What is the absolute minimum power needed to turn on FW laptop without battery connected? (I tested and 65W seems to be enough, 18W not enough, so wondering what would be the exact value)
There is no ‘exact’ value as it depends upon your configuration.
60 Watts is the official power supply output max. and you can run it without a battery.
Startup uses the whole 60W for a two or three seconds on my Gen 1165 with Expansion Drive 256Gb and 1 USB A included.
I use a dc to dc 12V car adapter via batteries and solar, and each day I enable output form the Victron controller I can see the power drain.
Why are you asking I wonder . . . what is the use case?
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You mean a 12v → USB-PD? Or are you doing direct conversion to the 20v or whatever that it needs and somehow feed it it? If the latter, I’m quite interested out of curiousity. Otherwise, I do what you do, 12v → USB-PD for my trailer for working there on the road remote.
18W is not enough because running in BIOS consume about 18W so you need at least 18W to even POST, let alone boot up your computer.
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I use the following car adapter which outputs 60W via PD
More or less what I thought. I’ve got a 100W one from Amazon, works well so far.
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Thanks for the replies, but I am looking for more of an exact value than recommended or safe or whatever. I know 65W will work and 18W won’t, because these I tired. I am expecting the value to be somewhere in 30-50W range.
The use case is a 10" tablet I have been struggling to design for quite some time. With battery and board layout as in a standard FW13, the surface area is too big. With battery rotated 180 degrees and over the mainboard, battery overheats. I need a smaller battery. So I am using a powerbank board and 4 lipo cells to try and power it, giving it roughly 40-45Wh and fitting the form factor.
For some reason I hoped 18W would be enough to power it, that the board would sense the max current and slow down the CPU accordingly (because I can get it to run at 15W when turned on), but it won’t run for more than 3 seconds. So I was wondering where is the minimum, then I would add a few watts just to be safe. But meanwhile I ordered a 100W powerbank module so this may not be a problem anymore.
Sounds like quite a jump up in power. Be careful not to exceed the safe discharge rate of your cells.
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It’s about how much power the battery can provide not how much the laptop wants.
It wants 60W to start. So if you have a 12V battery it much be able to give 5w at some point. The capacity of the battery is not important.
For example:
The 55W provided wouldn’t last an hour at 60W but I get 5 hours.
If use a 10W battery I would only get 30min
The four cells are in series to provide the 16V so they provide a max of 4A to get 64W
If you use smaller cells the output would be lower than 4A with the same type of battery.
Though say 48W battery would only give 3A, foir a short time I’m sure it could give 4A
get the specs of the batteries etc.