Power supply question

[OverTork]

Is it feasable to connect a 0-120 volt variac directly to a 120/12 volt
transformer to get a 0-12 volt power supply. The variac puts out 3 amps and
the transformer has a 25 amp output rating. The output will be rectified,
filtered and fused for 15 amps as that's all I will be needing. The reason
for this approach is I would like to use parts I have on available. This
will be used for anodizing aluminum.

Thank you in advance.

 

[John Larkin]

On Mon, 12 Apr 2004 17:01:38 -0400, "OverTork" <OverTork@comcast.net>
wrote:

Is it feasable to connect a 0-120 volt variac directly to a 120/12 volt
transformer to get a 0-12 volt power supply. The variac puts out 3 amps and
the transformer has a 25 amp output rating. The output will be rectified,
filtered and fused for 15 amps as that's all I will be needing. The reason
for this approach is I would like to use parts I have on available. This
will be used for anodizing aluminum.

Thank you in advance.

Sure, should work fine.

John

 

[John Fields]

On Mon, 12 Apr 2004 17:01:38 -0400, "OverTork" <OverTork@comcast.net>
wrote:

Is it feasable to connect a 0-120 volt variac directly to a 120/12 volt
transformer to get a 0-12 volt power supply. The variac puts out 3 amps and
the transformer has a 25 amp output rating. The output will be rectified,
filtered and fused for 15 amps as that's all I will be needing. The reason
for this approach is I would like to use parts I have on available. This
will be used for anodizing aluminum.

---
With 120VRMS out of the variac, you'll get about 15.5 Peak DC volts
out of the bridge. I don't think you'll need the filter caps, since
you'll be anodizing with the DC out of the rectifier and what'll be
doing the work is the _average_ current going into the workpiece. In
addition, not having to filter will save you some money and will
reduce the load on the transformer and the variac. As far as fusing
goes, you should fuse on the mains side of the variac so that if
anything _does_ go wrong nothing downstream from the mains will be
hot.

--
John Fields

 

[CFoley1064]

Subject: Power supply question
From: "OverTork" OverTork@comcast.net
Date: 4/12/2004 4:01 PM Central Standard Time
Message-id: <jKadne--64ApnubdRVn-ig@giganews.com

Is it feasable to connect a 0-120 volt variac directly to a 120/12 volt
transformer to get a 0-12 volt power supply. The variac puts out 3 amps and
the transformer has a 25 amp output rating. The output will be rectified,
filtered and fused for 15 amps as that's all I will be needing. The reason
for this approach is I would like to use parts I have on available. This
will be used for anodizing aluminum.

Thank you in advance.

Variacs have always been used for plating power supplies -- you'll be fine.
Just remember you're limited to the output current rating of the variac on the
primary of the transformer, and the current rating of the secondary on the
output side of the transformer. That means the variac is good for 3A, whether
it's set for 120VAC out or 20VAC out. I would put a 3A fuse in front of the
variac, just to be safe.

By the way, be careful about fumes -- they'll corrode the surface of the
variac, causing discontinuities which lead to burning of the contact points.
Wipe the contacts occasionally with a soft, clean cloth, and keep the plating
fumes away.

Good luck
Chris