Mini-oven for your temperature controlled projects - Page 1
Forum section: electronics / general

author: DC1MC
author_rank: Super Contributor
timestamp: January 05, 2019, 11:29:59 pm
content: Sometimes I wanted to play with some temperature controlled stuff (i.e check tempco of some resistors or diodes) or just "grill" some precision things to accelerate the aging, the forum has quite a few interesting projects regarding this self-made ovens, but sometimes one wants a quick and cheap solution.So while searching fleabay I've found this ovenized quartz crystal, and while most of them are potted and mostly useless for anything else than their initial purpose, I've got a couple of them because they were costing very little.Long story short, it was a winning move, the device it's not potted at all, it can be fully disassembled and it has a 27ohm (cold) restive element and a thermocouple, the quartz is socketed and can be used to hold your device and the whole assembly can be easily opened and closed, when closed, it's reasonable watertight to keep your silicone oil in.12V/.5A raises the temperature pretty fast around 100C and I bet it could go higher, just wanted to get some really high resistance oil that can stand this temperature (suggestions welcome).For 2,95EUR in Germany, I think it's a nice solution for a small oven, and bonus points, one can use some inexpensive tube sockets to connect to it.Size of the whole device: 50 x 25 x 35 mm and the quartz frequency is: 56,99375 MHz (is it useful for something, or just some old military radio band ? ).Please look at the pictures for more details.Standard disclaimer: no connection whatsoever with the seller, just some happy customer and to comply with even more draconian 2019 EU rules, link removed, you should be able to find it yourself if you want one, or else PM me.Cheers,DC1MC

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2019, 02:22:30 am
content: "They don't make them like that any more!"That actually looks large enough to enclose many (most?) of the small adjustable (for example, raltron) quartz oscillators they sell inside of it. that might work pretty well if you were able to adjust the frequency to where it should be when at a temperature just a bit higher than ambient ever got and then used the application or reduction of heat to maintain it at that stable temp...

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2019, 07:55:01 am
content: If not absolutely needed I would not mess around with silicone oil. Even with just air, this should be good enough for a crude TC test of small DUTs.The crystal is almost certain getting the 57 MHz in a higher harmonic mode. The lowest resonance is likely much lower. So it would need a special oscillator circuit with another LC resonator to choose the suitable resonance.This is not a very common case and I don't know how stable it is - it may not be that bad, as 3 rd harmonics in the 20 Mhz range can be quite good. For bests performance the crystals are specially made to work at the oven temperature - so if at all the crystal would be useful with the oven, hardly without.

author: coppercone2
author_rank: Super Contributor
timestamp: January 12, 2019, 11:06:11 am
content: yea oil is nasty, if you need a liquid use flourinert. if you have the money.

author: DC1MC
author_rank: Super Contributor
timestamp: January 12, 2019, 03:55:32 pm
content: Quote from: coppercone2 on January 12, 2019, 11:06:11 amIs this this some 100$/ml stuff made out of unicorns tits juice?, any recommendations, I just want to play with some of my grab-bag resistors, some of them are really 500ppm/C ( I didn't even know that they make such things, and they are rally looking nice.But of the whole bag, I did find couple of EXTRAORDINARY stability pieces, including the 10000.01 ohm one, made by Dale for space and military, that internally looks like a small bobbin of some wire, with strange conductive and temperature compensating wrappings, that was almost impossible to move with temperature.In the little oven I use now some piece of thermoresistive foam saved form an old oven to press it against the wall, but I've thought that a fluid will allow for more uniform heating, and the first thing it come to mind was silicone oil.Cheers,DC1MC

author: Kleinstein
author_rank: Super Contributor
timestamp: January 12, 2019, 04:04:39 pm
content: Silicone oil is not really that conductive and it needs quite some gradients to get convection going. For low power parts, that don't produce much heat by them-self I keep them in air and rely on the thermal conduction of the case and radiation. For higher power parts I would consider a larger oven and a small fan inside.

