Happy 4th Roger,
Sent from my iPod
On Jul 4, 2009, at 9:14 PM, Roger Stockton <
[hidden email]> wrote:
Jeff Mccabe wrote:
My problem today, actually for over a year, I just didn't
know it, is this dc-dc converter(transformer) for my HID headlights.
I also wanted to know if the noise was inductive or
conductive, so I powered the transformer from a separate 12v
battery (all interference went away, so its Inductive, right ? )
The more usual terms are conducted and radiated. Conducted means the interference is getting from the source to the destination via a conductive path (the 12V power or ground connections). Radiated means the interference is getting from the source through the air as RF energy (same as the signal from the radio station gets to your radio receiver).
If powering the DC/DC from a separate source eliminated the interference, then you have determined that the interference is conducted.
Good, got that one right
Tried capacitors on the 12v input (220uf & 2200uf), lights
wouldn't come on !
I can't think of any reason why capacitors between 12V and ground would possibly interfere with the DC/DC starting. You did try the caps between 12V and ground, not between 12V and the DC/DC, right?
Oops , no , I tried them in series with the positive side .
You are on the right track with the capacitors. I would try much smaller values, such as 0.1uF or 1uF,and connect it/them between 12V and ground as close to the input to the DC/DC as you can.
Thanks, I'll try this one tomarrow.
The idea here is that capacitors look nearly like a short circuit to high frequencies, so connecting one or more capacitors between 12V and ground "shorts" out the high-frequeny noise that comes out of the DC/DC on the 12V or ground lines.
Smaller value capacitors are more effective for higher frequencies. The 220uF and 2200uF caps you tried are relatively large values and will be electrolytic types, which may not be very effective if the noise from the DC/DC is fairly high frequency.
I would start with a 0.1uF film or ceramic capacitor and see how it does. If the noise isn't reduced enough, add a 1uF film in parallel with it. If it still isn't reduced enough, add the 220uF or 2200uF in parallel with the other caps.
Sounds like a plan, thanks
If you can't reduce the noise sufficiently with caps alone, try adding an inductor in series with the 12V line, between the caps and the car. If the noise still isn't reduced sufficiently, try moving the inductor to between the caps and the DC/DC.
This article may explain a bit better or in greater detail:
<
http://www.popularmechanics.com/how_to_central/automotive/1272491.html?page=3>
You may be able to find an off-the-shelf noise filter that you can install between the DC/DC and the 12V system. From your pictures, we can see that the DC/DC draws 3.2A in normal operation and a peak of 20A, so you need a filter capable of handling these sorts of currents.
This one, for instance is rated 15A/250W:
<
http://www.mcmelectronics.com/product/60-1055>
As long as it can tolerate the 20A peak (I'm assuming it is a turn-on surge), this is an inexpensive option.
Yes, the current quikly drops as the lights brighten.
Here's some beefier (and more costly) options:
<
http://www.tessco.com/products/displayProducts.do?groupId=619&subgroupId=65>
Diode to ground on the input side
I wouldn't expect this to help.
ran the 12v source through a relay directly from my 12v
This has the potential of helping, but you would need to use a double-pole relay so that you switch both 12V and ground to the DC/DC. Twist the 12V and ground leads together between the battery and relay and between the relay and DC/DC, and use the double-pole relay to connect the DC/DC directly to the 12V battery.
I'll try this also, I have a double pole laying around someware.
Cheers,
Roger.
Thanks again Roger !
Jeff
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