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.
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
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.
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? .
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.
Still looking at well over the three hour projected power cuts then?
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.
Yes, you'd have higher losses, the powerbank's not a bad idea, just don't believe the numbers ...
0/10 :-(
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:
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).
Something like this
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.
It is very good but perhaps not for a relaxing, domestic ambience.
On Fri, 04 Nov 2022 05:13:12 +1100, farter snipped-for-privacy@gmail.com wrote: [snip]
BTW Mr Farter, my dad's brother was called Will and I used to say he could fart at Will :-)
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.
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.
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