Would like advice on heater for small bread dough incubator - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: December 24, 2020, 06:24:06 pm
content: I have a small refrigerator to which I added a digital temperature controller to keep more accurate temperatures and to allow control of higher temperatures (anything below ambient). It has been used to age cheese. I’ve now been asked to add a heater so that it can be used for rising bread dough. Maximum temp would be 37C (99F). The digital controller has heat and cool features, separate output terminals for both, provision for a temp gap between cooling and heating, and ability to set gap between cut-in and cut-out temps for both cycles. The inside volume is 0.11 cu m (3.7 cu ft). Power is 120 VAC, 60 Hz.I’d like advice on an appropriate heater element and small fan to use. These would be mounted in a small, perforated metal box placed in the bottom of the refrigerator. Compactness is important. Ambient temps range from 10C (50F) to 32C (90F). Rate of rise does not need to be very fast … 15 minutes to go from ambient to within 1C of set temp would be fine. Bread dough would be 21C (70F) to 27C(80F) when placed in the incubator. Temp sensor is suspended in air midway between top and bottom.I’m guessing 50 W would be sufficient. So a 100W, 300 ohm wire-wound resistor would be about right (48 W at 120 VAC). And use a 60 mm axial fan.I plan on running some tests with incandescent bulbs as heaters to get a better idea of the needed wattage. Can adjust resistor size accordingly. Would appreciate advice.Mike in California

author: tooki
author_rank: Super Contributor
timestamp: December 24, 2020, 08:13:35 pm
content: I’d look on AliExpress for PTC heater film. It’s thin as can be, but above all, being PTC, its maximum temperature is self-limiting, reducing risk of fire if the control circuitry should fail. Most of it is sold for underfloor heating, but it’s also used for shoe heaters, etc. I think it’s also sold for keeping outdoor electronics from getting too cold, and maybe for pipes as well.

author: fourfathom
author_rank: Super Contributor
timestamp: December 24, 2020, 08:39:44 pm
content: Is this a compressor-style refrigerator or a Peltier unit? You can reverse the polarity on a Peltier TEC and make it a heater.

author: calzap
author_rank: Frequent Contributor
timestamp: December 24, 2020, 09:17:21 pm
content: The fridge is an old GE with a compressor. I'll have a look at PTC film; I don't know anything about it.Mike in California

author: dcarr
author_rank: Regular Contributor
timestamp: December 24, 2020, 11:33:10 pm
content: Incandescent light bulb was my first thought. It seems you came to that conclusion as well so maybe there's something to it.

author: Nusa
author_rank: Super Contributor
timestamp: December 24, 2020, 11:42:00 pm
content: The only reason incandescent bulbs are semi-banned is because most people used them solely for illumination, dumping most of the energy as unwanted heat. But when you WANT the heat, they're extremely efficient. No reason not to use them for this purpose, if they physically fit.If space is tight, you might use something like this:https://www.walmart.com/ip/ABN-Silicone-Heating-Pad-120V-2-x-5-Inch-Universal-Engine-Heater-Pad-50W/503608503

author: Mr.B
author_rank: Unknown
timestamp: December 25, 2020, 12:05:42 am
content: A couple of years ago I built a bread proofing cupboard.I used a heater/fan combo very close to the AliExpress one below.Slightly different to your supply specifications - it is 12VDC 100W. But you could use a separate power supply.Nice small form factor: 60mm x 60mm x 42mm (2.4 x 2.4 x 1.7 inches)Fan independently supplied, so it can be always on.https://www.aliexpress.com/item/33051107352.html?spm=a2g0o.productlist.0.0.70281ce7tRFooy&algo_pvid=7d2a9e1f-187f-44db-bb0e-828db676483d&algo_expid=7d2a9e1f-187f-44db-bb0e-828db676483d-2&btsid=0b0a555716088541431543217ea186&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

author: Gregg
author_rank: Super Contributor
timestamp: December 25, 2020, 12:26:50 am
content: A long time ago I made a heater to keep my Celestron telescope from fogging on the corrector plate during cold nights, I used the silicone covered element from an old heating pad like you'd use for sore muscles. The element was about 1/8 inch diameter, about 6 feet long and about 35 watts. I used about half of the element material with a small 12V LA battery and a rheostat; it worked perfectly.If you have a thrift store near you, a used heating pad should be really cheap; try feeling for the heating element inside to determine if it is suitable. To spread the heat more, you could glue the element to a sheet of aluminum with some silicone glue.

