Zalman 750W Heatpipe Cooled PSU - 550W Tests and Final Thoughts

Article Index
Zalman 750W Heatpipe Cooled PSU
ZM750-HP Features and Specs
ZM750-HP Cables and Inside
Test Setup, Methods and Testing
550W Tests and Final Thoughts

550W Load Tests:

We've seen the Zalman PSU start off quite well with non-load and faltered a bit at the 280W load test, so it will be interesting to see how it holds up with a larger load.  Is there a reason Zalman had to relax the Output Ripple & Noise limits on this PSU?  Will it be out of spec with a larger load?  It is rated for 750W, and while we can't run this at 100% load, we can still push it with a pretty powerful system in real world tests.  We record the results with a Tektronix TDS2002 scope, and this is how it shapes up under some pretty heavy testing.  I was pleased to see Power Factor stay at 0.98 through these tests as well.

3.3v at 550W
3.3v at 550W
5v at 550W
5v at 550W


Once we increased the load from 280W to 550W the noise on both the 3.3v and 5v lines actually decreased and we are now within ATX spec and well within Zalman's generous limitations.  The 3.3v line measures 40mV and the 5v line measures 42mV.  These are acceptable values.

As we jump into the 12v rails, we'll cover what each rail does as we go.

 12v1 at 550W
12v1 at 550W
 12v2 at 550W
12v2 at 550W


The 12v1 line still remains noisy; albeit not as much.  It measures 106mV while the 12v2 line also improves and now measures 10mV lower than at 280W showing better results with more stress.

As we wrap up the 12v lines, we take a look at 12v3 and 12v4.

 12v3 at 550W
12v3 at 550W
 12v4 at 550W
12v4 at 550W


Both of these 12v rails stabilized as more load was drawn from the Power Supply.  The 12v3 line settled down 22mV and the 12v4 line stabilized by 6mV.  These now sit in a very respectable range and should offer great system stability when running loaded.  Although I haven't really touched on it yet, actual voltage levels in this PSU are actually a little high - even when running loaded.  At 550W load the 12v lines all report 12.4v.  The 3.3v and 5v lines are much closer to rated output, but the 12v line remains high through all of the tests.  In the non-load tests we saw the 12v lines all report in at 12.6v.  This is only 5% high and within spec, but it could be regulated a bit closer to actual required output.


Below are the charts that show average voltage as well as average peak-to-peak ripple and noise.

 Average Ripple


 Average Voltage



The Zalman ZM750-HP PSU is a very decent mid-range PSU from Zalman.  Along with its promise of being quiet, it offers a nice powerful package of 750W with four 20 Amp 12v rails.  Zalman has oddly changed the DC Output Ripple & Noise specification for this PSU to be poorer than the ATX specification and for that we are a little disappointed.  It seems as if they don't think that this PSU will stay within the tighter spec, so they loosen it.  Even stranger is the noisy performance of the 12v1 rail - especially in medium-load situations.  It remained noisy at any load, but did manage to (barely) stay within ATX specification.  The 3.3v and 5v rails looked shaky at 280W load, but smoothed out very nicely at 550W load.  Overall, this PSU is a decent choice as it will power most systems without costing an arm and a leg.



  • Very quiet PSU
  • 12cm fan & heatpipes keep things cool
  • Lots of connections for a 750W PSU
  • Stable under hefty load 



  • Ripple of 12v1 line is fairly high at medium load
  • Half-modular design
  • Lack of dedicated FDD connector(s)

Because of the high ripple and noise at a 280W load, I can't award this unit a Top Pick, but it deserves to be looked at if you're building a system that requires a good PSU that is very quiet.




I'd like to thank ZalmanUSA for sending over this unit for us to review.  It's been a good unit to test out some 8800GTX SLI on a large display and showcase our test rig at a gaming conference.  Please post your thoughts and comments regarding this review in our forum at the "Comments" link below.