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How to make a battery-powered lamp?

John Jones

New Member
I want a portable desk lamp that's powered by some kind of rechargeable battery cell. (A lamp with a normal bulb fitting, not LED.)

Can anyone advise me on this? I'm clueless with electronics and can't solder!
 

alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO!
What do you consider "a normal bulb"?
Why not a LED?
 

Diver300

Well-Known Member
Most Helpful Member
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John Jones

New Member
Welcome to ETO!
Thanks! :)

It would be hard to beat one of these:- https://www.ikea.com/gb/en/p/jansjoe-led-usb-lamp-black-70291232/ plugged into a power bank.
Thanks but it's way too small and too targeted - I just want to light the room softly with a regular bulb, with a shade.

Plus how to power a USB light? I recently bought an LED to use as a flashlight and tried powering it with a power bank, but it didn't work due to incompatibility with the current. I came to the conclusion that power banks are only designed for recharging stuff, not powering lights. That's what the manufacturer told me anyway.

What do you consider "a normal bulb"?
Why not a LED?
Well I just meant a regular lamp that I can attach a shade of my choice to, with a bayonet or screw lightbulb fitting, so I can use whatever bulb I like. In my case, I only use incandescent bulbs.

For what it's worth (if anyone's interested), I am highly sensitive to modern bulb types, and anything other than incandescent burns my skin and eyes. When I got my first LCD I started going blind before I realised what was causing it.

CFL bulbs burn my skin badly, plus they're absolutely vile - so flickery and depressing. LEDs aren't quite as bad, and OK for something quick like a flashlight, but I still cannot stand LEDs for prolonged use. They're flickery, too intense/dazzling, not at all gentle, plus I don't like that they don't give any heat.

So I cannot use LED screens. My TV is a 17-year-old plasma, which is the only TV I can look at. For my computer monitor, I used CRTs as long as possible, and now I use a small 12-year-old CCFL screen with the brightness turned down really low. That is the only way I'm able to get online and write this. Anything else burns my eyes severely. I really wanted a new monitor last year, so I tried buying 4 different LED monitors, but had to send them all back - they were all so flickery and intense that it hurt my eyes just trying to focus on them.

So that's why my home is an incandescent only zone! :)

But even if I wasn't sensitive to LEDs, I'd still find them distasteful. The light they produce just isn't to my taste. I find it very poor quality. CFLs even moreso. They're so hideously flickery. I don't get why such bulbs are so popular, but each to his own. Even incandescent bulbs are too flickery for my tastes, but they're the most solid bulb you can get so it has to be that.
 
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audioguru

Well-Known Member
Most Helpful Member
Are you thinking about using a car light bulb or many of them and a huge car battery to power them?
 

Diver300

Well-Known Member
Most Helpful Member
You are probably being affected by LED flicker.

There are two main reasons that some LEDs flicker. Firstly LED lightbulbs run from main electricity will often flicker at twice the mains frequency, so 100 Hz in the UK. However it depends on the design of the circuit inside the lightbulb. Secondly, some circuits turn the LEDs on and off very quickly to control the brightness. That is called PWM, for Pulse Width Modulation.

Lots of factors affect how visible the flicker is, and people are often affected by flicker without being aware of it. When we move our eyes, we don't move them smoothly and slowly, but we will look at one point and then jump to looking at another point. That jumping from one point of view to another is made more difficult if the lighting is changing at the same time. There is a big variation between people as to how bad the effect is.

Fluorescent light will flicker somewhat when they have traditional mains supply circuits. The effect of the flickering light was first noticed and studied on fluorescent lighting, before LED lighting was available.

I am quite sensitive to the flicker created by LEDs flickering, and I've often modified circuits to reduce the flicker. With CRT monitors I would always make sure that the refresh rate was as high as possible, even if it meant a lower pixel resolution.

LCD monitors will flicker if the backlight flickers. The older ones with CFL backlights generally didn't flicker, because the backlight were run using high frequency inverters so that they could be dimmed. Some modern LED backlight monitors will still use PWM, but often the frequency is so high that the effect is minimal, and at high frequency it's possible to practically eliminate flicker with quite small and cheap capacitors, so that is often done.

