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# Powering laptop via DC source

#### Cone

Sep 20, 2022
3
Hi everyone,
I have to power my Lenovo Yoga laptop via 12V DC source. The needed input voltage for laptop is 20V. I use step up to increase voltage to 20V. The needed current is 2.25A, but the current measured at source is less than 0.1A. The problem is not at source, it can give more ampers when I attach other devices. The conclusion is that laptop (or something before it reaches laptop) does not take the current.

DC Source 12V -> Step up to 20V -> laptop
Final voltage is ok, only the problem is in the current.
Thanks!

#### Alec_t

Jul 7, 2015
3,246
Welcome to maker.pro.
It sounds as though the current drawn by the laptop via the step-up device is greater than the rated output current of the source. The source is going into self-protect mode and shutting down.
Your laptop needs 20V x 2.25A = 45W. Assuming 100% efficiency (85% is more realistic) your source must provide those 45W, i.e. 45W/12V = ~4A. What is its power/current rating?

#### Cone

Sep 20, 2022
3
Welcome to maker.pro.
It sounds as though the current drawn by the laptop via the step-up device is greater than the rated output current of the source. The source is going into self-protect mode and shutting down.
Your laptop needs 20V x 2.25A = 45W. Assuming 100% efficiency (85% is more realistic) your source must provide those 45W, i.e. 45W/12V = ~4A. What is its power/current rating?
I think that power is at least 48W. Because it could power other devices such as DC motor.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,756
I think that power is at least 48W. Because it could power other devices such as DC motor.
Why does that make you think the power source can deliver at least 48 W? Many DC motors require much less power. SO this is no indication - unless you care to reveal the specifications of the motor.
Otoh: why not reveal the specs of the power supply instead?
Also: What are the specs of the step-up converter? Can it supply the required 2.25 A or more?

#### Cone

Sep 20, 2022
3
Why does that make you think the power source can deliver at least 48 W? Many DC motors require much less power. SO this is no indication - unless you care to reveal the specifications of the motor.
Otoh: why not reveal the specs of the power supply instead?
Also: What are the specs of the step-up converter? Can it supply the required 2.25 A or more?
Power source is able to supply more than 4.1A of current, for sure, and possibly more but I don't have exact number because it was bought a long time ago and not by me. I've tried this. I also tried different step up converters and both were capable of supplying 2.25A (one is 5A, and another 10A), and I concluded that they are not problematic.

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