Overclocked CPU Heat Production and Peltier Sizing

UPDATE 1/17/00: Toby at BxBoards has a neat formula to size peltiers:

Delta T = (1 – (heat load/max cooling power))*max temp difference

where heat load = CPU’s heat output in watts, max cooling power = Maximum peltier rating in watts and max temp = Peltier’s maximum temperature rating, in degrees C. So if your TEC’s maximum ratings are 60W and 68C then loading it with 40 W will give you about (1 – 40/60)*68 = 22.7C temp. difference.

UPDATE 12/4/99: Eric sent me an Excel spreadsheet that lets you input different FSBs and volts: DOWNLOAD HERE

The following Table lists all current Intel and AMD Athlon CPU specifications for spec watts, spec voltage and heat production in watts for 4 conditions: FSB speeds increased by 50%, FSB at +50% and voltage increased by 0.1 volts, then 0.2 volts, then 0.3 volts. Note the high wattages of the Athlon series, especially the 0.25 micron part – Athlons have a reputation for running very hot, especially at overclocked speeds.

This Table does not mean that you can hit these combinations – it is meant to show what increases in heat production are likely under the conditions specified. It is unlikely that the PIII 733 will hit 1100 MHz, so consider this table a starting point for heat dissipation calculations.

If you are thinking of using a peltier and if the peltier is less than or equal to your overclocking target, the best possible cooling you can expect is to keep the CPU at ambient temp. If you are expecting to increase your CPU’s overclocking performance over an air-cooled solution, the peltier you are using must exceed the target FSB and voltage watts by some margin – selecting a peltier that is twice the expected heat production should lead to substantial cooling over ambient temps.

For example, if you have a Celeron 366 PPGA and want to run it at 500 and 2.3 volts, the C366 will throw off 43 watts of heat. Just to stay even, a peltier must be at least 43 watts. If you want to super-cool the C366 to hit 600+ at 2.0 volts, then a peltier in the range of 70-80 watts or using two lower rated peltiers is required. Needless to say that the heat production of the pletiers and the CPU will be considerable, and air cooled solutions at these levels is difficult such that water cooling is preferred.

The formula used: Heat Production = CPU Spec Watts * (New FSB/Spec FSB) * ((New Volts/Spec Volts)^2)

C366 PPGA @ 550, 2.3 Volts = 21.7 * (550/366) * ((2.3/2.0)^2) = 43.1

Note the table reads 43.0 – I have used 50% (1.5) in all cases, and 550/366 = 1.503 which leads to a slightly higher result.