OK, here come the sums.
Can't get the formatting for the divisions quite right.
163Mohm 173Mohm
0.000797546 0.000751445
1300 )1630000 1300 )1730000
0.08mA 0.075mA
Some decimal point trouble here.
First, you have 163Mohm and 173Mohm when you should have 1.63 Mohm and 1.73 Mohm.
Then your long divisions are actually correct.
1300 / 1,630,000 = 0.000797546
1300 / 1,730,000 = 0.000751445
But now when you divide by 1000 to produce the answer in milliAmps you've misplaced the decimal.
To divide by 1000 simply move the decimal point three places to the right:
0.000797546 A = 0.797546 mA
0.000751445 A = 0.751445 mA
so with rounding and discarding false precision we have 0.80 mA and 0.75 mA as the max and min currents.
Working left to right in the diagram I posted earlier, and using P=I^2*R :
I^2 = I^2 =
0.0008^2* = 0.00075^2 =
0.00000064 0.000000563
Correct. You have used the correct values for the current here.
& &
100,000* 100,000*
0.00000064 0.000000563
0.064 0.05625
the 100Kohm pot = 0.064Watts. the 100Kohm pots = 0.05625Watts each.
330,000* 330,000*
0.00000064 0.000000563
0.2112 0.18579
the 330Kohm = 0.2112Watts. the 330Kohm = 0.18579Watts.
200,000* 200,000*
0.00000064 0.000000563
0.128 0.1126
the 200Kohm = 0.128 Watts. the 200Kohm = 0.2112Watts.
1,000,000* 1,000,000*
0.00000064 0.000000563
0.64
and the 1Mohm = 0.64 Watts. and the 1Mohm = 0.563 Watts.
So the suggested wattages are, at least for the final resistor in the chain, a little on the low side, and the 1 Watt rated are an acceptable choice.
All good. However, you should consider being conservative here. Myself, I'd use 2 Watt resistors out of an abundance of caution, at least for the 1M, and I might even use 1/2 Watt for the pots.
Voltages. Using V=I*R, I calculated the drops thus:
100K Ohm 80V 100K Ohm 75V
330K Ohm 264V 100K Ohm 75V
200K Ohm 160V 330K Ohm 247V
1M Ohm 800V 200K Ohm 150V
_____ 1M Ohm 750V
SUM 1384V _______________
SUM 1297.5V
Considering I didn't do enough rounding, I think the final figures aren't too far from actual values. They look quite reasonable, at least to me.
How did I really go?
Clay.
Close enough. Also, if there is room, you can mount the resistors standing up off the board by their leads a bit to allow for better cooling.