DC-to-AC Inverter for Powering Electroluminscent wire or tape

Discussion in 'The Completed Projects Collection' started by wayneh, Jan 29, 2019.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
    A few years ago I started on a project to add some EL lighting to my small boat. Some of the boaters near me have some really nice lighting and I though it would be fun to do something like that. I eventually abandoned the idea of mounting the project to my boat, though, because there's basically nowhere on my boat where the fragile EL tape would be safe from bumps and impacts. Plus there are the issues of water and high voltage. It's too expensive and would be difficult to replace, so I decided it just wouldn't be practical. But I still like the looks of EL tape and wanted to play with it.​

    EL products are described as being like capacitors that make light as they're charging. So they need an AC source to charge and discharge them at a high frequency (400Hz - 2,000Hz) and they require a high voltage (50-250VAC). They will glow dimly if attached directly to 120VAC mains at 60Hz, but they really need more voltage and higher frequency to reach their intended brightness.

    The inexpensive (<$10) inverters often sold with small EL kits are capable of lighting a few meters (at most) of EL wire. An inverter with enough output power for a substantial amount of EL area such as tape or panels is much more expensive. I decided I could make my own from parts I mostly already had on hand.​

    There are several ways that this could be done.
    My related threads as I looked for a solution:
    I considered (but abandoned) using a full-wave bridge and a big filter capacitor to provide a 170VDC reservoir, and then drive a chopper with a MOSFET that would deliver that voltage to the EL tape at whatever frequency I wanted.

    A number of 555 timer circuits can be found online for making inverters. These drive a step-up transformer to give the high-voltage output. I didn't want to be limited to the ~200mA max current of a 555, though, and once you add power transistors, you don't need a 555 to make a square wave. Any op-amp will do. So that's the direction I chose - an op-amp square wave to drive a couple MOSFETs for a high current inverter.

    I additionally chose to use the N-channel MOSFETs I have on hand, and that meant I needed to generate the higher gate voltage for the high-side switch. For this I used the 2nd op-amp in the package to drive a charge pump voltage doubler at ~6kHz.

    I might go even further and upgrade my switcher to an H-bridge. This would double the voltage output. But in the meanwhile I can accomplish the same thing by using a lower voltage AC transformer.​

    Screen Shot 2019-01-29 at 5.02.25 PM.png

    V1 – I used an aging 9V battery at ~6V for testing. My final version runs off a 19.5V laptop power brick. In between I was using a 12VDC PSU from an old hard drive enclosure.
    U1 – I used LM358 because I have them on hand, but a wide output range is important. Rail-rail would be even better.
    Q1 – Just about any NPN should be fine for Q1. I just happened to have a bunch of that particular transistor.
    D3 – I doubt that the part number matters much.
    L1 and L2 are a wall wart run in reverse.
    R1 is not used but is required for the simulation.
    C7,8,9 and all that is an attempt to model the EL tape.
    This simulation doesn't show the output-on LED indicator.
    Screen Shot 2019-01-29 at 5.30.04 PM.png
    The 19.5VDC power brick and the 4.5VAC wall-wart transformer are not shown.
    The build mostly follows the drawing except that I offset C5 one position and probably put a few wires in different spots. Note that the photo was taken before all the wires were added. Choose R12 for the LED and supply voltage you are using. I'm using 33K and a tiny LED, the little white thing between N13 and O13. (It's laying on its side because I couldn't get it soldered to the board standing up.)​

    Parts List
    Part Description Mouser part no.
    C1, 2 0.1µF ceramic capacitor K104K15X7RF5UH5
    C4 0.22µF ceramic capacitor FK24X7R1E225K
    C5 22-47µF electrolytic capacitor
    C6 1000µF electrolytic capacitor
    D1, D2 Schottky diode SB140-E3/54
    D3 diode
    M1, M2 N-channel MOSFET IRF540N
    Q1 NPN transistor
    R1, 9, 11 4.7K resistor MF1/4DC4701F
    R10 47K resistor
    R12 33K resistor MF1/4DC3302F
    R2,3,4,6,7,8 100K resistor MF1/4DC1003F
    R5 10K resistor MF1/4DC1002F
    VR1 50K pot T18503KT10
    Screen Shot 2019-01-29 at 6.35.47 PM.png
    It works!
    The big 1000µF, 25V capacitor (C6) I used (in the photo) turned out to be bad and had to be replaced. I'm also noticing now that the little 4.5VAC, 120mA, 4W wall wart is getting quite warm while lighting 1 meter of tape (1cm wide). I'll have to find something else. I didn't notice this while running the breadboard prototype, only for the final build. So I may look into that to see if the breadboard version also gets warm.
    The VR1 is optional, really. Once you get this up and working, you'll never touch VR1 again. My rig doesn't hold voltage as I increase the frequency beyond some level, so the brightness doesn't keep increasing.​
    Last edited: Jan 30, 2019
    xox and OBW0549 like this.
  2. wayneh

    Thread Starter Expert

    Sep 9, 2010
    The EL tape I'm using for testing came from Adafruit. It's 100cm long and the lit part is 1cm wide. The specs offered at Adafruit show the power usage is: Current Draw: 0.14mA/cm2 (max) @ 110V / 400Hz
    That means it should draw maybe 30mA at 220V and 500Hz, or 6.6W. That explains why my small 4W wall wart is getting warm.

    [update] I found a 9VAC, 16W transformer and it's working much better despite the lower voltage. I see about 120V at the EL tape and now when I vary VR1, the effect on brightness is very noticeable. It's not getting hot like the little one did.
    Last edited: Jan 30, 2019
  3. wayneh

    Thread Starter Expert

    Sep 9, 2010
    For anyone interested in this topic, you should take a good look at this part:

    It's got some great features and I may yet give it a try but I was turned off by
    • It is limited to ~42 square inches of EL. That would be enough for many hobby projects.
    • It's tiny and surface mount and that would be hard for me to deal with. Maybe I'll look for a solution for that.
    • It still needs a handful of external components including an inductor and MOSFET.

  4. wayneh

    Thread Starter Expert

    Sep 9, 2010
    Just a little follow up. I have a smart outlet that can monitor and log the power consumption by any device plugged into it. I used this to measure my project, which again is an old Dell laptop power brick ==> my circuit board ==> step-up wall wart ==> 2 meters of 1cm wide EL tape.

    To my amazement, the reported power draw is just 2-3W. (I only get one digit, and sometimes it's 2 and others 3.) I'm impressed that the power brick is so efficient, and that my project must not be too bad either.
  5. wayneh

    Thread Starter Expert

    Sep 9, 2010
    The build in the enclosure, an old gift tin.


    The power brick and enclosure before mounting under the cabinet.

    My kitchen sink.

    Night view.

  6. tawm

    New Member

    Feb 8, 2019
    Pretty cool, came out super clean and with a nice short BOM.
    wayneh likes this.
  7. wayneh

    Thread Starter Expert

    Sep 9, 2010
    Yeah I'm quite happy about it. I didn't set out for that location for the EL tape but it was a near perfect fit and I actually like having a night light over the sink. I discovered that the tape fit nicely onto a piece of scrap 1/2" x 3/4" lumber I had. It was much easier to mount the tape on that, and then mount the stick with just a couple finishing nails.

    One thing I like about the electronics is that it repurposes stuff from my junk pile, especially the wallwart and laptop power brick. All I had to build was a buzzer circuit.
    tawm likes this.