I wrote most of this yesterday & didn't send it.
Could be shorter :-) - but hopefully covers the point.


> Bob said:
>
>
> >no, the purpose of the capacitor is to capture the PEAK voltage which is
> >being lost due to wiring losses, The capacitor is allowed to charge to a
> >peak, then the mosfet switch is engaged to apply a pulse of energy at
> >the peak voltage.
>
> Jim said:

> I'm not picturing it, but I won't burden you by asking for more info.
>
> I will say that my comments re: Pulse Charging come from 35 years as a
> Process Engineer in the lead-acid battery industry where I wrote material
> specs and designed processes for battery manufacturing as well as had
> plenty
> of hands-on experience.  The same company also manufactured chargers and
> UPS
> systems.  And its research labs did extensive investigation into pulse
> charging.  The short story is that it has no advantage over constant
> potential or modified constant potential charging
> ...
>

__________

Lets see if I can provide some sort of a "bridge" between these two
understandings.
Bob mentioned a situation that I have heard mentioned elsewhere as being
one where they had used pulse charging to advantage.
This is in solar powered systems where insolation (sunshine) levels are low
 - and equally applies where battery capacity is large relative to the
available PV panel wattage.

For much  of its charging range a lead acid battery can be charged at
whatever current level is available. Charging in the first and longest part
of the charging cycle may be at any current available up to some specified
maximum. Once a certain maximum voltage is reached the battery is charged
at constant voltage with current decreasing under control of the battery
chemistry. The battery may be floated at this specified constant voltage
indefinitely except for the special actions mentioned below. Actual float
voltage depends on the type of lead acid battery (flooded, AGM, gel, ... ),
sometimes construction style (eg Gates spiral wound differ from the norm)
and, very importantly whether the battery is long term floated in standby
mode, or deep or semi-deep discharged. So far all these could (probably) be
handled by a low and variable charging source such as solar may provide.

Then there is boost / equalisation mode. The battery is run at a higher CV
mode for a limited period and caused to take additional charge for a
limited period. The ability to implement this high voltage charging is
vital to the long term life of the battery. An excessively limited solar
source may not have the combination of energy transfer rate and voltage
needed to implement this mode.
With a low enough energy source relative to "leakage" current the battery
may not even properly enter the float mode.
Battery University say: "The switch from Stage 1 to 2 occurs seamlessly and
happens when the battery reaches the set voltage limit. The current begins
to drop as the battery starts to saturate, and full charge is reached when
the current decreases to the three percent level of the rated current. A
battery with high leakage may never attain this low saturation current, and
a plateau timer takes over to initialize the charge termination."

In addition to leakage compensation, Bob notes the effect of long wiring
runs. The effect of this is obviously complex due to interaction between
source voltage, circuit resistance, battery state of charge and changes in
the voltage drop which occur when the battery responds to lower voltage.
What Bob is reporting is that having a cycled source of higher voltage
allows charging when a high resistance continuous source does not. This is
outside Jim's area of charging scenarios and Bob's experiences here are
complementary rather than opposed.



     Russell


            Battery University - charging lead acid batteries:

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery


          Sealed lead acid battery charging basics
           http://www.powerstream.com/SLA.htm

          SLA fast charging
           http://www.powerstream.com/SLA-fast-charge.htm
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.