Charging dictation machine from USB mains charger

[nospam]

some do, but it's often not something that's easily replaced, as in requires soldering.

[James Wilkinson Sword]

On Sun, 12 Feb 2017 21:03:09 -0000, nospam wrote= :

There is nothing non-compliant about shutting off a port which is overlo= aded. The device should not be drawing over 500mA unless given permissi= on to do so.

There is nothing in the USB spec to say it should limit current.

My point exactly. The recorder in question should be able to handle wha= tever current is there, and won't rely on the PC to limit the current.

Oh look, your (2nd) link shows exactly what I said, that the PC shuts of= f the port if 500mA is exceeded. This makes my point nicely, that the d= evice cannot possibly rely on current limiting, since it does not exist = on most USB ports.

The OP was concerned the device might break if more than 500mA was issue= d.

Wrong. I have often taken up to 500mA from a USB port without any elect= ronics to make a request. The port will not prevent me from doing so un= til it exceeds 500mA.

What, all 30 of them?

The OP was concerned the charger didn't have circuitry and relied on som= e kind of current limiter in the USB port itself.

cs inside your PC.

The spec means nothing. I prefer reality.

-- =

A hand job a day keeps arthritis away.

[James Wilkinson Sword]

Electronic fuses do not need replaced, they are circuit breakers, they reset on restarting the PC.

[Tim+]

How about looking at this troll's posting history before feeding his habit?

Tim

[James Wilkinson Sword]

How about believing the person who knows about it, instead of the person who reads a spec and thinks everyone sticks precisely to it?

Hey look! The speed limit is 30mph, so no car could possibly be going 40, I'll just walk in front of it shall I?

[nospam]

that's what i said.

there is, and it does.

it *is* relying on the pc.

it says that it is only guaranteed 100ma. anything above that must be requested.

current is not 'issued'. a device will draw as much as it needs up to the limit of the source. if the source is poorly designed, the voltage might sag or other problems might occur.

then your port is noncompliant.

unfortunately, there's a lot of noncompliant crap out there.

apparently so.

wtf do you need 30 usb ports??

it draws as much as it needs.

the spec *is* reality.

[nospam]

i didn't say everyone sticks to the spec. some companies do not, which is a problem, as is people who buy said products and think they're ok.

if something is non-compliant then *anything* goes. it might work or it might not. it could fry the device and it could even kill the user in extreme cases.

there's a reason why there's a spec, so that the results are safe and predictable.

[James Wilkinson Sword]

Then manufacturers ignore the silly parts of it an improve things.

[Mike Tomlinson]

En el artículo , nospam escribió:

/Must/ you feed the troll?

[James Wilkinson Sword]

Where "troll" =3D someone who understands the problem and is trying to e= ducate the resident idiot.

Or.... someone like YOU who is using the followup header to divert any r= eplies.

-- =

A thousand monkeys pounding on a thousand keyboards will eventually prod= uce either the bible, or a system error.

[Tim+]

I fear "nospam" is just another incarnation of our resident troll.

Tim

[James Wilkinson Sword]

Yeah right, I'd argue against myself.

And you've just got yourself killfiled for using followup headers. It's= unbelievable that you call someone else a troll then go and do their nu= mber one tactic of redirecting things without warning.

-- =

My memory sucks, so I changed my computer password to incorrect. That w= ay if I forget it, it tells me "your password is incorrect".

[Daniel James]

A lot of PC motherboards do, though. They're cheap.

[Daniel James]

Actually that's not quite right.

If the recorder is connected to a PC USB port it is only allowed to draw 100mA (0.5W at 5V) without negotiating a higher current. If it draws more without going through the negotiation process it is not a compliant USB2 device (and shouldn't carry any of the official USB labelling).

Once it has been through the negotiation it is permitted to draw up to

500mA (2.5W) from a USB2 port. [For USB3 these values are increased to 150mA and 900mA, respectively.]

Designers of compliant USB devices can do one of two things:

- Draw no more than 100mA.

- Initially draw 100mA, but negotiate to draw 500mA, and then do so.

Note that this applies to USB2. Other USB specifications -- notably the USB battery charging spec -- may allow higher current to be drawn. It doesn't sound as though those apply in this case, though.

Typical PC USB ports will actually allow 500mA to be drawn regardless of negotiation (it's easier to provide 500mA all the time than to provide hardware to vary the supply) but a device should, properly speaking, not make use of that without negotiation. Nevertheless, many do.

Does this mean that a low-power 100mA USB device can be damaged by plugging it into a PC USB port that's wired to make 500mA available all the time? Not at all. The current that actually flows depends on the resistance of the device, not the power available from the PC.

[pamela]

It is exactly that sort of setup I was wondering I may have in my recording device.

The device has it has it's own pop out USB-A plug to go into a PC port which made me wonder if it was (poorly) designed to be charged only from a PC USB port.

See it here:

I want to charge it from a 2 Amp USB mains charger.

I've had problems with USB-based digital voice recorders in the past. I've damanged their ability to hold day-date info for a few seconds between battery changes. No one at the manufacturer could explain this except by guessing that had been a problem with the USB connection.

True enough but I have no idea what resistance the device presents across its charging connection.

[nospam]

usb absolutely is designed to be current limited and the concept of 'issuing current' is bogus. current is not issued.

no it doesn't.

the usb spec. try reading it.

false. ports on a bus-powered hub *can't* source 500ma.

the request is only made if more is needed. to do otherwise makes no sense.

you're *way* over your head.

reputable manufacturers follow the spec because if they don't, the usb consortium won't allow the usb logo to be used. most people want quality products that are safe.

[nospam]

all correct.

no they won't.

typical usb ports are compliant with the spec and will work properly.

yep. it doesn't make a difference unless the charger is *really* shitty (which sadly, exist).

[nospam]

nonsense. no reputable manufacturer ignores 'the silly parts'.

some might go beyond the spec and make it more robust or more capable, but that comes at a price. they don't do that for the hell of it.

other manufacturers cut corners to compete on price, hoping suckers buy because it's cheap and then when something goes wrong, they blame the user, assuming the company is still in business.

where are you going to go when that noname charger you got off ebay for a buck fries your phone?

[nospam]

he's wrong.

typical usb ports will *not* source 500ma unless explicitly requested because the spec prohibits that.

any port that does that is *not* usb compliant and therefore anything goes. if you plug your recorder into a noncompliant port, you risk damaging it. chances are nothing bad will happen, but there are no guarantees with out of spec devices. you take your chances.

more than likely, it'll work just fine. stop overthinking it.

they don't want to take responsibility for a defective product.

batteries sometimes fail.

chargers don't work that way.

[James Wilkinson Sword]

So, they remove and add things from the spec like I said.

Doesn't happen.