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Place any diode on you bench on the 7805 regulator ground. The regulated voltage out should now be 5.6 volts rather than 5 volts. This extra .6 volts should be enough to prevent the pi brown out condition. You did not hear this from me as I would never stoop to such dirty tricks.
That's one trick I've used in the past for or'ing several 5V supplies with series diodes while still getting a steady 5V with no significant drop.
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That doesn't work for a pi unless you want to ruin it at the same time though.
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Update: I've changed the cable again and it works well now. Apparently, I have serious issues identifying a good cable for my application.
FYI, cat6 and cat7 cables use thicker wire than cat5. Helpful for PoE
Indeed high power/current PoE benefit from Cat6 cables, they cost more than Cat5 as well. We all agreed that it's better to increase voltage than price of the cable
Many may not know that while shopping for lowest cost Ethernet cable, you can get copper clad aluminium cable which may work for some time up-to some cable length (not even close to 100m), but is nearly useless for PoE applications due to high DC resistance. Obviously such CCA cable does not conform to Ethernet specs:
https://www.belden.com/blog/digital-building/not-in-my-network-copper-clad-aluminum-is-a-recipe-for-failureSo provide pads for a header, or include an onboard regulator for the 5V like is already there for the core voltage and then it could run from 9-12V adapters.
Increased size of the board, increased cost of BOM. And then deal with all those people with non existing soldering skills destroying their devices. 5V usb is something relatively certain, basically plug and play. 9-12 V adapters can have different polarity and often are not even regulated, simply transformer + rectifier.
Indeed USB shall stay for many reasons. On the other hand I agree that DC jack accepting 5-15VDC with some protection would be nice. Yes, socket and buck regulator with bypass for 5V will add to price. They could spin one more version and name it.. dunno... rPI embedded or something like that
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Options to power the Raspberry Pi properly with a long cable, in approx. the order of preference:
1) Use local mains power brick. (Preferably at least 2A.)
2) Use local buck regulation from higher DC voltage (e.g., from around 10-20V). Again, at least around 2A.
If impossible,
3) Use thick enough cable for the 5V.
Additionally, whichever you choose (and especially for #3), I strongly recommend adding some electrolytic bulk capacitance on the 5V line, because the Raspberry Pi is designed without such capacitance for ultimate cost and size reduction. A high-ESR, large value cap has two purposes:
1) it dampens any inductive ringing which can happen with a long cable, given the ultimately low ESR of the ceramic bypassing on the Raspberry power itself. Without it, a quick 1V drop may be followed by a 1V overshoot, risking blowing something up. Not something I have actually seen on a Raspi, but a typical failure mode in general.
2) The large capacitance also helps with spiky power consumption; without it, while you measure acceptable DC drop (the DC consumption is typically around 1A only), but the spikes may easily take 2A, doubling the voltage drop below unacceptable level. Now, these spikes can be long enough that you need considerable energy storage, the ceramic bulk (on the RasPi itself) is not enough.
A 6.3V 1000uF electrolytic is a cheap and relatively small fix for this. -
So provide pads for a header, or include an onboard regulator for the 5V like is already there for the core voltage and then it could run from 9-12V adapters. I've had so many micro USB cables that wouldn't work and have seen countless forum posts by users trying to get by with inadequate cables. This is especially true if you want to utilize the onboard USB ports to power devices like hard drives that can draw significant power.
Increased size of the board, increased cost of BOM. And then deal with all those people with non existing soldering skills destroying their devices. 5V usb is something relatively certain, basically plug and play. 9-12 V adapters can have different polarity and often are not even regulated, simply transformer + rectifier. Some "12V" adapters output 19V without load. It's like opening Pandora's box.QuoteI've ended up powering most of my pis by soldering on wires to a barrel jack. I have lots of nicely regulated 5V wall warts.
Geez, it's not that hard to get a decent cable
... unless you shop for cheapest garbage. Heck, just buy official RPi cable/charger if you are desperate.
