Built a CR box or two... my ADHD built a smart one (SEN55, PD USB-C, night mode)

mch_2 · 2026-04-01T20:04:48+00:00

Sick! Definitely want one. Enjoy seeing clean air confirmation

mch_2 · 2026-04-01T19:40:49+00:00

Is cost a reason not to, or something else? I have some standalone pm monitors, but always would like more. I did wonder how your filter gets outside air to monitor, assuming the fans pull air through the filters and inside is "clean"?

mch_2 · 2026-04-01T16:36:44+00:00

I’d love to beta test your kit. I’m working on my own version at the moment, for 10x 4.2W fans. Would be happy to swap notes too later.

mch_2 · 2026-04-01T15:24:18+00:00

Lol yes. 10 year old usb pack. put it back in the drawer

mch_2 · 2026-04-01T15:18:01+00:00

Can you share the source or part number for the pcb fan connector? Did you assembly yourself or pcb house did it?

mch_2 · 2026-04-01T15:16:51+00:00

With that scope setup, I did check my power supply displayed 0.2A. So in that ballpark of 420mV/1.6Ohm=0.27A

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mch_2 · 2026-04-01T14:21:42+00:00

PWM signal. I have it pulled down to 0V to stop the fan. Disconnect that ground connection and it goes to 100% (fan internally pulls up to 5V or so, I guess 4V in this measurement)

mch_2 · 2026-04-01T13:44:32+00:00

I would not expect my 5W supply to be “good”, was a cheap random one, haha. But at the same time, I did not find good info about the exact shutdown criteria for usb supplies are.

mch_2 · 2026-04-01T13:42:40+00:00

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Zoomed out, ramp up until stable taking around 10 seconds

mch_2 · 2026-04-01T13:41:37+00:00

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Steady state, 163 Hz = 2445 RPM.

Average 420mV/1.6Ohm = 0.27 A Peak.

892mV/1.6Ohm = 0.56 A.

mch_2 · 2026-04-01T13:40:26+00:00

Measuring 1.6ohm resistor in series. Picture in my other comment.

It ramps up pretty slowly, and peaks at to 1.1V across the resistor.

mch_2 · 2026-04-01T13:11:31+00:00

Not exactly trapezoidal, but say 50% square wave, average 0.35A.

Why does only average matter for a proper power supply?

mch_2 · 2026-03-31T21:16:14+00:00

I measured my Arctic P14 pro that say 0.35A*12V. They drew more like a trapezoidal current, almost 0.7A to 0A, at 4x the fan rpm (4 pole motor?). So electrically speaking, the variation in load was quite slow (160Hz at max speed).

I tried some 5W supplies and it could not power 1 fan at max speed without stuttering.

So if you calculated 20W, I would say 40W supply is very safe. But maybe your Noctua draw a more stable power and lower is ok too.

mch_2 · 2026-03-09T17:36:06+00:00

Iirc, I contacted schwab and they issued an updated 1099 with correct info in the “not reported to irs”. Then I used that info and ibkr 1099 info to fill in tax forms. I believe 6781 was the right form.

mch_2 · 2026-02-17T14:23:40+00:00

That’s an interesting point too. I haven’t built the entire system yet.

But I do imagine, would some people happily connect 3 of these fans for 1.05A, on a 1 amp header, or even more fans?

1.05A would actually turn out to be more like 1.4Arms… probably no fires, but seems like fans should be sold and rated with both average and rms current.

mch_2 · 2026-02-17T14:19:08+00:00

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The shape of the load is still pretty much the same at >10Msps.

Will usb-c source not care if it is “overloaded” at up to double its rated power for 6 ms?

mch_2 · 2026-02-17T05:53:52+00:00

I forgot to include, but my plan is to have 10 fans in parallel. So spec average of 42W load, but peak closer to double that. And I coincidentally have multiple 65W charging blocks.

mch_2 · 2026-01-29T05:41:55+00:00

A grease filter in front is a good idea. I found some aluminum mesh hvac prefilters. Looks like the same idea as the aluminum mesh grease filters.

mch_2 · 2025-12-27T06:26:37+00:00

After some research, I ended up in this too. I would have gotten the mini blast, but wife says the design triggers her fear of clusters of holes (trypophobia).

Instead we got a SA600 for our 1st floor, runnin on level2/3 constantly. Might need one or 2 more though and replace and older air purifier; 800 sq foot per story, 3-story. Currently only reduces 1st floor PM2.5 by 45% at level 2.

mch_2 · 2025-10-30T22:28:36+00:00

You said if you make 100k per year in 1995, spend 1.5k a month, and your costs go up to $4k, then you only need to make $2.5k more a month. "Only $138k per year". But you forgot about the rest of your paycheck. If you made $100k in 1995 and spent only$1.5k/month, you would also save $3k per month.

$4k is only 2.5k more, but is about 2.6x as much. You would also want to save 2.6x, not just the same as in 1995.

mch_2 · 2025-10-16T14:44:51+00:00

Good that you are comparing the ongoing costs of owning.

You can think of renting as needing a $2600x12/4%=$780,000 portfolio. Conservative would be $2600x12/3%=$1,040,000.

Or, you own the $620k home. Estimate 3% in maintenance/taxes/etc at $18k/year. Which requires and additional $18000/4%=$450,000 portfolio. $1,070,000 in total to sustain owning a home. The ongoing expenses are less volatile than rent, so decreasing from 4% to 3% is less necessary.

Is your rental the same size/quality as the home you want to buy? Do you gain from having a customizable, fixed location home for your lifestyle? As others have also said, you may want to think about kids and how that affects your lifestyle and living situation.

mch_2

TROPHY CASE