Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The hole fits a 25 mm fan, but the thing runs cool enough it should survive without forced air; think of it as a contingency. Mounting the case on standoffs seems like a Good Idea, however, as the bottom plate includes many vent slots for Good Circulation.
The top plate builds upside-down, so I had Slic3r add teeny support plugs inside the recessed screw holes. I think button-head screws would fit neatly in the recesses, but we’re obviously not in this for the looks.
The tiny white stud is a Reset switch hot-melt glued into the slot. I plan to just turn off the AC power after shutting the RPi down, so a power-on will suffice as a reset.
A laptop-style power brick supplies 24 V for the MPCNC’s stepper motors, but I didn’t want it wandering around on the Basement Laboratory floor and getting in trouble, so a pair of brackets seemed in order:
Power Supply Brick Mount – trial fit
They build flat on their backs to avoid support material:
Power Supply Brick Mount – Slic3r
The nicely rounded corners produce a very thin line of plastic on the first layer, so the model now has thicker base plates to improve the situation. A set of mouse ears would keep the tips pasted to the glass.
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This will eventually end up on a board supporting the GRBL controller box:
Control Box – Connector Mount – Slic3r
It’s a direct cut-n-paste descendant of the old NEMA motor mount.
The nut threads onto the connector behind the bulkhead, so you must either wire it in place or make very sure you can feed all the terminations through the hole:
Connector Mount
Given the previous hairball, I think in-situ soldering has a lot to recommend it:
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The longer traces show their original capacity, back in the day.
Whacking a chisel into the obvious split lines broke the solvent glue bonds holding the case sections together, after which some slow prying defeated the double sticky foam tape on the cells:
Baofeng BL-5 battery pack – innards
A closer look at the (dis)charge controller PCB:
Baofeng BL-5 battery pack – protection PCB
The other side of the PCB has no components, so what you see is what you get. The larger IC proclaims FS8205A EP050C, which may indicate a vague relation to an S8205 protection IC. The datasheet shows a 16 pin TSSOP package containing an IC for four or five cell batteries, completely unlike the 8 pin package on the PCB, but when you buy enough of anything, you can get anything you want.
In common with all cheap lithium batteries around here, the “thermistor” terminal connects to a 10 kΩ SMD resistor steadfastly maintaining its resistance in the face of all temperature variations.
Some probing shows one feeble cell in each pack. Perhaps a Frankenbattery built from the debris will have enough capacity for a standard ride around the block.
I have often asserted, in public, in writing, that you can’t change the speed of a fan’s BLDC motor by varying its voltage, because the fan controller generates the waveforms responsible for the motor speed based on its internal timing.
A pair of BLDC blowers recently arrived and a quick test showed I’m pretty much completely wrong:
BLDC Blower – RPM I P vs V
The data points come from this blower:
Blower label – 24V 0.2A
The blower specs from the eBay listing:
75MM 24V Brushless DC Blower Cooling Fan Exhaust Fan
Dimension:75(L)x75(W)x30(H)mm
Connector:2Pin-PH2.0
Rated Voltage: DC24V
Rated Current: 0.2±10% Amp
Rated Speed: 3800±10%rpm
Air flow:1.8CFM
Noise: 23±10%dBA
Bearing Type: Sleeve
Life: 35000 hours
Cable Lenght: 32cm(12.5in)
Weight: 75g/pcs
The case is about 75 mm × 75 mm × 30 mm, so the generic part number seems to be 7530, with many variations. However, they all seem to resolve to the same blower with different models drawing different current at specific voltages (clicky for more dots, JPG blurriness in original):
GDT7530S12B BLDC blower parameter table
The blower in hand roughly corresponds to the bottom line of the 24 V section:
0.21 A
4000 RPM
16.3 CFM
1.1 inch H2O pressure
43 dBA
There’s a gross discrepancy between the eBay 1.8 CFM and the chart 16.3 CFM, but the other parameters seem within handwaving distance and, yo, it’s from eBay. ‘Nuff said.
The graph up top shows the results with an unrestricted output opening.
For more realistic results with some resistance to air flow, I taped a small anemometer to the blower output:
Blower air flow test
Which produced:
BLDC Blower – RPM Flow vs V – anemometer
In very round numbers, the anemometer aperture is 400 mm², so the 9 m/s air flow at 24 V works out to 3.6×10-3 m3/s = 0.13 CFS = 7.6 CFM. Which is maybe half the 16.3 CFM spec, but they’re surely using a fancier anemometer with much lower back pressure. Close enough, anyway. Fer shure, 1.8 CFM is wrong.
Completely blocking the inlet with a plastic sheet to simulate the blower pulling air from, e.g., a vacuum table:
BLDC Blower – RPM vs V – blocked inlet
The RPM varies more linearly with voltage when the blower isn’t accelerating any air.
Some current waveform show why you really shouldn’t run fans in series to “split the power supply”, as seems common in 3D printers with 24 VDC power supplies.
From a 24 V supply, the current drops to 50 mA every 75 ms (200 mA/div):
BLDC 24V Blower – 24 V – 200mA-div
From a 12 V supply, even weirder things happen (50 mA/div):
BLDC 24V Blower – 12 V – 50mA-div
Note that you can’t reduce the fan’s supply voltage by applying PWM to the current, as happens in essentially all 3D printers for “speed control”. Basically, PWM turns the fan off several hundred times every second, which does not modulate the voltage.
I have no way to measure pressure, but if the 1.1 inch H2O number comes close to reality, the blower can produce 1.5 lb of clamping force per square foot. Which isn’t a lot, granted, but it might suffice for paper and vinyl cutting.
Yes, the SSR negative output goes to the Protoneer + Power Input.
I should drive the SSR from the Motor Enable output (in the external motor control header), rather than +5 V, to let GRBL control the motors, with a manual E-Stop override. The A4988 drivers require -Enable, so:
-Enable to SSR -Control input (replaces GND)
+5 V to BRS to SSR +Control input (as before)
The SSR Control input draws 13 mA at 5 V, suggesting I should drive the AC SSR (for the spindle motor) from the DC SSR output, rather than paralleling the two on a single Arduino output pin.
I belatedly recognized the E-Stop BRS as an instantiation of an SCP-001-JKeter-class anomaly; it is now appropriately labeled:
MPCNC EStop as SCP-001-J
I can attest to its effect on rational thought; a molly-guard may be required.
After a year of fairly light use, the lens holder (and “attack ring”) of my J5-V2 flashlight worked loose and began to rattle. The ring holding the lens in place turned out to be finger-loose, but that wasn’t the entire problem, so I removed it and looked inside:
The aluminum ring holding the LED assembly in place was also finger-loose, so I unwound it to take the whole front end apart:
J5-V2 Flashlight – front parts
Reassembly with a few dabs of Loctite in appropriate places should prevent future rattles.
Given the number of … issues … accompanying this thing, I’d say it’s not been a good cost performer. The Anker LC40 and LC90 flashlights work much better.
The Smell of Molten Projects in the Morning 