[NSRCA-discussion] LIPO Question

[J N Hiller]

Thanks all.
We get what we pay for may apply here but how much do I really need.
Most of my pattern flying is done during the summer in ambient temperature
between 85 and 95 degrees and I was looking for a way to predict temperature
rise associated with battery resistance. Unless I'm completely off base,
kicking some rough numbers yesterday led me to believe battery resistance
would produce 15 / 30 BTUh, likely to increase with ongoing usage, but I
couldn't begin to guess the specific heat of a LIPO to get a predictable
temperature rise. I may have to back flush a usable constant from collected
data.
I'm about out of fuel and it looks like I can start flying the E-160
tomorrow. I guess the data logger will give me additional battery comparison
and flight performance information.

Jim

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of SilentAV8R
Sent: Friday, July 26, 2013 1:59 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] LIPO Question

The math is nice, but now I am confused. I have a set of old tired packs
that consistently have IR around 1.5 milli-ohms per cell.
I have some newer cells that run around 2.5 milli-ohms per cell.
Yet the newer packs (with the higher IR) come down cooler, produce more
power (same prop/motor/plane) and have higher voltages at the end of the
flight.

Seems to me that there is more to this story than simply internal
resistance.

I also wonder just how precise and accurate the chargers we have that we
measure the cell IR with really are.

Bill



On 7/26/13 1:34 PM, Peter Vogel wrote:
> IT's actually I^2*R, not just I*R, but since the resistance is the
> linear term here, you are basically looking at 2x the heat from Brand
> B vs. Brand A.  The heat has to come from somewhere, and in this case
> that's battery power that could have turned your prop and is instead
> going to self-destruction via heat.
>
> Peter+
>

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