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This question already has an answer here:

I know that putting two resistors in parallel will double the wattage from the input to output, but only with half the resistance.

Example Parallel Circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

I know that putting two resistors in series will double the resistance, with the same wattage.

schematic

simulate this circuit


However: I need to double the wattage without the affecting resistance. Would this work?:

schematic

simulate this circuit

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marked as duplicate by Passerby, PeterJ, Matt Young, Anindo Ghosh, Dave Tweed Aug 11 '13 at 15:21

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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Your four resistor circuit will give you 100 ohms at 2 watts.

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  • \$\begingroup\$ Succinct and to the point +1 \$\endgroup\$ – Andy aka Aug 11 '13 at 0:12
  • \$\begingroup\$ Just watch out for thermal runaway. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 11 '13 at 0:16
  • \$\begingroup\$ Are we seeing different circuits or am I just so tired that I'm messing up the simplest calculations? I don't see 50 ohms in that last circuit. \$\endgroup\$ – us2012 Aug 11 '13 at 0:32
  • \$\begingroup\$ I agree with @us2012, I'm not seeing why it would be 50Ω OR 2W. \$\endgroup\$ – Passerby Aug 11 '13 at 0:49
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    \$\begingroup\$ Requirement for 2 watts: the four resistors are mounted far enough apart that they don't heat each other. \$\endgroup\$ – Phil Frost Aug 11 '13 at 13:16
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No. It will not work as a 50R load, rather it is 100R and you get twice the resistance and 4x the W capacity, not twice the power with four parts.

If the wanted twice the power, you only need 2x equal values. If you wanted 4x the power, your simulation would work at 50 Ohms using 4x 200R in parallel or 4x 12R5 in series might be possible , but only in theory as this is not a common value.

The sensible solution is your circuit with 50R parts. i.e. 1/4W in 2S2P array to handle 1W @ 50R.

Using N parts of equal value in symmetrical arrays gives you N times the power capacity and the same resistance as the each resistor, because it is linear.

In the case of batteries and LEDs, you may increase the string voltage and current and increase power capacity by N times using N EQUAL parts. The array you created is strings of 2 elements in series with 2 strings in parallel, using standard notation would be 2S2P. The same notation is used with LED arrays and batteries to increase power in rechargeable batteries, with care taken to ensure they are equal at all times by design. E.g. Add ESR to LED's to "normalize" and limit current or add shunt limiters to large battery arrays to match each cell.

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    \$\begingroup\$ They want 100Ω at the end... \$\endgroup\$ – Passerby Aug 11 '13 at 10:18

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