UVC Sterlization Cabinet - Page 1
Forum section: electronics / projects

author: redgear
author_rank: Frequent Contributor
timestamp: June 23, 2020, 12:28:02 pm
content: Hi all,I am planning to build a disinfection cabinet using UVC radiation. Many of my friends and family work in the health sector and I plan to gift it to them. I am a beginner, i'm sorry if my questions are too easy or stupid. I have been collecting information online about the same and I am pretty confused. The cabinet will have a surface area of 7300 cm2. I am planning to use 6 XPhilips TUV T5 16Wtubes with UVC wattage of 4W and irradiance of 45 uW/cm2at 1m. The maximum distance between the object and the tube will be 30cm in my case, as irradiance is inversely proportional to distance, I am simply multiplying the irradiance value by 3, so I get 135 uW/cm2. The total UVC wattage will be 24W(6*4) and irradiance will be 810 uW/cm2(6*135)(correct me if I'm wrong). I will be covering the interiors of the box with polished aluminium sheets to increase reflectivity.Different resources suggest different dosages and different formulas to calculate the dosage. Studies based on SARS-CoV-1 suggest a dosage of 7-2410 J/m2. TheIUVArecommends 1-3 J/cm2for real world conditions but only 10-20 mJ/cm2under controlled lab conditions. Since the cabinet will be closed and effectively almost all UVC radiation will reach the object can I achieve 99.9% deactivation using UVC dosage in order of few hundred mJ?The next problem is properly calculating the exposure time. I find different formulas that give completely different results.According to thisstudy, the exposure time formula is given by : Exposure Time(s) = UV Dose(J/cm2)/Irradiance(W/cm2), substituting values I get around 62 minutesAccording to thisResearch gate answer, the exposure time is given by : Exposure Time(s) =( Desired_UV_dose(J/m2* 4 * pi * (UV_bulb_distance(m)^2 )/ UV_bulb_power(W), substituting values, I get 23.55 minutes.A Youtube video uses the formula, Exposure Time(s) = Surface Area(cm2) * Dosage(J/cm2)/Power(W), substituting values I get around 15 minutes.As you can see, the differences are huge, idk which is the correct one.Do I still need a Ballast for the tube if I step down the voltage to the tube's operating voltage?I'm also planning to include a timer, will any 555 timer or timer relay be enough?Since, UVC is harmful to humans, I will have to add some mechanism to stop the equipment from being operator if the doors of the cabinet are opened, I planning to use a contact switch.Thanks

author: orolo
author_rank: Frequent Contributor
timestamp: June 23, 2020, 01:42:58 pm
content: Quote from: redgear on June 23, 2020, 12:28:02 pmI would expect irradiance being inversely proportional to the square of the distance, so you should multiply by 9, to get 405 uW/cm2.When you later multiply by 6, that could be big underestimate, since if your face of the object is 30cm away from one of the lights, it probably is quite closer to another, and if the closer one is at say 15cm, then it counts as 4 sources at 30cm, due to the inverse square law. Multiplying by 6 could also be a overestimate, because some lightsources (tipically half?) should be occluded (or not facing directly), so only half reach your face of the object, and probably not at a right angle. Then again, the walls are reflective.I think a good idea is to consider first how will you place the light sources, which are not point-like, and then to get the lower bound of irradiance, try to imagine the face of atypicalobject that will be farthest (in the inverse square sense) from all light sources, and the more ocluded / facing away. That will be your lower bound. And that doesn't consider the reflectivity of the walls.Maybe the best advice for your project I can give: try using 4-pin CFLs, because there are goood, compact and efficient electronic ballasts for them, which also give a longer life.I've put together something like your project recently, but much more crude, with just one 4W Philips CFL. Those two pin CFLs have an internal ballast, so you just need to limit the mains current going into the lightbulb with some kind of inductance. Since I didn't own a limiter, I improvised one with two 12V transformers back to back. They get hot, but get the work done. It would have been much better if I had bought four pin CFLs with the correct electronic ballasts. I was under very strict lockdown then, so I had to stick to this scheme.Edit: another thing about my crude project. I wanted it to sterilize masks. Just leaving the mask lying in the box doesn't work, because there are always parts of it in complete shadow. So I considered (but didn't have time to) using a small synchronous motor from a microwave oven to make a rotating stand for the mask. That way I wouldn't need to manually turn it several times to make sure it is disinfected.

author: redgear
author_rank: Frequent Contributor
timestamp: June 23, 2020, 02:07:33 pm
content: Hi, Thanks for the reply.Quote from: orolo on June 23, 2020, 01:42:58 pmThanks for the correction. I plan to anyway double the exposure time I get. So, I choose not to worry about occluded surfaces. I will also be placing stoppers on all side to ensure the surfaces are not fully hidden. Since the aluminium walls are highly reflective I hope I can effectively achieve 360deg coverage. I checked out few products in the market and they all seem to use the same.Quote from: orolo on June 23, 2020, 01:42:58 pmThat's a nice idea, I will try it.Quote from: orolo on June 23, 2020, 01:42:58 pmWhere did you get UVC CFL lamps? Would be great if you can leave a link here.The main problem is with the dosages, if I considered 0.1 J/cm2of the effective dosage, even 2 tubes seem to be a overkill. What dosage did you consider for your project?Quote from: orolo on June 23, 2020, 01:42:58 pmThat's cool. I initially thought of using just 2 lamps, and moving them with a stepper motor(just like how the nozzle moves in a 3d printer). But that would increase the total time taken for disinfection as it has to wait few seconds after every step.

