Transformers in parallel

Question

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.

Answer 1

Your plan to test the motor to determine exactly what current it pulls is a good one. From there you can select a suitable 50Hz/60Hz mains transformer. If you cannot find a single transformer to supply the power required under all operating conditions, then using multiple transformers is an option provided that you follow a simple rule:

At least one set of windings must be connected in series, rather than parallel.

For example, you could use 2 x 230V/6.3V transformers, each with its primary winding connected across the 230V AC supply, and with the 6.3V secondary windings connected in series. This arrangement forces the current in the LV windings to be equal, which avoids the issue you raised (circulating currents, leading to unequal sharing of the load current which could cause problems).