Powerbank / USB question

[S Viemeister]

I log in to my library account on my computer, select a book, then send it to my Kindle.

[S Viemeister]

Returning is taken care of, automatically.

[Chris Green]

So you can't do it all from the Kindle? Essentially it'sjust like buying a book from Amazon.

With the Kobo it's much more integrated with the library. You can quite easily choose and borrow books using the Kobo (no need for computer) and the books just appear on the Kobo.

[Andy Bennet]

Also the stated capacity in mAh is only for the lithium cell ie at 3.7V. After the DC-DC converter to bring it up to 5V when the capacity is lower due to the stepup ratio. If only they would specify the capacity in Wh!

[Pancho]

POE Ethernet and POTS Telephones are in the region of 48V. So it is nothing new.

[John Walliker]

The safety standard for computer and AV equipment is IEC62368.1 which has a limit of 60V for "energy source class 1" sources which are considered safe to touch.

Here is the definition: Under normal operating conditions and abnormal operating conditions, the energy in a class 1 source, in contact with a body part, may be detectable, but is not painful nor is it likely to cause an injury. For fire, the energy in a class 1 source is not likely to cause ignition. Under single fault conditions, a class 1 energy source, under contact with a body part, may be painful, but is not likely to cause injury. and No safeguards are required between a class 1 energy source and an ordinary person (see Figure 9). Consequently, a class 1 energy source may be accessible to an ordinary person.

In other words, anything up to 60V (after worst case tolerances have been applied) is fine.

There are special exceptions for telephone ringing signals and loudspeaker outputs which allow higher voltages to be touchable that would not otherwise be permitted. POE+ and POE++ are rated for voltages up to 57V, so they just fall within the safety limits for touchable circuits.

John

[S Viemeister]

I haven't actually tried - I find it easier to browse books on my computer, then request them from the library - decent keyboard, colour book covers.

[Dave Plowman (News]

Because it looks better to those who don't understand such things?

[Dave Plowman (News]

Some time ago, got this from Lidl. It looks like a small version of an outdoors flood light. Came with a desk stand, so can be pointed in most directions. Built in battery and wall wart charger. Plenty output as a work light. Bounce off the ceiling for general lighting of a room. Lasts about 4 hours on a charge.

I'm sure you could buy similar from a cordless drill maker which uses the same batteries as the drill, etc. Bound to be better value than something made for computers.

[The Natural Philosopher]

Well its a very simple sum. Just multiply by...whatever the voltage turns out to be throughout the discharge cycle.

[The Natural Philosopher]

I got a hefty belt of the back of a PA amplifier generating the odd

100W, which into 8 ohm would a sinusoid of a mere 28V AC.

[alan_m]

As far as I'm aware it has to be instructed by the receiving end what voltage to output. Remove the connection and it probably defaults to 5V

[Robin]

Thanks.

With that pointer I see IEC62368.1 Class 1 has a lower limit for AC, which reminds me I'd completely overlooked the AC/DC issue. I can't recall if the USB-C spec has anything similar.

[Theo]

I have something like this:

I used it to work in the loft before I installed lighting.

It takes 18650 lithium cells - in my case it shipped with a low capacity

1200mAh battery, but 18650s are widely available either new or from scrapped laptop batteries.

Charges via USB and also works as a power bank. With two cells you might get up to about 7000mAh in there. You can swap in other 18650s to make it go for longer.

There's something to be said for not having everything relying on a single battery, so you can have light in multiple rooms.

Theo

[Andy Burns]

Given that it's DC, then anything under 120V is classed as ELV, it's only AC where it becomes LV above 50V

[John Walliker]

It does. 48V+/-5% @ 5A maximum, so long as a special cable is used that has an appropriate identity chip. That means that the maximum possible voltage from a USB connector is 50.4V.

John

[charles]

some PA amps use 100v !

[Pancho]

I previously tested my 5000mAh power banks and got between 4.8 and 5 hours for an approximately 5w lamp.

I was comparing an expensive Anker power bank, with some cheapo no name ones. They lit the lamp for the same duration. They recharged in the same time. The only real difference is that the Anker charges my mobile phone astonishingly fast, whereas the no names didn't.

At that time, I didn't understand the 3.7v/5v rating convention, so thought nothing of it. i.e Why they lit the light for longer than expected.

I'll charge a power bank up and test again. The only problem is I don't know how to accurately measure the wattage of the lamp. How to accurately measure USB power, The lamp is 5 watt measured via a usb transformer plugged into a power meter smart plug.

The test starts now 16:40.

[Robin]

Sorry, I meant anything that similarly restricts the 48V to DC. (I had a quick search of the spec without finding anything about AC power. I also couldn't find anything that explicitly forbids it but that may be 'cos it's considered apparent to anyone with 2 brain cells to rub together.)

[Robin]

Yes, thanks, another "D'Oh!" from me.