# Transformers in parallel

I Have an issue with an electric gate motor, it originally had a Toroidal 250va 13.5V. Naturally this is an unusual sized transformer and the space allocated makes a replacement difficult.

The Unit is marked as having a max capacity of 200W.

I could get a 225VA/15V TX that will not fit and will require me to put it in a custom enclosure which is just a pain or i could potentially get two Toroidal transformers and put them in // 100VA/15V.

I Understand its not 13.5V but with the fluctuation in grid supply i do not believe 1.5V will make much of a difference, it also appears they rectify this voltage so i am assuming there is a regulator somewhere. TAU K125M https://www.automatismes.net/doc/Notice%20TAU%20K125M.pdf

Schematic VTX-146-100-215 (2x primary 2 x secondary) in // = 4x primary 4x secondary

The only concern I have with connecting them in // is checking for circulating currents, as it's been a long time ago since I conducted this test and just wanted to double check. My Primary voltage here is 230v

Primary would be Blue = Neutral, (Grey + Violet), Brown Active

Secondary would be join Yellow + Red together and measure voltage across Black and Orange if i get a reading of 0 that would indicate i am in phase and no circulating current.

Now the question that i have coming around to the second transformer what would that test look like?

I also find some conflicting information on the unit itself. The manual says 50W but the name plate reads 200W. looking at the motor it is a MP56M. So i am going to connect my Variac (500VA) to the unit and test it under load to see what it actually pulls, as i am wondering if this transformer was just oversized to begin with.

• a simple test is to run them with no load for a bit and see if they warm up. Commented Sep 25, 2023 at 23:34
• you can drop 15v AC to ~13.5v AC with a chain of ~3 10A diodes in series, then repeat that, reverse, and parallel with the first chain to form a short "magic wire" that drops 1.5v both directions. Note: you might need two of those paralleled in order to handle the current, didn't realize the motor was so beefy. A block of a dozen diodes would look cool. Commented Sep 25, 2023 at 23:49
• Its funny you mention that, i had a thought, if you look at the pcb secureentry.com.au/product/tau-k125m-control-board looks like they have 2x 10A diode in series, after the filter capacitors, that would take their 13.5 to 12.01v ac i wonder if this transformer was just used as they had them. i might be able to use a 12v TX and just remove the diodes. Commented Sep 26, 2023 at 1:27
• @epicfatigue - Hi, You used the text box below labeled "Your Answer" to post an "answer", but it was asking a question. This isn't allowed on Stack Exchange, as it breaks the whole "Q&A are in different places" approach. It is also too late to extend the question, as you have already received an answer to your original question - extending the question would make that answer look incomplete (see discussions about "chameleon questions" on Meta.SE). Commented Sep 26, 2023 at 8:04
• (continued) My least bad option is to treat the question which you posted as an answer, as a clarification question to the answer you got. Clarification questions get posted as comments on Stack Exchange. Therefore I moved your post to be that. FYI If you want to add image links in a comment, you can use this technique. Note that the draft answer (or question) must not be submitted. It is used only to upload the image & is then discarded. Thanks. Commented Sep 26, 2023 at 8:04