Macintosh Portable, safe operating voltage?

[flecom]

So I have been doing some reading about the Macintosh Portable and it's power supply and batteries... from what I have read it seems that you can actually turn on the portable from the 9V backup battery and run it for a moment (sans hard drive since the 9v can't sink that much current), is it therefore safe to assume that the portable can run from 9V?

Reason I ask is I am looking to substitute the internal lead acid battery and replace it with a 7.4V LiPO battery, which when fully charged will hover around 8.2~8.4V MAX but obviously don't want to fry any of the regulators so I figured I would ask and see if anyone knew any details about this?

 

[techknight]

Its not safe to run the portable in its entirety over 7.5V So please keep it 7.5V and under. 

the 9V battery is only designed to keep the memory for sleep state during a main battery change.

 

[flecom]

particular reasoning? I know there is an LT1070 in there, which is rated for 60v, obviously the caps in the input are not rated that high but still... mind you I am talking about the battery connection, not the power inlet in the back... I can use a buck converter to bring down the 8.4 to 7.5v but it's going to be a tight squeeze getting it in there just to drop .9v

 

[techknight]

use a couple diodes in series. easy peasy. 

Voltage references and other shit, thats why... The voltage regulator is linear, not switching... 

 

[flecom]

well how is it going to reference if you don't know what your battery voltage is going to be? battery could be anywhere from 7.5v if fully topped off till whatever the machine knocks out at, you can discharge a 6v SLA under load till about 5.4v

a couple diodes would do it, I am just curious since there is virtually no documentation on the power sections of the logic board

 

[techknight]

I have the official schematics to that machine, I know how the circuitry works. 

The reference is generated by a chip. it uses its output and the batterys output and creates an error difference to run a MOSFET. 

The internal 5V should be 5.2V all the time. The greater the power input, the more heat you produce and more stresses induced in the regulator. 

The machine locks out around 5.6 to 5.8VDC.