How does weapon power work in FTL

Question

I cannot seem to work out how the power works for weapons in FTL.

I picked up a Hull Laser II that consumes 3 power. I already had the Burst Laser II (consumes 1 power). I upgraded my power and got another bar, then upgraded my weapon system so I have 4 bars available in my weapon systems.

So I should be able to power up my Burst Laser power 1 and Hull Laser power 3 = 4 but it keeps saying I don't have enough power.

I can turn off everything and have plenty of actual power available but i still can't power up the hull laser. I don't get it.

Answer 1

Burst Laser II uses 2 power. Upgrade weapons system capacity one more and buy an additional bar of power.

Answer 2

You have the weapons capacity and then you have overall power budget. So you need enough weapons-power slots, and then you need to fill those slots with power from your reactor.

If you are routing all your reactor power to other systems, you will not be able to supply power to the weapon(s). To remove power from a system, right click it.

If you decide to take all power from the 02 system, don't forget that you have done so or your crew will suffocate