| Electronics > Beginners |
| Transformer wiring in reverse |
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| kelemvor:
Is there any reason not to wire a transformer in reverse? Meaning, this transformer: https://www.mouser.com/datasheet/2/410/media-845803.pdf Wired from a 28vac source (home made pure sine inverter) to produce 110/220 on the secondary. Clearly the datasheet indicates it's meant to be used as a step-down from 120vac to 28vac (for example) but I want to use it as a step-up. As an aside, it's only 1kva rated. I need 4kva so I guess I'll need four of them at $183USD each. Pricey. Is this the wrong solution to step-up inverter voltage? |
| MosherIV:
Depends on what the input and output voltages are. The output (secondary) was not designed for mains voltages. The insulation will not withstand mains voltages. The impedance of the secondary will be way too low to directly connect across mains, it may trip breakers. The input (primary) was design to take mains voltages, not high voltages. You can try it. It may work, for some time but the insulation may break down at some point. |
| kelemvor:
--- Quote from: blueskull on September 30, 2019, 07:16:31 pm ---I don't think the OP intended to wire 28V into mains and get kilovolts. He just wants to wire 28V OUTPUT side to a 28V sine source and use the input source as an output. --- End quote --- Correct. Not sure why I'm struggling to find 28v-120v transformers. With the popularity of 28v solar battery systems it seems like those would be all over the place. |
| capt bullshot:
Inverters (to create mains voltage from battery voltage) often use a switching mode step up converter (often including the isolation) and an H-Bridge PWM circuit to generate the output voltage from an intermediate DC rail (the output of the step up converter). This saves the bulky and heavy line frequency transformers. Otherwise, products exists that use a line frequency transformer and an H-Bridge operated at the battery voltage. But these transformers aren't ordinary mains transformers, they have a nominal line voltage secondary and a lower than the minimum battery voltage primary to have some headroom for the PWM circuit to create a stable output voltage from the varying battery input. These transformers usually are custom made and not available as off-the-shelf components. And don't forget the sqrt(2) factor from DC voltage to RMS AC (as blueskull said) |
| floobydust:
As mentioned, power transformers are slightly overwound, to correct for sag due to losses in the windings and core. 120:28VAC looks like 4.3:1 turns ratio but could be closer to 3.7:1 (assuming 15% regulation) so running the transformer backwards can give lower than expected results. That would give, with 28VAC in only 104VAC out. It depends on the transformer's quality. edit: large 1kVA transformer, assuming better 5% regulation would give, with 28VAC in only 114VAC out. (assuming 5% regulation) For your power levels, running transformers at mains frequency means they are bulky and huge. Modern inverters use high frequency SMPS to step-up to HV DC and then commutate that to a pseudo-sine wave. |
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