author: DC1MC
author_rank: Super Contributor
timestamp: January 12, 2019, 05:03:48 pm
content: Quote from: Kleinstein on January 12, 2019, 04:04:39 pmThanks Kleinstein, for a permanent assembly this is, of course, the sane way of doing it, but I just wanted to have "something", that heats the device, either resistor or zener or voltage reference in an uniform way and I've read an old document linked somewhere in a metrology thread about measuring the tempco of pars with a bridge and a mineral oil bath.If you have any ideas regarding this, I'm all ears, everybody will benefit from your expertise.Thank you,DC1MC

author: coppercone2
author_rank: Super Contributor
timestamp: January 12, 2019, 05:33:01 pm
content: tips for flourinert : hard as fuck to seal and its surface tension is ridiculously low so it will get all over the place in a hurry, much worse then water, so it leaks easier too.Also expensive as fuck and it probably can get dirty so you don't want to reuse it without distillation.tips for using it: get expensive parts so you don't feel like a fool with disproportionate costs. use a swageed connector like hoke when you seal it.on the plus side its supposed to be fairly non toxic, evaporates easily, high boiling point. but it will eat certain plastics kind of. Otherwise it does not dirty very much compared to pretty much anything else.if its for testing I would highly recommend flourinert unless the components have sensitive plastic. for permament high voltage etc use silicone oil but it will be a bitch to clean in comparison. Oil just will make a complete mess and you will destroy a ultrasonic bath with it etc. Its just not friendly for the laboratory or even work shop IMO. Foams are particularly reactive with flourinert, and they will discolor on contact but when it evaporates it will be pretty normal just discolored.If you do get oil, be sure to buy some oil absorbing pads for clean up, and buy abrasive soap to clean your hands with, try to wear gloves, be aware of the fact that when you spill it on the floor its a extreme slip hazard and it will soak into wood with rather nasty hard to remove stains (i.e. particleboard). Work in a big tray and do a precise examination of your apparatus before you remove it from the tray to get rid of any oil drippings, after you seal it. When you use bottles or funnels with oil be sure to keep them in trays until you clean them so you don't set down a bottle on something that will drip down and mess it up. When you drain something of oil be sure to figure out how to build it so the oil will drain nicely and not get trapped in a nook/cranny so you can leave it upside down for a few days to get as much as possible out into a reclamation funnel before you take it apart to keep the mess down.Keep extra gloves and rags (in addition to the oil absorbant cloth) near your work bench when you work with oil in case you need to do something else do you don't grease the joint up.Also make nice funnels if you can that screw into the project and into your storage bottles so when you fill, you won't accidentally have a funnel tip on you and make a mess, or make a jig (like a laboratory ring stand). Make sure these funnels don't leak. Also it might help to warm up the thing you are filling with oil for a while (say 50C in the oven for a few hours) to clean all the moisture out.If you have more complicated oil systems you need to clean it gets more complicated but if its just a container that relies on convection/conduction without flow pumps etc then this should cover you.As for cleaning the parts after you drained them as much as possible, I don't really know. I would recommend using a dishwasher but you might not want to dump oil into the septic. I don't think you will have a fun time cleaning a ultrasonic cleaner after it gets oil into it . Not sure if you want to use break-cleaner on electronics and it won't do that good of a job anyway IMO, its meant to clean a flat surface. A nylon brush might end up absorbing some oil etc, it will be a pain in the ass without a dishwasher to do it right without alot of waste IMO unless its something small and easy to clean with a disposable rag.If you have a seperate machine shop ultrasonic cleaner then its fine, but don't put it in your electronics one. FYI the best way to actually clean steel for painting after its been cut with oil etc is to heat it up to 400C for a while then paint it while its still warm.......... its a mother fucker!Flourinert is expensive but it will just nicely evaporate with extremely low residues.Also if something is filled too much rather then trying to tip it etc try to get a transfer pipett to get some out before you do it, it will be much cleaner.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 12, 2019, 05:50:30 pm
content: Quote from: DC1MC on January 12, 2019, 05:03:48 pmHmmm. Old? Conrad's mini-metrology lab? That is still the way to go--mineral oil is non-toxic and readily available. I just keep some in the freezer and haul it out to dunk the resistors and measure the DeltaR using a DMM (we're modern, now!) and calculate tempco using the box method.Also, do you know about Wenzel's oven circuit? Easier than buying something off ebay! See tl431 circuit at end:http://www.techlib.com/Electronics/ovenckts.htm

