Could someone check my homework please :-)

I am thinking about a USB powered lamp in the event of future power
cuts - linked to a powerbank. I believe the typical output from a
powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
should be more than adequate to power the lamp.

Am I missing something?

On 03/11/2022 15:10, Scott wrote:
> Could someone check my homework please :-)
>
> I am thinking about a USB powered lamp in the event of future power
> cuts - linked to a powerbank. I believe the typical output from a
> powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
> more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
> should be more than adequate to power the lamp.
>
> Am I missing something?

The capacity of the battery. The power bank may supply 2A @ 5V but for
only 10 minutes.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

alan_m wrote:

> The capacity of the battery. The power bank may supply 2A @ 5V but for only 10
> minutes.

Also the powerbank may quote the capacity as e.g. 20,000mAh (why not 20Ah?) but
that's at the cell voltage of 3.7V and will be less when converted to 5V USB output

On 03/11/2022 15:32, Andy Burns wrote:
> alan_m wrote:
>
>
>> The capacity of the battery. The power bank may supply 2A @ 5V but for
>> only 10 minutes.
>
> Also the powerbank may quote the capacity as e.g. 20,000mAh (why not
> 20Ah?)

More zeros mean a better product :) It also depends on if it's a Chinese
20Ah or a real world 20Ah. Ebay is full of batteries claimed to be 4x
the capacity of those same size, same technology, batteries from
reputable manufacturers.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Thu, 3 Nov 2022 15:22:39 +0000, alan_m <junk@admac.myzen.co.uk>
wrote:

>On 03/11/2022 15:10, Scott wrote:
>> Could someone check my homework please :-)
>>
>> I am thinking about a USB powered lamp in the event of future power
>> cuts - linked to a powerbank. I believe the typical output from a
>> powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
>> more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
>> should be more than adequate to power the lamp.
>>
>> Am I missing something?
>
>The capacity of the battery. The power bank may supply 2A @ 5V but for
>only 10 minutes.

Thanks. There's a Belkin offering 20000 mAh at Argos - that's 20 amp
hours. If I revert to my original premise that the bulb is likely to
be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
would last for 20 hours. Is this correct? .

Scott wrote:

> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
> hours. If I revert to my original premise that the bulb is likely to
> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
> would last for 20 hours. Is this correct? .

Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
few percent for conversion losses, 16000mAh at 5V

And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
to start with.

On Thu, 3 Nov 2022 16:09:32 +0000, Andy Burns <usenet@andyburns.uk>
wrote:

>Scott wrote:
>
>> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
>> hours. If I revert to my original premise that the bulb is likely to
>> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
>> would last for 20 hours. Is this correct? .
>
>Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
>few percent for conversion losses, 16000mAh at 5V

Still looking at well over the three hour projected power cuts then?
>
>And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
>to start with.

Even it it's Belkin :-)

I suppose I could use an inverter instead and a normal lamp, but it
seems to me that taking mains voltage, transforming it to 12 volts,
rectifying it to DC, charging a battery, putting it though an inverter
to return it to 230 volts then powering a lamp would not be an
efficient process.

Scott wrote:

> I suppose I could use an inverter instead and a normal lamp, but it
> seems to me that taking mains voltage, transforming it to 12 volts,
> rectifying it to DC, charging a battery, putting it though an inverter
> to return it to 230 volts then powering a lamp would not be an
> efficient process.

Yes, you'd have higher losses, the powerbank's not a bad idea, just don't
believe the numbers ...

On Fri, 04 Nov 2022 02:10:39 +1100, Scott <newsgroups@gefion.myzen.co.uk>
wrote:

> Could someone check my homework please :-)

0/10 :-(

> I am thinking about a USB powered lamp in the event of future power
> cuts - linked to a powerbank. I believe the typical output from a
> powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
> more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
> should be more than adequate to power the lamp.
>
> Am I missing something?

Yep, watts are irrelevant. The only thing that matters
is amps and volts and a 5W led will only take 1A at 5V.

But the other consideration is how long the powerbank will
last before it needs recharging and you didn't list its mAh.

On Fri, 04 Nov 2022 05:13:12 +1100, farter <tsruhf@gmail.com> wrote:

>On Fri, 04 Nov 2022 02:10:39 +1100, Scott <newsgroups@gefion.myzen.co.uk>
>wrote:
>
>> Could someone check my homework please :-)
>
>0/10 :-(
>
>> I am thinking about a USB powered lamp in the event of future power
>> cuts - linked to a powerbank. I believe the typical output from a
>> powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
>> more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
>> should be more than adequate to power the lamp.
>>
>> Am I missing something?
>
>Yep, watts are irrelevant. The only thing that matters
>is amps and volts and a 5W led will only take 1A at 5V.
>
>But the other consideration is how long the powerbank will
>last before it needs recharging and you didn't list its mAh.

