Searching for three spaces in a line

i trying find 3 spaces in line contains multiple spaces, once found  replace comma e.g.

before:

aaa   bbb   ccc   ddd    eee   fff

after:

aaa,bbb,ccc,ddd    eee   fff

the regex query i have used so far finds spaces , tabs "\s{3,}|\t+". want return first three. has done before using regex queries?

here's own question answered, maybe bring clarity original question asking

$string = "aaaa              bbbbccc     c   dddd    eeee    ffff   gggg"
[regex]$pattern = "\s+"
$pattern.replace($string, ",", 3)  

output:

aaaa,bbbbccc,c,dddd    eeee    ffff   gggg

Windows Server  >  Windows PowerShell