High Wattage Fan Replacement w/ Noctua? (Keithley 219) - Page 1
Forum section: electronics / testgear

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 20, 2022, 11:55:05 pm
content: I want to run this unit all the time but the fan is too loud. Turns out its quite as high wattage fan.I usually replace fans with Noctua fans, but in this instance, I don't see they have one that handles this kind of power draw, the model I have says 6/8 watts.https://www.connex-electronics.com/html/products/etri/etrifanspecs/99ac.pdfHas anyone encountered a fan like this, and if so a replacement?

author: taste_tester
author_rank: Regular Contributor
timestamp: May 21, 2022, 12:20:07 am
content: Doubt youre going to find a cross section of quiet and that kind of high power.you could use a noctua or other pc case type fan with a current limiting resistor and see if the amount of cooling is adequate...

author: nightfire
author_rank: Frequent Contributor
timestamp: May 21, 2022, 01:19:25 am
content: Replacing a fan means that you have to take into account basically three things:1) Airflow managed by the fan, as in volume (liters/cubic meters etc. by the hour)2) supply voltage3) control circuit of the fan (feedback of rpm etc.)So a replacement fan has to be able to move at least the same amount of air as the previous one, and then you can worry about the connectors...Depending on the system that is cooled, sometimes it is easier to run a fan off of AC, therefore the 230VAC options.The power drawn is usually of little concern, as power gets drawn by the fan, not pushed to it...Of course, the power supply (or PCB traces etc.) should be able to supply the needed amount of power to the fan.So I would not worry about the Wattage the replacement fan would draw, as long as the overall environment is healthy- I would rather worry that the airflow is guaranteed.From a look at the datasheet I would imply that the fan you already mentioned has to be able to move approx 30 cubic feet per minute, and it is a fan with 92mm size and 25mm thickness, that gets fed from a 115VAC/220VAC source.PC case fans usually run with 12VDC, so a direct replacement would not work, as long as there is no power converter used.I see two approaches to the issue:1) Depending on the airflow really needed, throttling the existing fan via a resistor or pot, or some more elaborate temperature control circuit2) replacing the fan depending on the case size with a bigger fan, like 120mm- for the same airflow you need less rpm, and therefore those fans usually run quieter

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 21, 2022, 01:54:04 am
content: Argh. I just noticed you are correct, this fan runs at 115v ac. I'm so used to seeing nominal voltage fans I just had my eyes fixated on that large power draw compared to typical computer type fans.You're correct, this isn't going to work unless I find 12v on the board to steal from a rail.Fan size is fixed, unfortunately. Perhaps a resistor is the solution, just knock the RPM down enough to get -3 or 6db.

author: bdunham7
author_rank: Super Contributor
timestamp: May 21, 2022, 02:06:38 am
content: Quote from: mapleLC on May 20, 2022, 11:55:05 pmIt is an inefficient shaded-pole design, so I wouldn't let the 8-watt power consumption lead you astray. The biggest obstacle to replacing these with a low-noise alternative (other than sourcing the power) is the static pressure needed. Your fan apparently can produce 5mm H2O static pressure, the Noctua replacement is less than half that. You have to determine whether that matters or not in your device.

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 21, 2022, 06:11:20 am
content: It's a Keithley 219, so the transistors in the center get quite hot and that fan blows directly on them. This fan also pulls air in, not out.The CFM does matter, but that is only localized. I would be fine adding a second fan in series in the chassis somewhere else to improve airflow, and even adding small holes to the chassis of which their are none.I would like this thing to be on all the time, but there is no way I can sit near it and listen to that shit all the time, especially if I have music going.Here are 3 ideas I had to resolve it, what are do you guys think? Option 2 here is just to deal with the fan as AC, but I have the DC fans already so I would rather use them.

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 21, 2022, 11:02:58 am
content: Your Keithly 219 is no longer worthy until you make this modI plodded away at it and found a solution. At least in so much as I am letting it run a few days and seeing if the tap I used has any impact.I managed to find the 9v tap which actually measured 10v, and I put a pair of jumpers to the Noctua fan, it started right up, no errors.The unit isn't showing any unusual temp rises and there seems to be plenty of airflow.An additional mod I made was removing that magic foam that turns to dust and replacing it with a fitted piece of Acoustiblok to further dampen sound, though the chassis is thick enough for that. The Acoustiblok didn't do much after measuring, but I want the quietest lab... so every db is precious.datasheet:https://www.acoustiblok.com/wp-content/uploads/AB-16-Product-Data-Sheet.pdfAttached are some measurements, but at the rack where it matters most I managed to produce a -18db reduction so this unit is now whisper quiet and can stay on full time.You may find a more exact sized fan, mine was a bit small but worked fine anyway but its what I had around. A bigger fan would make it even quieter. The one it needs is 90mm.Well worth the effort, but if anyone has any concerns about where I tapped, please mention something. I can't see any issue tapping where I did in the photo, but please chime in the interests of getting it right for others.Photos in 2 posts

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 21, 2022, 11:03:48 am
content: This is the end result DB measurement and the location of where I did the taps.

author: bdunham7
author_rank: Super Contributor
timestamp: May 21, 2022, 02:21:21 pm
content: Quote from: mapleLC on May 21, 2022, 11:02:58 amI would have thought you would use a Noctua NF-A9 as it would be pretty much an exact fit as far as I can tell--and it would be quieter at the same or greater airflow. I think your connection spot is fine, as long as everything stays cool enough.

author: mapleLC
author_rank: Frequent Contributor
timestamp: May 21, 2022, 03:41:39 pm
content: Quote from: bdunham7 on May 21, 2022, 02:21:21 pmIt's because I had this one laying around, it wants the 90mm size for a perfect fit.