USB Port Current Boost (solved)

[toxibunny]

Would the 'scribble on it with a graphite pencil' trick work on this for a cheap, quick, easy, reversible, but imprecise fix?

[lrvick]

Hmm. Interesting that others are doing the same mod and not having the bottom port die. I am very positive there is no bridging

What gauge wire are you guys using? Perhaps mine is too thick.

Can one that has both ports working snap a photo perhaps?

[jbuehl]

Here's mine. I used 30ga wire. I doubt that bigger wire would be a problem.

IMG_0812.JPG (55.39 KiB) Viewed 6833 times

[mahjongg]

If the capacitance on the +5V pins of the USB ports of the R-PI is too small, and there isn't a current limiting resistance anymore in series to the USB port (what a side effect was of the polyfuses), the plugging in of any USB device that contains a capacitor will have the effect of placing that empty capacitor across the +5V of the R-PI leading to a temporary short across the 5V while the USB capacitor fills up (a phenomena known as "inrush current"), But if there is a capacitance (much) larger on the PI's +5 (near the USB port) than is available on the USB device this current will be delivered by this (PI's) capacitor (not the PSU), so the +5V will not "dip", and the PI won't reset. Another solution would be to place a very small resistance < 1 ohm in the path to the USB port, so a very short short-out won't result in a dip on the +5V.

The USB specifications adresses this (and may other) issues in great detail.

[Ed Raket]

So if i follow the tread correctly;

Pi-pass: cures the powershortage on the USB ports, but the lack of a Cap. makes hot swapping unsucsessful (sertainly when Cap's are inside the USB device -explained nicely by mahjongg) allso some mention that the bottom port dies... but this is not allways the case...

Shorting polyfuses: cures powershortage on USB ports, leaves the small 47pico Cap. operational but this is probably way to small to be really usefull in preventing a powerdip from accuring...

Maybe i could conclude that the best option could be shorting the polyfuses, and replaceing the 47pico Cap. for say... 220pico? has anyone tried this allready? i still have to wait like 9 weeks on my Pi, otherwise my soldering iron was smokin allready

[mahjongg]

The best solution would be to bypass the USB polyfuses with two 1 ohm resistors, low enough for a minimal voltage drop, but high enough to limit inrush current to something the 47uF cap can deliver, if that doesn't work mount a new 220uF (microfarad, not picofarad) capacitor near (but not behind) the polyfuses.

[Ed Raket]

The best solution would be to bypass the USB polyfuses with two 1 ohm resistors, low enough for a minimal voltage drop, but high enough to limit inrush current to something the 47uF cap can deliver, if that doesn't work mount a new 220uF (microfarad, not picofarad) capacitor near (but not behind) the polyfuses.

This makes sence! have you (or anyone) tried this allready?

Oh yes, i meant "microfarad" off course....

[g4eml]

For those having problems after fitting the 'pi-pass' it might be worth trying adding a second wire to bypass the pcb tracks of the ground connection. (When increasing the current capability you need to consider both the supply and the ground Impedances.) Additional capacitance as mentioned above also wouldn't hurt, although I haven't found this necessary in my case.

This can be achieved by running a second wire from the end of D17 nearest the board edge to the two USB ground pins. Actually I used a 30swg twisted pair of wires to bypass both the power and ground.

I did this mod some time ago on two Pis and have so far not seen any problems with hot swapping devices or non responsive ports.


...Colin.

[selsinork]

The best solution would be to bypass the USB polyfuses with two 1 ohm resistors, low enough for a minimal voltage drop, but high enough to limit inrush current to something the 47uF cap can deliver, if that doesn't work mount a new 220uF (microfarad, not picofarad) capacitor near (but not behind) the polyfuses.

Sorted http://picasaweb.google.com/selsinork/R ... 0457917346

[mahjongg]

yes, that should do the trick
I guess the RPI simply continues working for several seconds after you turn off the power.

[Ed Raket]

The best solution would be to bypass the USB polyfuses with two 1 ohm resistors, low enough for a minimal voltage drop, but high enough to limit inrush current to something the 47uF cap can deliver, if that doesn't work mount a new 220uF (microfarad, not picofarad) capacitor near (but not behind) the polyfuses.

Sorted http://picasaweb.google.com/selsinork/R ... 0457917346

Is that a USB frying device i see before me?

[Alan M]

The best solution would be to bypass the USB polyfuses with two 1 ohm resistors, low enough for a minimal voltage drop, but high enough to limit inrush current to something the 47uF cap can deliver, if that doesn't work mount a new 220uF (microfarad, not picofarad) capacitor near (but not behind) the polyfuses.

Sorted http://picasaweb.google.com/selsinork/R ... 0457917346

Is that a USB frying device i see before me?

LOL, that cap could probably run the Pi itself for a fair time when fully charged.

[lrvick]

So here is where I am at:

1. Tried USB-N10 wifi dongle, failed to enumerate the device every time. Not enough power, clearly.

2. Did "pi-pass". Bottom USB port stopped working, but the top port could support the dongle only if the device was started with it. (no hotplug)

3. Fearing I damaged my board, I removed the wire. Both USB ports resumed working.

4. Attempted pipass again, this time with mahjongg's suggestion of a 220uF cap in-line. Sure enough I can now hot-plug my wifi dongle and scan without issue, so clearly the cap did the trick. The bottom port however, fails to work again.

