[Elecraft] KX3 internal battery charger

[JP O'Connor]

Hi Ed,

Terminology can be a tricky thing! So can the specifics of different
battery types and how to charge them. You raise a number of excellent
questions.

In order to assist other readers who may not be as familiar with the topic,
and to assure I am being clear, I will go in to some detail.

--

Balance and Equalize

I think we are using these two terms synonymously.

Balancing chargers have access to each cell and during the charge cycle
will send different amounts of energy to each cell so that each cell is
properly "topped off" on its own. If a multi-cell pack is rapid charged,
there is the risk of undercharging some cells (an inconvenience) and
overcharging other cells (causing damage, and in some cases causing
catastrophic failure). I suspect this is exactly the same as equalizing. I
purchased my LiFePO4 packs and iCHarger 106B+ balancing charger from a
vendor (EP Buddy) in the radio control model hobby, so that is why I picked
up the "balance" term.

One must/should use a balancing/equalizing charger when rapid charging a
battery pack, especially when using extremely high charge rates. When slow
charging, the balancing/equalizing function, though beneficial, is not
required.

--

Charging LiFePO4 Batteries

When talking about charging batteries using this specific chemistry, one
must clearly state if they are talking about charging a pack that has no
internal electronics (for charge control and safety) or a pack that is set
up with cells and a control board inside. The latter style is often
configured as a drop in replacement for a traditional sealed lead acid
(SLA) battery. I did not make that distinction in my earlier post in this
thread, thus introducing the possibility of confusion.

Some LiFePO4 batteries are the exact same size and shape as SLA batteries
and are advertised as drop in replacements. These units have an internal
charge controller that handles the actual charging of the cells, often (but
not always) with balancing/equalizing capability included. Externally, the
battery is connected to whatever was charging the original SLA in the
application. Thus, an uninterruptible power supply, any application using a
standard SLA charger, or a solar power application may gain the benefits of
the LiFePO4 chemistry and still provide charging current/profile as if the
battery is an SLA. The controller inside the battery does the "translation"
to manage the actual LiFePO4 cells. In these types of applications, a
"standard" solar charge controller (which is designed for lead acid
batteries) may be used as is because the battery mimics an SLA.

Some LifePO4 battery packs are just made up of cells only, have no control
board, and must be charged by a system that is designed for this specific
chemistry. Just as with any other type of battery, slow charging may be
performed without balancing/equalizing and rapid charging does require
balancing/equalizing. This is the type of pack I am using. They are
supplied by EP Buddy, BuddiPople, and many others.

Note that a LiFePO4 pack of the same nominal capacity as an SLA battery
will have significantly more actual usable capacity within a single charge.
SLA batteries have dramatically reduced life if discharged more than 50% of
capacity and have significant voltage drop even at that point. LiFePO4
batteries on the other hand may be safely discharged much more (80% or
more?) without damage or diminished life, while retaining almost full
voltage until discharged about 80% or so. LiFePO4 also seem to have a
significantly longer "shelf life" and "service life" than SLA batteries.
Those who have experience with overall life of these types of batteries may
wish to comment with their findings.

--

Solar Charge Controllers

There is nothing magic about solar charge controllers. They are like any
other charger, except that they are designed to handle the wide voltage and
current range presented by a solar panel or array. Just as with any type of
charger, they must know the type of chemistry utilized by the battery so
that the proper charge profile is used. It is commonly known that lead
acid, NiMh, and Li-ion all use different charge profiles, so the proper
type of charger (or solar charge controller) must be used with each.

Just as with "standard" battery chargers, solar charge controllers are not
all alike. Choose the proper type for your battery chemistry or battery
pack profile. This isn't always made obvious to the prospective purchaser
since, historically, most general purpose consumer solar applications
involve SLA batteries.

--

For the KX3 I plan to use the following portable power options and charging
equipment/methods:

Internal lithium primary cells (8 AA size Energizer L92 Ultimate Lithium)
- Non-rechargeable - used only as emergency spares (Alkaline make very poor
spares in this application, although due to their common availability are
the ultimate spares of last resort.)

Internal NiMh low self discharge (LSD) cells (8 AA size Eneloop XX nominal
2500mAh)
- Normal charging (with batteries inside the radio) using low current timed
charge without balance/equalize - Elecraft KXBC3 fed from external DC power
supply
- Periodic testing with balance/equalize charging (with the batteries
outside the radio) - Maha MH-C9000

External LiFePO4 pack (4S1P 26650 size A123 nominal 2300 mAh)
- Field solar charging using low current controlled charge without
balance/equalize  - BuddiPole Solar Battery Charge Controller
- Fixed location periodic testing with balance/equalize charging - iCharger
106B+ fed from external DC power supply

Another solar option for the LiFePO4 packs:
- Field solar charging (including possibility of medium to high current)
controlled charge with balance/equalize - larger capacity solar panel/array
feeding DC-to-DC regulator feeding iCharger 106B+

All battery packs, regardless of chemistry, benefit from a periodic
balance/equalize charge.

--

Hopefully this has clears up more questions than it generates!

72/73 de JP WF4Z


On Mon, Jul 2, 2012 at 1:47 PM, Edward R. Cole <kl7uw at acsalaska.net> wrote:

> Not exactly sure what "balancing" means but suspect this is the same
> as equalizing charge.  I have used solar charge controllers at remote
> sites for two panels charging two batteries and do not recall any
> equalizing function in them.  The Buddipole appears to be a simple
> current regulator.  It may be adequate for your situation?
>
> Solar regulators are widely available, just google them.  Prices
> about $150+ (from memory - may be higher now days).
>
>
> 73, Ed - KL7UW, WD2XSH/45
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