Macintosh Portable, feeding 7,5V, 1A instead of 1,5A - will it work

[Aektann]

Hmm, if the video is correct then that's quite unusual and an example of a poor design from Apple. He's basically saying that there's no battery charging circuitry in the Portable: it just directly connects the AC adapter to the battery and relies on the fact that the adapter isn't capable of providing more than 1.5 amps before its output voltage will sag below the battery voltage and charging will stop. If that's the case, then a higher current AC adapter more than 1.5A could indeed be a problem. On the other hand, I would think a lower current AC adapter would work fine, just with slower charging times, since the computer is actually powered from the battery and not the adapter.

I came to the same conclusion initially. The power adapter is using only to charge a battery, that's all.

 

[bdurbrow]

And you'd need an adapter that was designed to droop the voltage, instead of overheating and/or outright shutting down. If that is indeed the case, then I'd be inclined to fix the poor design by modifying the portable itself to have a charging controller inline between the power input jack and the battery.

 

[LaPorta]

Now, if it was the case that it ONLY powered the battery, and was not otherwise connected to the power circuit, then how did people dangerously "jump start" the Portable with later PowerBook adapters with higher amperage rating in the presence of no battery?

 

[Aektann]

Now, if it was the case that it ONLY powered the battery, and was not otherwise connected to the power circuit, then how did people dangerously "jump start" the Portable with later PowerBook adapters with higher amperage rating in the presence of no battery?

I’ve read a late thread on this board where it was told of never plugging Portable without a battery due to having the power circuit becoming dangerously unstable.

 

[LaPorta]

Correct, I agree....I just wonder, how could a totally separate circuit manage to power the whole machine?

 

[bdurbrow]

Does anybody actually have the schematics for the Portable?

 

[demik]

Does anybody actually have the schematics for the Portable?

Here it is:

nubus-se30/Schematics/apple/Macintosh Portable Schematic.pdf at master · nickpunt/nubus-se30

Various files. Contribute to nickpunt/nubus-se30 development by creating an account on GitHub.

github.com

 

[nottomhanks]

I restored a backlit Portable with SCSI2SD, 8 Mb ram card and new lead acid battery. I can verify that this power supply works fantastic: https://www.amazon.com/dp/B015PXUHYA/ref=cm_sw_r_cp_api_glt_fabc_KES053EVR0QXJZEJKMBR

 

[mitchW]

As far as my knowledge goes, the non-backlit Portables must use 7V 1.5A power supply which is designed to soft limit the current at 1.5 amps. So if the computer will try to take more than 1.5A, the power supply will lower the voltage to keep it happy. So when the current will hit 1.5A, the voltage will be lowered. Imagine something with a preset wattage, but with fixed current and adjustable voltage. Also that model needs battery to be present all the times to serve as a buffer. Newer styled power bricks will provide too much current and will also not regulate the voltage if the current exceeds maximum - they just shut down.

But the backlit Portables are completely different story. Their logic board is completely different with much newer styled circuits. They can use higher amp units with no damage. They can be even used without a battery, but might have problems starting up, especially if the original HD is hooked up. I used my friend's unit with SDtoSCSI module and it always started without battery present.

 

[LaPorta]

I'd rope TechKnight into this. He would be your definitive source.

 

[aplmak]

If Techknight saw this thread he’d blow his top. As he said in many, many threads never to use any other adapter than the one designed for the portable and a good battery. It is so easy to fry a board or the hybrid or any of the other chips for that ma. If you cherish your Portable please only use the one (recapped) designed for the Macintosh Portable (usually white in color, not gray)

The Macintosh Portables power management and how it operates through the battery is very unique than many other laptops.

I’m only chiming in here to help out and don’t want to see anyone’s portable destroyed….