Well, we all have different ideas and philosophys. My take is to reduce or eliminate the 2 x 5R and make sure your layout is conducive to getting the 7824 to do most of work with ripple reduction. Make sure the ground/earth/-ve wire/track is such that the 7824 takes it's feed from the capacitor bank.
Especially now YMMV Dave
Especially now YMMV Dave
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Thanks, Dave. Not sure if what I'm up to rises to the level of philosophy just yet 🙂
Pondering your advice, it occurred to me that the longest run on my breadboard is between the filter and rectifier -- it's so long in fact that while I was thinking the options through, I kinda missed the fact that my .33 regulator input cap is effectively paralleled across a 4700uF filter cap already. I could put a bigger one in that position, but it costs me nothing to just take R2 out of the filter, see how much that affects ripple on the output (or IF it does...) and then see if the damn thing starts up.
I'll report back.
Pondering your advice, it occurred to me that the longest run on my breadboard is between the filter and rectifier -- it's so long in fact that while I was thinking the options through, I kinda missed the fact that my .33 regulator input cap is effectively paralleled across a 4700uF filter cap already. I could put a bigger one in that position, but it costs me nothing to just take R2 out of the filter, see how much that affects ripple on the output (or IF it does...) and then see if the damn thing starts up.
I'll report back.
Thanks for the kind words.
Last night: Removed R2 from the filter. Series resistance is now 5 ohms (+ESR, etc). I also drastically shortened the physical distance between the end of the filter bank and the regulator input. Drum roll, pls...
Image 1: Startup to 33rpm. Image 2: Startup to 45rpm. Image 3: Startup to 78rpm
Undervoltage issue solved. All three speeds start up like a dream, and I can change speeds at will while the platter is running. Sag after the switch throw is greatly reduced (~2v), the magnitude is the same regardless of speed selection, and I've got a clear picture of how long it takes for the controller to get a handle on things and settle into the nominal RPM.
For 33 and 45, the magnitude of the overshoot is diminished (now 6v, vs 8v overshoot before). But I expected the 78 overshoot to be equal if not greater - consistent with the DMM current measurements I took using the SMPS. But instead it's halved. Any ideas as to why that is?
This all looks like good news. With one important caveat – according to RPM app, the deck runs about .01 faster, and the W&F % has doubled. Yes, it's still low, but if its higher than it is with the switcher, all this effort is nil. Zoomed in to 20mV/div, the ripple looked... different. Not much greater in amplitude, but definitely different. Tonight I'll investigate that further.
Thanks for sticking with me, Dave and everyone.
Last night: Removed R2 from the filter. Series resistance is now 5 ohms (+ESR, etc). I also drastically shortened the physical distance between the end of the filter bank and the regulator input. Drum roll, pls...
Image 1: Startup to 33rpm. Image 2: Startup to 45rpm. Image 3: Startup to 78rpm
Undervoltage issue solved. All three speeds start up like a dream, and I can change speeds at will while the platter is running. Sag after the switch throw is greatly reduced (~2v), the magnitude is the same regardless of speed selection, and I've got a clear picture of how long it takes for the controller to get a handle on things and settle into the nominal RPM.
For 33 and 45, the magnitude of the overshoot is diminished (now 6v, vs 8v overshoot before). But I expected the 78 overshoot to be equal if not greater - consistent with the DMM current measurements I took using the SMPS. But instead it's halved. Any ideas as to why that is?
This all looks like good news. With one important caveat – according to RPM app, the deck runs about .01 faster, and the W&F % has doubled. Yes, it's still low, but if its higher than it is with the switcher, all this effort is nil. Zoomed in to 20mV/div, the ripple looked... different. Not much greater in amplitude, but definitely different. Tonight I'll investigate that further.
Thanks for sticking with me, Dave and everyone.
Btw - I've been working on a plan for the actual wiring layout in the build. Currently the plan is to have the last cap of the filter, the regulator input bypass cap, and the 7824's input pin all on the same solder tab.
@mcrushing What size capacitor do you have at the 7824 output? I was looking but it's not exactly clear...
It’s 4700uF. (And I’m considering bypassing it with a couple uF film to take care of any HF junk the big cap is missing.)
Here’s a quickie schematic I drew to keep track of things while wiring it up.
Note - I’ve now removed the second 5 ohm resistor. Also, I forgot to draw the ground point for my rail return paths - but the breadboard does actually have one 😅
Here’s a quickie schematic I drew to keep track of things while wiring it up.
Note - I’ve now removed the second 5 ohm resistor. Also, I forgot to draw the ground point for my rail return paths - but the breadboard does actually have one 😅
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Hey, guys. So I don't happen to have a 1uF cap on hand...Amazon will be delivering a couple assortments of cheap small value films and ceramics later today. But for the moment I have that 4700uF regulator output cap bypassed with a .022uF tropical fish I happened to have in the drawer (which is probably doing not much).
Anyway, I've been scoping ripple across the output of my PSU with the motor running. Above are captures at 33, 45 and 78 rpm, zoomed to 20mv/div. Below, a quickie chart of RMS and Pk-Pk noise on the 24v rail.
| Speed | RMS Noise | Peak-to-Peak | |
|---|---|---|---|
| 33 RPM | 11.03 mV | 96 mV | |
| 45 RPM | 8.34 mV | 39.2 mV | |
| 78 RPM | 21.23 mV | 132 mV |
On their own, these data aren't all that interesting. What IS interesting is that they show a fair amount less noise on the rail at 45 rpm... and EVERY single W&F measurement I've taken with the iphone RPM app has shown a BETTER W&F FIGURE at 45 than at 33.
Yes, I know, the RPM phone app isn't all that accurate, BUT... If an iphone accelerometer can see a measurable difference in W&F from a ~2.6mV RMS reduction in power rail noise, it definitely seems worth eliminating. Gonna see what some bypass caps will do.