Agilent U8001A power supply fan mod - Page 1
Forum section: electronics / testgear

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2017, 01:55:40 pm
content: I picked up a used U8001A a few months ago, and while it functions well, the fan is repugnantly loud, so as others have done, I bought a replacement.I got the seemingly brand-new Sunon HA60251V4-1000U-A99, which is a very quiet fan. However, in the U8001A, it won't start. A bit of scoping the other day (numbers may be slightly off) shows that the two fan speeds are 40Hz PWM at duty cycles of about 85 and 95%, resulting in Vrms of about 10.5 and 11V. (I was really surprised at how close they are.) Putting a 100uF capacitor in parallel will allow it to start, but smooths the Vrms enough to be just over 11V in both speeds, with no noticeable difference in speed. (In limited testing with a thermocouple, it also seemed to run hotter, as expected, by about 10-15C depending on where I probed. The stock fan keeps it barely above ambient under load.)So a) is using a cap to allow the fan to run at all a bad idea? and b) am I tempting fate by allowing it to run so hot? Or should I be looking at a different fan? (What's not really an option is leaving the stock fan. It's just too obnoxious.)The max temp I got was about 50C, which seems OK, but I'm not sure what output taxes it the most. It doesn't use multiple transformer taps like most linear supplies. Does this mean it's actually dissipating the most heat when at low voltage/high current? (As with the output shorted.) I also assume that this model (the 3A one) doesn't have as much cooling demands as the larger 5A model, which seems to use the same stock fan.Thanks!

author: HighVoltage
author_rank: Super Contributor
timestamp: October 24, 2017, 02:24:47 pm
content: I have a U8002A and have been using it for about 1 year, this is the 5A version but I usually only use up to 1A from it.But the fan runs almost all the time at a fixed speed or it is only very little regulated. At least the sound from it, never changes.

author: tooki
author_rank: Super Contributor
timestamp: October 25, 2017, 01:21:02 pm
content: In the U8001A, the fan kicks to high speed at 2A load. I assume the U8002A is similar, probably has a fixed decision point.

author: hugo
author_rank: Regular Contributor
timestamp: October 25, 2017, 11:53:04 pm
content: Do you have the specs for the original fan?

author: tooki
author_rank: Super Contributor
timestamp: October 26, 2017, 05:31:28 pm
content: Quote from: hugo on October 25, 2017, 11:53:04 pmYep, see the attached PDF.

author: tooki
author_rank: Super Contributor
timestamp: October 26, 2017, 05:33:04 pm
content: Just to be clear, I'm well aware that my attempted replacement (specs attached) is nowhere near as powerful, my question is about whether this is tempting fate, and whether the mod to allow it to start at all is viable or not.

author: hugo
author_rank: Regular Contributor
timestamp: October 26, 2017, 11:57:11 pm
content: I would look for a silent, reliable starting fan, something like GELID Silent Series 60 mm case fan.SpecificationsAir Flow (CFM/CMH): 16/27.2Current (A): 0.22Dimension (mm): 60 x 60 x 15.5Fan Speed (RPM): 3200Noise Level (dBA): 24Static Pressure (mmAq): 2.6DC Voltage (V): 12Note:I've replaced both DS1054Z and DS1052E stock fans with GELID fans and I'm happy so far.If you intend to use the power supply at high (full) current, it is not recommended to replace the stock fan with a less capable one and that's a no brainer.

author: tooki
author_rank: Super Contributor
timestamp: October 27, 2017, 05:12:15 am
content: Actually I have a Gelid in my 1054Z, too! Just much harder to find, and much more expensive, around these parts!The reason I thought it might be possible to get away with a lesser fan is because this model at maximum current (3A) is still only 60% the current of the beefier version (5A). As best I have been able to tell, they use the same stock fan.And my question about the capacitor, whether as a practical or hypothetical question, still remains.

author: jmw
author_rank: Frequent Contributor
timestamp: February 03, 2018, 02:08:32 am
content: I also bought a used U8001A and found the fan a bit obnoxious. I tried connecting the header to a Noctua 60mm and found it wouldn't start as well. I did some scoping and found that Q7 controls the output to the fan. It is a TIP122G Darlington pair; the fan + terminal is connected to a 12 V rail, and - terminal connects to the collector of Q7, whose emitter is tied to ground. Instead of putting a cap across the fan terminals, I shorted the collector and emitter of Q7, which makes the fan run at 100% duty cycle, which is not so bad if the fan is quiet. The controller has a power-on delay of a few seconds before it starts the PWM signal, as a side effect the fan will now start immediately after flipping the front panel switch. My temperature rise went from 5 C to 6 C under a 2.5 A load for 10 minutes, so I think it will probably be fine long term.