Winter is coming...

So I was about to purchase an electric blanket/pad to minimize my heating costs… but then I discovered a 12V blanket… Which started the hacking cogs turning…

Dual Purpose Bed Heating Pad?

  • Preheating.
  • Pwm / regulated power for subtle nightly warmth
  • Alarm/timer - Full power GTFOUTABED.

Existing hacks are really just controlling the blankets controller through button hacks… This seems safer for working with A/C

  • I would feel comfortable doing this with 12v but may be inefficient and require a big power supply (4-6a peak per amazon comments)

Thoughts? Collaborators? -This might be a good use for a free Teensy!

You’re sick. GTFOUTABED. Ha.

Yea I’m sure that worked so well for the frog in the boiling pot right ? :stuck_out_tongue:

That’s an excellent point. I’ve had the thermostat break on my waterbed heater and by the time it got hot enough to wake me up, I was seriously overheated.

Well, I slept on one as my primary heat source in China. They don't heat fast enough or get hot enough to be dangerous... Well, atleast not to me, I'm not on any sleeping pills!

I was hacking on one of these blankets for some project. I got one of
these from Amazon,

If you want some technical details, inside the blanket it's just a
wire (around 27 AWG) in a serpentine pattern (with a couple inches of
spacing). I measured 2.17A at 6.83V at room temperature (my power
supply can only do 2A). So that makes it about 3.15Ω or 46W at 12V.
The wire is copper, which has a positive temperature coefficient, so
at higher temperatures you'll get a slightly higher resistance and
slightly lower current. The wire is connected in series to two
bimetallic switches/thermostats. The model in mine is V7AM-020, which
turns on at around 45°C and turns off at around 65°C(!!)
( So
if you want to sleep on it (and don't want to smell like cooked meat
in the morning), you probably want to change them to lower temperature
switches, or better yet use actual temperature sensors or measure the
wire resistance to calculate temperature.

Jim! Thank you for tech details, I’m relieved I’m not alone on blanket hacking amidst the accusations of suicide by immolation!

So these two bimetallic switches… They are in series? So is one just for redundancy? I understand the switches, but are they implemented to regulate the current/temp some how? (45C turn ON?!)

If I wanted to PWM the blanket and monitor it with a thermoresistor, is it as easy as placing a power transistor (several amp rating) in series with the blanket? …I’d probably leave the bimetallic switches in place for safety

For the record, my anecdote was about “you won’t like being woken up that way”, not “you will die.” :slight_smile:

One option, that is no fun for makers because it doesn’t require making anything, would be to put the blanket on a relay timer and then layer it under a pile of blankets. That way the blankets and the unpowered electric blanket keep you warm all night, but then the power kicks on to wake you up.

And I have to say, my experience with this strategy is that you will always wake up sweaty, so you’ll need to shower in the morning.

I’ve considering making one of these:

It’s a low table with a heater under it surrounded by a blanket (or comforter) skirt.

Instructables has a couple articles about Kotatsu:

I’ve considered making one of these. I haven’t because it would require too much change from my normal routine. I might decide to drop the thermostat a lot more this winter and use more localized heat.

{I got a little carried away with this. Sorry for the hijack.}

A lot of my friends let their houses cool to 50-55F during the day. I use 63 or 64 with a bump to 68 around 7pm for 2 hours. (I arrive home late after work). At 9pm, it goes to 65 or 66, usually, but (embarrassed!) 71 for wake up and morning showers.

There are four daily temperature zones, and the times are adjustable:

The zones are: Wake, Leave, Return, Sleep (something like this—there are only four).
I use 6am, 8am, 7pm, 10pm
Temps are: 71, 64, 68, 65

71 is great for getting out of bed and showering.
68 is really nice for working at home in the evening. The kitchen is often warmer because of cooking. 68 is also pretty good for evening showers.
As the house cools off starting around 9pm (it’s a weird thing how the schedule programming works), you actually start to get sleepy. If you tend to stay up late, try dropping the temperature a bit early in the evening.
65 is really nice for sleeping. The thermostat is on the first floor, and I sleep on the second, so it’s actually colder in my room, which I love.
The cat doesn’t seem to mind 64, although I notice she favors sunny spots.

I never realized until writing this that I only really care about the temperature for 3 hours at night (after that I want it to slowly cool off), and 2 hours in the morning. That’s pretty cool. If there were kids around, I’d probably go for 68 from 4 to 8pm or 4 to 9pm. It’s pretty cool how just dropping the temperature affects kids—they get sleepy.

Also, I’m going to experiment with the 71 setting. That might be why I wake up sweaty. I’m pretty sure I arrived at it by experiment, but I’ll check it out. I’m thinking even if I use 68 I’ll still wake up sweaty because I’m bundled up under blankets for lower temps.

The real trick to all of this is that if you you’re off the normal schedule, or are just are cold, you can just change the thermostat and specify how long to hold that temperature.

When I’m home, like on Saturday, I use a blanket at the computer and for watching TV. Years ago I visited a friend whose wife was English. She said she didn’t like the American norm of having a warm house in the winter. She felt it was much nicer to actually wear long sleeves and sweaters. I basically agree with her, except for the morning shower.

One completely unexpected benefit of having a thermostat that varies temperatures on a schedule is that my basement is much much drier than it used to be. I really can’t explain why, but I think the longer warm-up periods cause the air to move more down there.

