1. Q1 Controls current flowing through R5 and thus, C1 while charging. Use N-channel logic level (Vgs on <= 3V) device.
2. Q2 is error amp, controlling gate voltage on Q1. D3 compensates for B-E voltage drop on Q2. R1 determines gain of
error amp, R2 provides bias current for D3.
3. Voltage at Q1 source should be maintained close to voltage set by R4. Thus, R4 sets the current limiting level.
■ FIGURE 7
want to monitor a narrow range of a
greater voltage input — an expanded
scale voltmeter, for example, that
would monitor a 12-volt gel-cell between 11.0 and 13.2 volts to
determine percentage of charge.
QBatteries are divided into
two types: dry and wet.
For sealed and non-sealed
lead-acid batteries, are both
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AIn a manner of speaking, all
lead-acid batteries are wet.
As to how wet is a matter of
definition. Most unsealed
lead-acid batteries — like those under
the hood of your car — are categorized
as flooded. That means they have
water as their base with a hint of
sulfuric acid. If they are tipped
sideways, they spill out corrosive
liquid water (the newer cap-less
batteries to a lesser extent — but still).
Gel-cells use a thixotropic gelled
electrolyte that behaves more like
Silly Putty than water (think the Steve
McQueen movie The Blob). Therefore,
it can be operated in virtually any
position — although upside-down
is not recommended. The “liquid”
is trapped in the cell by special
pressurized sealing vents. The sealing
vent is critical to the performance of
the gel-cell. The cell must maintain a
positive internal pressure. If opened,
the cell will quickly evaporate and not