Non electrical background trying to make a cool little custom project - Help please?

Question

Brief bit of background - I've built my own PC's, I've repaired phones, changed plugs, fit light fittings from diy stores, and have a basic (very basic) understanding of electronics, but have found myself wanting for various reasons trying to build a custom project with light bulbs in series.

I've got mine and my partners initials in 10 inch high wood pieces from hobbycraft, (these style) and wanted to add some bulbs (these type) in series, to prove an aesthetic/design concept. I would use these light bulb holders and this battery pack to power it all.

The end result would ultimately look something like this (just not dog related...)

My question relates to whether using the bits I've researched and chosen, whether it would a) work, b) be bright enough, c) look decent. Each letter I anticipate will use 15 mini bulbs.

Could 4 AA batteries power all 45 bulbs or shall I split into 3 circuits of 15 for each letter? Would I be better off on mains power or is that way too much? Can I connect all these bulbs in series?

Any other tips and advice welcome.

If this works, I'd like to then recreate this on a bigger scale for our wedding day, which would sit at the side in the venue - I like the idea of creating this, as I'm quite craft-sy, and enjoy building things and again I have a very specific vision of what I want, which isn't achieved by hiring them.

I've chosen to build rather than buy because also nothing out there is exactly the way I want it - I want lots of smaller bulbs, instead of bigger ones. I also don't like the white globe look, and want the bulbs to be filament style.

Any help? Thanks in advance!

Answer 1

4 AA's ? not a chance ... these are 1.5V 0.3A = 0.45W * 45 = 20 Watts.

But here's the kicker. For the conductor to reach a nice warm 2100'C it takes 10x or 200 watts to start and that decays to 20 Watts as/if it ever reaches that temperature.

Otherwise it is a short circuit and then the battery starts to rise in temp.

Better stick to Xmas lights with lower power or LEDs. and get much a better battery that can handle the current.

Answer 2

You're going to struggle with only 4 AA cells.

First 15x1.5V bulbs = 22.5V. But 4x1.5V cells = 6V. So if you're wiring them in series, then the voltage is all wrong. You would need 15 AA cells to get the right voltage.

Those lamps take 0.3A. You want three strings of them, running at once, which gives 3x0.3A = 0.9A. AA cells will just about do that, but not for very long - an hour if you're lucky.

Mains voltage will be too high - all 45 bulbs in series is still only 67.5V. Higher voltage bulbs would work, but could be lethal if not wired properly.

A safer option would be to use a ready-made power supply, maybe 12V or 24V. Adjust the number of bulbs in series and/or the voltages of the bulbs. But make sure you don't exceed the current capacity of the power supply.

Answer 3

If you insist on these bulbs rather than more efficient LEDs, you can use a "brick" type 12V or so switching power supply powered by the mains.

You need to have substantially more capacity than the running power of the lamps to allow it to start, as @Tony suggests, since switching power supplies have short-circuit protection.

If you run them at nominal voltage, you can put 8 in series for 12V and add a couple 1N4004 diodes in series with a chain of 7 for each letter. That will draw 0.6A per letter, for a total of 1.8A. A 12V 5A (60W) supply may be adequate.

I would be inclined to try a 60-90W spare 19V-ish laptop supply with a string of 15 bulbs in series for each letter. That's about 18% less voltage than nominal so the bulbs will last longer.

As well as getting dimmer, less efficient at turning electrical watts into lumens and lasting longer, the lamps get redder in color as you reduce the voltage (and thus the filament operating temperature), which may matter to you.