Today's Message Index:
----------------------
1. 05:12 AM - USB (BobbyPaulk@comcast.net)
2. 06:13 AM - Re: Re: 5 Volt Converter Product Review (rnjcurtis)
3. 07:49 AM - Re: USB (Robert L. Nuckolls, III)
4. 08:03 AM - Re: Re: 5 Volt Converter Product Review (Eric Page)
5. 08:47 AM - Solder-sleeves with pigtails (Robert L. Nuckolls, III)
6. 02:29 PM - Re: A couple of questions about Fuses (Robert L. Nuckolls, III)
Message 1
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Guys
I have noticed some USB ports will charge a Samsung or other device and not an
I-phone or other I-thingy.
Is one available that wold do both or do I have a faulty port.
Bobby
analog guy in a digital world
Message 2
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Subject: | Re: 5 Volt Converter Product Review |
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Message 3
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At 07:11 AM 12/29/2016, you wrote:
Guys
I have noticed some USB ports will charge a Samsung or other device
and not an I-phone or other I-thingy.
Is one available that wold do both or do I have a faulty port.
There are USB ports . . . and then their are USB ports.
The legacy USB port was conceived as a bi-directional,
serial data port for SMALL accessories like thumb drives,
mice, keyboards, etc. Power supplied from this port was
offered at rather small rates . . . 100 to 500 milliamperes.
Many computers were fitted with positive temperature
coefficient current limiters (poly-fuses) to protect the
computer from damage should the +5 volt USB power line
become overloaded.
Years later, new kids on the block (phones, tablets, etc.)
found it useful to exploit that handy source of regulated
voltage to charge internal batteries while in communication
with a host computer . . . or even as a low-power charging
source where leaving one's device on-charge overnight was
no big deal.
Simultaneously, demands on performance for USB ports
evolved with ever higher transfer speeds. Accessories
that exploited USB ports also evolved . . . there are
electro-mechanical hard drives that will function
solely on a 5 volt power supply while demanding less
than 500mA.
Then came the big kids. Tablets and larger smart
phones that communicate with other devices
via, you guessed it, USB ports. At he same time,
their energy needs for both function and battery
charging grew to 3 or 4 times that which the
computer-based USB port could provide.
This gave rise to proprietary chargers capable of
1 amp or more of 5v power. Problem was that if you
configured your mini-super-pc to demand say 2A of
battery recharge current, how do you keep it from
overwhelming the 5v source on a legacy USB computer
port?
Instead of 'smart source ports' on computers, high-demand
appliances evolved into 'smart-loads'. When the USB
port was being used for only functional and/or battery
charging power, then idle data lines could be used
to tell the smart load how much power was available.
Over the years, proprietary chargers lead the way
to mostly accepted standards for tying idle data
lines to each other or perhaps tying them to +5
or ground with certain size resistors.
This little hat-dance in the source connector
informed smart-loads as to how much
energy was available. I have at least one device
that annunciates "slow charging" behavior when
plugged into a computer . . . with no such
annunciation when being powered with a high-current
source.
The SHORT story in this thread tells us that it
is insufficient to simply craft robustly powered,
panel-mounted USB receptacles with an expectation
of maximizing exploitation of that source.
I've not taken time to study USB charging philosophies
in detail but know that there is a lot of data on
the techniques available on the 'net. It's a sure
bet that any DIY power sources for your favorite
cockpit companion may need a bit more information
as to who much power is available. lacking such
information will most certainly force the appliance
into a 'slow charge' mode.
Bob . . .
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Message 4
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Subject: | Re: 5 Volt Converter Product Review |
I'm not sure what an Android device (a generic term for devices from many ma
nufacturers) will make of an Apple charger. It won't do it any harm, but I d
on't know if it will charge. Samsung, for example, uses a common (shorted) 1
.25V on both data pins.
Someone mentioned that the data pins on his charger are shorted together. T
hat defines a Dedicated Charging Port (and a Chinese standard). Most device
s will accept this scheme, but will only draw 0.5A in accordance with the US
B standard. That's why a device will hold steady under use but not add char
ge.
There are integrated circuits designed for this purpose that monitor a USB p
ort and automatically configure the port to satisfy the device that's plugge
d into it. They work fine, but they're a pain to use as they're all in tiny
surface-mount packages.
Eric
> On Dec 29, 2016, at 7:11 AM, rnjcurtis <rnjcurtis@charter.net> wrote:
>
> Am I correct in assuming that if I wire a USB port this way for an Apple d
evice, that it will be comparable with all other Android devices.
>
> Roger
>
>
>
> Sent from: YOGA TABLET 10 HD+
>
> Eric Page <edpav8r@yahoo.com> wrote:
>
> In the four years since I wrote that, Apple has released a fourth charging
scheme for their 12-watt (5V, 2.4A) chargers that began shipping with the i
Pad Air. If you configure your USB port as follows, it will rapid-charge al
l but the earliest Apple iDevices:
>
> Pin 1 (+V): 5.0V-5.2V
> Pin 2 (D-): 2.75V
> Pin 3 (D+): 2.75V
> Pin 4: Ground
>
> Note that Pins 2 and 3 are the same voltage, but they must *not* be shorte
d together. Use two identical voltage dividers to provide the same voltage t
o both pins separately.
