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HP Forum Archive 13

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HP-49G+ Power consumption
Message #1 Posted by Daniel Diggelmann on 10 Sept 2003, 7:10 p.m.

[pre]As my home page is gone I'll go on posting my news here. When I received my new calc the batteries where already dead as they were of most other buyers. So I suspected the machine would draw excessive current even when off. So I measured the current of the the new HP-49G+ vs HP-49G:

HP-49G+ ------- OFF: 0.02 mA ON: 10 mA (doing nothing) Running: 80 mA

HP-49G ------ OFF: 0.02 mA ON: 7 mA (doing nothing) Running: 20 mA

The Test shows that the new calc draws four times more power when it's running a program. Actually the current is approx proportional to the speed gain. As the calc is usually not doing much most of the time I don't expect it to eat too much batteries. So I take the installed batteries were of poor quality. The off current is just the same.

Re: HP-49G+ Power consumption
Message #2 Posted by Tom (UK) on 11 Sept 2003, 3:50 a.m.,
in response to message #1 by Daniel Diggelmann

The power sometimes is not in proportion to the speed gain as smaller technology versions of the same design have lower current (as internal capacitance is lower). Also newer technology usually HAS to run on a lower voltage - the HP49G+ could run on 3V rather than 4.5V? (I assume the HP49G+ runs from 3 x 1.5V batteries). I wonder what voltage is connected to the ARM processor.

Saturn design may have been more efficient as it wasn't trying to 'emulate' anything. The new design may have lower power 'per instruction' but the emulation may require 2 or 3 instructions each, so no net gain.

The stand by current of 10mA doesn't look too good, a large improvement can be gained by turning off or reducing the clock speed to the processor (not the display) when it's not doing anything. The down side is a tiny start up delay when you start pressing keys, but this should not be noticable.

Do you know the Off / Standby / Running current of other HP calcs using the Saturn processor (e.g. '28, '42, '32, '48)

If the speed is 4x and the running current is 4x then for a given set of tasks the batteries should last the same time. With most electronics the battery life is dominated by the standby current (10mA vs 7mA) so I would guess the batteries will only last about 70% of the time as the older calculator. From memory the AAA batteries used to last about 6 months of light use in the HP49G, so the HP49G+ should need new batteries every 4 months?

I presume there is no connector for an external power supply. HP could have done a 'docking station' including the data connection and power / charger for the internal batteries - oh well may be in the next series of calcs :-)

Re: HP-49G+ Power consumption
Message #3 Posted by Veli-Pekka Nousiainen on 11 Sept 2003, 4:04 a.m.,
in response to message #2 by Tom (UK)

I Assume (I make "Ass" out of "u" and "me") the CPU is Samsung S34210 - the same used HP iPAQ h1940. I/O 3V, core 1.8V, slow mode = 12MHz, running 48/75MHz (calculator) and about 203MHz on a PDA. Maybe the slow mode could be halved to 6MHz, to cut off even more from the stand-by current, but otherwise it is a very good design. OFF has every possible circuitry OFF - even annuciators, which don't have a dedicated line anymore (like they did in Yorke/Clarke).

Standard usage is maybe one month of battery life. The fast IrDA, fast USB (serial on 48gII), SD card, 25% more LCD, etc. will eat more batteries. So a "typical" heavy user may need to buy a new set before every weekend. (-;

Re: HP-49G+ Power consumption
Message #4 Posted by Brandon Del Bel on 11 Sept 2003, 1:21 p.m.,
in response to message #3 by Veli-Pekka Nousiainen

Hmmmm... I think you're pushing it with your power consumption estimates; nonetheless, I use rechargeable batteries, so I'm in good shape.

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