car electronics - rectifier

M

Matt Warnock

Guest
I'm connecting some electronics to the power in my car. I know that the car
electrical system can be a little harsh, so I'm wondering the best way to
protect delicate electronics. The device in question is an LCD screen I
have installed. The device came with an AC power supply and a cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. My question is, if I want to connect to this to the power, what
kind of circuitry should I build? I was going to use a 12v rectifier to
keep the voltage from going over 12 volts, and a cap between the input
voltage and ground and another one between the output voltage and ground.
Is this a sufficient design for this application, and what value caps should
I use? I think I used small ceramic caps .22uf maybe? last time I made
something like this. Also, I don't want to cut up my cigarette lighter cord
and use the rectifier, but this is an option too.

let me know if you have any ideas. thanks!
 
I'm connecting some electronics to the power in my car. I know that the
car
electrical system can be a little harsh, so I'm wondering the best way to
protect delicate electronics. The device in question is an LCD screen I
have installed. The device came with an AC power supply and a cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. My question is, if I want to connect to this to the power,
what
kind of circuitry should I build? I was going to use a 12v rectifier to
keep the voltage from going over 12 volts, and a cap between the input
voltage and ground and another one between the output voltage and ground.
Is this a sufficient design for this application, and what value caps
should
I use? I think I used small ceramic caps .22uf maybe? last time I made
something like this. Also, I don't want to cut up my cigarette lighter
cord
and use the rectifier, but this is an option too.

let me know if you have any ideas. thanks!
Click to expand...
You could always hit Radio Shack and buy a female cig lighter adapter. Then
you wouldn't have to cut the cord.
 
On Thu, 04 Nov 2004 22:37:30 -0500, Matt Warnock wrote:

I'm connecting some electronics to the power in my car. I know that the car
electrical system can be a little harsh, so I'm wondering the best way to
protect delicate electronics. The device in question is an LCD screen I
have installed. The device came with an AC power supply and a cigarette
^^^^^^^^^ ^^^^^^^^^
lighter adaptor. The adaptor appears to have some power rectifying
^^^^^^^^^^^^^^^
circuitry. My question is, if I want to connect to this to the power,
what kind of circuitry should I build? I was going to use a 12v
rectifier to keep the voltage from going over 12 volts, and a cap
between the input voltage and ground and another one between the output
voltage and ground. Is this a sufficient design for this application,
and what value caps should I use? I think I used small ceramic caps
.22uf maybe? last time I made something like this. Also, I don't want
to cut up my cigarette lighter cord and use the rectifier, but this is
an option too.

let me know if you have any ideas. thanks!
Click to expand...
Isn't the lighter adapter that came with it intended to just plug in
to the lighter socket?

???
Rich
 
In article <UzCid.7639$ep3.1328@lakeread02>,
"Matt Warnock" <warnockmREM@OVEcox.net> wrote:

I'm connecting some electronics to the power in my car. I know that the car
electrical system can be a little harsh, so I'm wondering the best way to
protect delicate electronics. The device in question is an LCD screen I
have installed. The device came with an AC power supply and a cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. My question is, if I want to connect to this to the power, what
kind of circuitry should I build? I was going to use a 12v rectifier to
keep the voltage from going over 12 volts, and a cap between the input
voltage and ground and another one between the output voltage and ground.
Is this a sufficient design for this application, and what value caps should
I use? I think I used small ceramic caps .22uf maybe? last time I made
something like this. Also, I don't want to cut up my cigarette lighter cord
and use the rectifier, but this is an option too.

let me know if you have any ideas. thanks!
Click to expand...
A rectifier won't limit output to 12V.

Make sure that it runs off 12V, not 9V. The car adaptor could really
contain a voltage regulator.

A simple LC or RC filter works for automotive power spikes. LC
(inductor + capacitor) filters are available as "noise eliminator" kits.
RC (resistor + capacitor) filters work fine for low power equipment. 1
Ohm series on the input then 2200 microfarads to ground works. It will
loose 1 volt per amp drawn. Make sure you use a single ground.
 
"Matt Warnock" <warnockmREM@OVEcox.net> wrote in message
news:UzCid.7639$ep3.1328@lakeread02...
I'm connecting some electronics to the power in my car. I know that the
car electrical system can be a little harsh, so I'm wondering the best way
to protect delicate electronics. The device in question is an LCD screen
I have installed. The device came with an AC power supply and a cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. My question is, if I want to connect to this to the power,
what kind of circuitry should I build? I was going to use a 12v rectifier
to keep the voltage from going over 12 volts, and a cap between the input
voltage and ground and another one between the output voltage and ground.
Is this a sufficient design for this application, and what value caps
should I use? I think I used small ceramic caps .22uf maybe? last time I
made something like this. Also, I don't want to cut up my cigarette
lighter cord and use the rectifier, but this is an option too.

let me know if you have any ideas. thanks!

I don't know what you mean by 12 V rectifier. If you mean 12 V zener, keep
Click to expand...
in mind that nominal battery voltage with the engine running will probably
be over 14 volts, and it could go higher under a trouble condition. To limit
high voltage spikes, you could add an automotive transient suppressor. These
generally limit at about 20 V.

Tam
 
On Fri, 5 Nov 2004 10:10:35 -0500, "Tam/WB2TT" <t-tammaru@c0mca$t.net>
wrote:

"Matt Warnock" <warnockmREM@OVEcox.net> wrote in message
news:UzCid.7639$ep3.1328@lakeread02...
I'm connecting some electronics to the power in my car. I know that the
car electrical system can be a little harsh, so I'm wondering the best way
to protect delicate electronics. The device in question is an LCD screen
I have installed. The device came with an AC power supply and a cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. My question is, if I want to connect to this to the power,
what kind of circuitry should I build? I was going to use a 12v rectifier
to keep the voltage from going over 12 volts, and a cap between the input
voltage and ground and another one between the output voltage and ground.
Is this a sufficient design for this application, and what value caps
should I use? I think I used small ceramic caps .22uf maybe? last time I
made something like this. Also, I don't want to cut up my cigarette
lighter cord and use the rectifier, but this is an option too.

let me know if you have any ideas. thanks!

I don't know what you mean by 12 V rectifier. If you mean 12 V zener, keep
in mind that nominal battery voltage with the engine running will probably
be over 14 volts, and it could go higher under a trouble condition. To limit
high voltage spikes, you could add an automotive transient suppressor. These
generally limit at about 20 V.

Tam
Click to expand...
A zener would require the appropriate resistor in series with it,
based on current draw and potential difference, to drop the excess
voltage also.

Tom
 
A zener would require the appropriate resistor in series with it,
based on current draw and potential difference, to drop the excess
voltage also.
Click to expand...
I smell dead battery.

A zener-resistor circuit alone is not the answer, short of triggering it
with the ignition wire. Even then, the zener will probably get pretty hot.
The car voltage and LCD current draw fluctuates too much to be able to
accurately choose a resistor that will work well with a small zener.

(when I refer to the LCD current draw fluctuating, I mean that it changes
based on the brightness setting on the LCD. I change mine based on whether
or not it's dark outside)
 
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