I am looking for an absolutely RF quiet, regulated 5V (preferably 5.1) 3 amp supply for a a portable Raspberry PI4 I am putting together. Unfortunately every battery bank I see seems to be running a buck/boost arrangement or something else. I should add I have just about completely silenced the RPI4 in a “Wicked Aluminum” fully enclosed case.
I want to preserve the almost completely noise free environment of some of the summits I visit and I want a 5v 3amp lithium battery bank with only a regulator inside…and preferably one I don’t have to build myself as my time is so tight lately. I expect current drain to be typically about .750 amps with some spikes.
Does anyone in the ham world make regulated 5v portable banks? There must be a market somewhere for something bigger than ham radio that needs absolutely silent ripple free 5v portable supplies…
Any ideas where to look or am I building this on my own? Its hard even to find low voltage drop 3amp regulators for 5v…
How about two lithium-ion cells in series for 7.4 V, then some diodes to drop the voltage down to near 5 V?
But where’s the regulation as the batteries discharge or as drain increases?
Hmm, looks like the Pi needs 5.0V ±5%, so you’ll need a regulator to keep it between 4.75 and 5.25 V.
Seem like a simple linear regulator should work. These are 5 V 3 A low-drop-out regulators. That should be a start.
I’m fairly sure I read somewhere that LDO linear regulators, especially thru-hole are lifetime/last order status. There is much reduced demand as everything uses switching regulators nowadays. I’ll see if I can find the article / forum and post a link.
Could I suggest the KISS approach. A 7805, 1 A regulator chip with 0.01 ceramic caps on input and output (to maintain loop stability) and remove residual noise, powered by a 7.4 V Lipo. If supply is a difficulty please send E maIl to email@example.com and I will post chip, circuit and caps out FOC.
KISS yes, but because of the high dropout voltage of this regulator family, an LDO type would be more suitable here, e.g. an LT1085
I thought about that 7805 but its about 2 amps short of what I need. Also paralleling them together seems to require some additional sophistication which surprised me a bit.
I have found that a RPI will produce corrupt files if its occasionally high transients in current draw are not adequately met…this can be a big headache. I did not completely eradicate corrupt file issues on my MFJ-1234 until I ran a dramatically over-sized home supply (the ADAFRUIT 5v 10amp)…so I am not keen on running my own home brew portable setup on something less than the 3amps of its official specification even if that is a bit of overkill…
I have experimented with a 5v 2.4 amp battery bank without issue but mysterious corrupt files are awful to deal with so I really would like to keep to a 3amp solution.
But certainly someone has to be selling a regulated, completely RF quiet bank already, no? We can’t be the only hobby/profession that needs absolutely RF quiet battery banks, can we??
The market provides what sells i.e. what people buy. People are miserable cheap skate penny pinching mingers. So they buy the absolute cheapest tat from China which may or may not work very well where RF noise is not on the agenda. For a whole raft of definitions of “very well”. Then when it fails or the plastic breaks or whatever they say well it was only $2.95 including shipping from China so I’ve not lost much and continue to pump the tat markets for more rubbish that barely functions. (*)
Who would want an RF quiet power supply apart from people interested in weak radio reception? Professional/business class market will not be using a Pi and USB PSU, they’ll be paying big bucks and passing the cost on to the consumers. Consumers tend to fall many into the above description and wont pay.
You can get them, selection is mainly luck based along careful study of the photos to see if it may be half-decent. Or make your own switcher. Plenty of data on the interwebz though it’s more tricky if you want to use thru-hole components.
Or buy one and finish of the job by screening and adding some RF supression caps and chokes. It’s not going to be beyond the ken of a home constructor to make a significant improvement to what’s being sold.
I have to say that a linear supply is just so “Edison” I’d not consider it.
I have a Pi B+ with a radio control switching 12V > 5V supply and an Iridium 1.5GHz satellite modem running off its own LiPo. All in plastic boxes. Not a sniff of HF noise from it. So you can find the bits. I was lucky.
That is market worth looking at, radio control equipment. Universal battery eliminator or UBEC is the eBay keyword.
(*) You can get very high quality goods from China. They’re not cheap.
Wasteful yes—but I like this idea! Thanks! I wasn’t finding the LDO regulator I needed before—
I will be running FT-8 and other modes on 2m and the higher bands as well so really wanted to make sure everything was quiet…perhaps overkill but why not? The home QTH has such horrific local noise I that one thing I really love about SOTA is the RF quiet summits.
Use it as the reference for a power transistor (plus a couple of resistors) that can handle the current . A linear solution to supply “N” amps is not a problem - it just wastes the excess voltage as heat hence the use of switchers with all the RFI implications.
There was an article in radcom several years ago where the author put a buck/boost module in a diecast box with substantial filtering on the battery input line and output line with Faraday shielding on either side of the boost module with feed through caps etc. It may be possible to find a copy online