Belkin do one that is nominally 20,000 mAh:
https://www.belkin.com/uk/power-bank-20k/P-BPB003.html

On 03/11/2022 16:33, Scott wrote:
> On Thu, 3 Nov 2022 16:09:32 +0000, Andy Burns <usenet@andyburns.uk>
> wrote:
>
>> Scott wrote:
>>
>>> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
>>> hours. If I revert to my original premise that the bulb is likely to
>>> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
>>> would last for 20 hours. Is this correct? .
>>
>> Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
>> few percent for conversion losses, 16000mAh at 5V
>
> Still looking at well over the three hour projected power cuts then?
>>
>> And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
>> to start with.
>
> Even it it's Belkin :-)
>
> I suppose I could use an inverter instead and a normal lamp, but it
> seems to me that taking mains voltage, transforming it to 12 volts,
> rectifying it to DC, charging a battery, putting it though an inverter
> to return it to 230 volts then powering a lamp would not be an
> efficient process.

why not have 12 V LED MR16 bulbs on the 12 V car battery and have a 12V
battery charger on it?

You could then use a deep cycle leisure battery which will withstand
more abuse than a car battery.

On Thu, 3 Nov 2022 18:59:39 +0000, SH <i.love.spam@spam.com> wrote:

>On 03/11/2022 16:33, Scott wrote:
>> On Thu, 3 Nov 2022 16:09:32 +0000, Andy Burns <usenet@andyburns.uk>
>> wrote:
>>
>>> Scott wrote:
>>>
>>>> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
>>>> hours. If I revert to my original premise that the bulb is likely to
>>>> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
>>>> would last for 20 hours. Is this correct? .
>>>
>>> Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
>>> few percent for conversion losses, 16000mAh at 5V
>>
>> Still looking at well over the three hour projected power cuts then?
>>>
>>> And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
>>> to start with.
>>
>> Even it it's Belkin :-)
>>
>> I suppose I could use an inverter instead and a normal lamp, but it
>> seems to me that taking mains voltage, transforming it to 12 volts,
>> rectifying it to DC, charging a battery, putting it though an inverter
>> to return it to 230 volts then powering a lamp would not be an
>> efficient process.
>
>why not have 12 V LED MR16 bulbs on the 12 V car battery and have a 12V
>battery charger on it?
>
>You could then use a deep cycle leisure battery which will withstand
>more abuse than a car battery.

Actually, this was my first thought. The problem is that all the 12
volt lamps seem to be for caravans and are fixed mounting (for obvious
reasons). I wanted a standalone lamp that can be moved around and
maybe stored away when not needed.

On 03/11/2022 19:37, Scott wrote:
> On Thu, 3 Nov 2022 18:59:39 +0000, SH <i.love.spam@spam.com> wrote:
>
>> On 03/11/2022 16:33, Scott wrote:
>>> On Thu, 3 Nov 2022 16:09:32 +0000, Andy Burns <usenet@andyburns.uk>
>>> wrote:
>>>
>>>> Scott wrote:
>>>>
>>>>> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
>>>>> hours. If I revert to my original premise that the bulb is likely to
>>>>> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
>>>>> would last for 20 hours. Is this correct? .
>>>>
>>>> Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
>>>> few percent for conversion losses, 16000mAh at 5V
>>>
>>> Still looking at well over the three hour projected power cuts then?
>>>>
>>>> And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
>>>> to start with.
>>>
>>> Even it it's Belkin :-)
>>>
>>> I suppose I could use an inverter instead and a normal lamp, but it
>>> seems to me that taking mains voltage, transforming it to 12 volts,
>>> rectifying it to DC, charging a battery, putting it though an inverter
>>> to return it to 230 volts then powering a lamp would not be an
>>> efficient process.
>>
>> why not have 12 V LED MR16 bulbs on the 12 V car battery and have a 12V
>> battery charger on it?
>>
>> You could then use a deep cycle leisure battery which will withstand
>> more abuse than a car battery.
>
> Actually, this was my first thought. The problem is that all the 12
> volt lamps seem to be for caravans and are fixed mounting (for obvious
> reasons). I wanted a standalone lamp that can be moved around and
> maybe stored away when not needed.