Providing pads on the board costs nothing, there is space. If someone damages their board by poor soldering or connecting it backwards, who's fault is that? If someone uses an obsolete non-regulated wall wart to power something that needs a regulated voltage again who's fault is that?
Why should I buy a special cable and hope that it's adequate when I have piles of them that have come with various devices? Why should I have to guess if a cable or power supply will work? Out of probably 30 cables and a dozen USB power bricks I have, maybe 1-2 cables have proven to be marginally adequate for the RPi, provided I don't have anything pulling a significant load from the USB ports, and maybe 5 of the power adapters. On the other hand I have lots of 5V and 12V wall warts and bricks that put out their rated voltage, can supply their rated current without any issues. I've never had one single problem with one of them, the USB garbage was headache after headache, it's a stupid way to power something. I would wager that probably 75% of RPis returned as defective actually had nothing wrong with them, but were unstable due to crappy power cables which are practically ubiquitous. Even a mini USB would be a big improvement over the micro USB trash.
Well whatever, I'll just keep modifying my RPi's because once modded they are rock solid, no more headaches. -
Why should I buy a special cable and hope that it's adequate when I have piles of them that have come with various devices? Why should I have to guess if a cable or power supply will work? Out of probably 30 cables and a dozen USB power bricks I have, maybe 1-2 cables have proven to be marginally adequate for the RPi, provided I don't have anything pulling a significant load from the USB ports, and maybe 5 of the power adapters. On the other hand I have lots of 5V and 12V wall warts and bricks that put out their rated voltage, can supply their rated current without any issues. I've never had one single problem with one of them, the USB garbage was headache after headache, it's a stupid way to power something. I would wager that probably 75% of RPis returned as defective actually had nothing wrong with them, but were unstable due to crappy power cables which are practically ubiquitous. Even a mini USB would be a big improvement over the micro USB trash.
I' wager that those cables just come with devices that are less tolerant to power drops and/or just use it for charging so voltage drop does not bother them. On top of it, various "fast" charging standards just put more voltage on it so it is less affected, Dropping 1V at 9V/1A is much easier to tolerate than dropping that at 5V.
And let's not forget USB standard was originally 5V/500mA, a lot of cables you have might be just fine standard-wiseQuoteEven a mini USB would be a big improvement over the micro USB trash.
Mini-usb is worse in almost every way. Mini-USB is mechanically flawed and it just degrades much faster than micro-usb, on top of being bigger and having worse latching. And (at least few I've checked) micro-USB connectors are rated@1.8A so current should not be the problem either. -
And let's not forget USB standard was originally 5V/500mA, a lot of cables you have might be just fine standard-wise
Yep. AFAIK, only USB 3.0 introduced more than 500 mA max (900 mA) for non-charging use. So, many cables are just designed and tested for 500 mA. Getting more than that requires a proper cable and the right identification (if you're using a PC or a true phone charger), which I believe is some combination of pull-up/pull-down resistors on the data lines.
I you tear any micro-usb cable down, you'll often see tiny conductors for power (+5V, GND). No way they can hold even 2A without a massive voltage drop and possibly worrying heating.
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I only power the Raspberry Pis through the GPIO header. There are two dedicated 5V pins and at least 3-4 GNDs fairly close to them.
Never had an issue with "lacking input protection". It's such a cheap device; if you mess up and blow it up, just get a new one. I have installed dozens and never blown any.
Cumulative cost in sourcing proper USB cables (i.e., specified for USB3 charging) that are not con artist junk, and paying premium for such cables - worst case, chasing problems for weeks due to poor power -, quickly exceeds the cost of a single board blowing up once due to your wiring mistake.
