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| Can two inputs make an isolation transformer? |
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| scuzzyTerminator:
I just acquired a toroidal transformer with two 120V input coils. I figure that the inputs are indended to be wired in parallel for double current or series for double volts. Is there any reason that one can not be used as an isolated output? Perhaps insulation is a problem? Sorry the specs are scant. |
| tecman:
It is okay to use as an isolation transformer. Just be aware that you can only use it at 1/2 the rated power, since each primary coil is designed to handle 1/2 of the power. One issue is that there will be no shielding between these two primary windings. Therefore there will be come capacitive coupling between the windings, which can result in some voltage present on the second winding with respect to ground (on the first winding). While generally low current, you can get a nice tickle from the secondary winding to ground. A proper isolation transformer will have an electrostatic shield to prevent this from occurring. paul |
| Gyro:
Firstly, as a "Medical Isolation Transformer" it's intended for the purpose - and a very good one. The two input primary windings are intended to be wired either in parallel (100-120V supply) or in series (200-240V supply). You need to connect both primary windings to achieve the rated wattage of the transformer. As for the question I think you're asking - can I use one of the primary windings as an isolated secondary? The answer is a definitely not. Firstly, for the reason above, and secondly (as you guessed) because of insulation. The primary and secondary windings are formed in very particular and very well insulated layer sections, with a protective ground screen (green/yellow), also insulated, between them. The two primary windings are together, in the same layer section. You need to use the secondary windings, as intended. |
| scuzzyTerminator:
OK, thanks. But if they can be wired in series wouldn't that create the same potential difference between the input coils as if they were wired for isolation? I would think they would need enough insulation either way. Maybe they are not intended to be wired in series? |
| Gyro:
Yes, they are insulated enough for series / parallel configuration across the mains (a few hundred volts), that's not the same insulation quality as between the primary and secondary windings of a mains transformer (several kV) and a safety isolating transformer in particular. Stick with the intended secondary windings: Red-White and Blue-White (Check!). P.S. You've got a very nice quality 300VA safety isolating transformer there, the medical ones are the best you can get. Be nice to it! :) |
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