Re: [VACList] Univolt Hum

["Jim Dunmyer" <jdunmyer@xxxxxxxxxxx>]

Tom,
 The Charge Wizard is an addon specifically designed for the Inteli-Power
converter, and I don't really understand why it's not standard equipment. It
sells for something like $25.00 above the price of the I-P converter itself.

Here's the deal on RV converters:

Most of them are what is called "Constant Voltage Output", usually set at
13.8 volts. This will charge a "low" battery fairly quickly until it's at
about 50% charge, then much more slowly until the battery is fully charged.
Although the charge rate definitely tapers off as the battery approaches
full charge, the converter doesn't really "do" anything to make that happen,
it's just a function of the way things work. (see below for an analogy)

Modern converters are "smart" and perform charging in 3 distinct stages:
They set themselves to a high voltage, 14.4VDC in the case of the I-P w/C.W.
This causes a heavy charge into "low" batteries, but will not harm them
because they're capable of accepting that charge when they're discharged.
When the battery is about 80% charged, they adjust their output voltage to
13.6, causing the charge rate to drop to a low value to top off the charge.
After 24 hours, the I-P drops to 13.2 volts, low enough to keep the battery
charged, but not enough to cause water loss. To avoid stratification of the
electrolyte, the I-P goes to 14.4 volts for 15 minutes every 23 hours.

The net result is fast charging when you need it, without overcharging the
batteries once they're fully charged. Perversely, a standard
constant-voltage converter not only charges "low" batteries quite slowly,
but over-charges them once they're "full".

It's a physical law that batteries require a higher-than-nominal voltage in
order to cause charging to occur. The greater the differential, the faster
the charge, but the more potential for over-charge and damage. For that
reason, conventional converters are a compromise at best.

Think of it this way: Let's connect a small water tank to a larger one, the
larger one mounted on an elevating mechanism so the relative elevations can
be adjusted. The connection is a small hose, and the large tank is of
infinite size, so it can never be emptied. Let's close off a valve in the
hose (or disconnect it) and use water out of the small tank until it's
nearly empty. Setting the elevation of the large tank to slightly above the
small one, we connect the hose so as to fill the little one. You'll notice
that the flow rate will be fairly high at first, slowing as the level of the
water approaches that of the larger tank. If we leave the hose open, the
small tank will eventually fill, then start running over.

This is about what happens in your electrical system; think of the small
tank as your battery and the large one as the converter/charger.

Now, let's adjust the elevation of that larger tank, depending on the level
of the small one. Set it quite a bit higher, and you'll notice that the flow
rate is much higher also. When the small tank is about 3/4 full, lower the
larger tank so it's just above the "full" mark on the small tank. When the
small tank becomes full, lower the large tank's elevation so it's just even
with the small one. No overflow! Yet, when the small tank was low, we had a
high flow rate so as to fill it faster.

This illustrates the operation of a smart charger.

Does that help?

                                                                <<Jim>>