Electronics > Beginners

Transformer wiring in reverse

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Kleinstein:
At the 1 KVAR level the efficiency is usually rather high and thus the tuns ratio is pretty close to the nominal voltage ratio. So the output voltage would be a little smaller than expected from the pure voltages, but not that much. I would expect only some 5% less.

Usually larger transformers will be even more efficient and often smaller than 4 small ones in parallel.

Due to the weight and shipping costs I would no necessary see Mouser as a good source for a large transformer.

With an inverter one has to be careful with 2 effects: one is a possible DC part that can saturate the transformer, that might cause hum and peak current problems. The other are spikes that could exceed the design voltage and stress the insulation.

Zero999:
When you mean 28VAC is that the peak voltage, i.e. the battery voltage? If so, then transformers are specified in RMS voltage, so you need a 28/root(2) = 28/1.414 = 19.8V primary, probably a little lower, to make up for the regulation so that's 18V.

kelemvor:

--- Quote from: blueskull on September 30, 2019, 07:21:50 pm ---With 28V bus voltage, how are you getting 28V rms sine wave? The best you can get is 20V rms, and you won't have any regulation margin and you will have bad clipping distortion. I would use a 120v to 15v or even 12v transformer and use the SPWM inverter to adjust low side AC voltage in a closed loop.

--- End quote ---

You're right, I hadn't considered it. When I connected the inverter circuit to my scope and meter, I'm actually getting 20v rms out of it (unloaded) so.. there ya go.

L_Euler:
I’ve been running a 480-120 3KVA transformer backward for more than 20 years with no problems at all. I use it to single phase source 2 VFDs, one on my lathe and one on my drill press.  Go for it.

kelemvor:

--- Quote from: Kleinstein on September 30, 2019, 08:59:34 pm ---Due to the weight and shipping costs I would no necessary see Mouser as a good source for a large transformer.

With an inverter one has to be careful with 2 effects: one is a possible DC part that can saturate the transformer, that might cause hum and peak current problems. The other are spikes that could exceed the design voltage and stress the insulation.

--- End quote ---
I'd love to hear suggestions for other sources, if you'd care to make any. 

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