author: wilfred
author_rank: Super Contributor
timestamp: December 25, 2020, 12:46:24 am
content: A basic breadmaker appliance does this so why not take the guts out of one of these? I have recently taken several apart and they already have a metal box a heater element and a temp sensor. Once you ditch the motor and drive belt they get much smaller. Some of the ones I took apart had separate PCBs for the control panel and drive electronics for the heater/motor.

author: fourfathom
author_rank: Super Contributor
timestamp: December 25, 2020, 12:51:32 am
content: The child's toy "E-Z Bake Oven" used a lightbulb as the heating element. Any resistive element should work fine as a heater, some advantages of a light bulb is that they self-regulate and are designed to run hot, and it's also pretty obvious when they blow out. But a properly-sized power resistor will probably be more reliable over time.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 25, 2020, 01:07:46 am
content: Use two incandescent bulbs in series in increase the lifetime. There also are ceramic "heat bulbs" often used for keeping pets warm.

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 25, 2020, 09:18:37 am
content: You might consider a reptile heating pad, for example,this 40W unit.

author: cdev
author_rank: Super Contributor
timestamp: December 25, 2020, 03:23:13 pm
content: You probably know this but this could also be used to make yogurt or kefir.Its best if you have a local dairy, to buy milk from. (Pasteurized milk is desirable, it doesn't need to be raw, and in fact raw milk may even be illegal. It can carry dangerous bacteria so use pasteurized milk!)I also would not be surprised if some/much commercial milk had antibiotics in it making it useless to make yogurt. The better the milk, the better the yogurt. You can also freeze it and freezing really good yogurt gives you really good frozen yogurt.You need a small amount of starter yogurt at the beginning. Get the best you can find. (or the whole effort is pointless)Some yogurts are really heavenly and much better than others.Here in the US "Chobani" brand yogurt comes to mind, as an example of spectacularly delicious artisan yogurt. I don't know if its available elsewhere.That would make good starter.

author: cdev
author_rank: Super Contributor
timestamp: December 25, 2020, 03:29:54 pm
content: Apparently, OCXO and other similar uses use TRANSISTORS, not resistors for the most precisely controllable and efficient heat. Look in the recent threads under OCXO and GPSDO to find the discussion.

author: Mr.B
author_rank: Unknown
timestamp: December 26, 2020, 02:10:23 am
content: You don't need precise control for bread.Commercial bread proofers usually have a bi-metalic switch thermostat.36 deg C +/- 1 degree is fine.

author: tooki
author_rank: Super Contributor
timestamp: December 26, 2020, 05:23:54 pm
content: Quote from: cdev on December 25, 2020, 03:23:13 pmYour post was going well until you called Chobani “artisan”. Chobani is certainly better than garbage yogurt like Yoplait, but it’s still a hideously sweet (for flavored variants) mass-produced product. The Greek style Chobani uses added thickeners. Etc etc.Above average? Yes. Artisan? Not in a million years.([I’m an American living in Switzerland.] For what it’s worth, I’ve never found any yogurt in USA that was quite as good as the best yogurt here in Switzerland. But of course, I don’t think there’s any country on earth that is as obsessive about its cows as Switzerland... Ordinary grocery store yogurt here is already above-average, but there is bona fide artisan yogurt here which is truly heavenly.)

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 26, 2020, 06:17:00 pm
content: I am not sure how Chobani manages it, but all their flavors I have tried tasted of lemon.How would you rateMövenipick's creme yogurt? They actually have Bauer (D-83512 Wasserburg/Inn) make the ones I buy in Northern Germany. I also buy Bauer's own production and quite like three of their four winter edition flavors (near the bottom of this page).

author: tooki
author_rank: Super Contributor
timestamp: December 26, 2020, 09:56:00 pm
content: Quote from: jfiresto on December 26, 2020, 06:17:00 pmI've never had it, and I don't actually think they even sell it in Switzerland. (The few mentions of it I could find on .ch domains appear to be archival content. It looks like they introduced it around 10 years ago. But the grocery chain here that used to carry it doesn't list it on their website any more.)Mövenpick is a strange beast — the original "fine dining for everyone" restaurants in Zurich (which launched the company) are long gone, and it seems the company has moved largely into hotels and brand licensing. (Heck, the famous, and IMHO overrated, Mövenpick ice cream was sold to Nestle almost 20 years ago. No wonder it's just modern industrial ice cream thickened with guar gum and citrus fiber instead of, well, cream and eggs.)

