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!

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!

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" 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!

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" 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

On Fri, 5 Nov 2004 10:10:35 -0500, "Tam/WB2TT"
wrote:


"Matt Warnock" 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


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.

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)

"Tom MacIntyre" wrote in message
...
On Fri, 5 Nov 2004 10:10:35 -0500, "Tam/WB2TT"
wrote:


"Matt Warnock" 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


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

That's impractical. an LDO series regulator would work, but be overkill.

Tam

"Tam/WB2TT" wrote in message
...

"Matt Warnock" 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


A chip that limits the voltage to whatever its specified. I have one for 6
volts, there are ones for 6 and 9 and 12v. it has 3 pins, 1 in, 1 out, 1
shared ground. I guess I really mean a regulator, not rectifier.

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 a ...... cigarette
lighter adaptor. The adaptor appears to have some power rectifying
circuitry. ****

NO ! A cigarette lighter outlet provides DC. Therefore this adaptor doesn't need
to provide any *rectification*.

More likely, it adjusts ( regulates ) the car battery voltage ( which varies
somewhat in use ) to the correct voltage for the LCD.

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,

Rectifiers don't do that.

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?

Far too small to do anything. You would need several, tens maybe, of thousands
of uF to significantly affect supply disturbances *plus* a series resistor or
choke.

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.

Do you know what voltage the LCD requires ? I suspect that the adaptor may
contain a voltage regulator that steps down the car's nominal 12 volts to the
needed value.


Graham

"Matt Warnock" wrote in message
news:FcTid.5$FE.4@lakeread06...
"Tam/WB2TT" wrote in message
...

"Matt Warnock" 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


A chip that limits the voltage to whatever its specified. I have one for
6 volts, there are ones for 6 and 9 and 12v. it has 3 pins, 1 in, 1 out,
1 shared ground. I guess I really mean a regulator, not rectifier.


Regulator, yes. Those are typically TO220 packages. They should be able to
handle just about anything automotive electrically speaking. Even in a
worst case scenario.

If the car adaptor has the regulation, why do you need to build anything
else? You might want to open up the cigarette adapter and see if there is
any regulator in the adaptor.. If there isn't, then just hook it straight to
power and don't worry about it.