bjtheone
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 12:36 pm

jcyr wrote:
Thu Sep 12, 2019 1:39 am
Actually the whole point of rigorous standards, such as USB, USB 2.0, USB 3.0, and USB C, is to provide interoperability between vendors. A good thing, no?

Why wouldn't I buy a RFP/RPT power supply for each Pi? Because I've already got plenty of 5V supplies sitting around doing nothing. Many of them, specially the cheaper ones, work fine with the Pi.
3 potential issues:

Rigorous adherence to standards and generic no name adaptors from China are not terms I would put in the same sentence.

Chargers/adaptors are not power supplies, and may not deliver the voltage regulation required. This is likely the biggest issue people face with trying to use phone chargers as Pi power supplies.

Does a standards compliant adaptor meet the Pi's requirements in all cases? Certainly USB 1.0 came out before such high current loads were envisioned. Not sure about USB 2.0 either. For USB 3.0 the requirement of +- 5% at the source's connector against the 5V nominal which puts a legal adaptor at 4.75V. Add in a connection adaptor if you are using a micro USB cable and you are likely going to have issues.

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davidcoton
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 12:58 pm

bjtheone wrote:
Thu Sep 12, 2019 12:36 pm
Does a standards compliant adaptor meet the Pi's requirements in all cases? Certainly USB 1.0 came out before such high current loads were envisioned. Not sure about USB 2.0 either. For USB 3.0 the requirement of +- 5% at the source's connector against the 5V nominal which puts a legal adaptor at 4.75V. Add in a connection adaptor if you are using a micro USB cable and you are likely going to have issues.
The voltage standard on USB is 5V +/- 0.25V, AFAIK the same for the three USB generations. The Pi is designed to work with that, though it can be marginal at the lower end (bottom limit voltage in will not guarantee compliant voltage out). This only affects peripherals, the Pi itself will happily work with input voltage well below the USB spec.

The minimum current standard even for USB3 (0.9A) is not enough for the newer Pis (probably OK for a Pi0). So any power supply designed for Pi2, 3 or 4 will need to exceed the minimum specification.

The other issue is the design error on the Pi4B USB-C power input, which means that active (e-marked) cables will not be compatible. This is where adherence to standards is a good idea, and the problem is listed for correction on some future board revision.
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W. H. Heydt
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 2:08 pm

davidcoton wrote:
Thu Sep 12, 2019 12:58 pm
The minimum current standard even for USB3 (0.9A) is not enough for the newer Pis (probably OK for a Pi0). So any power supply designed for Pi2, 3 or 4 will need to exceed the minimum specification.
Agree about the default 0.9A. Since the Model B originally spec'd 700mA, and the Pi0/Pi0W use the same SoC and don't have the LAN chip, 900mA is *plenty* for those boards.

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rpdom
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 2:21 pm

W. H. Heydt wrote:
Thu Sep 12, 2019 2:08 pm
davidcoton wrote:
Thu Sep 12, 2019 12:58 pm
The minimum current standard even for USB3 (0.9A) is not enough for the newer Pis (probably OK for a Pi0). So any power supply designed for Pi2, 3 or 4 will need to exceed the minimum specification.
Agree about the default 0.9A. Since the Model B originally spec'd 700mA, and the Pi0/Pi0W use the same SoC and don't have the LAN chip, 900mA is *plenty* for those boards.
Don't forget that on the 1B, 280mA of that 700mA were for the two USB ports with 140mA fuses on each port. That means the Pi was expected to use up to 420mA at the original 600MHz clock speed.

I've measured a Pi 0W at a little over 300mA when loaded, and about 120mA when idling.
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 4:31 pm

The clue is this line:
The circuitry required to manage the charging rate and voltage limits for lithium ion batteries is typically part of the device being charged (such as your cell phone or laptop), not the charger.
With the charging control managed by the device that a charger brick is connected to, there is only a vague requirement to regulate the output voltage of this type of power supply.

When Pi 1 was released, many micro-USB chargers sold with phones of the time were found to be grossly inadequate, as at rated load they would deliver only about 4.2V due to sloppy feedback implementations.

The set of "good" devices encompasses both types, but you are more likely to get problems with a device that is advertised as a "charger".
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drgeoff
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 5:47 pm

jcyr wrote:
Thu Sep 12, 2019 5:00 pm
Sure, if a 5V 'charger' doesn't regulate to 5V at advertised max. load then it is out of spec.
I disagree. If the charger supplied with a device has adequate performance to charge the device's battery then it is not out of spec. That it might have "5V xA" on the label does not necessarily mean it is supposed to give 5 Volts when delivering that x Amps.
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 8:11 pm

Seems to are repeating ad nauseum the same old stuff. Lock the thread?
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Re: RPI 4 USB-C supply

Thu Sep 12, 2019 8:52 pm

jamesh wrote:
Thu Sep 12, 2019 8:11 pm
Seems to are repeating ad nauseum the same old stuff. Lock the thread?
Yes please.
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