usb as a power source

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USB Devices

iPod shuffle

iPod photo

Sony Clie PDA

USB As A Power Source http://www.girr.org/mac_stuff/usb_stuff.html

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USB A A P S h // i / ff/ b ff h l


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Dell Axim PDA

Holux Model GR-230XX Bluetooth GPS receiver

USB powered battery charger


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USB A A P S htt // gi g/ t ff/ b t ff ht l


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I've also got these USB power sources:

USB Power Sources

The Apple 15" PowerBook has two USB 2.0 ports apple_albook.jpg

The Apple iBook also has two USB 1.1 ports

The Apple Airport Express base station has a USB port that is intended to drive a printer, but italso provides power


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USB As A Power Source http://www girr org/mac stuff/usb stuff html


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The Apple USB power brick is specifically intended to charge iPods

Apple USB keyboard unpowered hub has two low power USB 1.1 ports

This generic USB 1.1 powered hub can power 4 high power devices


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This generic USB 2.0 hub can also power 4 high power devices

This AA battery powered USB source was pretty much disappointing. It really didn't do anythingthat was especially interesting

Virtual Reality Sounds Lab FM transmitter/MP3 player that has a port for a USB jump drive. Asan FM transmitter, it works well enough, as an MP3 play (using a jump drive for memory), it doesnot work very well.


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This is the 12 volt USB charger that came with the Holux GPS receiver. This charger workedquite well, it can source about an amp.

The 110-240 VAC charger that came with the Holux GPS receiver is also good for about an amp.

This 12 volt USB charger that came with a 4-in-1 travel kit for a Sony PDA also sources about anamp.


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The 110/250 VAC USB charger that also came in the 4-in-1 travel kit was good for about an amp.

The 110 VAC 100 watt inverter with a USB port (Xantrex XPower Pocket Inverter 100) is a goodlightweight inverter and the USB port is quite capable.

The iGo Juice 70 with a Dual Port adaptor and A46 USB tip also works. The Juice can charge acomputer at the same time and it will run from 110-240 volts or 12 volts.

p g g

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The Mysoldius universal solar powered charger does indeed work in bright sun, but it can't quitesource a high power load.

The VR 3 Power Inverter/FM Transmitter/USB charger seems to do everything right. It works wellas an FM transmitter, it will charge anything and the inverter works pretty well too.

The object is to be able to recharge any of the USB loads with a subset of the USB chargers, one 110 VAC and one 12 VDC. The question is whichones?

USB Power Test MethodThe method I've selected to use to test this stuff is to load each source at 100 mA and 500 mA to see if the voltage remains in spec. I also test each

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load for current draw. To this end, I've built a simple test adaptor out of a USB extension cable.

This is the diagram of the test cable. A USB extension cable is cut andspliced to reconnect the ground, shield and data lines. The +5 volt line isinterrupted so that a regular current meter can be inserted. Another voltmeter is used to monitor the source voltage. The two resistors act as thetest loads at 100 mA or 500 mA. A clip lead is used to connect oneresistor or the other. It is not necessary to use two different meters asonly one is needed at a time.

Source Voltage Tests

During this round of tests, the USB load is not used, neither is the current meter. The test cable is connected to the source and the voltmeter isconnected as shown. Three readings are taken, one at no load (neither resistor connected) one at low load (47 to 51 ohm resistor connected) andone at high load (10 ohm resistor connected). The voltage is compared to the spec of 4.75 to 5.25 volts (4.4 to 5.25 volts for a lower power device).An out of spec voltage indicates that that particular source may not be suitable. The term OOS means Out Of Spec. Higher voltages tend to be lessof a problem than low voltages, but some devices will not accept charge from an OSS high source as a means of self protection.

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USB Source Voltage Test Results

Source

Voltages (volts) In Spec?

CommentsNoLoad

LowLoad

HighLoad

NoLoad

LowLoad

HighLoad

Virtual Reality LabsFM TX/MP3 player 4.98 4.83 3.27 yes yes

OOSlow

This is a low power device. This makes sense because the USB port isintended only to power a USB jump drive. However, as an FMtransmitter, it works fine using an iPod as an audio source. As an MP3

player, it sucks.

Holux GPS RX DCadaptor 5.40 5.43 5.37

OOShigh

OOShigh

OOShigh

This adaptor will probably power most USB devices, it is good for atleast 850 mA because it will drive the Dell Axim. It is also efficient. It

runs cool even at 850 mA.

Clie 4-in-1 TravelKit DC adaptor 5.33 5.31 5.25

OOShigh

OOShigh

OOShigh

The output voltage is just slightly high but it would probably work inmost applications. It also powers the Dell Axim and runs cool.

Apple USB Power Adaptor 5.17 5.15 5.09 yes yes yes

Fully in spec. However at $29, it's a little expensive. It will not power the Dell Axim properly.

Clie 4-in-1 TravelKit AC Adaptor 5.57 5.54 5.48

OOShigh

OOShigh

OOShigh This one is the highest voltage of the bunch. It does power the Dell.

