Question about dual primary's

Thread Starter

chaseBank

Joined Dec 14, 2013
13
Hello all,

Long time lurker and first time poster. I have just bought a 250va 50/60Hz 30+30 toroidal transformer and just opened it to realize it has two primary's. My question is, Do I connect both primary's to the same plug in? For example, the primary wire colors are blue/grey and the other brown/violet, would I connect blue and brown to side and grey and violet to the other ac channel? I can't image needing two totally separate plug inns to power this thing.
 

MikeML

Joined Oct 2, 2009
5,444
If running it on 120Vac, the two primary windings need to be in parallel (with the appropriate phasing).

If running on 240V, the two primary windings need to be in series (with the appropriate phasing).
 

Thread Starter

chaseBank

Joined Dec 14, 2013
13
If running it on 120Vac, the two primary windings need to be in parallel (with the appropriate phasing).

If running on 240V, the two primary windings need to be in series (with the appropriate phasing).
Can you elaborate on that. I just planned on connecting it to the 120v wall outlet. I've only dealt with one primary before in which I just soldered the primary wires to an ac wire.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
18,873
For 120v If you do not have the connection details, what you could do is connect the one end of each primary pair together and connect this to one side of the 120v supply, then connect the end of ONE of the pair to the other side of the supply.
Then measure from the single connected conductor to the one that is left unconnected and if it is close to zero, then you can connect this one to the other single conductor.
If it is 240v then reverse one pair only and try again.
Once you have a pair identified as zero between the single pair, connect both to the 120v supply
Max.
 

Thread Starter

chaseBank

Joined Dec 14, 2013
13
For 120v If you do not have the connection details, what you could do is connect the one end of each primary pair together and connect this to one side of the 120v supply, then connect the end of ONE of the pair to the other side of the supply.
Then measure from the single connected conductor to the one that is left unconnected and if it is close to zero, then you can connect this one to the other single conductor.
If it is 240v then reverse one pair only and try again.
Once you have a pair identified as zero between the single pair, connect both to the 120v supply
Max.
Something like this then, as in the 115v

 

MaxHeadRoom

Joined Jul 18, 2013
18,873
Yes, but you need to identify 1-2 3-4 if you do not have the colour identification.
Per my previous post you would connect 1-3 and leave 2 & 4 open, and initially only connect 2 OR 4 to the other supply
terminal for 0v between 2-4.
The alternative result would be 240v measured between 2-4.
Max..
 

Thread Starter

chaseBank

Joined Dec 14, 2013
13
Yes, but you need to identify 1-2 3-4 if you do not have the colour identification.
Per my previous post you would connect 1-3 and leave 2 & 4 open, and initially only connect 2 OR 4 to the other supply terminal.
Max..
My top primary is blu/gry or 1,2, and bottom primary is vio/brn or 3,4. So I would connect blu/vio and then either of the other colors. If I know colors its ok to connect them then, or still just one first and test with my DMM?
 

crutschow

Joined Mar 14, 2008
23,159
As a safety factor and to avoid popping the breaker/fuse you could temporarily connect a 120V incandescent bulb in series with the transformer primary. If the connections are wrong, it will light brightly. If correct, it will be dark or glow only dimly.
 

Thread Starter

chaseBank

Joined Dec 14, 2013
13
Thanks for the replies, I think I got the gist of it. As long as I don't ruin my transformer I'll be ok.
 

MaxHeadRoom

Joined Jul 18, 2013
18,873
My top primary is blu/gry or 1,2, and bottom primary is vio/brn or 3,4. So I would connect blu/vio and then either of the other colors. If I know colors its ok to connect them then, or still just one first and test with my DMM?
Yes, connect Blue & Vio and say gry across 120v, then between gry & brn you will get either ~0v or 240, if 0 then connect gry & brn, if 240v, connect blu & brn and try again.
Max.
 

Thread Starter

chaseBank

Joined Dec 14, 2013
13
Thanks guys It worked without blowing anything up! Now I have to build my power supply for my amp project for Electronic engineering capstone
 
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