Sterilizing masks with a Crock Pot slow cooker - Page 1
Forum section: electronics / projects

author: Peabody
author_rank: Super Contributor
timestamp: April 12, 2020, 05:24:26 pm
content: I'm seeing that heating a mask to 70°C (158°F) for at least 30 minutes will kill any coronavirus on the mask. I have an ancient Crock Pot from the 80's that I thought might be good to use for this purpose. Mine just has Low and High settings, and there are two heating elements. There are no thermostats, diodes, triacs, etc., just a switch with turns on one (75W) or both (150W) elements. I understand more modern slow cookers do have these things.Anyway, my oven thermometer tells me the Crock Pot on Low is still too hot - getting up to about 200°F. But I have a light dimmer that I used for years with my old Radio Shack soldering irons, and since this particular Crock Pot is just resistive, it seems it ought to work. After calibrating, I would turn on the cooker before I go to the store for food, and let it preheat, then just dump the mask into it for a couple hours when I get home. I think this temperature range should do no damage to the mask.The dimmer is rated at 600W. From the electronics point of view at least, does it sound like this would work?

author: ejeffrey
author_rank: Super Contributor
timestamp: April 12, 2020, 05:50:50 pm
content: Should work fine electrically. Two things to watch out for is that the heating element doesn't overheat when there is no liquid in the pot and that the surfaces may get substantially hotter than the air so you want to hold the mask up with something heat resistant with poor thermal conductivity to avoid local overheating.

author: wraper
author_rank: Unknown
timestamp: April 12, 2020, 05:59:13 pm
content: Quote from: Peabody on April 12, 2020, 05:24:26 pmNope since there is no temperature control. And heating element likely would burn due to lack of water. You'd be far better with using electric kitchen oven which normally does have it.

author: Gregg
author_rank: Super Contributor
timestamp: April 12, 2020, 09:01:07 pm
content: What you are proposing will work with diligent monitoring. You might want to put a few layers of aluminum foil on the bottom to spread out the heat and support the mask on something like an old coffee mug so it doesn't touch the crock. The dimmer will keep the heating element from becoming too hot. Maybe later either buy or make a temperature control.I have one of these:https://www.amazon.com/Inkbird-Max-1200W-Temperature-Controller-Greenhouse/dp/B01HXM5UACthat I use with a dimmer and a generic crock pot to melt chocolate; it works well.

author: Peabody
author_rank: Super Contributor
timestamp: April 13, 2020, 04:31:55 am
content: Thanks for the responses. It seems my stove's oven is a better choice, with temperature control and no local overheating.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 13, 2020, 04:04:16 pm
content: I was wondering if an Instant Pot could be used as an autoclave. You need 121C for 30 minutes at 15 psi of saturated steam. That takes care of just about everything. Not sure what the parameters of the Instant Pot are for various settings.

author: wraper
author_rank: Unknown
timestamp: April 13, 2020, 04:27:38 pm
content: Quote from: Conrad Hoffman on April 13, 2020, 04:04:16 pmIncluding destroying the mask. It might look OK externally after that, but air filtration will no longer be there.

author: Bud
author_rank: Super Contributor
timestamp: April 13, 2020, 06:06:48 pm
content: There was a lab test paper published saying 70C for 45 min does it. So no need to go beyond 100C. There are Exo Terra reptile egg incubators that go up to 60C, and i think with a little hack can be adjusted to 70C or just run it for a longer time. They also have a water tray to create moist, so instead of water hydrogen peroxide can be put in it to create vapours to further sanitize stuff.

author: profdc9
author_rank: Frequent Contributor
timestamp: April 13, 2020, 07:43:45 pm
content: I designed a heating unit that uses a light bulb as a heater. It seems to be better at not melting the plastic of the mask.https://drive.google.com/open?id=1NDP7rlqqLaXC3IBCSmcZSbiw1HuZUOUfIt uses an Arduino temperature control unit I designed as well.

author: wraper
author_rank: Unknown
timestamp: April 13, 2020, 07:51:16 pm
content: Quote from: profdc9 on April 13, 2020, 07:43:45 pmPCB layout is poor. You have low creepage distance between mains voltage and low voltage traces with completely no reason. Traces can be simply moved even without touching any parts and it would triple the creepage distance.

author: profdc9
author_rank: Frequent Contributor
timestamp: April 13, 2020, 09:18:59 pm
content: The only mains lines are the thick lines. How much further could I space them from the coil side? The trace is 1.5 mm in width, and there's about 3 mm width. 3 mm is good for at least 500 volts.https://www.smps.us/pcbtracespacing.htmlAnyways, I could see it could be improved, so I improved it. Thank you.

author: wraper
author_rank: Unknown
timestamp: April 13, 2020, 09:47:30 pm
content: Quote from: profdc9 on April 13, 2020, 09:18:59 pmThis PCB is not earthed, so you should use reinforced creepage. BTW you did not fix it completely.

author: profdc9
author_rank: Frequent Contributor
timestamp: April 13, 2020, 10:21:38 pm
content: Ok, I moved the relay away and moved the track. Should be ok now?

author: wraper
author_rank: Unknown
timestamp: April 13, 2020, 10:45:08 pm
content: Should be fine in terms of safety. BTW some pads you use are too small.