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12 volt temperature controlled warming box

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delgriffith

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I'm trying to figure out a way to keep cell phones alive that sit overnight in vehicles that are parked outside in northern Minnesota. I was wondering how difficult it might be to engineer a temperature controlled insulated box that stays in the vehicle and is either wired in to the car battery or has a separate battery pack. I thought since it would only have to stay above about 35 degrees F for approximately 12 hours, it might not use too much battery power.

My first thought was to use a vacuum insulated food jar that I sealed the phone into at the end of the day when the vehicles were warm and parked for the night. My phone was frozen solid after last night in the vacuum insulated jar (it was -20F outside). I'm trying it again tonight with some pennies added to the jar, but I'm not optimistic.

Any suggestions much appreciated...

-Dave
 
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I think there's a risk something like that would kill your car battery. It is a heater after all and to overcome the cold takes a bit of energy (much more energy than like an MP3 player or some other electronic device). 0C might not seem to be asking too much, but you gotta consider that it's fighting the fact that the air outside is -30C.

WHat if you just threw a heat pack in with the phone into the thermos and use a thermos that is smaller (or wait do you want one that's bigger? Smaller is more surface area to volume to lose heat through, but less air inside to keep warm. Unfortunately, the longest lasting way to keep anything warm is through the use of fuel of some kind (and it's efficient too since it's the heat you need...not some kind of mechanical motion).

Why are the phones being left in the car overnight anyways?
 
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I just looked at the temperature in Minnesota, you're going to need a GIANT battery to keep those cell phones warm. Seriously though, check out some motorcycle handlebar grip heaters. Most have variable heat controls and will plug right in to the auto's accessory plug. I can guarantee Minnesota motorcycle and snowmobile dealers carry them. But anything that will keep a cell phone warm at those temperatures will need help with some decent insulation or the car batteries won't make through the night.

I just did a quick measurement on my heated grips, from Whitehorse Gear. A 6 amp hour battery would keep the grips heated at the minimum setting, about 1/2 amp, for about 12 hours. The minimum setting is fairly comfortable when it 20 deg F at 70 mph. So maybe the car battery might survive after all.
 
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I'm trying to figure out a way to keep cell phones alive that sit overnight in vehicles that are parked outside in northern Minnesota. I was wondering how difficult it might be to engineer a temperature controlled insulated box that stays in the vehicle and is either wired in to the car battery or has a separate battery pack. I thought since it would only have to stay above about 35 degrees F for approximately 12 hours, it might not use too much battery power.

My first thought was to use a vacuum insulated food jar that I sealed the phone into at the end of the day when the vehicles were warm and parked for the night. My phone was frozen solid after last night in the vacuum insulated jar (it was -20F outside). I'm trying it again tonight with some pennies added to the jar, but I'm not optimistic.

Any suggestions much appreciated...

-Dave

It's a simple question of insulation, my homemade yoghurt maker is a simple styrofoam 6-pack holder, and without any significant sealing I get about 3C rise per watt (it's a simple experiment to perform). You need about 30C rise or 10W. Double the insulation, seal the air gaps and you are probably down to 3W, don't know what you are prepared to draw from a cold battery.

One of the big problems is preventing heat escaping along the power conductors (remember that thermal and electrical conductivity go together), you could look at using a rechargable battery pack inside the cooler. No wires to the outside may reduce the power you need, 3W x 12hr = 36WH, some of the Li ion packs for video cameras provide over 40WH.

Alternatively, throw them into some insulation with a heat pack each night (you know the ones - iron powder and cellulose I think). Something like: Hotteeze.com.au - I've used similar - they are incredible. Depends on what fits your problem.
 
I'd just bring the phone in with me, but then again I'm from coastal California, what do I know about -20F :eek:

Lefty
 
I only ask because the OP said it was -20F outside hehe.


On the Pravda web site a few days ago they had a video on how to warm up a truck in Siberia. The first step was to pile wood under the truck then set the wood on fire. When the engine area was engulfed in fire they got into the truck and started it. It seemed to work pretty good. Might work for cell phones also.
 
I heard about some guy that tried it because his fuel line was frozen...that didn't work well.
 