Note that the Raspberry really needs over 2A during the short peaks. Standard USB cable rated for 500mA is going to have quite a lot of voltage drop. Even the cables designed for higher current are designed for charging devices that have internal battery; if you charge at 2A, and there is too much voltage drop, the charging current is just reduced slightly, and the charger IC is fine with this condition. This is completely different to powering a computer with no battery and miniscule amount of capacitance on its power lines. Even the shortest peaks must be within specs, otherwise it'll crash; and often do it in the most peculiar ways. -
Absolutely. The micro-USB connector was designed to explicitly improve on mini-USB’s shortcomings, not only to be smaller.QuoteEven a mini USB would be a big improvement over the micro USB trash.
Mini-usb is worse in almost every way. Mini-USB is mechanically flawed and it just degrades much faster than micro-usb, on top of being bigger and having worse latching. And (at least few I've checked) micro-USB connectors are rated@1.8A so current should not be the problem either. -
I would wager that probably 75% of RPis returned as defective actually had nothing wrong with them, but were unstable due to crappy power cables which are practically ubiquitous. Even a mini USB would be a big improvement over the micro USB trash.
IME (>1000 of returned RPi), less than 30% were non defective.QuoteWell whatever, I'll just keep modifying my RPi's because once modded they are rock solid, no more headaches.
You should have fantastic inability to buy a decent cable.QuoteEven a mini USB would be a big improvement over the micro USB trash.
Micro USB is one of the most reliable connectors. Order of magnitude more reliable than barrel jack. Connector itself almost never fails. Intermittent connection (with slight wiggling) in barrel jacks is so widespread that it eventually developed in like every third device I've seen. Very rarely happens with micro USB.
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Cumulative cost in sourcing proper USB cables (i.e., specified for USB3 charging) that are not con artist junk, and paying premium for such cables - worst case, chasing problems for weeks due to poor power -, quickly exceeds the cost of a single board blowing up once due to your wiring mistake.
There are no "500mA" cables among those which are barely decent. No smartphone in the last 5 years uses only 500mA for charging. They normally go 1A+, and drop current when detecting voltage drop. USB3 has nothing to do with charging current. Computer port is not a primary source for charging to begin with. Many phones just won't sink more than 500 mA when detect they are connected to computer.
Note that the Raspberry really needs over 2A during the short peaks. Standard USB cable rated for 500mA is going to have quite a lot of voltage drop. Even the cables designed for higher current are designed for charging devices that have internal battery; if you charge at 2A, and there is too much voltage drop, the charging current is just reduced slightly, and the charger IC is fine with this condition. This is completely different to powering a computer with no battery and miniscule amount of capacitance on its power lines. Even the shortest peaks must be within specs, otherwise it'll crash; and often do it in the most peculiar ways. -
Micro USB is one of the most reliable connectors. Order of magnitude more reliable than barrel jack. Connector itself almost never fails. Intermittent connection (with slight wiggling) in barrel jacks is so widespread that it eventually developed in like every third device I've seen. Very rarely happens with micro USB.
The reliability issue I'm seeing with microUSBs is not the connector itself failing, but the solder joints failing. Stress reliefing the power input cable is the fix - or just being careful.
Still, microUSB was not developed to supply 2A with minimal voltage drop for non-charging purposes, i.e., where 2A delivery without significant voltage drop is critical, and not only a factor of reduced rate charging.
Really, the use case for powering the Raspi is completely different from what these USB cables are typically used for:
1) data communication
2) low current (typically <500mA) power supply
3) higher current charging, where it's enough for a linear reg or buck converter to be able to convert to li-ion voltage, down to below 4V, where a voltage drop isn't critical, and worst case, the rate is reduced. And indeed, people do report different charging rates for fast charging using different quality cables!
Instead of going circles of babbling about "good" cables, maybe you should give us some exact recommendations of your known good cables? You know, the requirements for the Raspberry are well outside the USB specification, so having a "good compliant cable" isn't necessarily enough.
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There are no "500mA" cables among those which are barely decent. No smartphone in the last 5 years uses only 500mA for charging. They normally go 1A+, and drop current when detecting voltage drop.
Exactly this. You have completely proved my point. 1A+, and dropping current when detecting voltage drop.