Generic USB 2.0Hub 5.03 4.95 4.66 yes yes

OOSlow

I've been using this hub to charge the iPod photo for months. Eventhough the voltage at high load is low, it behaves fine.

Generic USB 1.1Hub 5.11 5.06 4.89 yes yes yes in spec all around

Apple USBKeyboard Hub 5.09 4.94 4.46 yes yes

OOSlow

this is an unpowered hub within the keyboard, it is running from theUSB 1.1 hub.

Apple 15"PowerBook 5.02 4.99 4.86 yes yes yes

Apple 12" 500 MHziBook 5.07 5.03 4.86 yes yes yes

Holux GPS RX ACAdaptor 5.38 5.35 5.28

OOShigh

OOShigh

OOShigh

Like its DC sibling, it also has high output voltage. It also powers theDell Axim.

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AA battery poweredUSB charger 5.62 5.16 4.66

OOShigh yes

OOSlow

The unit had freshly charged NiMH batteries. With partially discharged batteries, the no load voltage would be in spec but the high load voltagewould be even lower.

Airport ExpressBase Station 5.02 4.99 4.88 yes yes yes

Xantrex XPower Pocket Inverter 5.06 4.95 4.57 yes yes

OOSlow This unit also provides 110 VAC at 80 watts

iGo Juice 70 withUSB iTip 5.02 4.99 4.92 yes yes yes

This unit also powers/charges a laptop and other devices depending onwhich iTip is used

mysoldius solar charger 5.72 5.47 3.22

OOShigh

OOShigh

OOSlow

The output of the unit is somewhat dependent on the intensity of thelight it receives. If the light level is too low, it goes dormant for a fewseconds and charges itself up. Then it provides a short burst of power until it needs to recharge itself again. As tested in bright winter light at7000 feet, it would not charge a high power device at all. The unit isspecified at 320 mA max so it does not meet the requirements of a high

powered USB load even in the most intense sun. It is not rated to chargean iPod photo.

VR 3 Power Inverter/FMTransmitter/USBcharger

5.26 5.26 5.24 OOShighOOShigh yes

The USB port charges the iPod photo and shuffle fine and has the bestregulation of the bunch even though the output voltage is a tad high. Theinverter part doesn't like surge loads, such as incandescent bulbs. It willshut down. In that case, plug in the load and THEN plug in the inverter.

Load Current TestsThe load current tests serve to reveal which loads will not tolerate the which sources. This could be done by cut and try as well, but as long as thetest cable was handy ... well, data is good.

In this test, the voltmeter and the load resistors are not used. The test cable merely serves to allow a place to insert a current meter between thesource and the load. If the current measured was less than 100 mA or 500 mA, then the load should work with a low current or high current sourcerespectively. The source varied from test to test, but it was always an in-spec high power source so that it should not impact the current drawn bythe load to any great extent.

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sleeping 240

Dell AximX50

chargedrunning 420

OOS high

The Axim is a good test case for USB sources. Only the best of them will

drive this puppy. The current on this particular one might be a little higher than normal because it has a 4 GB microdrive in it.

sleeping 130

dischargedrunning 840

sleeping 620

Responses of Sensitive Loads

The real proof is in performance. This table summarizes the response of the three loads that had some issues with one charger or another. The proper response for an iPod shuffle varies depending on conditions. If the shuffle has disk mode enabled it will mount in the Finder and will displaya blinking yellow light until it is dismounted. Once dismounted (and iTunes is done with it) the light will be solid yellow until it is charged and greenwhen charged. If the shuffle is in disk mode, the light will blink yellow until dismounted, charged or not. This is the "do not disconnect" signal.

The proper response of the iPod photo (and other iPods as well) is somewhat different. If the iPod photo has disk mode enabled, it will display a"Do Not Disconnect" message until is is dismounted. It will also display this message until iTunes is done with it. When dismounted, the display will

change to the regular menu. Charging is indicated by the blinking battery icon with a lightning bolt in it. When charged, the battery icon will have asmall power plug symbol in it. If the iPod is then put to sleep, the battery icon will be much larger.

The Dell Axim does not interact with a Macintosh directly. I don't know what it does on a PC. When it is trying to charge, an orange indicator above the screen will illuminate, but this doesn't mean that it is actually receiving a charge. To determine that, it is necessary to look at the Power

pane in the System settings. The display will show the current state of charge and it will also indicate through a blinking status bar that the unit isactually charging. If the voltage supplying the Axim is too low, the entire display will flicker. At that point, you can be sure that it is not charging.

Note that this particular Dell Axim may draw more current than most because it has a 4 GB microdrive plugged into the CF card slot.

For each of the devices below, I determined if it was really charging or not by the current that it would draw. If the device was drawing the samecurrent that it would draw from an ideal source, it was deemed to be charging.

