Battery Voltage & Current - Monaco 2002 Diplomat Service Manual

NOTE: Any time more than one or two ounces of distilled
water is added per-cell per-thousand miles, check the
motorhome charging system for overcharging. Prolonged
overcharging generates excessive heat inside the battery,
which buckles the plates and destroys the battery. It is a
fact that over 50% of battery failures are caused by over-
charging.
Why does the voltage on a discharged battery measure the same as a fully
charged battery until the loads are applied? The simple answer to this might
go as follows: A battery creates electrical power by converting energy from a
chemical reaction into electrical energy. As this reaction slows down the bat-
tery voltage will drop. In a lead acid battery the electrolyte conductivity (how
well electrical current can flow through it) changes. The same current may be
available but the rate of the reaction decreases, causing a voltage drop.
Another way of looking at this is to use the analogy of a water pump
(a battery is an electric pump). The pressure in psi (pounds per square inch)
that a pump delivers is like a battery's voltage. The volume of water in GPM
(gallons per minute) is like the electrical current. Look at a 12 psi pump with
no loads (the pump is running but the outflow valve is turned off). The pump
will run and the internal pressure of the pump will build up to some point higher
than 12 psi. When the valve is opened, and the water is free to flow into the
loads, the pressure will drop to the rated output pressure of 12 psi, but only if
the load is not too big. If the pump is designed to maintain 12 psi at 15 GPM,
and a load demanding 20 GPM is connected, the pump will not be able to
keep up and the pressure will get sucked down to a lower psi. If the load is
reduced or removed the pump will catch up and return to its rated 12 psi pres-
sure. If the pump has an infinite source of water, such as a lake or the water
utility (this is like the grid, no battery), the pump will never run out of pres-
sure. If the pump never runs out of pressure, and is operated at or below its 15
GPM level, it will hold 12 psi. However, a pump that is connected to a water
tank with a finite capacity will start to lose the ability to hold pressure as the
level of water in the tank drops. Think of siphoning water from a bucket. As
the level of the water drops, the volume of water exiting the siphon slows
down.
When the tank is full it is capable of feeding more "pressure" to the pump
inlet due to gravity, and the pump always has enough water available to
maintain its rated pressure and volume. However, if the water tank gets low
the pump will not have enough water volume coming in to maintain 12 psi at
15 GPM. If the loads are removed from the pump by closing the valve on the
outflow, even with low pressure in the tank the pump will eventually pressure
up to 12 psi. It will just take it longer to get there. When the valve is opened
the pump will sustain 12 psi for a brief period, but since the tank is no longer
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D I P L O M A T
Electrical Systems - House
Battery Voltage &
Current
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