author: orolo
author_rank: Frequent Contributor
timestamp: June 23, 2020, 02:27:10 pm
content: Quote from: redgear on June 23, 2020, 02:07:33 pmThe lamps I got from Amazon, they seem to be popular for disinfecting the water in fish tanks.Amazon link to the CFLs I bought.Amazon link to the ones I'd bought had I known better.Maybe lower power, but with the four pins.Regarding dosage, I read a lot about this. First, it seems that to kill the virus the best is hot air, because UVC attacks the masks and degrades their efficiency. So maybe a simpleclosedoven at about 80ºC is best just for masks and coronavirus.I attach two of the best articles I found (I read quite a lot, but can't find them / deleted them). One is the implementation of UVC in a hospital. The other is about LED UVC, but gives a nice table of different bugs and kill ratio vs irradiance. I figured covid should be similar to its relatives in the table, and determined irradiance from there. Then doubled the time, just in case.

author: redgear
author_rank: Frequent Contributor
timestamp: June 23, 2020, 02:33:15 pm
content: Thanks a lot man! Appreciate it!I am building it primarily for disinfecting daily use items like food packets, watches, phones,etc.

author: Gyro
author_rank: Super Contributor
timestamp: June 23, 2020, 02:53:56 pm
content: If you do a forum search for UVC you will find a number of threads. Not surprisingly, it has been a common question in recent months. You might have to trawl through them a bit, but there are elements of useful information in some of them.

author: redgear
author_rank: Frequent Contributor
timestamp: June 24, 2020, 12:56:15 pm
content: I have now decided on the dosage. I need to start making the main board. I will using two micro switches to detect if the cabinet door's closed, relay,timer relay and 6 ballasts(one for each tube). The ballasts are designed to work with ac mains. How do I start working on the main board? Can I just use the connectors found on the back of the smps to connect the ballasts to mains? What safety devices(fuse?) do I need? I'm also planning to make the timer with display myself. I can do it use arduino or any other microcontroller but will it be as reliable as using a IC7555 or 555?Thanks

author: jogri
author_rank: Frequent Contributor
timestamp: June 24, 2020, 03:10:28 pm
content: Quote from: redgear on June 23, 2020, 02:33:15 pmFood packets are wrapped in plastic-> not a good idea to radiate something that has to stay airtight with massive amounts of UVC that will destroy the polymer. Same goes for watches and phones, they aren't designed to handle high UVC doses. You might want to give steam disinfection a shot for food packets and use Ethanol/iPA wipes for phones and watches.Edit: You are aware that you are basically building an oven? 100W of heat will roast phones/watches rather quick... Each of your six lamps creates 15W of heat (11 initially and 4W in the form of UV light that gets converted into heat eventually), and since the walls are made of IR reflectors the items placed inside are going to absorb a lot of that heat.Ask yourself this: Is UVC really the best option for disinfecting food packets and phones? If you want to disinfect your phone you have to disinfect the handle of your chamber after you put the phone in (because it is now contaminated after you touched the phone), thus needing a disinfecting wipe-> Why not just wipe down the phone? UVC is only a valid option when every other method can't be applied: Mostly when the surface area is just too big to wipe it down (hospital rooms/fume hoods).Let's break it down: Which items need to be disinfected that don't react well to steam, dry heat or 70% ethanol/iPA water mixtures? And where can it be harmfull (N95 masks that are getting destroyed by UV/ other destroyed plastic in phones/possible exposure to high intensity UV radiation)?If you really want to stick with UVC consider buying on of those together with a timer clock:https://www.amazon.com/Inkbird-Thermostat-Temperature-Controller-Fermentation/dp/B015E2UFGM/A few cycles of heating the box up to 50 °C (to save the phones) should produce enough UV radiation, and you also have safety against overcooking.

author: robca
author_rank: Frequent Contributor
timestamp: June 25, 2020, 09:21:46 pm
content: I built a UV-C chamber at the beginning of the outbreak, mostly to sterilize things arriving from outside of the house (groceries, mail, etc)I have not used i as much as I thought for all of the following:When left at a normal room temperature, coronavirus is basically undetectable after 2-6 days (depending on the material). so, unless something is truly urgent, might as well just leave it in a safe "decontamination" area for a few daysUV-C ruins a lot of things, so can't be used safely on cellphones, and other stuff that in any case can be sanitized safely with 70% IPAThe only "dangerous" groceries are things that you put in your fridge, where the conditions are ideal for SARS-CoV2 to survive. But you can't expose those groceries to >30 minutes of hot lamps without creating worse health problems. Put those in the fridge, wash your hands, and cook them before eating hem (washing your hands after preparing them)Masks and fabrics cannot be sanitized with UV-C, because the light will not penetrate everywhere, even rotating the items a few times. Also, most of those are damaged by UV-C exposure, since all UV filters work mostly in the UVA-UVB spectrum: on a normal earth environment, all UV-C is filtered by the ozone layer. That's why UV-C is so effective: life evolved without need to worry about UV-C, and there's no defense.Masks can be safely sanitized by >15 minutes in a 70C oven, with no damage.Anything exposed to UV-C must be rotated multiple times, or suspended in some wayAlmost anything can be sanitized by time, heat, IPA or water and soap. In the end, the UV-C chamber has not seen much use