author: cdev
author_rank: Super Contributor
timestamp: December 26, 2020, 10:25:50 pm
content: When you return to the US, what yogurts do you like?Many years ago I had a Swiss girlfriend who was a chef at one of the best restaurants in the Mission District in SF and she used to tell me the same thing. For many years, while hanging out with a lot of Europeans, who were living there, including my next door neighbors, I also ate muesli as my default breakfast. Always in yogurt. I don't know if its sold around here in bulk as I used to buy it there. It was cheap in bulk.I think my friends used to buy the same yogurt I did. Nancy's Oh, those were the days!In San Francisco, I used to shop at the Rainbow Grocery, and was happy, after moving very far away, to see both Trader Joes and "Whole Foods" enter the area where I now live. Trader Joes is great and their prices are quite good.. but they dont have a super lot of variety when it comes to yogurt. They have basic, plain decent and cheap yogurt, which is unbranded, but which reminds me of Nancy's honey yogurt, from Springfield, OR. So its pretty good. But not so fancy. Or expensive.OTOH, since being bought by Amazon, it seems that Whole Foods, which was already pricey, has become more expensive, except perhaps for their house brands.But they likely do have a substantial variety of yogurts. That could be used as starters, I suppose. But they are so pricey, trying a bunch doesn't seem appealing like it would otherwise be. I'm weird that way. I suppose I am becoming a "cranky old man" *sigh*Quote from: tooki on December 26, 2020, 05:23:54 pmWhen I was a child, my mom and I spent a month staying in a village in Switzerland with a friend of my mothers. In a village whose name I still remember, Bienville Am See. She had a farm, and cows, as well as goats., And goat cheese, which was heavenly. Also, yogurt. All of which I remember. Also muesli. And tame deer. The local deer were tame, it seems. It was really pretty there.We have lots of deer here too, but they are not tame. Fortunately, because periodically they shoot them.So, I'm wondering what kind of yogurt would make a good starter, were we to start making it ourselves. If Chobani is used as a starter, whatever added flavors wouldn't, of course, propagate to the yogurt made. also it would vary depending on what kind of milk was used too.That might be a good choice to start out, because I know I like it. And I wouldn't have to give Jeff Bezos any more money.

author: tooki
author_rank: Super Contributor
timestamp: December 27, 2020, 01:08:12 am
content: Quote from: cdev on December 26, 2020, 10:25:50 pmHonestly, I'm not a huuuuge yogurt eater (if I have it at all, it's as a quick breakfast before work, eaten more or less against my will, before my stomach is awake, because I have to take a medication that causes nausea if taken without food), so I rarely buy yogurt when I'm back visiting. :/ I had Chobani because that's what United always gave with breakfast when flying over!Back when I lived in MD, I think I bought my yogurt at Trader Joe's.Quote from: cdev on December 26, 2020, 10:25:50 pmWas it Birchermüesli? (A common, basic form here is yogurt with grated apple, some berries, a bit of plain, raw rolled oats, some seeds or nuts, and a bit of honey if desired. It's such a common breakfast that they sell graters specifically for this, "Bircher graters"!)As an aside, the German spelling for muesli, "Müsli", is a corruption of the Swiss German "Müesli". What's amusing about this to a Swiss German speaker is that in Swiss German, "Müsli" means "little mouse"! ("Müesli" means "little puree".) Birchermüesli was invented by Dr. Bircher here in Zurich, so Swiss German was the original language.Quote from: cdev on December 26, 2020, 10:25:50 pmAmazon bought Whole Foods? Booooooo… (Fun fact: it was at a Whole Foods that I met the guy who'd ultimately become my ex-fiancé! And I had also dated another guy who worked at the same store. Who had also dated the future-ex-fiancé at some point… I'm sure there's some half-true joke about gays and WFM in there…)Did WFM's relative cost vs. ordinary supermarkets go up even more?!? Or did its prices go up along with overall grocery prices? (I've been kinda shocked on more recent visits at how expensive groceries in USA have become. When I first moved to Switzerland in 1992, groceries in USA werefarcheaper than here. That difference has largely evaporated — some things, like meat, are still a bit cheaper in USA, but others, like spices, are cheaper here now!)Quote from: cdev on December 26, 2020, 10:25:50 pmBeinwil am See? ("Beinwil" is pronounced "bine-veal", which I think is what your spelling was indicating?) Never been there though. But farms with cows and goats is definitely something you see lots of here!Tame deer? That's odd!Quote from: cdev on December 26, 2020, 10:25:50 pmAye. I have an uncle in the states who is a skilled hunter. He sometimes helps out on a farm in MD doing odd jobs. One summer around 1999 or so, there were so many deer that they were OK'ed to cull them. That summer he shot and butchered over 35 deer,all with a bow and arrow, since a gun didn't require enough skill to be fun for him.He could reliably hit a 3" target with an arrow from appreciable distance. (Since he and my aunt couldn't possibly eat that much venison, he kept the tenderloins and gave away the rest to struggling families he knew.)

