I would think the worst case scenario is being cold soaked. Power is off for a week. Power comes back on. -40 outside, the chip will be –40.
Pour some liquid butane on it to warm it up... From: Bill Prince Sent: Tuesday, May 19, 2015 7:47 AM To: [email protected] Subject: Re: [AFMUG] Enclosure low temperature How about actual data? For the last week, the ambient outdoor temp at this site has been between 50 (night time), and 60 (daytime). The SiteMonitor temp inside this 18x16x10 enclosure has been like below. So for at least this situation, it's been running between 10 and 20 degrees above ambient. The daytime temp is probably higher because of sun exposure. bp <part15sbs{at}gmail{dot}com> On 5/19/2015 6:34 AM, Chuck McCown wrote: Back to the original question, need more data. It is a question of physics. Jaime touched on it. Live load. Ambient temp. Thermal conductivity of the enclosure. Surface area of the enclosure. Wind speed at coldest temp. Thermal convection currents inside the enclosure. Thermal conduction currents inside the enclosure. Not trivial. Perhaps use some transistor grease and place a rectangular type metal plate resistor on the memory. Add a tiny bit of foil and insulation. It would take so little energy to get the memory up into the safe region that it could probably happen in a few seconds. As has been mentioned, the pre-heat on boot would certainly do that. Once booted, measure the temperature and heat or not heat. Be a fun experiment. The memory thermal mass is so small the resistor probably would have more thermal mass. You could get a 50 degree rise in maybe 5 seconds with 1/4 watt if insulated properly. From: Forrest Christian (List Account) Sent: Monday, May 18, 2015 8:09 PM To: af Subject: [AFMUG] Enclosure low temperature What is the lowest temperature that each of you would normally expect to see in your enclosures? The reason I'm asking is that I'm in the process of developing up a few new products. To date, all of the packetflux products are designed with components rated -40 to +85C (I.E way cold to way hot). I'd like to retain this rating, but I'm running into a minor snag: For storage, I'm planning on integrating a SD card (probably microSD) in a socket. I only need a GB or so, and SD card memory is inexpensive at that range. Unfortunately, all the reasonably priced SD cards are only rated down to about -25C or -13F. which are about ~$3 in qty. "Industrial temperature range" ones which are good down to -40C/F are available but they add at least $30 to the cost for non-name brand, and even more for known brands. When you're talking about a $100 end-user price, a $30 1GB SD card seems excessive - and probably isn't even possible if I want to meet the $100 price with some margin. So, I'm currently playing the 'what options do I have' game. I hate to ship a product only rated down to -25C/-13F, but I know for at least a large chunk of my customer base they never see below this temperature, especially when you add a watt of power dissipation in the case with the device. Which leads me back to my original question: What's the lowest temperature most people would expect to see inside their enclosures. -- Forrest Christian CEO, PacketFlux Technologies, Inc. Tel: 406-449-3345 | Address: 3577 Countryside Road, Helena, MT 59602 [email protected] | http://www.packetflux.com
