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.

 

[Drummo1995]

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.

Thankyou, will I have to attach anything to the chassis mount resistor? And how long can I run it on a 12 v battery before the battery dies

 

[mainline]

Thankyou, will I have to attach anything to the chassis mount resistor? And how long can I run it on a 12 v battery before the battery dies

View: https://www.youtube.com/watch?v=9mAmg0D5ArY

 

[Avo Mk8]

Thankyou, will I have to attach anything to the chassis mount resistor? And how long can I run it on a 12 v battery before the battery dies

It would be a good idea to attach the resistor to a small piece of metal, as advised in the post you responded to, but from the spec. the resistor is capable of dissipating 9W without a heatsink, so it shouldn't come to any harm if you don't.

How long it will run depends on the battery you use, and how healthy and charged it is. Your battery will likely be labelled with its capacity in Ampere hours (Ah). So as an example, if it was a 100Ah battery, it could supply 100Amps for 1 hour, or 1 Amp for 100 hours, or 2 Amps for 100/2= 50 hours etc. The suggested resistor would take (roughly) 0.5A, so the 100Ah battery would last 100/0.5=200 hours.

 

[UKMeterman]

The big question is how big do you want your target and how hot do you want your target?