You don't have to buy a low Wattage one. With 20mA flowing through 1Ω the power dissipated is only 400 micro-Watts, so almost any Wattage rating (within reason) will work. It's the package dimensions which matter. Try a parametric search on a distributor's site, such as this, to find a resistor of the same dimensions.

 

Why do I need low Wattage rating and approximately where the Watts should be? Thank you!

Well , I replaced the converter's SMD with a 1 Ω one , as you suggested and it doesn wotk properly. In fact , now it's maximum output current cannot even surpass 1mA , while it was not stable at all. What may got wrong? Is the 1 Ω SMD too big for the converter to function properly?

 

That's a pity, but swapping the resistor was only a trial.
As stated in post #12 :

you may well have trouble getting it to run at such a low setting. there is usually a minimum current required for them to work at.

 

That's a pity, but swapping the resistor was only a trial.
As stated in post #12 :

If I tried a 0,1 Ω SMD , do you beleive it would work?

 

There's no guarantee it will work, but you can try.

 

that looks an interesting board,
do you have a link to it please

https://gr.banggood.com/Geekcreit-4...se=CN&akmClientCountry=GR&akmClientCountry=GR

 

That's a pity, but swapping the resistor was only a trial.
As stated in post #12 :

Actually it turned out that the dc-dc converter worked both with the 1 ohm and 0.1 ohm SMD resistance! I just misundertood the situation, while it worked properly. The reason I returned here to you is to ask you something more about that. Would it be better to choose the SMD resistance wth the lowest possible Ohm value that fulfills my needs? Would it be better for the dc-dc power converter's functioanlity to avoid the high value resistance SMDs? Thank you!