Recent Posts

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Beginners / Re: Convert US standard 115V to International 230V

« Last post by Jwillis on Today at 10:34:26 pm »

I agree that the statement is a simplified explanation of how a SMPS works. But if you look at main stream switching power supplies on the market they are designed for a broad range of frequencies and input voltages. You need to choose a power supply rated for the application to which it is intended. There are SMPS's rated for medical applications. So why reinvent the wheel just get a power supply rated for your application.
Electrolytic's  standard testing is between 100Hz 20C^o and 120Hz at 25C^o. The DC ripple in a SMPS after rectification is either 100Hz or 120Hz.
Electrolytic capacitors show very little change to behaviour between 10Hz and 1kHz depending on temperature. So to say that there would be any significant change in behaviour between 50Hz and 60Hz at an ambient temperature of 20C^o to 25C^o is over thinking that a problem can occur. https://www.cde.com/resources/technical-papers/AEappGuide.pdf

You are missing my point. It has nothing to do with SMPS. The point is that a bridge rectifier followed by a capacitor is highly dependent on frequency because the capacitor needs to hold enough energy to power whatever it powers during a longer time, until the next pulse to recharge it comes along. Lower the input frequency and you increase the   ripple, decreasing the voltage level to which it falls. If you reduce the frequency by 50% you need to double the capacitance in order to maintain ripple and not increase voltage drop. It does not matter what follows, SMPS, linear or whatever.  I have dealt with adapting 120 V, 60 Hz machines to 220 V 50 Hz, including linear PSU, motors and transformers and I am quite familiar with the issues. That was long time ago, in a previous life.

The frequency of mains supply after rectification 100Hz or 120Hz depending on where you live. AND THERE IS NO SIGNIFICANT BEHAVIOUR CHANGE OF AN ELECTROLYTIC CAPACITOR BETWEEN 100Hz AND 120Hz AT 20 to 25C^o It makes no damn difference whether it's on a linear supply or an SMPS. That tiny change in Value and ESR between 100Hz and 120Hz won't make a damn bit of difference to the ripple voltage. Electrolytic capacitors have as much as 20% tolerance in value and your saying that a fraction of a uF can make a significant difference to ouptut ripple?  That's absurd! Just to reduce the output ripple voltage by half, the capacitance needs to double.

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Test Equipment / Re: Korad KA3005P power supply: UI changes

« Last post by jewelie on Today at 10:33:51 pm »

For reference the attached photos are of the Tenma 72-10480 I got from CPC Farnell late in 2022 ( https://cpc.farnell.com/tenma/72-10480/power-supply-1ch-30v-3a-adjustable/dp/IN06822 ) which is clearly a rebadged KA3003.

I had a noisy fan issue that went away with a 25V 220uF electrolytic (poked deep into the connector, which is a bit hacky but it fits nice and tightly.)

It's clear the fan doesn't cope that well with PWM.

Oddly, with the capacitor, the fan runs faster at "full" loaded speed, which seems odd, unless the output isn't actually DC when at full speed?

Excepting the risk of it falling out (which seems minimal, plus I can see it through the vents at the side) is it safe/okay to be using this 220uF cap like this?

(If you'd like a laugh... whilst experimenting with the capacitor and fan I forgot to watch the 10R power resistor which I was only intending to misuse as a 90W heater for a few moments... I was only alerted by the magic smoke coming from the melting plastic box it was slowly sinking in to. Cue quick transfer to emergency containment pie dish. FFS!  )

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Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by dj_holmes on Today at 10:33:28 pm »

  OK so Arcam had it perfect 30 years back!?

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Beginners / Re: Decent but cheap Trinocular stereo microscopes for soldering

« Last post by Sensorcat on Today at 10:33:08 pm »

Since we are on opposite sides of the planet, I do not know your purchasing options, but I can give a few hints, assuming that you are about to buy your first microscope:

• A stereo microscope is a game changer for soldering with precision on small components. Once you have it, you wonder how you survived without.
• Microscopes are long-living, and the innovation rate is low. At your budget, buying a used one could be the solution.
• A cap for every window not in use is a must-have and will belong to any serious new offer. If it is missing on a used offer, put adhesive tape on it as soon as you can, and then find a permanent solution (3D print?). Also, get a plastic cover for the whole instrument. Dust is one of the worst  problems!
• You don't need large magnifications for soldering work. A typical value will be 15-20, and you want to have approx. 5 to have an overview, perhaps 40 for inspection of problems.
• Do you really need a trinocular microscope? It depends on your priorities. Historically, the reason for developing such microscopes is this: For decades, almost all decent cameras used 135 film. The lens of these cameras are necessarily quite large, resulting in a poor match with the eyepieces of optical instruments. So there had to be a completely different optical path for the camera. You still need that if you want to use a DSLR, for best results. But today, we have good cameras on our smartphones, with very small lens, resulting in a much better match. The attachment will be a bit tricky, and you certainly loose productivity, but for a documentation photo here and there, using a smartphone can be an option. If you want to do so, you get a much wider selection of microscopes to choose from, but you won't find one to predict if your microscope model and your eyepiece work together well with your smartphone model. So the decision for a stereo microscope is a bit like gambling. However, getting a DSLR just for the microscope is above your budget anyway.
• Just holding a smartphone in front of the eyepiece does not work. You have to have a device to place the camera precisely on the optical axis and in the right distance, with very little tolerance.

HTH

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Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by moffy on Today at 10:31:25 pm »

Accordig to this post IR LED is even less noise!

https://www.diyaudio.com/community/threads/some-noise-measurements-for-leds-and-zener-diodes.35821/

What you want to know is not static noise or the noise as a reference, but the switching noise which will dominate, especially as it is synchronous with the output frequency and will readily convert to phase noise. The 1N4148 is a low capacitance fast diode, well matched for this circuit.

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General Technical Chat / Re: $20,000 dollars of software or licences on a thumbdrive ?

« Last post by Infraviolet on Today at 10:28:32 pm »

"Thumbdrives, especially modern ones, are 99% crap"
And I swear they get worse year by year, I've USB sticks from the 2010s still perfectly working despite enough gigabytes copied on/deleted/replaced to cover the capacity several times, versus drives from the last few years which die before they're even full once.

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Projects, Designs, and Technical Stuff / Re: How is a motor run capacitor sized?

« Last post by johansen on Today at 10:26:17 pm »

OTOH, if you can get the exact replacement for $30, that might be the way to go.

you can get a film cap which would last forever for that price.

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Programming / Re: Angle wrapping in code, "easy" problem, need to double check

« Last post by ejeffrey on Today at 10:25:49 pm »

For floating point the % operator isn't defined and you need to use fmodf and friends.  They broadly work the same way.  One trap is that negative zero is an allowed result which may need to be special cased if you want to ensure that the result is always non negative and strictly less than 360. 

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Test Equipment / Re: Heads up on MicSig Probe

« Last post by KungFuJosh on Today at 10:24:30 pm »

That's a decent deal. I have the same probe, but I got it 6 years ago for $115. That's almost $150 now, right? lol

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Security / Re: Microsoft repackages apps with a telemetry .NET wrapper

« Last post by Infraviolet on Today at 10:23:41 pm »

"Actually you can..."
There might be a simpler way, Windows locked away inside a VM, with some very strict firewalling of any potential telemetry which was trying to escape the VM performed by a trustworthy Linux host OS. That would be a solution for anyone needing to run a program on Windows which wasn;t Wine compatible (unfortunately not that great a fraction of Windows exe programs are Wine compatible, I'm lucky with the few legacy Windows programs I use).