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Originally Posted by BrianG
Patrick, I recently picked up a Turnigy pack (4s 5Ah 30C) to see what all the hubub is about. I made sure it was balanced and all set, then ran it in my 8th scale buggy geared for around 35-40mph. I was quite surprised to see the results were better than I had hoped for. It literally puts certain other lipo manufacturers/resellers to shame. No, they aren't the "best" out there, but still VERY good, especially for the price. And, how does your tech staff know the ESC was run on inferior batteries vs simply good batteries pushed too hard? I would think the result would be the same.
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The Chinese packs are getting better -- but consistency is still an issue. I spoke with a US battery maker a little while ago, and they told me that they reject about 15% of the cells they receive from their Chinese manufacturer, due to poor internal resistance. I'm sure that some of the Chinese pack manufacturers don't test to the same levels as other assemblers...
And yes, we can tell if the issue is current stress (pushed too hard) or voltage stress (bad battery for setup.)
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Originally Posted by BrianG
Personally, on the next generation of ESCs that contain data logging (and therefore hall effect sensors), the firmware should be set up to continuously monitor current flow and voltage sag. If the voltage sags below a certain % of the nominal value, the ESC would automatically dial in punch control to lessen the bursts. Likewise, it can also monitor reverse current (provided a bi-directional HE sensor is used) and voltage on braking, and if the voltage and/or reverse current is too high, have the ESC automatically dial down brake force. Yeah, would make driving a little more unpredictable, but I would rather err on the side of caution. I suppose you could make this feature defeatable, but provide a disclaimer that any warranty claims are denied if disabled (and could look at the ESC log files to verify on return). Would give people the choice, but discourage random setting changes just because Joe Sixpack wants to do double backflips with inferior batteries, or is using good batteries, but is geared unreasonable.
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Yes, on the Phoenix-ICE series we monitor voltage ripple both during braking and power -- and the controller automatically backs down if it sees voltage ripple go outside of a reasonable range. We are bringing this technology to the Mamba series in the future.
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Originally Posted by BrianG
Like Jeff and ticklechicken have asked: how does one determine their batteries are good or not using a logger? I personally look at voltage drop under load, and temps after a run as a guide. Loggers don't have sampling rates fast enough to catch ripple current, but I would imagine if v drop @ high currents is low, ripple currents will be low as well.
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Agreed -- the best way to tell if a battery is good quality (barring using a Phoenix-ICE logger (which logs voltage ripple)) is to measure voltage drop at the battery terminals under a controlled load.
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Originally Posted by BrianG
As far as the NiMH issue; it's true they have higher resistance, but remember they simply cannot provide the current levels that any decent lipo can. I'm sure there are ripple currents with NiMH too, but since overall current is lower, so is the ripple. Of course, since NiMHs have a higher resistance, they heat up a lot more, which brings other issues, but that's not the point here. IIRC, a good NiMH can output 100A, but the voltage drops substantially. So, on takeoff, current peaks and voltage sags a lot. As the vehicle nears the set speed, current dwindles and voltage climbs back up. The effect is a more gentle acceleration. Kind of like a forced punch control when you think about it.
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NiMh have the same issues as Lipos -- but as you point out, they also aren't as capable, so people are forced to use them in "softer" setups than Lipos.