>
> For the voltage converter that Joe purchased (output = 5.1V), I would us
e a voltage divider comprised of 11.8k over 13.7k.
>
> Connect as follows: 5V --> 11.8k --> USB Pin 2 or 3 --> 13.7k --> Ground
>
> Suitable resistors:
> http://www.digikey.com/product-detail/en/yageo/MFR-25FBF52-11K8/11.8KXBK-N
D/13232
> -and-
> http://www.digikey.com/product-detail/en/yageo/MFR-25FBF52-13K7/13.7KXBK-N
D/13244
>
> One other note. Use heavier wire on the 5V output than the charging curre
nt would normally call for. Resistive voltage drop can easily cause the 5V r
ail to fall below 5V over a modest wire length, which will change the D+ and
D- voltages as well. Apple devices are picky -- it's important that +V, D+
and D- are correct.
>
> Eric
>
>
>> On Dec 28, 2016, at 8:11 PM, user9253 <fransew@gmail.com> wrote:
>> Read this post about charging an iPad:
>> http://www.matronics.com/digest/aeroelectric-list/Digest.AeroElectric-Lis
t.2012-09-17.html#MESSAGE7
>> There must be voltage on USB pins 2 & 3 to signal the iPad to draw more c
harging current. Use a voltage divider with no resistor less than 10K ohm.
Below is quote from the above mentioned post:
>>
>>> Here's what your USB receptacle needs to provide to properly quick-charg
e your iPad (for iPhones, reverse pins 2 and 3):
>>> Pin 1 (+V): 5V (no less; ideally ~5.2V)
>>> Pin 2 (D-): 2.00V
>>> Pin 3 (D+): 2.75V
>>> Pin 4: Ground
Message 5
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Subject: | Solder-sleeves with pigtails |
Some time back, I had a fire-sale on solder-sleeves . . .
Demand was more than I could supply. Ran out in about
a week. For those who were left wishing, here's an
offer at MPJA
http://tinyurl.com/grp3z2c
Bob . . .
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Message 6
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Subject: | Re: A couple of questions about Fuses |
Some time back I wrote:
>When selecting wires and protection, you're
>never wrong with the "legacy pairs" of
>22AWG/5A, 20AWG/7A, 18AWG/10A, etc. etc.
>These are very conservative pairings.
I thought of a quality unique to fuses that
justifies a departure from the 'leggacy
pairing' cited above.
Fuses and Circuit breakers have one thing in
common . . . they operated based on the HEATING
effect of a current flowing in a component
having some resistance . . . I.e. a voltage
drop that liberates heat due to 'lost'
energy.
The similarity ends there.
Circuit breakers have bi-metal components
which are close cousins to thermostats. Heating
produces a change in shape that causes some
latching mechanism to release at a predictable
temperature rise.
On the other hand, the resistive current sensing
component of a fuse is solid metal alloy designed
to MELT when a certain temperature is reached.
Conversion from a SOLID to a LIQUID calls for
a phase change that exhibits a kind of plateau
that cannot be exceeded until a unique quantum
of heat has been delivered into the mass.
In water, the heat removed in the change of phase
from liquid to solid is called the 'heat of
fusion' and if memory serves, is about
80 cal/gm for water. This means that you can
have ice at 0C and water at 0C . . . but for
every gram of ice at 0C you have to pump
80 cal of heat into it just to convert to
liquid water.
Every material, including the melting link
in a fuse has a similar characteristic.
This is important in the specification of fuses
to a particular task. While a circuit breaker
is a simplified 'thermostat' . . . capable of
repeated operations with no change of calibration.
On the other hand a fuse can, if you will, be
'hammered'.
Let's say you have a 5A fuse loaded to 4A but
subjected to an 8A transient measured in tens of
milliseconds. On the bench you can subject
the fuse to this stress many times with no
failure. Such an event, say once per flight cycle
in an airplane, may never produced a nuisance trip . . .
or it may happen after tens or hundreds of flight
hours.
It doesn't happen very often, but ONE TIME may be
too many for individuals who suffer the event. An
excellent case in point . . .
http://tinyurl.com/msfmldj
Through a combination of events and poor design
choices, fuses in the accident aircraft were
subject to transient stresses that 'hammered'
at the edge for heat-of-fusion on first one
and then the second of two fuses . . . a failure
that insured simultaneous failure of both
ignition systems.
The point to be pondered here illustrates
the value of failure mode effects analysis in
deducing risks associated with the failure of
any single component. When unacceptable risks
are identified, changes to selection components
and system architecture will easily negate the
risk.
THE BEST prophylactics against risk for popping
a 'hammered' fuse is to design the system such that
loss of that system is no-big-deal. After all, there
a dozens of OTHER reasons the fuse might open. Be
prepared for ANY event.
Based on what we know about the relative fragility
of a 22AWG wire, a 5A, nuisance tripping fuse on
a 22AWG feeder can be comfortably replaced with
a 7A fuse.
As a general rule, the engineering data on fuses
suggests they not be continuously loaded to more
than 75% of rating at 25C.
http://tinyurl.com/zobgmdv
If situated in an environment routinely hotter than
25C, perhaps de-rating to 50% is in order. This
thinking supports the notion that a fuse under the
cowl driving a 22AWG feeder loaded to 4A continuously
might be 'protected' at 10A. It's not radical thinking
. . . they do this in cars all the time.
Bob . . .
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