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What's the Difference between a Start and a Run Capacitor?
</h1>
<p>
Capacitors in General
</p>
<p>
A capacitor is an energy storing device. It is a medium by which energy is
stored to either be released suddenly or over a period of time. The energy or
capacitance of an electric capacitor is measured in the form of micro-farads.
Essentially, two plates are separated by a material known as a dielectric or
insulator. These insulators can be mica, ceramic, porcelain, Mylar, Teflon, glass,
or rubber. Capacitors will also limit the current. They can be used to store
voltage or build it up until the call for it to be released is present.
</p>
<p>
Start Capacitors
</p>
<p>
A start capacitor is found in the circuit of start windings when the motor is
starting. This capacitor contains a higher capacitance than a run capacitor. It
varies, but a start capacitor will measure between 70 and 120 micro Farads. The
start capacitor provides an immediate electrical push to get the motor rotation
started. Without a start capacitor when the voltage is applied, the motor would
just hum. The start capacitor creates a current to voltage lag in the separate
start windings of the motor. The current builds up slowly, and the armature has an
opportunity to begin rotating with the field of current.
</p>
<p>
<a href="http://www.sokcapacitor.com/run-capacitor/" target="_self">Run
Capacitors</a>
</p>
<p>
A run capacitor uses the charge in the dielectric to boost the current which
provides power to the motor. It is used to maintain a charge. In AC units, there
are dual run capacitors. One capacitor provides power to the fan motor. The other
sends power to the compressor. Run capacitors measure in at approximately 7-9
micro-Farads. The value or rating of the run capacitor must be accurate. If the
value is too high, the phase shift will be less than perfect and the winding
current will be too high. If the capacitor value/rating is too low, the phase
shift will be higher and the winding current will be too low. If run capacitors
are not ideal, then the motor could overheat and the true torque will not be
enough to drive current.
</p>
<h2>
What is Equivalent Series Resistance?
</h2>
<p>
The equivalent series resistance of a <a
href="http://www.sokcapacitor.com/run-capacitor/resistant-capacitors.html"
target="_self">capacitor</a> is the internal resistance that appears in series
with the capacitance of the device. Almost all capacitors exhibit this property at
varying degrees depending on the construction, dielectric materials, quality, and
reliability of the capacitor. The equivalent series resistance (ESR) values range
from a few milliohms to several ohms, and results into power losses, reduced
efficiency, and instability of power supplies and regulators circuits.
</p>
<p>
Image source
</p>
<p>
The aluminum electrolytic capacitors and tantalum ones, have higher ESRs than
ceramic capacitors of the same capacitance and voltage rating. The polypropylene
and polyester capacitors fall in between, but are not commonly used in the SMPSs
due to their large physical sizes.
</p>
<p>
Main parts of an ESR
</p>
<p>
Metallic resistance
</p>
<p>
Electrolytic and paper resistance which is dependent on frequency and
temperature
</p>
<p>
Dielectric which depends on frequency
</p>
<p>
Factors that increase the ESR value
</p>
<p>
Bad electrical connections; – The connection between the copper leads and the
aluminum plates in the capacitor are usually welded or made using mechanical
crimps. This type of connections introduces some series resistance, and is used
because the aluminum cannot be soldered.
</p>
<p>
The drying of capacitor electrolyte solution. As the liquid component of the
electrolyte dries out due to elevated temperatures, the electrical resistance
increases.
</p>
<p>
ESR increases with increase in temperature and frequency. In power supplies
with high currents, the power dissipation associated with the ESR may further
increase the temperature and lead to capacitor failure.
</p>
<p>
Minimizing ESR in circuits
</p>
<p>
High performance applications use the low ESR capacitors such as the low ESR
solid polymer capacitors, tantalum capacitors and the multilayer ceramic
capacitors (MLCC).
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