An LED running from a constant current won't flicker. Most USB powered LED lamps won't flicker, and the flexible strips of LEDS lit from 12 V dc or 24 V dc are not likely to flicker, as long as you don't have the types that can change their colour.

Powerbanks can power lights. The issue with power banks is that they will turn themselves off if too little current is taken, and some lights will take too little current for some powerbanks, so trying different combinations, or using a USB hub to power several lamps from one powerbank may help. I've just tried a little plug-in USB light on my powerbank, and it turns off after about a minute.

For someone who wanted a portable table lamp, I modified an LED lightbulb to run on 5 V, and then the table lamp could be run from a power bank. The LED lightbulb was shaped like a traditional incandescent lamp, so a normal shade worked with it. It would have taken a lot more power than my tiny little USB light that the power bank doesn't detect.

For simple flicker-free lighting, ordinary car bulbs will work. You could just run them from any smoothed 12 V supply of sufficient current rating, and there will be no flicker. You will need big batteries to run house lighting if it's incandescent.
 

John Jones

New Member
Diver300, thanks so much for all that helpful information. Really interesting and I'm very grateful you took the time to write it! :) Also nice to meet someone else who's sensitive. (I seem to be sensitive to just about everything in the 21st century!)

My main problem with CFLs and LEDs isn't the flickering, it's the burning. I don't understand the electronics, but I'm pretty sure it has something to do with the interaction between light and EMFs. I've found that the same screen can burn my eyes far less depending on the building they're plugged into, and how much electrical activity there is going on in the vicinity.

You are right about LEDs not always flickering. Some flicker terribly, others seem solid (like the gentle backlit keyboard I'm currently using). Nevertheless, I don't like LEDs and wouldn't want to light a room with them. They tend to be really intense/dazzling, and an unpleasant, shallow colour (a low CRI that makes everything look ugly). Personally, I don't think you can beat incandescent. Plus I'd want to be able to use orange bulbs sometimes, and I don't think orange LED bulbs are common.

I modified an LED lightbulb to run on 5 V, and then the table lamp could be run from a power bank.
That is interesting, though I doubt I would be able to make that kind of modification, unless it's quite easy? Or could you do small modification jobs via the post? (I'm in England too.)

For simple flicker-free lighting, ordinary car bulbs will work. You could just run them from any smoothed 12 V supply of sufficient current rating, and there will be no flicker. You will need big batteries to run house lighting if it's incandescent.
How long do you reckon, say, a 20,000 MaH power bank might be able to run an incandescent bulb for? (30 minutes would be useful, 4 hours would be ideal. I don't really need more than that.)
 
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Diver300

Well-Known Member
Most Helpful Member
White LEDs are actually blue LEDs with a phosphor that changes some of the light to longer wavelengths. However the spectrum is never very even. Multicolour, or colour changing LEDs contain red, green and blue LEDs and the intensity of each can be varied. If you can find one that doesn't flicker, it might work better for you.

Power banks are rated to the batteries they contain, which are lithium-ion ones and average about 3.8 V. The output is at 5 V, so they actual charge that is put out is only about 3/4 of the rating. A 20,000 mAh power bank will only put out about 15,000 mAh. However, that is quite a lot. If you have a 1 A bulb, that should last 15 hours.

Low voltage incandescent bulbs are rare nowadays, but the GK4875 listed here:- http://reflectalite.com/kryptonpage.html should run for around 20 hours on a 20,000 mAh power bank. I would work from a smaller one, but it would last for a shorter time.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
One possible solution, needing nothing but a few wire connections electrically; not cheap but it fits the requirements:

A lamp that takes or can be adapted for MR16 bulbs; they are 12V and still readily available. Those are a standard size with many makes & lamp holders etc. available.

Or one adapted to take a 12V car filament lamp, eg. a headlight (50 - 60W) or indicator or brake lamp bulb (around 21W).

Or, you can still find 12V bulbs in standard 22mm bayonet style, but I don't know how long they will be available:


A power tool battery, 5 cell - 18 or 20V rated, 5AH size or thereabouts.
Specifically, some make that you can buy a connection adapter for, such as these:

The Aldi power tool batteries are the best value at £30 for a 5AH, half the price of such as Bosch - but I have never seen a commercial connector for those, unfortunately.
(I designed one, if you know anyone with a 3D printer: https://www.thingiverse.com/thing:4773542 )

And a high power step-down converter to get a stable 12V supply from the 18V battery, eg.