Guess what? Raspberry Pi hasn't got a battery to power itself from. It absolutely requires -- not 1A, not 1.5A, but at least 2A (depending on what you connect to it and how you configure it). When it detects a voltage drop, it... wait, can it "drop charging current"? Well, usually it flashes the voltage drop warning. Sometimes, it just corrupts the file system, or just crashes.
Charging a battery of a device powered by a battery is completely different beast from powering a device with very little bypass capacitance. Even if the voltage drops by a volt, it's going to work. Even if it browns out for a second, nothing bad happens.
Current ratings of good quality USB cables may be based on:
1) thermal ratings: it won't melt or the plastic won't degrade
2) useful charging - because that's what these cables are specified to do: charge the device: the voltage drop at that particular current typically doesn't result in reduced charge rate - at least to non-full battery (with more dropout to work with)
On low quality products, it's of course just marketing. But even if the quality is OK, and the specs hold, the specs are designed for a completely different, and much less demanding, use case.
An example:
Charging:
0A: 5.0V - all fine
1A: 4.5V - all fine
2A: 4.0V - charge to the empty battery still ok at almost 2A. With full battery, charging rate is reduced. No big deal.
Raspberry Pi:
0A: 5.0V - all fine
Powered up. WiFi or any USB device tries to sink 2A for 1 millisecond. Supply brown-outs to 4.0V. May work or may not. Reliability issues seen by the user.
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Guess what? Raspberry Pi hasn't got a battery to power itself from. It requires -- not 1A, not 1.5A, but at least 2A (depending on what you connect to it and how you configure it). When it detects a voltage drop, it... well, usually it flashes the voltage drop warning. Sometimes, it just corrupts the file system, or just crashes.
Raspberry pi 2 IIRC from my measurements don't go over 600mA and pi 3 don't go over 900mA (without overclock). All that exceeds this is from additional load you attached. Most recent phones use more than 1.5A for charging. -
Guess what? Raspberry Pi hasn't got a battery to power itself from. It requires -- not 1A, not 1.5A, but at least 2A (depending on what you connect to it and how you configure it). When it detects a voltage drop, it... well, usually it flashes the voltage drop warning. Sometimes, it just corrupts the file system, or just crashes.
Raspberry pi 2 IIRC from my measurements don't go over 600mA and pi 3 don't go over 900mA (without overclock). All that exceeds this is from additional load you attached.
These are DC measurements, I guess. Because I have measured around 1A DC from Pi3 as well.
DC measurement is completely irrelevant, as explained above, because there is little bulk capacitance. Any computer device is going to use spiky currents; think about how WiFi works, for example, or accessing an SD card. The capacitance on Raspberry3 board itself can supply the required load for hundreds of microseconds, maybe a millisecond max.
This is why I recommended adding a big bulk cap on the supply; it will help on the borderline cases. But adding a decent power supply without excess resistance (long, poor cable) is of course better; then the load variation is accounted by the feedback loop of the supply, which easily corrects in millisecond range. -
There are no "500mA" cables among those which are barely decent. No smartphone in the last 5 years uses only 500mA for charging. They normally go 1A+, and drop current when detecting voltage drop.
Exactly this. You have completely proved my point. 1A+, and dropping current when detecting voltage drop.
Most phones just take nominal current and do not mind voltage drop at all - because voltage of fully charged battery is around 4.2 volts. It does not matter you put in 4.5V or 5V - phone will happily charge your battery. BTW most phone chargers have quite poor voltage regulation, if it is written 5V 1500mA then you get one or another, but not both in the same time
This of course in addition to cable drop!! rPI on the other hand is very picky about voltage. So here we are.
Yes, I agree that micro USB is way more reliable than mini USB. Thou today I am fan of USB-C connector, USB PD and/or QC2.0/3.0 -
Charging:
Nonsense, no barely decent cable has 0,5V voltage drop at 1A.