author: DC1MC
author_rank: Super Contributor
timestamp: January 12, 2019, 09:03:19 pm
content: Quote from: RandallMcRee on January 12, 2019, 05:50:30 pmThat's the the document, Wenzel's the circuit is nice, but it's complimentary to the little oven from ebay, there are no more copper toilet floats around here and the metal body with heater resistor nicely assembled that can be sealed and has all the needed pins and stuff beats that piece of copper pipe used in the second design, for not too much more in costs. Also it has some mechanical stability, especially if one pours some oil into it (and has a cat).Bus as a newbie in the wonderful world of mineral oils, what kind of oil are you actually using, why do you keep it in the fridge?!? and from what I've heard, the silicone oil was recommended to sunk electronics in it being more inert and less prone to react with the part/wires isolation than other oils.Cheers and thanks,DC1MC

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2019, 06:34:15 am
content: Freezer so it does not get water adsorbed into it, as normally transformer oils are slightly hygroscopic, and you normally regenerate them by passing through a very fine filter to remove particulates, followed by running through a mixed bed resin to catch any salts and other ionic particles left there, then heating to over 100C to boil off the water that is left, followed by a final filtration step. Hard to do this in a small volume application, so much easier just to freeze the water out and keep it sealed when not in use.Myself I just buy refrigerant mineral oil. It is cheap, water free, additive free and available in a few viscosity grades. Will swell plastics that are not compatible, but works well with green butyl rubber seals that are common in refrigeration use. If totally sealed then you can use POE oil, though it is incredibly hygroscopic, and for applications where you only need heat transfer in a sealed system PAG oil works as well, though it is slightly conductive and hygroscopic.

author: JohnG
author_rank: Frequent Contributor
timestamp: January 19, 2019, 03:20:24 pm
content: My limited experience with silicone oil and fluorinert at some previous jobs...Silicone oil: You can never clean it up completely. If it spills on a linoleum floor, your shoes will squeak as you walk on it for years. It will spread everywhere and interfere with paints, other finishes, and some adhesives.Fluorinert: >$100 per liter, some kinds a lot more. You can lose gallons (!) pretty quickly through the tiniest pinhole...John

author: DC1MC
author_rank: Super Contributor
timestamp: January 19, 2019, 05:12:38 pm
content: Well, are there any non destructive or destructive AND expensive fluid options where I can submerge a resistor let's and NOT destroy it, the house and my credit together ?!?!?Cheers,DC1MC

author: nfmax
author_rank: Super Contributor
timestamp: January 19, 2019, 05:22:03 pm
content: Quote from: DC1MC on January 19, 2019, 05:12:38 pmIf the operating temperature is high enough, how about paraffin wax? An excellent electrical insulator, and pretty easy to clean if it spills. But remember that it expands on melting, so don't heat only from the bottom of the housing!

author: DC1MC
author_rank: Super Contributor
timestamp: January 19, 2019, 07:39:50 pm
content: Quote from: nfmax on January 19, 2019, 05:22:03 pmThat is an EXCELLENT ideaassuming that is confirmed it won't destroy or penetrate the usual coating of components, the temperature is ca 30-100C and the little oven that was the original topic do have a very uniform heating of the full surface, so we are gold here.Thanks,DC1MC