Low noise power supply from vehicle 12 volt?

[Ro]

Hi,

I am looking for a simple way of getting a low noise supply from my car's
12 volt supply.

I using it to power an Apple Ipod, which can accept anything between 7 and
18 volts. It runs fine directly off the vehicle supply, but there is
considerable interference when the engine is running, which is dependent on
the engine revs.

The voltage does not need to be regulated, but the supply needs to be free
of noise. I did read somewhere about a power supply which actually
generated a new ground, so that it was completely independent of the
vehicle's ground.

Thanks in advance

Ro

 

[Rheilly Phoull]

It would probably be worthwhile trying a choke in the supply to the Ipod,
followed by at least one capacitor ( not electrolytic).

 

[Ro]

Thanks for the information.

What value of choke and capacitor should I use?

Thanks,

Ro

 

[AC/DCdude17]

X-No-Archive: Yes

Use a 7809 9V 1A regulator. A linear 3 terminal regulator IC can minimize
ripple. It will give you ripple free 9V output from fluctuating 11 to 14V
input you'll encounter from vehicle's electrical system.

Here's a diagram:
http://www.hut.fi/Misc/Electronics/circuits/psu_5v.gif

Use a 7809 instead of a 7805. The capacitor capacitance is unimportant. Use
whatever you have rolling around.

 

[Rheilly Phoull]

If you go the choke route probably the simplest approach would be to get one
from a car radio installer to suit your current rating. The 'Dudes'
suggestion could work out cheaper and be as effective.

 

[Greg Neill]

I tried the L7809, but I still get the noise. it's coming from the ground
wire, because even if I disconnect the power, with the ground connected, I
get it.

Does anyone have any ideas?

Shield your circuit. Use shielded wiring and
employ bypass caps at either end of it. Make
sure that you've got a single ground point to
avoid current loops.

 

[Bob]

I tried the L7809, but I still get the noise. it's coming from the ground
wire, because even if I disconnect the power, with the ground connected, I
get it.

Does anyone have any ideas?

I just got a new van with VCP+LCD, which also looks noisy when
the engine is running. I found that simply applying a slight
pressure to the VCP power connector makes the noise go away.

Presumably this implies a weak ground connection...?
Try applying slight pressure to the power plugs and see if
that has an effect. May just need better grounding.

-Bob

'On the edge of sleep, I heard voices behind the door
The known and the nameless, familiar and faceless
My angels and my demons at war' -Rush, Double Agent