Re: More Battery Recharging Questions

On Fri, 23 Dec 2005 18:45:12 GMT, "BF Lake" <nomail@xxxxxxxxxx> wrote:

>
>"Neon John" <no@xxxxxxxxx> wrote in message
>news:khdoq1lcl5ftajjajj4icub70o612hmsr5@xxxxxxxxxx
>.
>> This why I don't use a hydrometer on a regular basis. The free space
>> electrolyte SG lags far behind that between the plates. If you could
>> leave the batteries alone for a day, the SG would rise significantly
>> as the liberated acid slowly diffuses out.
>
>Once again, I am grateful to have this cleared up. I have been putting the
>batteries on the 7355 when home and noticed that a couple days later the
>hydrometer says they are now really "full" I thought it was the 7355
>topping them off . So now I can feel better about my Vector . :)

You're welcome. After some fairly extensive testing, I consider that
vector line to be among the best chargers on the market as far as the
battery is concerned. I don't like having to start the thing manually
each time. But it sure does a battery good.
>>
>> A hydrometer is good for batteries that have been sitting for awhile
>> or batteries constantly on float charge, such as large standby
>> batteries. For highly dynamic batteries like ours, the hydrometer is
>> more of an annoyance.
>
>Especially when there isn't enough clearance over the batteries in their
>compartment to wield the hydrometer.
>
>This also negates the "disadvantage" for AGMs where you can't measure their
>state of charge when they have just been charged by checking their voltage
>(surface charge), and you can't use a hydrometer.

The only two disadvantages of AGMs that I know of are the cost and
that they require more attention to charging. You can't let it sit
there with a high voltage dumb charger and boil away for months at a
time. Other than that, I love 'em.
>
>> Our conventional definition of "fully charged", that is, when the
>> battery is accepting no more energy on trickle charge, is done just
>> fine with the Vector.
>
>All I need to do is redefine "full" from 100% to a lower number, and my
>anxieties will go away <G>. I wonder if their amphr rating capacity is
>measured from 100% or from a lower "full" too?
>>
>> After working with dozens, maybe hundreds of battery systems over the
>> years, I've observed that the absorption stage in wet deep cycle
>> batteries takes about 3 hours regardless of the size of the battery. A
>> function of plate geometry, I think.
>
>I saw where you said that going from a 20/10/2 to a 40/etc would only
>shorten the time for the bulk stage, so I inferred that once you have paid
>for a new 20 amp one there is no point paying again to get a 40 .(?) On the
>same lines, is there any real point in trading in a quite new 7355 for a PD
>with charge wizard?

I have enough experience with golf cart batteries now that I think I
can say with certainty that the benefits will be much less than if you
had several 12s (AGM or wet) in parallel. In addition to my MH
batteries, my EV has 72 volts' worth of cart batteries. For various
reasons I've had to charge the pack as sets of 12 volt batteries on
numerous occasions. My little car looks like it's under attack from
an octopus with all the chargers and wires hanging off it :-)

These behave just like the ones in my MH did. Early transition from
bulk to absorption. The higher current of those chargers would not
help all that much unless you deeply discharge the pack between
charges. With the relatively high internal impedance, it takes more
voltage to force more current. All that extra voltage does is heat
the battery and electrolyze the electrolyte.

I've tried the extra voltage approach despite my knowing that the
chemistry involved says it wouldn't work. I just had to see :-)

I set the bulk/absorption transition point on my CBC to 16 volts and
fired it off. The CBC quite merrily cranked 150 amps into the
batteries for some time, tapering off to about 100 amps. The result?
The batteries were on their way to thermal runaway when I shut down
the test and a good chunk of electrolyte had been ejected from the
violent gassing. Worse, the experiment didn't return a lot of charge
to the pack. I went ahead and charged them conventionally and saw
little difference.

One thing you CAN do to minimize the total run time of your generator
is charge in more than one sessions. I've verified this by
experiment. Stopping the charge, waiting awhile and then continuing
again lets the electrolyte equilibrate within the plates. If you stop
the first charge around the time of bulk/absorption transition, when
you return after a delay you'll find that the charger again runs in
bulk mode for quite some time. Frequently almost as long as the first
time. I haven't experimented to determine the optimum number of
intervals but I'd guess 2 to 3 with maybe an hour or 2 between
sessions.

If you do a lot of dry camping and want to get the maximum possible
amount of energy from the battery space you have, you might want to
consider wet NiCads. The BB600 jet engine starting battery is widely
available surplus. Here is a source:

http://www.sg-photo.com/nicad_batteries.htm

34ah, 1.25 volts per cell. $10/cell. Service life is rated at 30
years but the practical lifetime is far longer. Effectively a once in
a lifetime purchase. I have a 28 volt jet start pack of Korean war
vintage that still has its rated capacity.

There are so many advantages. The wet NiCad requires no special
charging algorithm. It can be run completely flat. In fact the
normal mode of storage is flat with the terminals shorted. Moderate
overcharging is harmless. In fact, it is recommended to charge to
gassing on each charge. The voltage is practically flat until total
discharge. VERY low impedance - a single 34ah pack can source
thousands of amps for a significant period. They parallel well with
no special precautions required. The potassium hydroxide electrolyte
is almost non-corrosive to ferrous metals and is much less corrosive
to skin than sulfuric acid. Plus it is quickly neutralized in air by
the CO2 in air. In fact, the only maintenance necessary on these
batteries other than watering them is replacing the electrolyte every
5-10 years as infiltrating air weakens the electrolyte.

The only disadvantage is cost. But that cost equals out after the
second or third Pb pack.

I'm going this route the next time. I think I'll start with 6 12 volt
strings in parallel for a total of 240 AH. At 10 cells per 12 volt
string, that's 60 cells. I imagine $5-8 each in that quantity will get
them. If so, about $480. If that isn't enough storage capacity then
I'll add a couple more strings. If I go this route then I'll remove
them when I sell the rig and take them to the next one. I'm also
saving my money for a NiCad pack for my EV but that's down the road a
bit.

Another advantage of these cells is that since they ARE individual
cells, the battery can be spread out over any available space. A few
tucked here, a few tucked there and so on. About the only
complication is that the connectors have to be nickel. Copper is
corroded by KOH.

A huge lot of these came up for sale mil surplus back in the summer.
Many EVers bought them. All are completely satisfied with the
performance.

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson
.

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