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1. 12:00 PM - Re: Re: Excessive Amperage (Robert L. Nuckolls, III)
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| Subject: | Re: Excessive Amperage |
Sorry for the long 'silence' . . . sorta overbooked with
pressing issues . . .
At 01:17 PM 7/2/2023, you wrote:
>Battery....Lithium
>
>Joe makes a very good point about the potential of Lithium base
>batteries to potentially cause charging problems.
Where is this premise documented? The lithium battery
market offers a constellation of products with and
without 'battery management systems'. I'm not aware
of any such product that does not claim plug-n-play
compatibility with most vehicular storage batteries.
Ever since generators were bolted to the earliest
vehicles, battery recharge currents after engine
cranking understandably 'spiked' for some duration
needed to replenish energy removed from the battery
since the engine ran last. This 'used' energy included
cranking, operating loads with the engine off and
self-discharge unique to the battery technology
and condition.
Battery technology has evolved from flooded,
lead acid, wood separator, rubber cased
devices to contemporary offerings with a
variety of chemistries and fabrication
techniques. Lithium and Lead-Acid are the
big kids on the block these days.
Over the years, power generation has evolved
from 3-brush generators with virtually no
current limiting up to contemporary 3-phase,
externally excited and some permanent magnet
alternators. Every successful example of an
engine driven power source has been tailored
to deliver a known amount of energy within
operating limits for temperature and rpm.
While generators have NO inherent current
limiting qualities, a skillfully designed
alternator is inherently limited by its
magnetics. This is why, unlike regulators
for generators, regulators for externally
excited alternators are not fitted with
alternator current sense and limit
features.
This tells us that the adequately cooled
wound field alternator is essentially
invincible when operated within well known
conditions.
The PM alternator is a little different
breed of critter. While they CAN be
designed and cooled to exploit the
magnetically defined, current limiting
qualities, they tend to be optimized for
size, weight and cost of the consumer
(garden tractors) and hobby aviation
(small engine) applications.
To my knowledge, B&C's latest PM
regulator product is the ONLY such
device fitted with alternator output
current sensing with the goal of
protecting an alternator with a
lower degree of robusness.
>The other side of this combo is that when a "normal" alternator
>is running at idle speeds the Lithium is able to handle receiving
>a very heavy current charge rate such that the alternator could easily
>overheat and burn some internal part due to lack of cooling for such
>a heavy current draw.
Let's unpack this assertion a bit: I'm aware
of no contemporary alternator installation
capable of rated or more-than-rated output
at idle speeds. Indeed, the legacy wound-
field alternators can be operated with belting
ratios that offer greater output than
a generator but this is only because they
easily tolerate the resulting high cruise rpm
. . . over 10,000 rpm is not uncommon on
a Lycoming installation. This would buzz-off
the brushes in a generator in an unacceptably
short period of time.
For PM alternators that drive at crank-shaft
speeds, one is saddled with very constraining
design trade-offs. Put enough turns of wire
on it to get nice taxi-rpm output and the
cruise voltage is going to be very difficult
to manage with the legacy, pass-thru, rectifier-
regulator designs.
>There are gizmos made to take control of the charge rate such that it
>stays under the alternators design limits. The marine and RV
>folks use these controllers to safeguard their expensive stuff.
How does any alternator become loaded 'beyond
design limits' . . . under what conditions?
How long would such conditions be expected to
last? Can you cite any examples of such
protective 'gizmos' and how they function
in the system?
>Below is from
><https://earthxbatteries.com/faqs/>https://earthxbatteries.com/faqs/.
I just captured the current version of this posting
on the EarthX website:
<b>I just installed my EarthX battery in my aircraft and started the
engine and my charging amps was really high, is this normal?
Yes, this is normal. A lithium battery can and will accept a much
higher charging current than an equal size lead acid battery. If your
battery is not fully charged, your alternator can potentially output
a current equal to or slightly above the alternator's rating for a
few minutes to top the battery off. Your fuse, breaker, or current
limiting device should be sized approximately 20% above the
alternator rating. Example, if you have a 40 amp alternator, use a
fuse, breaker, current limiter set to 48 amps (or 50amps).</b>
I'm mystified by the EarthX response to this question.
Yes, the internal impedance of a lithium cell is lower
than that of an SVLA cell of the same 'size'. But the
questioner's observations are not quantified. How big
is 'really high'? I presume that the observation
was made at idle rpm . . . and while it might understandably
be higher than previously observed recharge current
than a previous, perhaps worn-out SVLA . . . was
(1) the current 'alarming' with respect to alternator
ratings and (2) for how long did it persist?
For an institution presumably competent in the design,
manufacture and marketing of a plug-n-play battery,
their reply is painfully lacking in understanding of
battery/alternator dynamics. It's not physically
possible to load an alternator at idle. Further,
the advice on 'current limiting' by sizing the
b-lead protection is waaayyy out in left field!
To my way of thinking, this advice from EarthX
shoots their plug-n-play philosophy right
between the eyes!
There's more to offer on this thread but I
just received notice of a family crisis
250 miles from here. Need to saddle up
and boogy . . .
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
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