What AI isn't

[NewsVine_Mariyam]

LOL, It was funny.

I asked "ChatGPT" to confirm that two 100 Watt resistors in parallel would (at least on paper) handle 200 watts.

The resistance would drop (ohm's law), but I was only interested in the power handling.

So, to its credit, AI asked me for more specifics.

I shared that I'm building an audio dummy load for 4 ohm and 8 ohm loads, and I currently only have eight four 8 OHM 100W resistors (ceramics in an aluminum heatsink.)

I had already drawn it out and planned to use all eight four (series parallel) to get 8 ohms and two of the resistors in parallel for the 4 ohm load.

I was only trying to confirm the total power capacity. (Also, it was late, and I was being lazy)

Long story short, it tried to assure me that I could get a 4 ohm load using all eight four 8 ohm resistors. LOL!

Like this!

View attachment 1243061

I about ******* lost it as it went on to try to show the math, caught its mistake and then finally relented.

EDITED to correct the quantity of resistors on hand.
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Me: (after showing my AI Assistant your post)
I don't know enough about the problem to be able to comment on this but I'm curious what your response is though

AI Assistant:
This is actually a good discussion—and the confusion in that thread is very common. Let me break it down cleanly so you can see exactly what’s right vs. wrong.

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What the original person was trying to do​

They had:

• Four 8Ω, 100W resistors
• Wanted to build:
  • a 4Ω load
  • an 8Ω load
• And were thinking about power handling

---

The key mistake in that thread​

The claim was:

“Two 100W resistors in parallel handle 200W”

That’s only conditionally true, and this is where people get tripped up.

---

Parallel resistance (this part is correct)​

When resistors are equal:

• Two 8Ω in parallel:
  → 4Ω total

So:
Resistance math = correct

---

Power handling (this is where nuance matters)​

In theory:​

If you have:

• 2 resistors, each 100W
• In parallel

Total = 200W capacity

BUT ONLY IF:

• Power is evenly distributed
• They are truly identical
• Thermal conditions are ideal

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Real-world reality (this is what matters)​

In practice:

• Resistors are not perfectly matched
• One may take slightly more load
• Heat affects resistance → imbalance increases

So:

You can say 200W on paper
But engineers usually derate it

---

The second person’s comment (about 3 vs 4 resistors)​

They said:

“Three in series, then parallel with a fourth might get 6Ω”

Let’s check that:

• 3 × 8Ω in series = 24Ω
• Parallel with 8Ω:

1R=124+18=124+324=424\frac{1}{R} = \frac{1}{24} + \frac{1}{8} = \frac{1}{24} + \frac{3}{24} = \frac{4}{24}R1=241+81=241+243=244
→ R = 6Ω

That part is correct

---

But here’s the hidden issue​

Power distribution is now uneven:

• The single 8Ω resistor in parallel:
  → gets more current
• The 3-series branch:
  → splits power across 3 resistors

Result:

• That single resistor becomes the weak link

So even if total wattage seems high:

The system fails when that one resistor exceeds 100W

---

What a clean design would look like​

If you want:

4Ω load (balanced)​

Use:

• Two parallel pairs in series:

(8 || 8) + (8 || 8)
= 4Ω + 4Ω
= 8Ω total

Or for 4Ω:

• All four in parallel:

8 || 8 || 8 || 8 = 2Ω (too low)
So better approach:

• Depends on target, but symmetry matters

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Key takeaway (this is the real answer)​

The discussion you showed:

• Gets the resistance math mostly right
• Is sloppy about power handling assumptions

---

The principle to remember​

Resistance math is easy — power distribution is the real problem

And:

Any uneven configuration = weakest resistor determines failure

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Bottom line​

• The “200W in parallel” statement is technically correct but overly simplistic
• The alternate 6Ω design is mathematically correct but poorly balanced
• Neither approach fully accounts for real-world thermal and load imbalance