When dealing with transistors, one often has to wonder.
As the collector current increases, hfe falls.
With Ic = 300 mA, only 60 is already guaranteed, not 100. You want to get 600 mA.
And Fig. 5 gives the saturation voltage at Ic / Ib = 10.
The word is "saturate".
Look at the graph in #19. When you use the transistor as a switch, you do not want it just to amplify the current, you want it to have the lowest possible voltage across it to minimise heating and maximise efficiency. Whatever small-signal gain it has up to 630, to saturate, you use a gain of 10 to 20.
Note that even then, the saturation voltage increases with increasing collector current. It has actual resistance!
If you want better switching, you use a FET.
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I see. Thanks.
Then i just use mosfets. I see now that these bjt's are pretty useless. Cheap yes, but in my head is price the only positive with these regards to switching.
I have lot of iRF3708 that i can use, så i think i go for that. I also going to order more.
Thanks for all help 
Still curious why you had that 30A relay module in your first post.
That relay coil draws about 185mA, but has it's own transistor for that.
The opto coupler on that module, to drive it's base, only needs 5mA LED drive current.
Why did you post a picture of that module, and a (largely useless) breadboard supply.
Leo..
You are a tormentor.
Because i will use it to turn on/off an 2.000W heater in my basment. Breadboard supply is just for testing.
That still doesn't explain the questions about the transistor.
You don't need one if you're going to use an Arduino, because an Arduino pin is perfectly capable of providing the 5mA opto LED current that the module requires.
Leo..
See post #16.
My last questions isn't about the relay module.
Certainly not. A mosfet has a significant input capacitance. That can be a problem in some cases, as well as the associated gate charge. A BJT is your friend in such cases. Moreover, a mosfet virtually always has a much higher turn on voltage, which can also be an issue in cases where some drive current is feasible, but voltage drop is best left low (think e.g. constant current sources).
@Bjerknez, do not cross-post. Other thread closed.
For switching 2000W, relays or SSRs built on thyristors (SCR) are usually used.
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