It needs to be far higher rated than the lamp as filament lamps take much more current when turned on from cold than when the filament is up to working heat, like several times more.

Add a switch between the battery connector and step down converter for on/off.
The converter will need adjusting to 12V output using a voltmeter. after first connecting power and before connecting it to a lamp, a one-off setup.

You need a charger for the battery as well, and likely more than one battery if you want long-term use!


Be careful choosing a bulb; halogen types (with a parallel tubular capsule inside, or car headlamp bulbs) are most efficient in light vs power use terms, but emit a significant level of UV and need a UV blocking filter if they will be in proximity to skin or eyes. Normal filament lamps such as the car 21W types don't emit any significant UV but are less efficient.

With a 50W lamp and average voltage from the battery at around 18V, the discharge current will be near 3A as there will be some power loss in the converter.
So roughly 100 minutes runtime per battery charge.

With a 21W lamp, roughly 1.3A and near four hours runtime per charge.

Filament lamps are very inefficient as most of the power input is lost as heat, rather than light.


If portability was not a requirement, you could substitute two 12V deep cycle batteries for the power tool battery; they could be any capacity you like (as long as they are identical) wired in series to give a "24V" input to the power converter.
Use a commercial 24V battery charger.

You could just run a 12V car lamp direct from a 12V battery, but the brightness will vary significantly with the state of charge - at full charge the battery is near 15V but that drops down during discharge, to around 11V before its totally flat.
Lamps intended for non-vehicle use are not suitable for direct connection to a lead-acid battery as the higher voltage will kill them, they will only last a fraction as long as if on a regulated 12V source, while 12V vehicle lamps are designed to work with the higher voltages.

Note that any 12V lead acid battery must be a deep discharge or "leisure" battery, not a normal car battery; they have different constructions.
 

John Jones

New Member
Thank you once again, Diver300!

Gosh, rjenkinsgb, that is very detailed and helpful, thank you.

I had no idea this would be so complicated, with so many variable factors! I'm not an electronically-minded man and this is already going over my head.

For now, I'm tempted to go with the simpler option of a low voltage bulb + power bank. Though how do I connect the lamp to USB?

Also, can anyone explain (in simple terms) why bulbs use such a wide range of voltages? Is it simply that bright bulbs need lots of voltage? Will a 4.8V incandescent bulb be really dark?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Also, can anyone explain (in simple terms) why bulbs use such a wide range of voltages?
Power, the wattage, is simply current x voltage.
A 60W lamp at 12V takes five amps; at 120V 0.5A

That's why it is difficult to run a high power filament lamp from batteries, or at least for a significant time.

Different voltages are to suit different uses & power sources, from domestic through industrial & vehicle down to torches / flashlights.
 

Diver300

Well-Known Member
Most Helpful Member
Also, can anyone explain (in simple terms) why bulbs use such a wide range of voltages? Is it simply that bright bulbs need lots of voltage?
As rjenkinsgb said, there are a lot of different uses for bulbs, and bulbs will only work best on one voltage. A bulb will not last long if the voltage is 10% too high, and will be very dim and inefficient if the voltage is 10% too low, and bulbs already have quite a short life and are quite inefficient already.

Where the power comes from batteries, the voltage will drop a bit due to the current taken by the lamp, so the bulb is specified for a voltage a bit lower than the battery's nominal battery voltage, so the bulb might have to be different for different capacities of batteries or different chemistries.

Bulbs that take very small currents can result in very fragile filaments, so in some applications the voltage is reduced so that more current is taken and the filament is thicker and more robust.

LED lamps will sometimes have electronic control, so that they can work on a wide variety of voltages. Even if there is just a simple resistor to limit the current, an LED lamp is likely to be affected less by change in voltage than an incandescent light so that reduces the numbers of types needed. Also the LEDs in torches aren't replaceable, so there isn't a whole load of different LED bulbs like there is with incandescent.
 

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