author: calzap
author_rank: Frequent Contributor
timestamp: December 30, 2020, 03:44:44 pm
content: I conducted tests with incandescent bulbs to determine what would be a suitable wattage for turning the mini-fridge into an incubator. A ceramic bulb socket was placed at the bottom of the fridge. The temperature probe was suspended in air midway between the top and bottom. A small sheet of Al foil was placed a few cm below the probe to shield it from direct light from the bulb. The racks in the fridge are open grids. There was no fan.Results with 40 W bulb: zero time, 15.8C; 60 min, 31.6C; 120 min, 38.2 min; 180 min, 41.1C.Results with 60 W bulb: zero time, 16.4C; 60 min, 40.8C; 120 min, 51.4C.I conclude that a 300 ohm, 100 W resistor at 120 VAC (48 W output) should suffice. Resistor will be wire-wound and Al-encased, and I will attach a finned heat sink too. Resistor and heat sink will be in an Al case mounted with Teflon or ceramic standoffs. Ends of the case will have grids. At one end of the case, there will be a 60x60 mm fan which will blow air through it. Fan will produce another 4 W of thermal output in addition to mixing the air. May throw in a safety thermostat or thermal fuse too, and of course, there will be a ground wire on the case. I don’t think an electrical fuse is needed.Mike in California

author: cdev
author_rank: Super Contributor
timestamp: January 02, 2021, 01:29:58 am
content: Calzap, good luck on the baking! There is absolutely nothing as delicious as fresh baked goods!

author: calzap
author_rank: Frequent Contributor
timestamp: January 02, 2021, 03:30:23 pm
content: Thanks, cdev. We have a small goat dairy. In addition to being a national prize-winning cheese-maker, my wife is a state prize-winning baker. So, when she wanted a small cheese "cave" modified to heat as well as cool, it was a no-brainer.My usual way of making a cheese cave, is to buy a used, large, upright, non-frost-free freezer and a new, small window air conditioner. To do it, I remove the compressor and condenser coils from the freezer and modify the wiring in the AC so it will be controlled by a digital thermostat. Lastly, cut a hole in the back of the freezer and install the AC, carefully caulking it around the periphery.The mini-cave to which I added a heater is a little different in that it was/is a refrigerator and retains its compressor.Mike in California

author: Teledog
author_rank: Regular Contributor
timestamp: January 06, 2021, 07:38:30 pm
content: My apologies for dragging up an old thread, but I use W1209 controllers for heating/cooling (separate, of course).The W1209 are 12VDC units with an isolated relay, cheap like borscht on fleabay or WHY, configure to either control heating or cooling.I'd use a small reptile heating pad for an old fridge (there's also 12V silicone heater mats on fleabay)Lots of videos & instructions on the web as to the setup, they certainly are not PIDs, but for the price....pretty amazing little units!3D print .stl files on Thingiverse for the enclosures.G'luck!

