Hi Eric,
I agree with your comments about charging efficiencies not being directly related to Peukert. My only point was if you calculate efficiency by measuing the output voltage during the entire discharge cycle, you have already taken Peukert into account because the voltage will drop faster than it otherwise would have due to the capacity lost to Peukert effect.
By the way, while I happen to be an EE, I am definitely not a battery expert. I have learned a great deal from those on this forum including you.
Thanks,
Pat
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Pat,
>
> I agree with your comments about charger efficiency completely. I was hoping that somebody would read my post carefully enough to see that discrepancy. Still, regular chargers like Zivan publish their charger efficiency as >85% and PFC chargers like Elcon and others claim >92%. While the difference is half as dramatic as I stated before, the difference in efficiency is still noticable. In practice, PFC chargers deliver more amps for the same RMS rating than more traditional chargers. I also believe that underestimating performance sets more realistic expectations. ;)
>
> I don't think that the charging efficiencies due to voltage differences are directly related to Puekert Effect. You can see this by drawing down the batteries at the rated 20 hour rate (10A for 200Ah). There is no decrease in capacity from Peukert, but the difference between Wh in versus Wh out remains, due to the charging voltage spread. The Peukert calculations start with the same resting capacities for all battery chemistries, the formula only factors amps, there is no reference to voltage. The formula works regardless of the pack voltage. I think that this is why SOC meters focus on Ah instead of Wh when tracking the current in and out, one less variable to average out.
>
> But again, you may have caught a place where I have exaggerated the net effect; the charging efficiency should have been between the charging voltage and resting voltage, not the discharge voltage. This should isolate the charging and discharge efficiencies. So for Lithium and FLA, the charging efficiency for 12V should be 12.8V divided by 15V or 85%, and AGM should be 12.8V divided by 14.4V or 89%. There is still more complications in this calculation because much of the charging takes place at a rising voltage during the bulk charging phase, but I stack that smaller difference into the underestimation of performance to cover other random inefficiencies in the system like wiring and connection resistances.
>
> I'm not an EE, nor do I play one on TV, so if anyone has more to teach me about these topics, I'm all ears.
>
> Thank you for diving deeper into this topic.
>
> Eric
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