What refrigerator to use - Page 1
Forum section: electronics / general

author: Bondguy
author_rank: Contributor
timestamp: February 03, 2016, 09:10:49 pm
content: We need to store anisotropic conductive film( ACF) in a temperature range of -10°C to +5°C. The size of the tape roll is only 10x10x1cm. It would not be good( economic) to store a such small thing in a common fridge. Does a micro refrigerator exist or a fridge with very low power consumption?

author: Halcyon
author_rank: Unknown
timestamp: February 03, 2016, 09:55:42 pm
content: Would a 12 volt car/camping fridge/freezer do the job? ARB make a 35 litre model capable of -18°C to +10°C. Also has a wireless temperature display:http://www.arb.com.au/products/fridges-camping-accessories/arb-fridge-freezers/According to the specs, power consumption is ~850mAh @ 12v and a temperature setting of 3°C.

author: Supercharged
author_rank: Regular Contributor
timestamp: February 03, 2016, 10:07:41 pm
content: Fridges normally regulate at about +5°C so you're pushing the boundaries of the thermal limits, so you'll probably need a freezer of some sort.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 03, 2016, 10:15:09 pm
content: The 850 mA at 12 V is something like 80-100 kwh per year, depending on the 12 V supply. That is about the same as a good quality (A++ in europe) small household refrigerator. The standard use might include opening the unit several times - so actual consumption may be lower. There may be slightly lower power small units (for something like a mini-bar), but the cheap ones can also need quite some power.

author: Halcyon
author_rank: Unknown
timestamp: February 03, 2016, 10:56:00 pm
content: Quote from: Kleinstein on February 03, 2016, 10:15:09 pmTrue, but you could probably even run it off solar during the day to cut down on consumption if it's really an issue. Their figures are also based on a 26-31°C ambient temperature (such as the inside of a car on a mild day). If it's sitting in an air conditioned office, that would probably cut down on power consumption as well.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: February 06, 2016, 01:34:27 am
content: you could just get a heat sink, lay it down with rows of peltier modules, put a fan on it for cross sectional air flow (like a video card cooler), then put a flat plate on top and make a little cover for it like a butter dish. Get some quality thermal grease for this one time build.You could easily make a 10cmx10cmx1cm chill chamber using like 6 peltier modules and I bet you the power consumption would be pretty reasonable, plus it would not take up much floor space. I think the entire unit could be like a 12x10x7cm cube.styrofoam is a good insulation to use for the cover.So long its in a reasonably temperature stable room I think that you can easily just use constant voltage to power the thing, your temperature range is pretty wide. Determine what works using a lab power supply then spec an appropriate dedicated supply for it. The thermal mass you need to cool is tiny, and it sounds like a long term storage requirement, so I think peltier cools are perfect for your application.

author: uncle_bob
author_rank: Unknown
timestamp: February 06, 2016, 01:42:59 am
content: HiI've been down this road a couple of times. What is the film worth? Is the price of the fridge small in relation to the cost of the material?Small "low power" freezers are not as economical as you might think. The compressor in a "real one" runs rarely and isn't all that high power. Even if the material cost is not a major issue, you likely are not saving much power. The next issue is that the little guys are designed for very intermittent use. A real freezer is designed for 24/7/365 use. I burned through a number of little ones before that became apparent ....Get a small top side lid lab freezer and use that.Bob

author: sarepairman2
author_rank: Frequent Contributor
timestamp: February 06, 2016, 01:56:08 am
content: If you just leave it on indefinably and find a point that it reaches a thermal equilibrium naturally (so low constant power consumption), this thing will run forever. Thermal cycling is to be avoided.Stick a thermometer in there and see what the minimum voltage you need to run it to get basically in the middle of your temperature range, so it is resistant to room temperature variations. I would try not to over complicate it with thermal control since it has such a wide range.Measure the current it draws during start up, run, and then fuse it so it will disconnect if something shorts out. You could also glue a thermostat inside of the device to disconnect power above like, say 10c.If you put it upside down and it turns out the power you need is low enough, it might be possible to run it without a fan (natural convection), or just maybe tilt the thing so hot air can get through it. The fan wearing out would probobly be your biggest concern for this system (just get decent peltier modules).I trust you don't need this thing to rapidly cool down the tape every time you use it correct? If this is a requirement then you would need to make a real control system, making this project time prohibitive.If you get sealed peltier modules you can probobly use phase change thermal pads (like silpad that melts) to get very good thermal transfer. If you do this then do not move the unit as it will drip. The stuff is conductive so get sealed modules if you do it, and never move the device when it is hot.You might also be able to use an over sized plate as the bottom heat sink, so the heat will radiate around the cooled part (it should not be a problem so long you make a nicely shaped piece of styrofoam to comform over your cold chamber. You can glue/tape pieces of styrofoam together for this and slap some aluminum tape on it so it does not get heated. I can suggest the pink stuff used for home insulation.Possible fanless alternativeIf you could groove the base plate to increase its surface area (or even stick heat sinks on it!) it would be even better. Do not use this peltier topology if you need to actually cool something that generates heat. All you need to do in this case is maintain a very slight gradient with no load, which should be possible. I don't feel like doing thermal calculations for you.The benefits of this are that it is noiseless, efficient and will have no moving parts/last indefinably. Dust it off once in a while and make sure the power supply works and it is good.You can easily detect a failure by measuring voltage/current/room temperature. Be sure that your cover seats flush and there is no air gap. You can also embed a thermistor/rtd/thermocouple in there so you can easily spot check the temperature as a regular maintenance procedure in your factory/workshop. Or turn it into a major project and add a microcontroller to measure it/read out temp/use some kind of PID control (over complicated for a work place project, however fun, and adds failure modes, do not bang bang control peltiers or you will destroy them).Flush seal = no condensation.use a larger thermostat then 10c or it will never start lol, like above room temp, to prevent your tape from melting at least if it breaks.