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Re: HHB Portadisc

Subject: Re: HHB Portadisc
From: Walter Knapp <>
Date: Fri, 05 Sep 2003 00:55:56 -0400
Marty Michener wrote:

> TWO hours would be a nice contrast to twelve.

If you need it. I've always had the fast charging rate of 3-4 hours, not
as big a contrast. And have had less reason to need fast charging. So I
got two chargers to play with, but have not really committed to buying a
full set.

> Yeah, fiftyone bucks for one charger is morn I usually pay, and, again,
> thanks! I'm glad you cited your source, much less dinero -

I do not guarantee they are the cheapest. I've bought from them a fair
amount. Originally because they have the 9 volt NIMH that's a true 9
volt, actually 9.6 volts, that I use for charging the Telinga and in the
SASS MKH-110, and in my hydrophone. And any other place I need a 9 volt

> I used to make ALL my own chargers, then things got more complex, no
> published specs, so you're not really sure what you're building for or ne=
> . . .   constant current until V >=3D X ? ? ?

It's gotten to where microprocessor control is necessary. I'm sure it's
a pretty crude processor. It's not so necessary if you are willing to
stick with slower charging. It's when you want to cram it in fast
without ruining the battery or not fully charging it that it get's to be
real important.

Yes, I used to build my own chargers too. Simple, reliable, and slow.

> I didn't say the old Fuji's were unreliable, just relatively low voltage =
> full charge, so low readings on the HHb percent meter.

Thinking about how the load varies I've got a idea. There are two specs
that we are interested in with a battery. One is the capacity, that mAh
spec we keep quoting. But there is a second, and that's how much current
the battery can deliver, which relates to internal resistance and so on.
NIMH as a group can deliver the highest currents. But I'm suspecting
some are not as good at it as others. The Fuji's, for instance, may just
vary their voltage a lot more than normal under load due to a high
internal resistance. This would cause the fluctuations you see (but I

Such fluctuations seem to indicate to me a abnormally high internal
resistance in the batteries. Or your portadisc is taking far wider
current swings than mine. I generally consider high internal resistance
or varying internal resistance a indication of a failed or failing battery.

> Again, if HHb would just say WHAT voltages, timing, and or currents it
> needs not to "call it quits" . . .it is like automobile or TV repair
> nowadays - you used to be able to figure it out and DO it.  Now the specs=

> are hidden so success is preserved for the licensed few . . .

Considering how much the current can vary, timing would be real hard to
predict. I think we can get a estimate of how our style will time. At
least I can with my more stable portadisc and batteries.

As far as voltage, Duracell states that 0.8volts/cell is considered the
end point of discharge for their coppertop alkalines. So, assuming HHb
followed that, zero on their scale would be 6.4 volts.

Again from Duracell's graphs of discharge by eyeball, the 50% mark
occurs between 1.0 & 1.1 volts for their coppertop cells when discharged
at the rate the Portadisc would do. So 50% in the Portadisc would then
fall between 8 & 8.8 volts.

You can easily check the cutoff point voltage by putting a voltmeter on
the pac while running the Portadisc. Cycle through a few times and you
will know.

Now to NiMH. Duracell has a technical publication on their NiMH as well.
The cutoff point they assign in multicell applications to prevent back
charge is 1.0 volts. Note from looking at the alkaline specs above,
that's going to be reached at about a 50% indication from the Portadisc.
It matters little that the Portadisc might keep going at below 50%, to
do so will eventually destroy your batteries.

Now where is a NiMH in terms of it's discharge capacity when it reaches
1.0 volts? According to charts in Duracell's publication it appears to
have contributed virtually all it's charge, say 99% discharged. It's
voltage is falling like a man off a cliff. So the equivalent Portadisc
"reading" for seeing 50% on it's display if using NiMH is more like 1%
remaining or less. To put it in car terms you are running on fumes and
can probably count your remaining time in seconds.

It's been a while since I ran the long recording tests on my portadisc,
but I vaguely remember it quitting at something like 30-40%, but my
memory could be off. It was dropping several percent per second when it
cut out each time.

I don't like to go so close to danger (both of it quitting and killing
the batteries), which is why I arbitrarily assign a little more leeway
and use a displayed 70% as my hard cutoff. And typically actually change
over at 90-95%.

Finally, the "knee" the point where a NiMH is rated, 80% discharged, 1.2
volts, where does this occur with a Alkaline? Again, eyeballing
duracell's graphs at about the discharge rate of the portadisc, it's
well above the 5% discharged mark for a Alkaline when it passes 1.2
volts. Which says when my portadisc says 97%, I'm close around 80%
discharged for the NiMH, the equivalent to saying 20% remaining for it.

All this handwaving agrees pretty much with what I get with my
portadisc. Rough translated readings for a Portadisc running NiMh: 97%
means 20%, 50% means 1%.

If you want Duracell's tech stuff, the pdf's can be hunted up from here:

Each battery manufacturer build cells different, so duracell's data
should not be pushed too far in examining all this. A slightly different
cell might not graph the same. But I expect those numbers won't be far off.

> Can anyone say why Li ion are so complicated to charge?  I mean it is a
> battery for gosh sake!    I didn't think so. . .

You can find discussions of this all over the place, here's a sample:

"Li-Ion Charging: Li-Ion batteries commonly require a constant current,
constant voltage (CCCV) type of charging algorithm. In other words, a
Li-Ion battery should be charged at a set current level (typically from
1 to 1.5 amperes) until it reaches its final voltage. At this point, the
charger circuitry should switch over to constant voltage mode, and
provide the current necessary to hold the battery at this final voltage
(typically 4.2 V per cell).Thus, the charger must be capable of
providing stable control loops for maintaining either current or voltage
at a constant value,depending on the state of the battery."

"The main challenge in charging a Li-Ion battery is to realize the
battery's full capacity without overcharging it, which could result in
catastrophic failure. There is little room for error, only =B11%.
Overcharging by more than +1% could result in battery failure, but
undercharging by more than 1% results in reduced capacity. For example,
undercharging a Li-Ion battery by only 100 mV (-2.4% for a 4.2-V Li-Ion
cell) results in about a 10% loss in capacity. Since the room for error
is so small, high accuracy is required of the charging-control
circuitry.To achieve this accuracy, the controller must have a precision
voltage reference, a low-offset high-gain feedback amplifier,and an
accurately matched resistance divider.The combined errors of all these
components must result in an overall error less than =B11%."

That's the idea anyway, now you know. The above was lifted from a ad
blurb for a particular charger. I expect more research would show that
if you charged it slow enough it might get easier. But for any
reasonable time they are touchy.



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