0A: 5.0V - all fine
1A: 4.5V - all fine
2A: 4.0V - charge to the empty battery still ok at almost 2A. With full battery, charging rate is reduced. No big deal.QuoteRaspberry Pi:
Nonsense again. You may not know but Raspberry pi has enough bulk capacitance for such short bursts of power. There are 47uF MLCCs on 1.2V, 1.8V and 3.3V power rails and 3 of such in parralel on USB. Also it's not like WIFI has short power bursts of high power, it's not GSM.
0A: 5.0V - all fine
Powered up. WiFi or any USB device tries to sink 2A for 1 millisecond. Supply brown-outs to 4.0V. May work or may not. Reliability issues seen by the user. -
The reliability issue I'm seeing with microUSBs is not the connector itself failing, but the solder joints failing. Stress reliefing the power input cable is the fix - or just being careful.
Well that’s not a property of the connector design, sorry! Look at how many good designs implement their connectors: heavy metal or plastic with a precision cutout for the plug, so that the plug is well-supported by said thick metal or plastic. (Look at how Apple machines the various jacks in a MacBook. By shifting strain relief to the housing, connector failure is far less common than in older machines where the PCB took the brunt of the strain.) Another good example is the cord on my Ultimate Ears Boom 2 speaker, which is recessed (so that it can take a rubber bung to waterproof it), so when the cord is plugged in, the jack isn’t seeing any strain at all. The downside is that most other micro-USB cords won’t fit in the recess at all. (The UE cords are expensive but lovely — they do not tangle. The UE charger is 2.1A, so I would assume the cable can handle that as well.)Instead of going circles of babbling about "good" cables, maybe you should give us some exact recommendations of your known good cables? You know, the requirements for the Raspberry are well outside the USB specification, so having a "good compliant cable" isn't necessarily enough.
If their Lightning cables are any indicator of the quality of their micro-USB cables, the AmazonBasics cables are superb and don’t cost an arm and a leg. (For sure, I know they’ve considered voltage drop, because their 2 meter Lightning cables use thicker cable than the shorter ones, and the 3 meter Lightning cables use far thicker cable still.)
It’s not nonsense, in that a TON of people don’t realize that many cheap gadgets come with obscenely bad cables, and that most cheap cables they buy separately are equally horrific. They see the $2.99 one and the $11.99 one at the store, and don’t realize the cheap one (whose eBay price would be 2 for 99¢ shipped) is garbage, so they buy it. And then they have no idea why their phone takes longer to charge than before...Charging:
Nonsense, no barely decent cable has 0,5V voltage drop at 1A.
0A: 5.0V - all fine
1A: 4.5V - all fine
2A: 4.0V - charge to the empty battery still ok at almost 2A. With full battery, charging rate is reduced. No big deal. -
Most phones just take nominal current and do not mind voltage drop at all - because voltage of fully battery is around 4.2 volts. It does not matter you put in 4.5V or 5V - phone will happily charge your battery.
Except that most phones detect said voltage drop and back off their charging rate at some point. The exact voltage where that happens varies, but it’s not going to be down at like 4.3V or so, because by that point it’s obvious that either the charger or cable is severely overburdened.BTW most phone chargers have quite poor voltage regulation, if it is written 5V 1500mA then you get one or another, but not both in the same time
Then you’re using garbage chargers. There are websites with tons of tests of USB chargers, and the original name brand chargers (Apple, Samsung, Microsoft, HP, etc.) all perform at least to spec, and often quite a bit beyond. Quality third-party chargers (Anker, IKEA, Belkin, etc) do equally well. All of these will produce clean output without voltage sag to at least their stated current. This of course in addition to cable drop!! rPI on the other hand is very picky about voltage. So here we are.
Meanwhile, the chinesium garbage death-chargers are often 500mA beasts no matter what the stated current is, and often plummet to below 4V on full load, or lose regulation and go ripply, or shut down. -
The reliability issue I'm seeing with microUSBs is not the connector itself failing, but the solder joints failing. Stress reliefing the power input cable is the fix - or just being careful.
