Vehicle battery as a power source

[James]

Warning: Don’t run the fuel tank dry when the heating element is turned on!​

Fixed the link now.
It’s 300w 12v
Instead of sand, fill the box with water.
Much lighter to carry home, although it is still heavy to carry it there.

 

[mainline]

I think it's going to depend on how large and hot the heat source needs to be for detection.

 

[James]

I think it's going to depend on how large and hot the heat source needs to be for detection.

Absolutely, if your trying to imitate a head sticking out of a trench, 10w in a 5 litre tin is fine, maybe a little bit too much.

If your trying to imitate a tank, 5000w is probably about right, maybe even a bit too small.

 

[brianmoooore]

Don't underestimate 15W of heat. My precision soldering iron is 15W, and it definitely gets hot.

 

[UKMeterman]

yes.
assuming it is a normal uk kettle it is normally 2 to 3kw at 230v
assuming it is 3kw
3000 / 230 x 12 =150watts

so it would warm the sand but not very quickly as it will only give out 1/20th of its normal power output as it is being run at 1/20th of its normal voltage.

P= (V*V)/R so the element resistance is 3000=(230*230)/R R=17.6 ohms, at 12V this will dissiapte 8W... as the current is 0.68A at 12V

 

[UKMeterman]

If you want something that is safe and less hassle than the kettle then try someihing like Arcol, 27Ω 25W Aluminium Chassis Mount Resistor HS25F 27R F ±1% | RS - https://uk.rs-online.com/web/p/chassis-mount-resistors/1860145?gb=s this will dissupate 5W, the same kind of heat as a sidelamp on a car and comes with wires ready attached. get it bolted to a small bit of metal say a couple of inches across after a few minutres I would expect a decent themal night site to see it from miles! To make 12V batteries safe you must have an inline fuse such as H7335 | iMaXX Fuse Holder | RS - https://uk.rs-online.com/web/p/fuse-holders/2884498 (holder) and a fuse such as 0287003.PXCN | Littelfuse 3A Purple Blade Car Fuse, 32V dc | RS - https://uk.rs-online.com/web/p/car-fuses/7874142 If you short out a car battery it will melt the offending item, probably cause a fire and the car battery may explode. RS have trade counters across the country and also do mail order.