Today I applied power to this Hammond tranny. I was a bit surprised at what happened. To me, this looks like a typical dual winding primary and secondary tranny. Based on the diagram, you would think you can simple wire the 2-sets of primary terminals in parallel to get the resulting 28VAC on each secondary.
The 1st image shows the schematic with 2 separate and independent windings. To test it I wired pins 2 & 3 together and pins 1 & 4 together and then connected to 115VAC. Now, I know it's been over 50yrs since I had basic transformer theory (I was never in the industry though), but there must be a critical part of the theory I'm clearly missing, despite having successfully wired lots of trannies over the past 10yrs without issue in my DIY audio projects.
After, about 45secs I began to smell something 'off' and immediately pulled the plug. The primary side (without any load on secondary), was too hot to touch! I never got around to measuring the voltage on the secondary.
So, I pulled the Hammond datasheet for this particular tranny and found that their wiring diagram (2nd image below) was different then the way I had wired it. Still both in parallel though. I don't understand why, the way I wired it, caused the overheating, unless it was a phase related issue. Would someone be so kind to remind me of why this happened and the proper way to wire primaries in parallel. It seems clear to me the windings on this transformer are completely independent of each other, except for the core. Could the tranny be defective?
The 1st image shows the schematic with 2 separate and independent windings. To test it I wired pins 2 & 3 together and pins 1 & 4 together and then connected to 115VAC. Now, I know it's been over 50yrs since I had basic transformer theory (I was never in the industry though), but there must be a critical part of the theory I'm clearly missing, despite having successfully wired lots of trannies over the past 10yrs without issue in my DIY audio projects.
After, about 45secs I began to smell something 'off' and immediately pulled the plug. The primary side (without any load on secondary), was too hot to touch! I never got around to measuring the voltage on the secondary.
So, I pulled the Hammond datasheet for this particular tranny and found that their wiring diagram (2nd image below) was different then the way I had wired it. Still both in parallel though. I don't understand why, the way I wired it, caused the overheating, unless it was a phase related issue. Would someone be so kind to remind me of why this happened and the proper way to wire primaries in parallel. It seems clear to me the windings on this transformer are completely independent of each other, except for the core. Could the tranny be defective?
Attachments
Last edited:
The primaries should be connected in parallel, not in antiparallel, as shown in the diagram.
Connect 1 and 3 together. Connect 2 and 4 together.
Connect 1 and 3 together. Connect 2 and 4 together.
Last edited:
Ok. Fair enough. Not sure what antiparallel is though. I always think of things in parallel as visually 'stacking ' the components. If we took each pri winding and stacked it visually, it would seem to me that pins 2 & 3 and pins 1 & 4 would make them 'in parallel'. But, if not, I learned something. Seems like antiparallel is the way Hammond has it wired, but obviously I am wrong.