What is the wattage rating of this circuit?

[mort]

If each resistor is 150w?

The green cross at teh bottom is a connection. This isn't my drawing, asking for a friend. I thought 112.5w and curious if I was correct.

[mort]

or is it 187.5w?

[The Dude]

I'm assuming this is for a dummy load. The way I see it, input current will split (roughly). Half will pass through the 33 ohm resistor. The other half passes through the series/parallel combination of the others. So, you are limited by the single resistor that is paralleled with the other 3. IMO, the circuit could handle a 300W amp (rating at 16 ohms). 150W each current path.

[Enzo]

Agree. But your question is poorly asked. resistances do not determine power capability. To meet the spec we assume, the 16 ohm need be 75 watt, the two 30 ohm need be 37.5w each.

But a context for the circuit would be helpful.

[mort]

This was basically the way he had asked it. I just ignored the ohm readings because that wasn't his question.

And yes he wants to build a dummy load for a 100w amp. So in reality, if he wants a 16ohm load, he could just use the bottom resistor and call it a day. I was more interested in the exercise of figuring the wattage of the network as drawn, which I now see how the 300w was tallied.

[mort]

Ok question #2 on this topic.

He said he tried the single 16ohm 150w resistor and at full power the heat sink got hot as a firecracker in about 10 minutes.

Does it make more sense to add resistors to dissipate less heat(?) or to use a bigger heat sink?

Also, how do you calculate what size heat sink to use?

[Enzo]

Yes, they will get real hot, that is why they have coling fins. They need to be bolted to a heat sink of some sort. Mine are on a thick sheet of aluminum.

100 watt heat sink? Then use 200 watt resistors, not 100 watt resistors. get four 100 watt 16 ohm resistors and wire them in series/parallel. Now you have a 400 watt load. Ten 160 ohm resistors wired in parallel, make them 25 watt for a 250 watt total.

I can see wanting a 16 ohm load made of more than one resistor, but why on earth would we use this odd combination?

[mort]

He's in a rural area that takes a while to get things shipped in and that just happens to be what he has on hand.

[mort]

He has a sink on it, and the sink is what is getting too hot so I suggested he get a larger one. But how large of one to buy? I haven't ever messed with dummy loads and heat sinks and what not and I'm on my phone right now and I hate trying to sift through unfamiliar info on my phone so I'm asking here as an alternative to googling.

[Enzo]

How much power is he trying to dissipate? How large a heat sink? Mine is about 18 inches square and 3/8".

SOmetimes you just have to bite the bullet and order what you need, even if it means waiting three days.

[mort]

100w @ 16ohms.

I thought I had read somewhere about heat sinks being rated for capacity, not so much the physical size. I don't remember the unit of measurement used, but I thought there was an equation that used wattage and resistance to come up with a target capacity and then you just upsize a little for fudge room. That way you remove any guess work on which sink to order.

[Enzo]

Are they fan cooled? Are there good routes for air? A heat sink is part of a system, and all it does is make it easier for heat to be conducted away. The larger my radiator, the more surface aerea there is to radiate heat away.

Look at the heat sink on a Peavey 400BH module. Usually used as a 200 watt amp into 4 ohms.