transformer and full wave bridge rectifier

[dwbauer]

I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked + AC -
with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center. What
do I do with the transformer three and four on the bridge?
Thanks for any help to a dummy; Don

 

[John Fields]

On Sun, 29 May 2005 10:19:32 -0400, "dwbauer" <dwbauer@bellsouth.net>
wrote:

I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked + AC -
with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center. What
do I do with the transformer three and four on the bridge?

---
Connect the yellow wires to the AC terminals of the bridge and either
cut off the center tap or cut off the exposed conductor and tape the
wire back out of the way so it won't touch anything that gets hot.
Connect the + terminal of the bridge to whatever was connected to the
+ terminal of the old bridge and connect the - terminal of the bridge
to whatever was connected to the - terminal of the old bridge.

I don't know what you mean by:
"What do I do with the transformer three and four on the bridge?".

--
John Fields
Professional Circuit Designer

 

[Art]

Terminals labeled AC on the rectifier bridge are connected to the ac source,
your transformer. The + and - are connected to the filtering circuitry and
eventually the load. Pay attention to the polarity of the + and -
connections, as to where the originals were connected. With your
transformer, as noted, connect the yellow leads to the AC terminals of the
rectifier bridge. Isolate and insulate the centre lead.
"John Fields" <jfields@austininstruments.com> wrote in message
news:a7kj9114e6pgp7lodijcae3lj1rq8j4kkg@4ax.com...

On Sun, 29 May 2005 10:19:32 -0400, "dwbauer" <dwbauer@bellsouth.net
wrote:

I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center
tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked +
AC -
with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center.
What
do I do with the transformer three and four on the bridge?

---
Connect the yellow wires to the AC terminals of the bridge and either
cut off the center tap or cut off the exposed conductor and tape the
wire back out of the way so it won't touch anything that gets hot.
Connect the + terminal of the bridge to whatever was connected to the
+ terminal of the old bridge and connect the - terminal of the bridge
to whatever was connected to the - terminal of the old bridge.

I don't know what you mean by:
"What do I do with the transformer three and four on the bridge?".

--
John Fields
Professional Circuit Designer

 

[dwbauer]

That worked great!
Thanks, so very Much; Don
"John Fields" <jfields@austininstruments.com> wrote in message
news:a7kj9114e6pgp7lodijcae3lj1rq8j4kkg@4ax.com...

On Sun, 29 May 2005 10:19:32 -0400, "dwbauer" <dwbauer@bellsouth.net
wrote:

I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center
tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked +
AC -
with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center.
What
do I do with the transformer three and four on the bridge?

---
Connect the yellow wires to the AC terminals of the bridge and either
cut off the center tap or cut off the exposed conductor and tape the
wire back out of the way so it won't touch anything that gets hot.
Connect the + terminal of the bridge to whatever was connected to the
+ terminal of the old bridge and connect the - terminal of the bridge
to whatever was connected to the - terminal of the old bridge.

I don't know what you mean by:
"What do I do with the transformer three and four on the bridge?".

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Sun, 29 May 2005 15:44:34 -0400, "Art" <plotsligt@comcast.net>
wrote:

Terminals labeled AC on the rectifier bridge are connected to the ac source,
your transformer. The + and - are connected to the filtering circuitry and
eventually the load. Pay attention to the polarity of the + and -
connections, as to where the originals were connected. With your
transformer, as noted, connect the yellow leads to the AC terminals of the
rectifier bridge. Isolate and insulate the centre lead.

---
I guess that's somehow different from what I wrote earlier?...

"John Fields" <jfields@austininstruments.com> wrote in message
news:a7kj9114e6pgp7lodijcae3lj1rq8j4kkg@4ax.com...

---
Connect the yellow wires to the AC terminals of the bridge and either
cut off the center tap or cut off the exposed conductor and tape the
wire back out of the way so it won't touch anything that gets hot.
Connect the + terminal of the bridge to whatever was connected to the
+ terminal of the old bridge and connect the - terminal of the bridge
to whatever was connected to the - terminal of the old bridge.

--
John Fields
Professional Circuit Designer

 

[Art]

no Pun, John: Sometimes repetitive info connects?? Duh: Have a fine
Holiday
"dwbauer" <dwbauer@bellsouth.net> wrote in message
news:_8pme.29106$8S5.7344@bignews3.bellsouth.net...

That worked great!
Thanks, so very Much; Don
"John Fields" <jfields@austininstruments.com> wrote in message
news:a7kj9114e6pgp7lodijcae3lj1rq8j4kkg@4ax.com...
On Sun, 29 May 2005 10:19:32 -0400, "dwbauer" <dwbauer@bellsouth.net
wrote:

I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center
tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked +
AC -
with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center.
What
do I do with the transformer three and four on the bridge?

---
Connect the yellow wires to the AC terminals of the bridge and either
cut off the center tap or cut off the exposed conductor and tape the
wire back out of the way so it won't touch anything that gets hot.
Connect the + terminal of the bridge to whatever was connected to the
+ terminal of the old bridge and connect the - terminal of the bridge
to whatever was connected to the - terminal of the old bridge.

I don't know what you mean by:
"What do I do with the transformer three and four on the bridge?".

--
John Fields
Professional Circuit Designer

 

[Gar]

Do not use the black center tap (tape it up). Connect one yellow wire to
either bridge AC terminal, then connect the other yellow wire to the other
AC terminal on the bridge. You will need about 14.2 volts to charge a
battery. The transformer is rated in RMS (.707 of the peak fullwave positive
sinewave cycles 0v --- ^^^^ --- ). Yellow to Yellow gives you 12.6 Volts
RMS which will work out to (1/.707)*12.6 = 17.82 volts peak. This is the
value that an unloaded electrolytic capacitor will charge if connected to
the + and - terminals of the bridge respecting the polarity markings of the
capacitor. You can check this. For practical purposes the 12.6 RMS voltage
is all you need to be concerned with.

You my run into another problem if the transformer internal resistance of
the primary or secondary is too high which is often the case for cheaper
transformers. This is determined by
Vt = Vo - ( Ri * I load )
where:

Vt is the closed terminal voltage across the load (battery)
Vo is the open terminal voltage ( no battery connection )
Iload is the charging current that your original charger provided.

Good Luck!