My new NOCO power pack can take a charge from a 60 W USB charger that meets the requirements of PD 3. I have ordered a "UGREEN" one that is on its way (I have other UGREEN stuff that has been OK).
It seems quite a lot of power to put our from something that is that small but we will see.
As a test of my memory of Ohm's law I think I can use this to charge other items as they will only draw the current they need. Does that sound right?
Advances in semiconductors mean that the iron 50Hz transformers of yesteryear are now replaced by high frequency switching circuits running at mains voltages that can use much smaller ferrite transformers. Broadly speaking the power that can be put through a transformer is the mass of iron(like) material times the frequency it's driven at.. So whereas at 50Hz a 60W transformer would be a mug sized lump of iron, at
100kHz it might be a matchbox sized lump of ferrite.Also the modern switching FETS have such a low on resistance that they don't get hot so the need for large heatsinks goes away
Yes and no. Batteries are not especially ohmic, but if they are inside something with a USB charge port some electronics will take care of everything
Made substantially easier by the ability of USB devices with power delivery compatibility to negotiate higher voltages than the original
5V. So at 20V, 60W is a much more manageable 3A
Yup. If the device has the smarts it will negotiate what it needs (and if it is not, it will get a basic 5V supply). Anything with modern batteries will have its own internal charge control electronics.
Yes, I found that out with the Raspberry Pi 5. It requires a 27W USB charger, so I assumed any USB charger with a similar wattage would do. But the Raspberry Pi requires 27W at 5V, rather than the modern USB PD devices that up the voltage.
Hopefully the next version of Raspberry Pi and similar will use USB PD with a higher voltage.
Latest PD is 240 Watts (5A at 48V) over the same type-C cable
Nowt to do with Ohms Law - the charger, and the device to charge, will negotiate between them what charge rate each can use.
At what point does the USB C cable become important? I've a variety that've been bundled with various gadgets. Some of them look very lightweight.
The cable may also be part of the negotiation. If the cable is permanently attached to the charger there is no problem, but cables that plug into the charger must contain an identity chip if they are to deliver high currents above 3A or voltages above
20V. John
It only needs that if you're going to hang a lot of things off it. The actual current for the board itself is more like 2A at 5V, which a standard
10-15W charger will handle (assuming it didn't lie).That circuit costs money and takes up extra space, so they cut that corner with the reasoning that most users won't need the extra power.
Theo
Some of the pi chargers stick out a bit over 5V to help compensate...
Moment you start using USB there's another 2.5A that may be needed
5V 5A is IIRC the standard spec
Being a cheapskate, I bought a rPi5 without the official charger. The rPi5 was unusable with any of my other USB chargers, ones I used for a rPi4 and an oPi5. The rPi5 would run for minutes at most and then crash. I really wondered if I had a duff one, but I bought the official charger, and it has been fine since.
Perhaps it would have worked with an official rPi4 charger, but I didn't have one.
Given my rPi5, without any extras, was unusable, I don't know what that means. I don't think it even ran headless, without hdmi.
Ah yeah, it is 5,1V 5A = 25.5W for the rPi5. Apparently it does PD too, although I've a vague memory it isn't quite standard. (could be wrong).
My Samsung Tablet circa 2010 used the same 5.1V trick.
Bah! I like standardisation.
They want enough voltage to charge a battery.
A 19V 3A laptop adapter would have sufficed.
The USBPD 3.1 20V @ 3A would also work as sufficient voltage.
Sufficient voltage, means the charging section can be dead simple as a design. If they started from a 5V source, they would need a boost converter.
It's charging a pack which is a substitute for a battery.
4SnP. Four cells in series, many cells in parallel (which gives current sourcing capability).The ampere hours (the time it can sustain a high current) is likely a short time. But by having a lot of cells in parallel, that is how it gets the cranking amps.
Big Clive did a video on this I think, took apart a pack to see how it was constructed or something.
Lithium foils, they "smoke" if you disturb them. That's why we let Big Clive do these experiments, so we don't have to.
Paul
I'm still waiting for someone to actually use that.
(Summary at bottom)
Paul
Pis are very sensitive to power supplies.
I have a Pi Zero W that was unstable till I switched to a better power supply.
The wifi takes a LOT of current when connecting or re-establsihing connections
My Pi 4 occasionally dumps on me on a allegedly compatible PSU
Remember that the cable connecting the charger is important too. I have found that changing the cable used to connect a 'generic' 5v supply will change things from unusable to perfectly OK.
What a palaver. It seems that the cable has smarts too:
I'm not sure that's smarts, or just not enough copper.
Andy
I asked some people I know. They tell me the Pi will run fine on a 15W charger, unless you are using a lot of USB power for external devices. That's when you need the 27W device.
Andy
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