I use 12V LED strip for emergency lighting run from old car battery or
from a "jump start" battery. You can cut it to the length/power
required; and attach it to whatever you want with as much or as little
regard to aesthetics you wish (or can get away with).

--
Robin
reply-to address is (intended to be) valid

>
> Actually, this was my first thought. The problem is that all the 12
> volt lamps seem to be for caravans and are fixed mounting (for obvious
> reasons). I wanted a standalone lamp that can be moved around and
> maybe stored away when not needed.

Something like this
https://www.screwfix.com/p/lap-rechargeable-led-work-light-1000lm/613kf

I know its not DIY, but they are good for the price.

On Thu, 3 Nov 2022 20:14:50 +0000, Robin <rbw@outlook.com> wrote:

>On 03/11/2022 19:37, Scott wrote:
>> On Thu, 3 Nov 2022 18:59:39 +0000, SH <i.love.spam@spam.com> wrote:
>>
>>> On 03/11/2022 16:33, Scott wrote:
>>>> On Thu, 3 Nov 2022 16:09:32 +0000, Andy Burns <usenet@andyburns.uk>
>>>> wrote:
>>>>
>>>>> Scott wrote:
>>>>>
>>>>>> There's a Belkin offering 20000 mAh at Argos - that's 20 amp
>>>>>> hours. If I revert to my original premise that the bulb is likely to
>>>>>> be closer to 5 watts, this would require 1 amp (5W/5V) and the lamp
>>>>>> would last for 20 hours. Is this correct? .
>>>>>
>>>>> Not likely, for the reason I mentioned, it could be 20000mAh * (3.7/5.0) minus a
>>>>> few percent for conversion losses, 16000mAh at 5V
>>>>
>>>> Still looking at well over the three hour projected power cuts then?
>>>>>
>>>>> And even less likely for the reason alan_m mentioned, i.e. the 20000mAh is a lie
>>>>> to start with.
>>>>
>>>> Even it it's Belkin :-)
>>>>
>>>> I suppose I could use an inverter instead and a normal lamp, but it
>>>> seems to me that taking mains voltage, transforming it to 12 volts,
>>>> rectifying it to DC, charging a battery, putting it though an inverter
>>>> to return it to 230 volts then powering a lamp would not be an
>>>> efficient process.
>>>
>>> why not have 12 V LED MR16 bulbs on the 12 V car battery and have a 12V
>>> battery charger on it?
>>>
>>> You could then use a deep cycle leisure battery which will withstand
>>> more abuse than a car battery.
>>
>> Actually, this was my first thought. The problem is that all the 12
>> volt lamps seem to be for caravans and are fixed mounting (for obvious
>> reasons). I wanted a standalone lamp that can be moved around and
>> maybe stored away when not needed.
>
>I use 12V LED strip for emergency lighting run from old car battery or
>from a "jump start" battery. You can cut it to the length/power
>required; and attach it to whatever you want with as much or as little
>regard to aesthetics you wish (or can get away with).

I already have an LED lantern for that purpose (which is rechargeable
but a very large battery). I am now looking for a desk type lamp so I
can read in bed if early nights become mandated.

On Thu, 3 Nov 2022 20:32:02 +0000, Robert <robert@invalid.invalid>
wrote:

>
>>
>> Actually, this was my first thought. The problem is that all the 12
>> volt lamps seem to be for caravans and are fixed mounting (for obvious
>> reasons). I wanted a standalone lamp that can be moved around and
>> maybe stored away when not needed.
>
>Something like this
>https://www.screwfix.com/p/lap-rechargeable-led-work-light-1000lm/613kf
>
>I know its not DIY, but they are good for the price.

It is very good but perhaps not for a relaxing, domestic ambience.

On Fri, 04 Nov 2022 05:13:12 +1100, farter <tsruhf@gmail.com> wrote:
[snip]

BTW Mr Farter, my dad's brother was called Will and I used to say he
could fart at Will :-)

On 03/11/2022 20:39, Scott wrote:

> I already have an LED lantern for that purpose (which is rechargeable
> but a very large battery). I am now looking for a desk type lamp so I
> can read in bed if early nights become mandated.
>
A Kindle Paperwhite self-illuminates, and I have a solar power bank for
recharging it.
I've found it very useful during power outages.

