I set up this test to satisfy my own curiosity about the Real Power Users in my PowerBook 140, then to guide me to getting the most out of a battery. Although the PB140 is gone, the basic principles still apply.
The electrical set up is very simple, you arrange for an Amp-meter to sit between the power supply and the PowerBook, and it shows you just how much power is being drawn at any time. The unit of measure is called Amperes and relates to the ‘Flow’ of electricity through a cable, for example. The Nicad battery in a PB140 or PB170 is rated at around two and a half Amperes for one hour, or for a reasonable Current Drain on this battery, I can expect the equivalent or 2.5 Amperes for 1 hour, or 1 Ampere for 2.5 hours, etc.
The Machine that I own is a PB140, 4 megabytes of RAM and a 40 megabyte. all Apple, ( Conner ), Hard Drive. The Testing device that I used was a PE-007 Digital Multimeter, using the 10 A range for all readings except the current drain while in the ‘Sleep’ Mode, also, the BackLight was always Full On, unless noted. The battery was removed during the tests. The readings are what I found on the display as each event happened, the display is updated about every half second which gives a reasonable average reading, which I rounded off to make the whole thing simpler.
So what did I find ? Well, yes, the back lighting drains a fair bit of the power. Average Running current drain settled down to around the 1.2 Ampere, or A, mark, or about 2 hours of running time, this will be shortened as the PowerBook will Shut Down when the Voltage measured across the battery falls below a certain level. This protects the battery and prevents the premature death of the battery by naughty people.
Anyway, the first set of readings are,
Backlight full on: 1.20 A
Backlight off: 0.78 A
Backlight Drain: 0.42 A
So we can save a lot of power by turning down the Backlight, setting it at about half way could mean an extra 20 minutes, or if you use a Backlight controller of some kind, or your finger, it would mean a very reasonable extension of the battery’s charge.
Another power saving feature of the PowerBook is the ability to slow the clock speed of the Microprocessor running inside the PowerBook, in this case it slows from 16 MegaHertz to around 1 MegaHertz, and it is worth the trouble,
CPU running at 16MHz: 1.20 A
CPU running at 1MHz: 0.90 A
CPU Drain Saving: 0.30 A
This, combined with turning down the Backlight, could be a good battery saver, and with the figures for the Hard Drive, it’s not hard to see that using a RAM disk would extend the battery life well past the 2 hour mark.
Hard Drive Running: 1.20 A
Hard Drive off: 0.90 A
Hard Drive Drain: 0.30 A
The King of them all is the Sleep Mode, at a tiny 0.005 A, it means that I may get up to 3 weeks out of a single battery, as long as I don’t actually use the computer.
Another Drain on the Battery is Sound. The PowerBook turns the Sound electronics off after a idle period and this produces the click that is heard just as you start to nod off in front of the keyboard.
Before System Beep: 1.20 A
After System Beeep: 1.30 A
‘Sound’ Drain: 0.10 A
The Microphone didn’t make any difference, until the Sound electronics was fired up, but that was expected.
The Serial Ports and AppleTalk are the next target, Printing to a StyleWriter only produced changes in current drain caused by normal system items, beeps, Hard Drive access, etc.
AppleTalk PhoneNet connector, out: 1.20 A
AppleTalk PhoneNet connector, in: 1.40 A
AppleTalk PhoneNet Drain: 0.20 A
Current drain was only there when the Serial Port had been used. This is not a normal configuration but would occur if, for example, you were connected to a network but had AppleTalk off and tried to use the Printer port. The extra current drain exists even if you swap ports using the Chooser. ( Add another 0.10 A if you are silly enough to do this with Both serial ports ).
Apart from the situation above, and normal running requirements, AppleTalk did not increase to drain, in fact when a second Mac accessed a shared folder and ran a game from my Hard Drive no increase in drain was seen because of the very short access time. My ‘Network’ being a 512ke connected with a PhoneNet LocalTalk network.
Real Usage figures are a little hard to get and the way that I do things is not the way that you do things, so a couple of other things to watch are at the start of your work. From Power On until the ‘Welcome…’ message, current drain ranged from 1.50 - 1.82 A, then from ‘Welcome…’ until we settle down in front of the Finder, it varied from 1.40 to 1.20 A,. The sorter this period is, the more you use the computer.
Accessing the Hard Disk varies the current drain by 0.04 - 0.14 A, this became worse as total Hard Drive / PowerBook current drain was 1.73 A, or higher, as the drive started up after being ‘spun down’ by the operating system, Mounting a floppy used less than current than the Hard Drive, until a floppy is accessed, you can overcome some of these problems by using the Disk Cache and a RAM disk
Mounting a Floppy, 1.20 - 1.48 A, Formatting a Floppy, 1.28 - 1.42 A, or about 1.30 A on average. Remember that Floppy Access may be longer that that of the Hard Drive.
To get better that two and a half hours out of a battery, I would have to watch the following areas. Use only the System Goodies, like INITs, that I need, this reduces the start up time. Install a Backlight controller to dim the screen when I’m Idle, or manually turn the screen down when I don’t need it on, during printing, or if I’m referring to some notes.
Balance the installed RAM between what the Applications need and the Disk Cache or a RAM disk. The more RAM that I have the better this will work, but a second, or third, battery is a lot cheaper that a 4 or 6 Megabyte RAM module. Avoid Virtual Memory as it not only uses the Hard Drive thus draining the battery, but it can slow down the machine dramatically.
Turn the Sound OFF, this will make some difference, for people like me and my Spelling Checker. Check the spelling at the end of a session or just before you save a document. Stopping the Finder from Calculating Folder Sizes will stop a bit of Hard Disk activity and make the Finder faster when it comes time to open a folder.
Why doesn’t someone write an Utility that adjusts the Power Saving settings to suit the type of Application. For example, a Quick shut down of my Hard Drive, limited use of the Backlight, and No sound while my Word Processor is running but leave the Backlight on and be less fussy with the Hard Drive when I’m drawing. If anyone does do it, please send me a copy.
Paul B Jones
Hardware and Software developer, Also a Telecom Technician in a small country town 180 kms North of wonderful Perth. Slowly converting the locals to Macintosh. I own 4 Macs from a 512k to a PB140 and have had a range of PD and Shareware published around the world.