Heat packs... main issues are the logistics and cost of keeping vehicles supplied with them. Trusting the employees to activate a heat pack when needed might be an issue also. And third issue is that they could be difficult to regulate to a good temperature. It looks to me like they could get hotter than what would be comfortable for a cell phone.

I was thinking perhaps if there were a tiny electric heating element I could install into the cap of the vacuum thermos, it might do the trick.... but it would be best with an automatic control system included.... lot of work(?)

We cannot "just bring the phones inside" due to logistics. Different employees take the vehicles each day, but the phone needs to stay with the vehicle. The vehicles are not parked near the main office either, so we cannot have employees drop off / collect phones from indoors before departure. Additionally we want the phones as close to "permanently installed" as possible due to issues with bonehead employees stuffing phones into their pocket and not hearing them ring, forgetting them at home, forgetting to pick them up in the morning, forgetting to drop them off at night, etc.


I wonder where I could source one of these things: Radioisotope heater unit - Wikipedia, the free encyclopedia That would be a perfect solution! ...except for the little radioactivity thing.
 
There is a 'cold pack' that you can buy ... the idea is to freeze the thing and then put it into a cooler ... in place of ice ....However, it also works to keep things warm. Just take it out and keep it in the heated vehicle cab during the day. Make sure that it is at least in the liquid state, if not warmer. At night, put it into a small lunch box insulated container .... or something similar. The advantage to this is that heat is liberated from the cold pack
due to a phase change from liquid to a solid. If one pack doesn't work, try two or three.
 
Ah ha.... Minco - Flexible Heaters; Flex Circuits; Temperature Sensors and Temperature Instruments

This looks a little more practical than the plutonium idea...

So toss the phone into the vacuum insulated jar and have one of these mini flex heaters rigged up inside as well. Ideally the phone's own battery could power the heater. By my calcs, I could get about 20 hours of 0.2 watts of heat from a typical cell battery. Not much, but inside a vacuum insulated jar it might do the trick. Further calculations necessary...
 
"We cannot "just bring the phones inside" due to logistics. Different employees take the vehicles each day, but the phone needs to stay with the vehicle."

Does that mean the keys to the vehicles stay in the vehicles also? Sorry, but it sounds to me like a management process problem/solution is what's really required rather then some klugy phone warmer.

If the keys stay inside, then there should be a way to store the phones and keys together and there be a check in/check out process that insures that the employees take and bring back what is required.

Lefty
 
If the keys stay inside, then there should be a way to store the phones and keys together and there be a check in/check out process that insures that the employees take and bring back what is required.
Lefty

Or just tie the phone to the keyring with a length of something (string, rope:D, chain :eek:, etc)
 
It appears the recent opinions advocate dumping the problem off on a supervisor or someone else in management.

Let management solve the problem ...hmmmm... has that ever really been a good idea?

Building a fire under the cars is by far a better idea. If something goes wrong your loses will be much less.
 
Does that mean the keys to the vehicles stay in the vehicles also? Sorry, but it sounds to me like a management process problem/solution is what's really required rather then some klugy phone warmer.
Lefty


No, the employees have keys for all vehicles, and the vehicles are not parked near any indoor location. There are about four employees per vehicle and the work schedule is such that there is no way employees could take phones home and still have the phone available for the employee starting out in the morning.
 
There are phones that are specified to meet this low temp requirement. Look into getting phones that meet the MIL-STD-810F spec.

I did my initial testing in the vacuum insulated food jar with a Motorola i355 phone. Motorola i355 (Nextel) Cell Phone reviews - CNET Reviews

it is a MIL-STD-810F phone. The problem is -20F is really effing cold, even for these phones. The battery is the weak link, mine is the high capacity one, and just 3 months old. It was fully charged when it went in at night but came out stone dead in the morning. The LCD display was also really struggling when it finally warmed up enough to power back on. It looked like a very bad thing to subject a phone to on a daily basis.

I did actually have some encouraging results with my latest test in the vacuum flask. I put pennies in with the phone last night and today the phone was actually on when I checked it after 12 hours. It wasn't very happy to be on, but it was on. I think maybe with a larger vacuum flask and more warm mass to put inside at night, it might be a viable solution.
 
How'd you know it wasn't happy? LCD screen? THat's just the screen. THey don't work well when cold.
 
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