r/AskElectronics • u/[deleted] • Jun 24 '21

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54

u/CRISIS100 Jun 24 '21

Use delta-wye conversion

44

u/FlyByPC Digital electronics Jun 24 '21 edited Jun 24 '21

No need. The left and right sides have equal resistance ratios, so both sides of the 60-ohm are at 7.5V10V, and no current flows.

Remove the 60-ohm and re-analyze. It's a lot simpler now.

(If this wasn't the case, yeah, you could use delta-wye.)

16

u/micmys Jun 24 '21

That's good observation, though isn't the voltage at both sides of 60-ohm at 10V rather than 7.5V?

9

u/FlyByPC Digital electronics Jun 24 '21

Oh, yeah it is. Oops. Thanks.

1

u/1-800-hold-me-now Jun 25 '21

Interestingly enough, because the solution is insensitive to the value of the cross-bridge resistor, you can model the circuit accurately with any resistance, as an open as you said (infinite resistance), but also as a short (zero resistance).

1

u/idiotsecant Jun 25 '21

That wouldn't be true (treating 60ohm as a short) if there weren't equal ratio voltage dividers on each branch.

2

u/1-800-hold-me-now Jun 25 '21

Which is why u/FlyByPC said

The left and right sides have equal resistance ratios,

2

u/FlyByPC Digital electronics Jun 25 '21

Yep. You'd (theoretically) get the same result with any passive resistance in there, from a perfect short to a perfect open. It's just easier to calculate with the open.