author: vk3em
author_rank: Contributor
timestamp: January 12, 2021, 12:16:35 pm
content: Apologies for providing a late reply.I have built my own bread dough proofer, predominantly for proofing croissants but it will work for bread dough.I use heater cable as the heat element - the type of cable people use in roof gutters and industrial refrigerator drains to de-ice them - connect mains power and it generates heat - I am not 100% of power output per unit length, but you can buy the cordThe cord is sandwiched between two 40cm x 40cm ceramic tiles which act as a thermal mass/heat spreader.Let me know if you want further detailsCheersLuke

author: cdev
author_rank: Super Contributor
timestamp: February 06, 2021, 12:16:27 am
content: Small breed dogue incubator? Or pain au chocolat?How long does it take for them to hatch?

author: Renate
author_rank: Super Contributor
timestamp: February 06, 2021, 08:54:41 pm
content: Hey, what about quark?This Greek yoghurt has taken over which is just regular yoghurt hung in cheesecloth.Quark is basically buttermilk hung in cheesecloth.I used to make yoghurt in my Ford Pinto in the sunshine with the windows rolled up.

author: calzap
author_rank: Frequent Contributor
timestamp: March 02, 2021, 04:50:29 am
content: I decided to build my own heater. Perhaps I could have found something like it prebuilt, but a quick search did not turn-up anything. 50 watts would be plenty of output; I pretested that with various wattages of incandescent light bulbs.BTW a light bulb would not be a good solution because: 1. it’s fragile. 2. it would burn out eventually. 3. to make it touch-safe, thermal shielding would be needed which would make it bulky. 4. light shielding would be needed to avoid algae growth. 5. if moisture was dripped on it, it might shatter. 6. used alone, passive convection would be distributing the heat, which would necessitate bottom placement (OK) and there would be uneven distribution of heat (not OK).I decided to use a 100-watt, 300-ohm, wire-wound, metal-encased resistor as the heat source. At 120 VAC, it would produce 48 watts. I also decided to use a heat sink and fan to distribute heat evenly and quickly and to keep the resistor cooler. A 66 C thermal fuse protects against fan failure or other unexpected high temperatures. The resistor, heat sink and thermal fuse are suspended in the middle of an aluminum “tunnel” through which the fan blows air. I would have preferred fiberglass for the tunnel but would have been forced to buy 10 times more than I needed at considerable cost. The aluminum housing has some advantages: a. added weight makes it less likely to flip over, and b. it helps with heat distribution. The aluminum housing is connected to the ground wire of the power cord.The accompanying pictures show the innards as well as the completed heater. The plastics are as follows: 1. the thick base is high-heat UHMW-PE, 2. the two machine screws on top are nylon as are the two screws fastening the PE block to the housing, 3. all other structural plastics are PTFE. The thin piece of PTFE above the thermal fuse: 1. provides thermal protection for the nylon screws, although they should be able to take more than 66 C with no problem, 2. focuses heat on the thermal fuse in the event of a fan failure, and 3. provides electrical insulation between the thermal fuse and housing. The thin piece of PTFE placed under the mounting block provides electrical and thermal insulation between the heads of the stainless steel screws that attach the Al standoffs to the block and the housing.With a reasonable search, I could not find recommended standards for maximum size openings for the exit grill. The smallest maximum among manufacturers was 6 mm square. Many listed space heaters have much larger grill openings than this. I used stainless steel screen with 5.6 mm square openings and an open area of 78%.To check performance, I plugged the heater directly into a wall socket and waited over an hour for things to stabilize. It was drawing 0.4 A; so, 48 watts. I expected a bit more because of the fan; apparently it doesn’t draw much. Temperatures were measured with a remote IR thermometer. Ambient air was 19 C. Temperature of the housing was 20 C near the exit. Temperature of the center of the exit grill was 31 C. Temperature of the hottest spot on the fins of the heat sink was 72 C. Temperature of the thermal fuse was 31 C. The external surface temperatures (housing and grill) are well under the maximums set by UL.The controller will be the familiar STC1000, which will control both the heater and the refrigerator compressor. I’ve used these controllers in a number of applications and never had one fail.Mike in California

author: sam_sam_sam
author_rank: Contributor
timestamp: March 02, 2021, 12:44:02 pm
content: Quote from: vk3em on January 12, 2021, 12:16:35 pmWhere do you buy this type of wire

author: Nusa
author_rank: Super Contributor
timestamp: March 02, 2021, 01:27:51 pm
content: Quote from: sam_sam_sam on March 02, 2021, 12:44:02 pmLook in plumbing. Their most important application is to keep exposed water pipes from freezing.