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stereo loses settings when startup



 
 
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  #21  
Old February 2nd 05, 04:19 AM
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Richard Bell wrote:
> In article > ,
> Bruce Chang > wrote:
> >
> >"sdlomi2" > wrote in message
> ...
> >> Help! Got a '55 Studebaker. Aftermkt. mp3/cd/amfm radio. If

I set
> >> stations, it remembers fine going from on to off to access to off.

But!
> >> When I start i, the starter seems to drop the "voltage

threshold"(at least
> >> that's what I visualize) such that all memory settings are lost.
> >> Ideas, please? Thank you, s
> >>
> >>
> >>

> >
> >Maybe a small 12V battery or large capacitor that's hooked up with a

diode
> >between it and the car battery so voltage to the stereo won't drop

when the
> >car battery voltage drops significantly.
> >

The large capacitor will cause a voltage
> spike, just after the motor starts, so a choke coil will be needed to
> protect the sound unit.


Inductors generate spikes, not capacitors. The best
arrangement has a choke in the supply line, with a capacitor between
the hot side of the choke and ground. That'll swallow most
interference. It would take a pretty big capacitor to keep a stereo
happy.
Spikes are generated by the starter solenoid and by the starter
itself when the current is cut off. A capacitor cannot provide any
higher voltage than it was provided with in the first place, but an
inductor like a solenoid can make a 600-volt spike. I've measured it.
It's the principle behind the ignition coil.

> Here, in the Great White North (How's it goin', eh?), we would advise

you that
> your battery is seriously short of cold cranking amperage and that

you
> should buy the biggest battery that will fit in the tray. However,

being
> designed for old-tech batteries, you should accept anything that

covers half
> of your '55 studebaker's battery tray. While cold weather starting

may be
> the least of your worries, a larger battery is the simplest (if not

the
> cheapest) solution to your problem.


A 35-watt electric battery blanket will make that battery
perform. Some guys use them instead of a block heater. A battery loses
something like 60% of its capacity at -25 degrees C.

Dan

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  #22  
Old February 4th 05, 04:42 AM
Richard Bell
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In article om>,
> wrote:
>
>Richard Bell wrote:
>The large capacitor will cause a voltage
>> spike, just after the motor starts, so a choke coil will be needed to
>> protect the sound unit.

>
>Inductors generate spikes, not capacitors. The best
>arrangement has a choke in the supply line, with a capacitor between
>the hot side of the choke and ground. That'll swallow most
>interference. It would take a pretty big capacitor to keep a stereo
>happy.



The car sits with the engine not running for a long time, so the voltage
on the capacitor drops to the battery terminal voltage (hopefully 12.6v).
During cranking, the battery voltage drops to below the keep-alive
threshold (whatever that is), but the low load of the audio system keep the
cap at about 12.6v. The engine catches, and the alternator now cranks out
current at a voltage that will charge the battery (14+ volts). The cap
draws a current appropriate to two or more volts divided by the wire's
resistance in ohms, or a few tens of amps. As all wires in the real world,
running close (or within) large steel objects have non-zero inductance, the
circuit will ring. Without the capacitor, the switching transient is not
as bad, as there is no apparent short circuit to a lower voltage, so there
is no inrush overcurrent.

Switching transients always happen. Capacitors make them worse. On some
powerlines, switched capacitor banks are more serious than lightning strikes.
 




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