neilneil2000
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[SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 11:22 am

Hi, I have been looking at the schematics of the Pi Zero W and it looks to me like the Zero W has no protection on the USB power socket, whereas other models have a clamp diode, polyfuse and current mirror.

Can anyone confirm whether my assertions are correct?
Last edited by neilneil2000 on Sat Oct 14, 2017 4:06 pm, edited 1 time in total.

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davidcoton
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Re: Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 12:13 pm

Correct. The power protection costs money, so it is not present on Pi0/Pi0W.
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W. H. Heydt
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Re: Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 3:52 pm

Actually, no Pi has undervolt protection. Other than the Pi0/Pi0W, they have overvolt protection. This is one of several reasons why I discourage absolute beginners from starting with a Pi0/Pi0W.

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mahjongg
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 4:23 pm

Actually most PIs (except the Zero) DO have under voltage protection, if the voltage sinks below 4.65Volt the power LED will turn off, and the kernel will issue a warning through the GPU by displaying an under voltage icon on the screen.

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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 4:50 pm

mahjongg wrote:
Sat Oct 14, 2017 4:23 pm
Actually most PIs (except the Zero) DO have under voltage protection, if the voltage sinks below 4.65Volt the power LED will turn off, and the kernel will issue a warning through the GPU by displaying an under voltage icon on the screen.
That's like saying that a low oil pressure light is low oil "protection" for an engine.

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davidcoton
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 6:00 pm

W. H. Heydt wrote:
Sat Oct 14, 2017 4:50 pm
mahjongg wrote:
Sat Oct 14, 2017 4:23 pm
Actually most PIs (except the Zero) DO have under voltage protection, if the voltage sinks below 4.65Volt the power LED will turn off, and the kernel will issue a warning through the GPU by displaying an under voltage icon on the screen.
That's like saying that a low oil pressure light is low oil "protection" for an engine.
I could argue that the warning light signals the driver to stop the vehicle and turn the engine off, thus protecting it. Putting a human in the path doesn't stop the system from protecting the engine.
However, the analogy is poor. Low oil pressure usually means that continuing to run is very likely to damage the engine, because the most likely scenario is that oil is leaking or being burnt. Pis (apart from USB and HDMI peripherals) can run quite happily on low voltage until it gets considerably worse than 4.65V, and even then is unlikely to suffer major damage (except perhaps the SDCard). In most cases the voltage will stabilise at some value -- if it is "leaking" it is likely to decline too quickly for any warning (even automatic) to perform a safe shutdown.
"If it ain't broke, fix it until it is."
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 10:05 pm

davidcoton wrote:
Sat Oct 14, 2017 6:00 pm
W. H. Heydt wrote:
Sat Oct 14, 2017 4:50 pm
mahjongg wrote:
Sat Oct 14, 2017 4:23 pm
Actually most PIs (except the Zero) DO have under voltage protection, if the voltage sinks below 4.65Volt the power LED will turn off, and the kernel will issue a warning through the GPU by displaying an under voltage icon on the screen.
That's like saying that a low oil pressure light is low oil "protection" for an engine.
I could argue that the warning light signals the driver to stop the vehicle and turn the engine off, thus protecting it. Putting a human in the path doesn't stop the system from protecting the engine.
However, the analogy is poor. Low oil pressure usually means that continuing to run is very likely to damage the engine, because the most likely scenario is that oil is leaking or being burnt. Pis (apart from USB and HDMI peripherals) can run quite happily on low voltage until it gets considerably worse than 4.65V, and even then is unlikely to suffer major damage (except perhaps the SDCard). In most cases the voltage will stabilise at some value -- if it is "leaking" it is likely to decline too quickly for any warning (even automatic) to perform a safe shutdown.
No analogy is perfect. My point was that the indication, whether the LED or the display icon on the Pi or the oil indicator light will not effect any protection in and of itself. It requires human attention and intervention. The overvoltage protection on the Pi *will* try to protect the Pi without the operator doing anything and therefore falls into the category of actual protective circuitry. (But the Pi0/Pi0W lack that protection.)

