Stereo Amp connected to Cigar Light voltage...battery got weaken.

I connected stereo amp power supply to the cigar light power source
(+12volt). The amp
worked fine with no problem. I played the amp for 2 hours and I started
the car. The car
didn't start. I figured that the battery must gotten weaken after the
high current were drawn out
to the cigar light for 2 hours. I recharged the battery for 30 min.
Then the car did start.
Is this normal? Does battery get weaken after 2 hours of current is
drawn into cigar light
power source? If not, is there something wrong with my car electrical
system?

 

It can happen.. How big an amp? A class A audio amp running
high power draws quite a bit of current. Your electrical system is
ok most likely. The alternator seems to be working. You just ran the
battery down. The battery could be getting a bit weak.. BTW, usually
a lighter plug is not a very good place to connect high current gear.
The wire is thin, and the voltage drop fairly high.
I run ham radios in my cars, trucks, and have to consider current
draw. I usually carry two batteries if I'm going out of town. My radio
runs about 100w output, and draws appx 20 amps at full power.
I run my power wires direct to the battery using thick wire. Less
voltage drop, which means more usually "on" time before the
voltage drops too low for the radio to work correctly.
Using thick wire to high power audio amps is a pretty good idea.
You'll have better dynamic range as the amp is not seeing as large
a voltage drop on current peaks. You are drawing some hefty
current, or your battery is about half shot with a dead cell, etc..
BTW, every time you run the battery down like that, it loses some
capacity. You might want to get it tested..
MK

 

Yeah the battery got dry after the cigar lite drawn high current. I
tried to start
for hour it failed. after I recharged the battery, it starts right
away but...here is
my car problem might related to the stereo amp. My amp is about 400W I
connected to the same source my HU is using which is just the normal
+12volt ( My amp is not ran directly to the battery) I never had the
big problem like drying the battery. The battery is ok but my car
sometimes could not started right away in the morning. I thought it's
related to the alarm problem which i've said here. Now I'm thinking
there might be some electrical problem related to stereo amp power
source that causing the
starter fail to engage. I get no sound no click whatsoever. I've to
wait about between let say 1 min to 3 min. It usually starts. I've
to run my amp directly to the battery as
suggest by stereo technician.