment, but I think I've already addressed your comments.
Do I have a meter? The post you quoted start with, "I purchased a "Watts Up" current meter..." Yes, I have a meter.
For the voltage drop at various loads, scroll up the page a couple posts to the one about measuring IR using the Ohm's Law calculation. It is complete with photos of my test rig, as well as a complete description of the testing.
I think the conclusion of thread is that:
1) my batteries are not performing as new, as I suspected
2) the actual maximum amp draw of the motor is lower than expected. Geared to 50+mph and on pavement, the maximum current draw I have measured is 115A, which translates to 16C for my batteries.
3) on a dirt track, the maximum amp draw is significantly lower than 115A. It's closer to an actual 10-12C (with a 7200mAh pack).
4) My batteries are not holding up to the demands placed on them, and those demands are much lower than I previously believed them to be. With all 6 packs being roughly equal, I conclude that my batteries are not as good as they are claimed to be.
Bonus content:
Voltage drop--there are two reasons for voltage drop. We know battery voltage drops under load, but what is less obvious is that voltage also drops due to resistance in the wires.
Wire gauges used in RC cars are not capable of handling much current. The standard 10awg stranded wire is rated at 15A continuous, but nearly every kind of RC car is capable of drawing more current than this.
What happens when you dump 100A through a 10awg? The wire heats up, and the voltage drops due to the wire heating up.
When the ESC senses a significant voltage drop, like down to 6v on 2S, it automatically reduces throttle to prevent the voltage from dropping further. But the battery voltage never dropped down to 6V. This 6V minimum is separate from the LVC. The LVC you program is the no-load voltage. I'm learning how voltage at the ESC drops well below the LVC on acceleration, but it isn't really a problem.
And here is a handy tip--if you want a current limiter, just wire your vehicle with smaller wires!
But if you want something stupid fast, get the fattest wires you can lay your hands on. Ten gauge is for slackers, what you need is 1awg!
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