It is safe to do but vario d5's aren't meant to be voltage controlled so reducing volts provides a limited rpm range before the pump just stops.
It's much like trying to control a Silverstone ap182 fan with a fan controller instead of the device it comes with.
I would much rather find a quiet speed manually with the dial and just leave it there.
First up, thanks you for taking the time to post a reply. These forums seem pretty slow so you're probably one of the few with the knowledge and inclination to answer my question.
I have a couple of short follow-up questions
1 - do you know the approximate RPM range of the D5 that is controllable through the Poweradjust and/or know where I might be able to find the exact range online? I'd like to understand how limited it is before deciding whether or not to bother installing the Poweradjust.
2 -
Koolance sells a physical (not software based) RPM controller that is compatible with D5 pumps. Have you ever come across this and if so, does it have the same limited control over RPM range as the Poweradjust?
Thanks again