# Heat issues with new Powerbooks?

Posted:
edited January 2014
According to the specs of the Freescale 7447B the 1,67GHz runs on a higher voltage than the 1,5GHz. 1,28v vs 1,2v.

Instead of power output scaling with clock-speed, the 1,67 now draws ~25% more power than the 1,5. I'm thinking this should result in a hotter computer and more fan activity.

Anyone receiving both models and can do a comparison?

• Reply 1 of 4
Posts: 371member
Quote:

Originally posted by palled

According to the specs of the Freescale 7447B the 1,67GHz runs on a higher voltage than the 1,5GHz. 1,28v vs 1,2v.

Instead of power output scaling with clock-speed, the 1,67 now draws ~25% more power than the 1,5.

I'm not an engineer but simple math tells me that 1.28V is 6.7% higher than 1.20V. I don't know how you got the 25% increase. Is there some complicated math involved?
• Reply 2 of 4
Posts: 7member
Quote:

Originally posted by BeigeUser

I'm not an engineer but simple math tells me that 1.28V is 6.7% higher than 1.20V. I don't know how you got the 25% increase. Is there some complicated math involved?

Not that complicated. To calculate power draw voltage is squared and MHz is linear. So to get the relative numbers I did the following:

1,67*1,28^2 = 2,736

1,5*1,2^2 = 2,16

The difference is about 25%.

Can't calculate exact wattage because I could not find any reference numbers.
• Reply 3 of 4
Posts: 1,515member
This will only apply when the CPU is running flat out. Most of the time the CPU is idle with short bursts of activity. If you set the Energy Saver to maximum performance and then convert a long piece of music to AAC you will see the highest battery draw. If you set it to maximum battery life there might be no little or no difference from the current PB.
• Reply 4 of 4
Posts: 7member
Thats true. But what I know the 7447B does not change Vcore when it clocks down (please correct me if I'm wrong) so the higher voltage adds heat anyway...