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Replacing the HP/Agilent 6060B DC load fan - inductance surge

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hellzakk:
Hi all, i recently acquire a 6060B that need a new fan.
The original one is a PAPST TYP 612 who operate in the range of 6-15 V-DC.
The service manual (pag. 28) define this voltage levels for the fan

--- Quote ---14.7V ±0.8V
10.7V ±0.6V
12.8V ±0.8V
9.7V ±0.5V
--- End quote ---

So i've chosen the TRACO POWER TEN5-1212

--- Quote ---TEN 5-1212

Input voltage range : 9 – 18 VDC (12 VDC nominal)

Output voltage : 12 VDC

Output current max. : VDC 500 mA

Efficiency typ. : 84 %

Surge voltage (1 sec. max.) - 12 Vin models: 25 V max.

Reverse voltage protection : 1.0 A max
--- End quote ---

to use with a Noctua NF-A6x25 FLX

--- Quote ---Max. input power 1,44 W
Max. input current 0,12 A
Operating voltage 12 V
--- End quote ---

have a bit less airflow than the PAPST but is much more quiet and i dont use high power dissipation.

My doubt is about the surge generated by the inductive load (fan) when i power off the unit, it can be dangerous for the DC/DC converter?
Someone can explain how to calculate this behavior?

Thank you.

AnalogSteph:
If you just need a new fan... why do you want to replace the fan driver as well? :-//

Here's some data for the Papst 612 fan, courtesy of an early-2000s catalog (that series was marked at obsolete even then):
Throughput 40 m³/h
Static pressure 75-80 Pa (~ 8 mm H2O) @ 0 m³/h
5300/min
2.5 W
40 dB(A) - 5.1 bels

They still make the replacement 600N series, the closest model would probably be the 612NN (42 m³/h, ~65 Pa, 5100/min, 1.6 W, 35 dB(A) / 5.2 bels). Your Noctua would be more along the lines of a 612NML (25 m³/h, ~25 Pa, 3000/min, 0.8 W, 19 dB(A) / 3.9 bels).

I wouldn't just install a weaker fan. If you want to tweak something, the entire cooling concept should be examined, which in (vintage) test instruments can be rather crude (but might be somewhat more refined in a device that is pretty much design to dissipate power).

* At the very least, can the fan be shock-mounted (preferably without introducing air leaks in the process)? That used to help a lot with low-RPM Papst fans in the day, which have relatively few motor poles. Nothing more annoying than having this ticking amplified by the entire case. The designers of Siemens PBXs still haven't gotten the memo.
* Would there be ways of maybe fitting a second one in parallel, so a lower RPM model can be used?
* Is there sufficient intake area? With axial fans, obstructions on the output side tend to hinder airflow far less than a constricted input. (Oddly enough, the hot trend in 2018 PC cases was almost closed-off front panels with mere millimeters of clearance for front intake fans. :palm:)
Now as for the question of indutive surge... anything wrong with the classic parallel diode trick?

hellzakk:
The old fan operate in the range of 6-15 V-DC and i dont know (no detailed datasheet available) if the noctua can work in the range reported (and measured) in the 6060B service manual.
I thought to use the noctua for the low noise and as it reported working with a stable 12V input so the need of replace the supply driver... but your points are all right and i will go with a new PAPST 612NN.

About your last question i think the flayback diode is ok, but id like to know how to calculate the surge spike generated by a 12v fan.

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