On Thu, 3 Nov 2022 21:14:44 +0000, S Viemeister
<firstname@lastname.oc.ku> wrote:

>On 03/11/2022 20:39, Scott wrote:
>
>> I already have an LED lantern for that purpose (which is rechargeable
>> but a very large battery). I am now looking for a desk type lamp so I
>> can read in bed if early nights become mandated.
>>
>A Kindle Paperwhite self-illuminates, and I have a solar power bank for
>recharging it.
>I've found it very useful during power outages.

That's an interesting idea.

Scott <newsgroups@gefion.myzen.co.uk> wrote:
>
> I already have an LED lantern for that purpose (which is rechargeable
> but a very large battery). I am now looking for a desk type lamp so I
> can read in bed if early nights become mandated.

Get a Kobo or a Kindle, much easier than a real book for reading in
bed and they have long-lasting backlights. I prefer Kobo mostly
because I can borrow books from my local (UK) library with it
directly.

--
Chris Green
·

On Thu, 3 Nov 2022 21:44:35 +0000, Chris Green <cl@isbd.net> wrote:

>Scott <newsgroups@gefion.myzen.co.uk> wrote:
>>
>> I already have an LED lantern for that purpose (which is rechargeable
>> but a very large battery). I am now looking for a desk type lamp so I
>> can read in bed if early nights become mandated.
>
>Get a Kobo or a Kindle, much easier than a real book for reading in
>bed and they have long-lasting backlights. I prefer Kobo mostly
>because I can borrow books from my local (UK) library with it
>directly.

I was given a Kindle about eight years ago. Is it likely to be okay
now, if I can find it?

Scott <newsgroups@gefion.myzen.co.uk> wrote:
> On Thu, 3 Nov 2022 21:44:35 +0000, Chris Green <cl@isbd.net> wrote:
>
> >Scott <newsgroups@gefion.myzen.co.uk> wrote:
> >>
> >> I already have an LED lantern for that purpose (which is rechargeable
> >> but a very large battery). I am now looking for a desk type lamp so I
> >> can read in bed if early nights become mandated.
> >
> >Get a Kobo or a Kindle, much easier than a real book for reading in
> >bed and they have long-lasting backlights. I prefer Kobo mostly
> >because I can borrow books from my local (UK) library with it
> >directly.
>
> I was given a Kindle about eight years ago. Is it likely to be okay
> now, if I can find it?

Possibly, plug it in to charge and leave it for a day (or more) and
see if it comes to life.

--
Chris Green
·

On 03/11/2022 21:44, Chris Green wrote:
> Scott <newsgroups@gefion.myzen.co.uk> wrote:
>>
>> I already have an LED lantern for that purpose (which is rechargeable
>> but a very large battery). I am now looking for a desk type lamp so I
>> can read in bed if early nights become mandated.
>
> Get a Kobo or a Kindle, much easier than a real book for reading in
> bed and they have long-lasting backlights. I prefer Kobo mostly
> because I can borrow books from my local (UK) library with it
> directly.
>
I borrow books from my local Scottish library with my Kindle.

On 03/11/2022 21:59, Scott wrote:
> On Thu, 3 Nov 2022 21:44:35 +0000, Chris Green <cl@isbd.net> wrote:
>
>> Scott <newsgroups@gefion.myzen.co.uk> wrote:
>>>
>>> I already have an LED lantern for that purpose (which is rechargeable
>>> but a very large battery). I am now looking for a desk type lamp so I
>>> can read in bed if early nights become mandated.
>>
>> Get a Kobo or a Kindle, much easier than a real book for reading in
>> bed and they have long-lasting backlights. I prefer Kobo mostly
>> because I can borrow books from my local (UK) library with it
>> directly.
>
> I was given a Kindle about eight years ago. Is it likely to be okay
> now, if I can find it?
>
If it's just a basic Kindle, you'll need a book light, too, which I find
rather annoying, compared to using my PaperWhite. The new Kindles, and
all the Kindle PaperWhites, self-illuminate.

I think officially 1 amp is the max current of standard USB sockets. Even
that seems to be pushing it a bit in my view.
Brian

--

--:
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"Scott" <newsgroups@gefion.myzen.co.uk> wrote in message
news:pul7mhdleaj66a2u4ebnvucfe3spci2226@4ax.com...
> Could someone check my homework please :-)
>
> I am thinking about a USB powered lamp in the event of future power
> cuts - linked to a powerbank. I believe the typical output from a
> powerbank is 2 amps at 5 volts. I assume an LED bulb will consume no
> more than 5 watts. If 2 amps at 5 volts is 10 watts (V x I ), this
> should be more than adequate to power the lamp.
>
> Am I missing something?