For reference here is a picture of the current attempt:



Any clues why this makes the bottom port fail? (now with two tests and very sure there are no shorts)

Also, I am using a 3A supply, so there should be _plenty_ of current.

[jbuehl]

Looking at Raspberry-Pi-Schematics-R1.0.pdf sheet 3, LAN9512 pins 14 (PRTCTRL2) ana 16 (PRTCTRL3) are attached to the anodes of D11 and D10 respectively. and are sensing the state of the power pins on the ports. They are NOT supplies to the 9512. On a different circuit they can be used to control a switch for the port power, but that isn't how they're used here.
If for some reason the voltage on the positive power pin of the port drops low enough, a zero is detected on the appropriate PRTCTRL, and the system can respond accordingly. See LAN9512/LAN9512i - USB 2.0 Hub and 10/100 Ethernet Controller Datasheet - SMSC

Maybe it has something to do with the PRTCTRL lines and the diodes, but I don't know what. Possibly the voltage on the lower port line is such that it thinks there is no device plugged in. Given that only one of the ports is affected and others, like myself, don't have the problem, maybe there's a defective component on your board.

[Lob0426]

Some people are losing the bottom port like you do. Try PiPassing just the lower port, no solder bridge between ports. See if it works then. If it does run a second wire to the other port. If you only need one higher amperage port, then only fix one.

[selsinork]

For reference here is a picture of the current attempt:

That's certainly an interesting way to connect the capacitor..

[hippy]

For reference here is a picture of the current attempt:

That's certainly an interesting way to connect the capacitor..

Especially as the black stripe on an electrolytic cap is the negative, which seems to go to the +5V USB. Perhaps I've missed something in the thread but it doesn't look right for what I thought the cap was meant to be doing.

[Ed Raket]

Has anyone bridged F1 & F2 and replaced the standard 47 microFarat for a 220 microFarat yet?
This way both USB ports may stay oparational...

[Burngate]

For reference here is a picture of the current attempt:

That's certainly an interesting way to connect the capacitor..

Especially as the black stripe on an electrolytic cap is the negative, which seems to go to the +5V USB. Perhaps I've missed something in the thread but it doesn't look right for what I thought the cap was meant to be doing.

Actually, it's the correct way round for what he's doing. + end to power in, - end to after the fuses.
So the USB gets power through the fuses as normal. If it tries to take extra current for a short while, the cap provides that direct from the power-in.

[Burngate]

Has anyone bridged F1 & F2 and replaced the standard 47 microFarat for a 220 microFarat yet?
This way both USB ports may stay oparational...

Not quite that ...
Back of board, did standard Pipass
Front of board, added 330uF/16v across port power.
https://sites.google.com/site/burngateh ... _0176b.JPG
For what it's worth, it didn't cure my problem, but then it turns out mine is not a power problem!
And I don't believe the Pipass could affect the lower port in the way implied. Something else is happening.

[lrvick]

On further testing I found that even when I am only supplying the extra power to only the bottom port, it still refuses to acknowledge the USB-N10.

I did find however that the bottom port however does continue to acknowledge other lower-powered devices.

When I supply the extra power to the top port, or to both ports, still only the top will acknowledge the USB-N10.

I have tested combinations of this several times now, unsoldering/resoldering each time to be sure I am not crazy.

The fact someone else was having the same bottom port issue with the USB-N10 leads me to believe there might be a small defect of some kind in the board that even with added power the bottom port simply can't support higher power devices.

I realize at the end of the day this is a dirty hack, but it is a dirty hack that logic dictates _should_ work. I am at a loss.

Anyone else willing to test for this pipass + low powered bottom port issue specifically?

[hippy]

That's certainly an interesting way to connect the capacitor..

Especially as the black stripe on an electrolytic cap is the negative, which seems to go to the +5V USB. Perhaps I've missed something in the thread but it doesn't look right for what I thought the cap was meant to be doing.

Actually, it's the correct way round for what he's doing. + end to power in, - end to after the fuses.
So the USB gets power through the fuses as normal. If it tries to take extra current for a short while, the cap provides that direct from the power-in.

Okay; though I'm not entirely convinced ! I thought it would be being used as a reservoir cap between +Vusb/0V. I guess I'll have to study the circuit and re-read the thread.

[lrvick]

Has anyone bridged F1 & F2 and replaced the standard 47 microFarat for a 220 microFarat yet?
This way both USB ports may stay oparational...

I just tried this exactly.

47uF -> 220uF and bypassed F1 & F2.

The result however was not any better than the non-cap pipass.

Top port could use higher powered devices connected before power-on but could not hot-plug them. Board would reset.

Bottom port could not deal with higher powered devices at all, but still worked with lower powered devices.

[HenryG]

What about feeding the USB device directly from the charger but isolating its power pins from the PI ones? I mean, using a modded cable in order to feed the USB device.

[Lob0426]

What about feeding the USB device directly from the charger but isolating its power pins from the PI ones? I mean, using a modded cable in order to feed the USB device.

That will work. What we are trying to do here is make modifications to the board that will allow plug and play use, without the built in limitations on the Rapi board. I have used your method to power a USB HDD as a internal drIve in a PC. You could split off a two pin connector from your USB cable and plug it into an extension fron your RasPi PSU. You will have hot swap issues though. That is one of the things we are trying to fix with high draw devices.