# I want to keep a controlled temperature in a thermal bag

Discussion in 'General Electronics Chat' started by mediamedia, Dec 22, 2013.

1. ### mediamedia Thread Starter New Member

Dec 22, 2013
1
0
I want to keep a controlled temperature in a thermal bag.
I will use it mainly to transport tropical fish but it can all have other used like for picnics ect
Im a total beginner to circuit boards so be kind people
I need a battery operated heater which is controllable and is safe to put in the bag.It can be easily attached to the top of the bag in a self made pocket or pouch inside the bag
I will be very please for all the help I recieve from all you knowledgeable guys

Regards

Stephen

Feb 27, 2010
222
19
Don't they make heated socks that could possibly serve your purpose?

3. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,980
1,138
Heat rises, so the bottom of the bag might be a better location.
How long will the fish have to survive in the bag? Heaters are current-hungry so expect limited battery duration.

4. ### #12 Expert

Nov 30, 2010
16,705
7,358
Pretty much all we know right now is that it isn't a pizza.

Feb 27, 2010
222
19

Word brotha!

6. ### dmshropshire Member

Dec 1, 2013
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Metalmann likes this.
7. ### #12 Expert

Nov 30, 2010
16,705
7,358
The amount of water isn't important unless it isn't the right temperature in the first place and therefore needs to be heated. The important part is the "boundaries of the system", the bag. BTU = 1/(thermal resistance) times area in square footies times temperature difference in F degrees.
One watt second per second = 3.413 btu's per hour.

Suppose you have 3 square feet of bag surface, the bag has an R value of 6, the inside is 80F and the outside is 50F.
(30 x 3)/(6 x 3.413) = watts
In this case, watts = 4.4

ps, nice heater, shropshire.

Metalmann and dmshropshire like this.
8. ### ronv AAC Fanatic!

Nov 12, 2008
3,404
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Thanks #12. Never knew that formula.

And yes, cool (hot?) heaters.

9. ### #12 Expert

Nov 30, 2010
16,705
7,358
The "other" important formula in that series is for air.
BTU = 1.08 CFM dt
Again in F degrees, Earth atmosphere, cubic feet per minute.
It works rather well for heating air but falls apart for cooling air because condensation of humidity becomes a large factor. The good part is that we in electronics rarely have to get rid of coldness. Therefore the formula is good for validating fan forced air flow over heat sinks.