I get a small trickle of A4-related questions. Since they might be of more general interest, I'm posting some of the answers here.
Hi, I need a power supply for an Acorn A4 laptop, I was thinking of making one out of a power supply from another laptop. Problem is I don't know the PSU specs, as you've made a site for A4 problems, do you know the voltage and amps plus the pin out of the D9 connector the PSU uses? Ive looked through google but can find any reference to this info. Thanks in advance.
Pinout is here The power supply is described in the Technical Reference Manual (page 27 and following in the PDF)
If you just want to power the laptop but not charge, you want to provide UMAIN which is 21V at, I think, 720mA. This isn't critical, so you can probably provide a lower voltage (down to about 15V I think) but you run a higher risk of blowing the internal power supply diodes.
If you want to charge the battery as well it's a bit more complicated because the power brick provides a switchable output current - read the TRM for the details. However you could probably get away with a constant trickle charge at the lower current (60-70mA constant current, the battery cell voltage is 14.4V so expect to have to provide a bit more than that to achieve that current).
Page by Theo Markettos (email at theo [at@] markettos.org.uk), last modified 2008-11-05
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