Looking for help - built a COVID-19 Killer, UV-C bulbs are not powering up.

A friends GF is a doctor, I’m trying to build her a disinfection box as she will be reusing masks.

Here is what I am working with

  • Power Supply Driver Transformer 100W 110V AC to 12V DC
  • DROK Adjustable Buck Converter Step Down Voltage Regulator 6V-32V 30V 24V 12V to 1.5-32V 5V 5A LCD Power Supply Volt Reducer Transformer Module Board
  • 4x GermGuardian UV-C 10.5v 4W .38A

So… the problem I’m having is the bulbs are only drawing .16A and barely powering it on. I cant crank it up any more voltage as I’m limited to 11.9V on the DROK and increasing amps stops at .16A, if I go lower, voltage drops. The drok itself is support to output 5A. What am I doing wrong and how can I get the power the bulbs need to operate at their recommended power requirements?

Any ideas or feedback is highly appreciated!

Can’t see your wiring but have you wired them in series instead of parallel by mistake?

Originally wired in series but changed it to parallel which is how it setup now

A bit late for this, but if anyone wants to do something similar, wouldn’t a regular tube-type bulb (or two, on opposite sides) work as well?

Just add a fixture-with-ballast, plug it into the mains. No cranky power-supplies or other rot to deal with.

I got one of those lying around somewhere. Used it as an ozonator æons ago.

(The white enamel on the fixture will discolor brown in no time, but I had an Al-foil “reflector” between bulb and fixture, and it still discolored at the ends where not protected by the foil.)

You can also sanitize a face mask by letting it sit for 2 days. 3 days if you want overkill. Honestly some studies say 4 hours is enough.
Wear a different mask as you wait.

Edit: or if waiting isn’t an option, dunk it in 70% IPA for 30 seconds.


Just hitting it with DC does nothing. You gotta “strike an arc” with a higher-voltage spike first.

I figured that despite its looks, it doesn’t run like any ol’ hotwire bulb, so…

Saw bulbs of that type recently in AliExpress. I think the problem lies in that these bulbs sort of work like leds, with their Vf being a lot higher when cold. Since your supply can not output more than 12 V, you cannot make the bulbs heat enough. You need to feed the buck module with way higher voltage, as the bulbs need a lot more voltage at startup. The buck module must operate in constant current mode, or the bulbs will blow up. You'll need one driver per bulb, too, or set some current limiting resistors with the bulbs if in parallel because no way the current will be shared with balance. Or a module with a lot higher output voltage and bulbs in series.

Read related user feedback information here and there, namely. In this other advertisement a user claims he makes it work with 220 V in series with a 4 µF capacitor (AC drive).

Now that I think of it, AC led drivers of 300 mA are common and very inexpensive. That would be a nice solution.

For example: https://www.aliexpress.com/item/32945889263.html

The 12 - 18 W or 18 - 25 W drivers with 330 - 350 mA claimed current would drive those 4 bulbs in series nicely; the cheaper 280 - 300 mA units too.

Crazy prices for standard 300 mA drivers here (boxed) and there, by the way.

Thu, 04/02/2020 - 05:43

Great feedback, I’ll have to source items on amazon because time is short with spread down here. So if I change the power supply to a variable voltage dc supply, get a buck converter that can do constant current and add current limiting resistors to + to the bulbs, that should get them going?

Edit: manufacturer of the bulb said it needs 25v to start and 11v to operate so you are correct that it has a higher vf. Ordered an adjustable voltage power supply.

Sounds like I may be able to do it in series if I can get a higher voltage through as well. Even though the bulbs are rated for 11v, higher voltage wont pop them?

If I went in parallel, what resistors could I add inline? Rookie with resistors here, my guess is those ohm resistors I can get in a variety pack?

remember its drawing more then the variety pack resisters, normally they are 1/4 watt types

i think you need a bit more then that

I see, so 4-5w resistors?

Edit: ok ordered 5w resistors

i went on manufacturer website, it does not say anything about voltage, have you tried powering up directly from 120v? i mean it has a candelabra base, with is almost always used with line ac voltage

The bulbs are for a germguardian pluggable into the outlet, it’s not designed to a direct 120v. I emailed them directly for the voltage requirements

if it needs 25V to start, don;t you now also need to know how exactly, to go back to the 11V operating voltage?

plus with them all in parallel, one might start at a different time from the others causing several possible issues

Was kinda thinking that myself, it wouldn’t lower voltage on its own?

Does this mean that there is a capacitor inside the OEM unit to burst 25v power?

You need 250 – 280nm wavelengths “light”. Otherwise you’ll get ayes damaging and expensive source of blue light only

Germguardian states they are 253.7nm

People, you should be a bit more patient.

There are two main ways to solve this problem:

One is using mains AC, some guys were speaking about 4 - 4.5 µF capacitors in series with 220 V AC to power up those 3 W bulbs on the AliExpress ads I posted above. These are 4 W, and you're using 115 - 120 V AC, so maybe a 10 µF capacitor will do. The capacitor must be non-polarized, ceramic or film type, and its voltage rating must be at least 200 V, as 120 V AC mains peaks at ≈170 V. This is a bit of a guesswork from my side, so you may want to wait for some other people's input here.

Other solution is DC. If you need from amazon:

  • Without changing your currently limited voltage output power supply of 12 V DC, get buck boost modules to power each bulb for peace of mind. This and that could do (they're pricey there). A single module could also do with all bulbs in parallel and some resistors in series. A 4.7 Ω resistor in series with each bulb, for example, should be more than enough to limit any unbalanced inrush current to the bulbs as they'll heat up in parallel. But if any bulb fails, the rest will have to bear with the failed one's current share (!).
  • Changing the power supply to a 24 V one (with at least 3 A rating), some models here with adjustable output voltage. Then, using a CC/CV buck module for each bulb like these XL4015 units.

The led driver solution would also work fine, but as with the above modules and supplies getting them from your mainland doesn't looks as cheap as directly from China.

Any DC/DC converters should be adjusted to the bulbs rated current (≈0.38 A) using their constant current trimpots, with sufficiently high no-load output voltage. The converters, as your flashlight led drivers do, adjust the output voltage to keep a steady current to the bulbs.

Thu, 04/02/2020 - 18:28