Re: desulfator - update

On Sun, 28 Sep 2008 10:35:16 -0500, Bob Giddings <bobg@xxxxxxxxxxxx> wrote:

On Sun, 28 Sep 2008 11:21:12 -0400, Neon John <no@xxxxxxxxx>
wrote:

Right now I'm thinking money well spent.

Yep. Thanks for verifying that vendor. I don't think that I could build one
for $25, even using perf board so I'm going to order some.

John

The Progressive Dynamics inverter/chargers with the Charge Wizard
have a desulfator mode built in that charges up to 14.6 V . Any
idea how that compares to this one?

That' more commonly known as an equalization charger. It's designed to
overcharge all the cells a little to make sure the weakest cell is brought up
to full charger - equalization.

When a battery discharges, the sponge lead and lead dioxide on the plates
converts to lead sulfate. In this form it is a soft spongy matrix of micro
crystals. The stuff is so soft that it crumbles at the merest touch.

Charging reverses this process if it goes to completion on ALL cells. The
weakest cell (by that I mean the one with the lowest charge acceptance
efficiency) will typically not have all its lead sulfate converted. Over time
this residual lead sulfate agglomerates into larger hard lead sulfate
crystals. These crystals are non-conductive and so insulate the underlying
active material from the electrolyte. They are also physically larger than
the active material they formed from and so they damage separators and jack
active materials off the plates. In a badly sulfated battery, the coating of
sulfate looks like frost covering the plate. Often times sharp crystals of
sulfate can be seen protruding from the plate like little glistening
hypodermic needles.

An equalizing charge stops this process by making sure all cells are fully
charged, that is, all the sulfate is converted.

The pulse desulfator works by a different mechanism that as far as I've been
able to learn, is not fully understood. It addresses the hard sulfate
crystals that have already formed. One theory is that the pulses stimulate
mechanical resonance in the sulfate crystals causing them to fracture and
allow electrolyte in. I'm not too sure of that theory because the crystals
aren't large enough to resonate at the low frequency involved. That one makes
as much sense as the alternative explanations that I've read, though. It's
one of those situations where the effect was accidentally observed and now
they're trying to figure out why it works.

From the outside, the battery does look like it has a resonant point. If a
variable frequency oscillator is connected to a battery and observed with a
scope, when the frequency is swept across the audio band, there will be one or
more frequencies where the battery is resonant. That is, it much more
strongly absorbs the AC signal than at surrounding frequencies.

The pulse desulfator does its thing by hitting the battery with a series of
narrow, fast rise time high voltage pulses. Typically 40-60 volts with a
pulse width of around a microsecond, repeated a couple thousand times a
second.

This very fast rising and falling pulse is rich in harmonics and one or more
is the right frequency to stimulate the resonance.

Several things lend credibility to the resonance (of some sort, at least)
theory. One, the higher the amplitude, the faster the action. Two, a power
oscillator running at the resonant frequency accomplishes the same thing.
Third, a battery plate that has been pulsed for awhile loses most of its
frosty look.

There are some rather loud-mouthed detractors (not in this group but elsewhere
on the net) who try to claim that extended equalizing charging does the same
thing. The fly in the ointment for that theory is that most all of the
pulsers available, either ready-made or as kits, are parasitic devices. That
is, they're powered by the battery being treated. No external power is
supplied. Extended high voltage (equalization or above) charging will bring
back some capacity but not to the extent that the pulsers do.

A pulser isn't strictly necessary for a new battery and a competent charger.
However, it doesn't hurt a healthy battery and is there if something happens
to the charger or connections that result in an incompletely charged battery.
Cheap insurance.

John

--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Democracy is three wolves and one sheep voting on what to have for supper.

.

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