Electronics > Beginners
external battery pack for laptop, current limiter
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purezerg:
Hi all,
I have a external power back that is rated to output 20v @ 7A peak
I am trying to figure out a way to limit the laptop from drawing too much current
I have a HP zbook workstation that is rated 200w on the power adapter.
however I managed to figure out that the middle pin is 220k ohms to trick it into believing that the DC power coming in is from a 120w power adapter.
I have successfully used the 120w adapter on the laptop for hours without problems.

the laptop knows it's power limit and adjust accordingly using extra power from the battery when the AC doesnt provide enough when it needs to boost.
the question is it's not full proof. I have blew the power bank's 20v output.

so the question is how to I limit it to 6a@20v

it doesnt always draw 6a. its usually doing 1-2a when idle and 4-6a when average loaded.

so how do I build a 20v @6a current limiter.
JustMeHere:
Don't brown out your laptop unless you want bad things to happen.
Jeroen3:
Change the maximum processor power state in energy management.

My Dell does this, very aggressively, when I plug in a power supply that isn't 240 Watt.
It goes to around 500 MHz on one core, locks the screen light to almost off and shuts down WiFi. It's very effective in reducing power.

Also, when you starve the chipset from power just the slightest, it turns off, no warnings.
JustMeHere:

--- Quote from: Jeroen3 on September 30, 2019, 06:39:25 pm ---My Dell does this, very aggressively, when I plug in a power supply that isn't 240 Watt.

--- End quote ---

I had a Dell that did this too well.  It couldn't tell what it's own power supply was as it aged.  The CPU stayed at min speed and the battery wouldn't charge.  Thankfully I don't think they make these types of power supplies anymore.
purezerg:
my zbook 15 comes with a 150w adapter. I have tried 120w adapter and 90w adapter.

plugging in 150w, the CPU can sustain 4ghz.

120w it does 3.6ghz.
 
90w it does 3.6ghz but doesnt charge the battery as fast.

150w with full charge battery and idle. the laptop consumes 15w.
when running prime95. it does 65w

charging an empty battery when the laptop is shut down, consumes 70w

i believe the quaddro on my laptop is 45w itself also.

that said. there is a middle pin in the chargers that help the zbook identify

200w (untested)
150w 120k ohms
120w 220k ohms
90w 300k ohms
65w 380k ohms

I have made a cable with 220k ohms. the power bank is rated for 135-140w

so how do i limit the amps to 6a? 20v@6a.
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