Also, if you want to add a thermstat with programming capability, they can be really cheap ($20-30) and really easy to install as long as your HVAC system is simple. Mine is a hodge-podge of new and old, and it’s complicated. If you have a heat pump, you might have to have it done professionally. The wifi-enabled thermstats are really tempting, but I’m gonna wait ten years (I hope) for the next big HVAC upgrade.

In 2007, I got a SEER 13 heat pump and a 95% efficient furnace. My circulation fan is on all the time, which I believe really helps. I get reports from Duke that my house is more efficient than others in my area, but I’m a little skeptical. I can definitely do better. I’ve got a lot more house than I need. I especially need to be more vigilant with setting a low temperature when I’m away for business or a weekend.

I think I’m going to experiment this winter with very low temperatures for the daytime and sleeptime. I want to see how much the temperatures actually drop—or if they stabilize (especially in the sun). What I think I want is for as little heating as possible when someone isn’t home, or is sleeping (it wakes me up sometimes). I’ve got a couple places where an extended “furnace off” time might cause a pipe to freeze. I’ll have to keep an eye on that.

Again, sorry for the long diversion.


Jim! Thank you for tech details, I'm relieved I'm not alone on blanket
hacking amidst the accusations of suicide by immolation!

Ha! I've been in some (heated) conversations over setting blankets on
fire as well.

So these two bimetallic switches... They are in series? So is one just for
redundancy? I understand the switches, but are they implemented to regulate
the current/temp some how? (45C turn ON?!)

There are two switches positioned diagonally at two different
locations, roughly 1/3 and 2/3 of the way, so that it's not responding
to temperature at a single spot. The switches have a "snap action" in
them for hysteresis. At room temperature they are normally on, but
turn off once they reach 65C; after that, they won't turn on again
until they cooled down to 45C; but after turning on, they won't turn
off again until they warmed up to 65C, and so on.

If I wanted to PWM the blanket and monitor it with a thermoresistor, is it
as easy as placing a power transistor (several amp rating) in series with
the blanket? ...I'd probably leave the bimetallic switches in place for

If you have a 12V/5A supply, you can just connect it directly to the
blanket through your relay, and PWM will ensure it stays in the target
temperature range.

Mathew: Some interesting diverging! I grew up in a house that had a thermostat set in a similar fashion… and it’s actually that morning heat which woke me up and has inspired this blanket!
Unfortunately my apartment has electric baseboard heaters with very simple integrated thermostats. Hacking these isn’t an option, I’ll likely just leave them set to LOW. Thus, the need for localized and programable heat! The kotatsu are interesting… and while I sleep on the floor like the Japanese… I don’t see this integrating into my lifestyle well either.

Jim: Thanks for the explanation! That makes sense now, and yes the power supply will be the biggest challenge! I wonder if there are any old PC power supplies I could scavenge around the Hive…

Has anyone used any of the donated Teensy factory seconds? Can you confirm if they are 2.0? 3.0?
(I’m thinking of using touch controls, the touchRead() on my Teensy3.1 is pretty nice!)

I was part of Duke Energy’s pilot program for programmable/controlled Thermostats… they aren’t all that expensive, and they used a neat cisco device (touch screen) so you could set the temp to an ‘away’ setting for when you weren’t home, you could even set weekends. It could also control your water heater if it was electric (turn down when you are not home)

I have also used the ‘blanket with a timer’ but it was an electric mattress pad ( better than a blanket) with a light timer, Set it to turn on just before you go to bed and you crawl into a toasty warm bed on a cold winter night.

You could just use enough Led strips to act as the heating elements and the light elements. call it the blanket of unapproachable light.

"It's time to wake up... HOLY CRAP IT'S HOT AND BRIGHT"

I think Jim’s idea is a winner.

Hmm Jim, I may have to leave an expansion port for a later pillowBright project! :stuck_out_tongue:

In other news I have commandeered an Xbox 360 PSU from purgatory, just an courtesy FYI.
It’s 14.2Amps and has a built in 5v for Teensy! USB Charging? I might as well design this into a charging dock!

The rf isn’t good for you. Keep in mind that some utilities send control signals over their lines. DC might be the only choice if you intend to keep it on. You will also need several thermisters and a failsafe shut off that kills the power if signal isn’t coming from all of the thermisters. Google for people burned by electric blankets.

Well, presently the IMMOLATOR is a bit of a dud.
I can sleep on it for about 7 hours before it gets too warm… coincidentally that’s perfect but requires a stable interior temperature. The blanket is just not powerful enough, and heats incredibly slowly.

I’m not sure that I will pursue further modification, as increasing power means increased responsibility…

If I did want to increase the output, is it as simple as increasing the voltage to the blanket?
Jim Chen, what are you doing to yours to keep food warm? -There is no way mine is coming close to those temperatures.

You could increase the voltage OR you could open the blanket and cut out a piece of the resistance wire. This will lower the resistance and increase current.

I’ll take, how to end up in a burn ward for 100. Seriously, if you are going to do any modifications to the device itself, test test test! Test it and test it again. Wrap 4-5 water cooler bottles–full–in it and measure their temperature over several consecutive days. The device itself is thoroughly tested before being approved for use. Get a second blanket if you want to increase the power output, don’t modify the internals of the device.

I’m not trying to be snarky, I’m just concerned about your safety.