There is no such issue with raspberry Pi. There are 4 through hole solder joints. I never seen solder joints failing, though I several times seen manufacturing defect when connector was soldered lifted on on side and several pins were not touching pads. I also have seen a few RPi with connector broken off together with pads but it requires extreme level of abuse. There are micro usb connectors which do not have through hole terminals, those are much easier to break off but it has nothing to do with RPi. -
Well, usually it flashes the voltage drop warning. Sometimes, it just corrupts the file system, or just crashes.
True. My raspberry just kept crashing at booting when I was getting the undervoltage warning. Well, if the voltage drop is critical, it does that. Sometimes it runs "normally" even with the warning. -
Most phones just take nominal current and do not mind voltage drop at all - because voltage of fully charged battery is around 4.2 volts. It does not matter you put in 4.5V or 5V - phone will happily charge your battery.
Buck converter is used for charging. There is still need for input voltage to exceed voltage on the battery. 0.1V or 0.2V above output is not enough for proper operation. And as tooki already said, phones do detect voltage drop and reduce charging current. -
The reliability issue I'm seeing with microUSBs is not the connector itself failing, but the solder joints failing. Stress reliefing the power input cable is the fix - or just being careful.
Well that’s not a property of the connector design, sorry! Look at how many good designs implement their connectors: heavy metal or plastic with a precision cutout for the plug, so that the plug is well-supported by said thick metal or plastic.
Properties aside: USB specification requires 5000 mating cycles for mini USB and 10000 cycles for micro USB. Those who are in doubt can check molex datasheets: mini micro. Other option : look for usb.org specs. -
Aaaand...? So what? Point is, the micro-USB was designed to significantly surpass the mini-USB performance. I would say that doubling the mating cycles counts as “significant”.
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There are 47uF MLCCs on 1.2V, 1.8V and 3.3V power rails and 3 of such in parralel on USB. Also it's not like WIFI has short power bursts of high power, it's not GSM.
We engineers tend to calculate things instead of sentimental "nonsense" shoutouts. I based my estimate on around 100-200uF MLCC, which seems to be fairly close. Please do the math yourself. 1 F = 1 As/V, which gives you the easy-to-remember, 1mF (1000uF) drops by 1V when drawn 1A for 1ms. So, depending on which rails are exactly the weakest links (i.e., the exact amount of voltage drop allowed), we are talking about the territory between 100us and 1ms there.
Any microcomputer is going to be a tricky on AC consumption, which is why a lot of local bypassing and local regulation happens. Local regulation happens on Raspi, as well; it's just that it's still a computer that is often powered by substandard supplies and cables.
What's actually tricky in the AC consumption is that there are many very low-duty loads that very seldomly appear all at once. It's well possible that in a typical use case, a Raspi3 eats:
1) 0.8A DC current with fairly high CPU duty cycle (i.e., when not idling)
2) 1ms peaks varying between 1 and maybe 1.5A
3) Once a year there is a 2A peak, because of the exact combination of timing and changing variables (such as WiFi signal strength, causing automatic adjustment of the transmit power).
And a 100us brown-out is enough to crash it. Completely unlike charging.
I don't know, I have quite limited specific experience on Raspberry Pi, the example values are more about the general principles. I have fixed a few Raspberry Pi2&3 issues by adding bulk capacitance and/or replacing the wiring. IMO, having to shop for specification-exceeding cables on the market literally saturated with variable-quality crap is a real risk (and tedious job IMHO!), when you can just use a bog standard cable of your choice of AWG, and connect it to the header directly. But I understand you skip the input protection "ideal diode" that way.
But I understand you desperately need to have this fight, and desperately need to be right. So be it.
I just find it very funny you guys keep repeating how the phones detect voltage drop and back off charging current. That's exactly proving the whole point; these cables have significant voltage drops happening, and the charging case is proving it. With charging, it's non-critical, because the device is powered by the stable battery supply.