C
Circuit Breaker
Guest
Hello all
I know this can be done. They do it to VCRs, TVs, DSS receivers... there
must be a way I can do this, but Google isn't helping, nor is ask.com.
I have a variable voltage, 450 milliampere, regulated DC power supply.
Without going into too much detail, I used a 2-conductor power cord. I
didn't think I'd need a grounding cord, because the box is entirely
plastic and the secondary electronics are physically and electrically
separated from the transformer (save but for the two secondary leads,
of course). So, I didn't think I'd need a three-conductor grounding
cord. If I *HAVE* to, I've got about a half dozen old computer supply
cords I can cut up, but I'd rather stick with the cord I have (since I
KNOW this can be done).
I am trying to get rid of a hum I get any time I use this supply for
radio-frequency projects (I have an FM-broadcast-band transmitter (less
than quarter watt input, and that's mostly the caps, LED, and other
non-transmitting components) (range is only a couple hundred feet), plus I
have played with receiver projects as well. For some reason, it never
dawned on me until a few days ago, that whether the hum is actually in the
power output or not, the source is the transformer. I could probably move
my projects a couple feet away using a long power feed wire (which I
vaguely recall having a positive effect before, indicating the hum was
picked up inductively as opposed to through the power leads), but that
becomes inconvenient compared to having them right there with the supply.
They do it on VCRs, DSS receivers, and other RF-based,
two-conductor-powered, metal-chassised devices, but how? I've taken one
VCR and one DSS unit apart to reverse engineer it, and in the case of the
VCR, they went through some circuitry I couldn't easily follow, and in the
DSS unit, they used simply what was a resistor between chassis ground and
line neutral (there was an unmarked capacitor also, but it connected the
neutral to what appeared to be nothing at all). The resistor was striped
green-silver-green-grey-gold, which I find odd, considering silver is a
tolerance indicator. I measure only 1.9 megohms resistance between
neutral and chassis, which oddly enough shoots up to over 8 megohms if I
touch the "hot" conductor. On the capacitor, it measured about 0.5
nanoFarads, and of course these readings will be slightly off since I
could not remove them without desoldering them.
So, how can I do this safely? All I want to do is shield the transformer,
or "ground" the casing of the transformer (which is what would normally
happen). I'm not worried about shock hazards, as the entire case is
plastic and the only time I ever open it is with it unplugged.
Directly connecting the case of the transformer to the "ground" side of
the DC circuitry (I guess "common" would be a better term -- the "negative
terminal", if you will) won't have any effect, will it? Could it be that
simple?
Any advice? Thanks in advance, you'll be finishing a two-day search on
the subject -- which is more than I usually waste on something like this.
CJ
--
THIS POST ORIGINATED FROM USENET, *NOT* ANY WEB-BASED FORUM! IF YOU ARE READING
IT FROM A WEB BROWSER SUCH AS INTERNET EXPLORER OR NETSCAPE, THEN YOU ARE NOT
READING THE ORIGINAL POST AND YOU SHOULD LEARN ABOUT "USENET" FROM
http://www.ibiblio.org/usenet-i/usenet-help.html
I know this can be done. They do it to VCRs, TVs, DSS receivers... there
must be a way I can do this, but Google isn't helping, nor is ask.com.
I have a variable voltage, 450 milliampere, regulated DC power supply.
Without going into too much detail, I used a 2-conductor power cord. I
didn't think I'd need a grounding cord, because the box is entirely
plastic and the secondary electronics are physically and electrically
separated from the transformer (save but for the two secondary leads,
of course). So, I didn't think I'd need a three-conductor grounding
cord. If I *HAVE* to, I've got about a half dozen old computer supply
cords I can cut up, but I'd rather stick with the cord I have (since I
KNOW this can be done).
I am trying to get rid of a hum I get any time I use this supply for
radio-frequency projects (I have an FM-broadcast-band transmitter (less
than quarter watt input, and that's mostly the caps, LED, and other
non-transmitting components) (range is only a couple hundred feet), plus I
have played with receiver projects as well. For some reason, it never
dawned on me until a few days ago, that whether the hum is actually in the
power output or not, the source is the transformer. I could probably move
my projects a couple feet away using a long power feed wire (which I
vaguely recall having a positive effect before, indicating the hum was
picked up inductively as opposed to through the power leads), but that
becomes inconvenient compared to having them right there with the supply.
They do it on VCRs, DSS receivers, and other RF-based,
two-conductor-powered, metal-chassised devices, but how? I've taken one
VCR and one DSS unit apart to reverse engineer it, and in the case of the
VCR, they went through some circuitry I couldn't easily follow, and in the
DSS unit, they used simply what was a resistor between chassis ground and
line neutral (there was an unmarked capacitor also, but it connected the
neutral to what appeared to be nothing at all). The resistor was striped
green-silver-green-grey-gold, which I find odd, considering silver is a
tolerance indicator. I measure only 1.9 megohms resistance between
neutral and chassis, which oddly enough shoots up to over 8 megohms if I
touch the "hot" conductor. On the capacitor, it measured about 0.5
nanoFarads, and of course these readings will be slightly off since I
could not remove them without desoldering them.
So, how can I do this safely? All I want to do is shield the transformer,
or "ground" the casing of the transformer (which is what would normally
happen). I'm not worried about shock hazards, as the entire case is
plastic and the only time I ever open it is with it unplugged.
Directly connecting the case of the transformer to the "ground" side of
the DC circuitry (I guess "common" would be a better term -- the "negative
terminal", if you will) won't have any effect, will it? Could it be that
simple?
Any advice? Thanks in advance, you'll be finishing a two-day search on
the subject -- which is more than I usually waste on something like this.
CJ
--
THIS POST ORIGINATED FROM USENET, *NOT* ANY WEB-BASED FORUM! IF YOU ARE READING
IT FROM A WEB BROWSER SUCH AS INTERNET EXPLORER OR NETSCAPE, THEN YOU ARE NOT
READING THE ORIGINAL POST AND YOU SHOULD LEARN ABOUT "USENET" FROM
http://www.ibiblio.org/usenet-i/usenet-help.html