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davidcoton
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sat Oct 14, 2017 10:47 pm

W. H. Heydt wrote: The overvoltage protection on the Pi *will* try to protect the Pi without the operator doing anything and therefore falls into the category of actual protective circuitry. (But the Pi0/Pi0W lack that protection.)
Indeed.
My point is that undervoltage protection does not have to be fully automatic, a warning to initiate manual intervention is adequate. In the case of the oil warning, there is a secondary consideration of getting the vehicle to a safe place, which until recently has required manual intervention, so that a fully automated protective system is inappropriate for different reasons.
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Sun Oct 15, 2017 2:46 am

davidcoton wrote:
Sat Oct 14, 2017 10:47 pm
W. H. Heydt wrote: The overvoltage protection on the Pi *will* try to protect the Pi without the operator doing anything and therefore falls into the category of actual protective circuitry. (But the Pi0/Pi0W lack that protection.)
Indeed.
My point is that undervoltage protection does not have to be fully automatic, a warning to initiate manual intervention is adequate. In the case of the oil warning, there is a secondary consideration of getting the vehicle to a safe place, which until recently has required manual intervention, so that a fully automated protective system is inappropriate for different reasons.
In general, I agree, but I think you're reading too much into the analogy. Perhaps I should have pcked a different one, such as a seat belt warning light or a high beam indicator. I would class the low voltage indicators on the Pi as "alerts", not "protection" (because they don't take any action on their own). Of course, we may just be arguing semantics. If you class the low voltage indicators on the Pi as "protection", in what way do they actually protect anything on their own? What if the Pi is remote from the operator? How does this "protection" work then?

Edit to add... The low oil pressure indicator is situational. If you're trying to escape the lateral blast from Mt. St. Helems and you stop the car because of the oil light, you *will* die. If you keep going you *may* still die, or you *may* live and might wreck the engine. The choice is yours...

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Imperf3kt
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Mon Oct 16, 2017 1:02 am

There've been a couple of people recently testing powering their Pi from a 3.7v lithium battery (with no boost circuit)
Apart from no USB and no HDMI, their Pis are working just fine, so undervoltage "protection" isn't even necessary until you hit ~3.4v
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Leeloo
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Re: Pi Zero W - No overvoltage protection?

Mon Oct 16, 2017 11:42 am

W. H. Heydt wrote:
Sat Oct 14, 2017 3:52 pm
Actually, no Pi has undervolt protection. Other than the Pi0/Pi0W, they have overvolt protection. This is one of several reasons why I discourage absolute beginners from starting with a Pi0/Pi0W.
I would have to agree zero isn't good for beginners and not just for that reason.

I liked the pi3 kit so much I went and got a cheaper zero board only except it wouldn't work with my wireless-keyboard or any of my usb hubs meaning by the time I buy a new keyboard and a hub its as big as the pi3 but messy and probably end up costing as much. zero isn't as good as the device I got it to replace so seems like its for more specific projects.

tldr agree zero is not for beginners

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mahjongg
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Mon Oct 16, 2017 12:10 pm

Imperf3kt wrote:
Mon Oct 16, 2017 1:02 am
Apart from no USB and no HDMI, their Pis are working just fine, so undervoltage "protection" isn't even necessary until you hit ~3.4v
No HDMI is probably only caused by not being able to read data from the monitors EEPROM, so if you override the automatic monitor capabilities detection, and use config.txt to set the right video mode for your display, then you might even be able to generate video with a 3.4V powered device.
Actually as long as the 3V3 (and 1V8) regulators get enough voltage your PI itself (the SoC) will work.

+1 about the PI Zero(w) not being for beginners, start with a PI3, then if you want to develop a PIzero project, best do so with a 2B, then port it to a zero(w).

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mikerr
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Re: [SOLVED] Pi Zero W - No overvoltage protection?

Mon Oct 16, 2017 2:17 pm

Imperf3kt wrote:
Mon Oct 16, 2017 1:02 am
There've been a couple of people recently testing powering their Pi from a 3.7v lithium battery (with no boost circuit)
Apart from no USB and no HDMI, their Pis are working just fine
Actually many USB devices continue to work on 3.3v even if it's out of spec
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