Re: Cpacpacitor bank in cars
Hello!
There is no "capacitor bank" in a gasoline car.
A capacitor or capacitor bank may be used to improve car stereo power supply,
that's all.
Now for the battery impedance, or let's say the internal resistance. It's
extremely low as said above. Look at you battery cables: depending on the
car, they can be, say 1cm or more in diameter, right? That's because the
current that flows in it is extremely high. Some car starters need about
250 amps, and for trucks it's probably around 1000.
Now if you have 12 V only, how can you draw, say, 240 amps (240 in order to
have easy calculation)? This means that the total impedance of the circuit
(impedance of the battery + impedance of the starter engine) should be
lower than 12 / 240, or 0.05 ohms.
Now what's the repartition?
If your battery has a higher impedance than the starter, then the battery
will consume most of the power. Now if the starter has a higher impedance
than the battery, that's fine. but it can be shown that the best combination
is when the battery and the starter have equal impedances.
And if you want to be sure that your car starts in winter at -20 degrees,
then it's better to be optimized. It's like in any system, the best efficiency
is when both impedances are the same. In the above case, we have therefore
impedances of 0.025 ohm (25 milliohms).
Now back to the capacitor bank: suppose you have a capacitor bank in
parallel with your batteries. If the cables are connected, both battery and
capacitors have the same voltage, right? Therefore they cannot cause
sparks. If you see sparks, then there is another reason.
Dora.
eem2am said:
Hello FvM,
If you disconnect your car battery then reconnect it you will see a small spark as you connect..thsi is due to the inrush into the large capacitor bank.
Lead acid batteries as i remember it have shocking internal impedances, it is very high internal impedance?
surely this is still the case?