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Source Vs. Load Compatibility

Source iPod photo iPodshuffle Dell Axim

15" Powerbook proper 1 proper doesn't charge

12" iBook proper 1 proper doesn't charge

USB 2.0 hub proper 1 proper doesn't charge

USB 1.1 hub proper 1 proper doesn't charge

Airport Express BaseStation

proper chargeindicator 2

Blinkingyellowforever 2

doesn't charge

Apple USB Power Adaptor proper proper

Doesn't charge while the Dell is running (screen flickers)Does charge if the Dell is shut off.

Apple Keyboard doesn't work 3doesn't

work 3 orange light, no charge

Virtual Reality LabsFM TX/MP3 player doesn't charge charges

4 doesn't charge

Holux GPS RX DCadaptor doesn't charge charges

4 proper

Holux GPS RX AC

Adaptor doesn't charge charges4

proper

Clie 4-in-1 Travel KitAC Adaptor doesn't charge charges

4 proper

Clie 4-in-1 Travel KitDC adaptor doesn't charge charges

4 proper

AA battery poweredUSB charger doesn't charge charges 4 flickers, doesn't charge

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Both of these solutions work, but the issue is that the computers have onlytwo USB ports and these cables consume both of them. Since TimeMachine works best when the drive is connected all the time, this meansthat I cannot plug in a mouse, jump drive, or PDA cable withoutdisconnecting the Time Machine disk.

Some powered USB hubs provide enough extra power on a single USB port to power the externalUSB disk drives. This generic hub does provide enough power and it works fine. The problem is thatit's power adaptor is 110 VAC only so that this particular hub is unsuitable for travel.

This HP travel hub is very small and it's power adaptor is 110/220 VAC.Like the generic hub, it has enough power available to run two externalUSB drives at the same time. However, it has two problems.

The power adaptor is sensitive to AC power transients. On a cruise ship,the Star Princess, every time the bathroom light was turned off, a transientin the ship's wiring would leak through the power adaptor and cause a USBwake event on the computer. If the computer was already sleeping itwould try to wake, but the drive would often not spin up instantly and thenthe computer would complain that it could not find the drive. Eventually,when the drive did spin up, the computer would find it and move along,

but the complaints from the computer were disturbing. Other wake events,such as a keyboard press or mouse click would result in a normal wake upsequence where the computer would sometimes wait for the drive in theexpected fashion.

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However, due to a problem with the HP hub, these wake events no matter how caused, would sometimes cause the computer to kernel panic (crash).This is bad. I suspect that this model of hub has a firmware problem

because its bigger brother, a combo USB/FireWire hub that came with it, would do exactly the same thing, even on other computers. The Mac OSmay indeed be overly sensitive to particular USB hubs, but still it made the hubs unusable. These hubs are no longer available from HP so they

might have found that they have a problem too.

This Vakoss TC-212-AS travel hub is only slightly larger than the HPtravel hub but it does not cause the kernel panics that the HP hubs did.However, it is similarly sensitive to power transients. On another cruise,this time on the Grand Princess (a sister ship to the Star Princess), the hub

reacted in the same way to the bathroom light as the HP hub, just withoutthe kernel panics. Further, it's power adaptor actually burned up (buzz,crackle, pop and smoke) after a week or so at sea. I went back to using atwo-headed cable for the rest of the cruise.

I had two of the Vakoss hubs so when I got home I started using theadaptor from the 2nd one. It hasn't burned up, but it is still sensitive tosomething because I still get unexpected wake events when using this hub

but without the complaints from the computer about the drive not beingthere.

Vakoss did replace the power adaptor at no charge with one of a differentdesign. I don't know yet if the replacement adaptor is as sensitive to power transients as the original design.

I saw strange looking USB hub on the web and bought one for $12 atusb.brando.com.hk . The part number is UHUBS004000. It would have

been perfect had it worked properly but so far, it has not.

It is a travel hub that uses two USB ports for power. It does not use a power adaptor. The red connector is the power only input, the black oneon the same side is the combination data/power connector. There are 4outputs, 3 standard USB jacks and one mini-connector that plugs right intoone of the external disk drives.

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The first one that I got worked as expected for a couple of hours and thenfailed. It refused to do anything at that point. I emailed the company thatshipped it and they send another one without charge. This one didn't fail,

but it didn't work with the PowerBook either. The drive would not spin upreliably. It would appear that the current limiting on the USB ports is just

at the level that the drives needs and if the drive draws just a little toomuch current, the hub shuts down to protect itself. However, it isinteresting that it DOES work properly with the iBook.

After some email conversations with the manufacturer, they agree that itisn't doing what it was intended to do and that they have a problem which they are "working" on. If they manage to fix it, this would be the solutionto my problem. It is small and light and could power the external USB drive and also allow connection of a mouse, jump drive and PDAsync/charger cable all at the same time. Since there is no power adaptor, it won't be sensitive to power transients.

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This page has been accessed times since 1 May 2005

2005-2008 George Schreyer Created 1 May 2005

Last Updated July 10, 2008

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usb as a power source

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