"Safe" non mains heated propagaters

[Sandancer]

Heater element for electric propagator

Interesting question Seahorse!

Maybe you can design a heated propagator which uses a hotwire from a Ni-Cad battery?
If someone could sort out the logistics where you could use two batteries and always have one on charge at home, I would certainly be interested.

Failing that, hook a small generator up to a hamsters wheel and give him a bit more grub!
A windmill or a water wheel is also a theoretical option!

The insulated heating element is the critical component here, typically this component would use nichrome wire whose resistance increases with temperature. Using ohms law (V = I* R) with the 'hot' resistance and the voltage to be used will give the current drawn but this current will be much higher until the wire heats up as 'cold' resistance is less. There are a number of related issues which unless you can find something suitable already on the market (not impossible if you give a search engine the right question!) e.g. the capability of the power supply/battery.

[burnie]

Batteries and water are a dangerous combination, ni-cad and lithium batteries explode if submerged.

[Jay-ell]

Electric Heated propagators use about 15-25w of power each hour so would use up to 600w a day which would be 50amp hours.

I haven't seen any dc electric propogator but you could look at pet warming pads to see if they would do.

You might be better off starting them off on your windowsill and moving them to a fleece tent in the greenhouse

[boatsman]

Jay-ell,
I think you have made a mistake in your calculations. using 25 Watts per hour you would consume 600 Watts every twenty-four hours. But then, that amount divided by the mains voltage of 240 v would give you a total consumption of 2.5 amps.

[Jay-ell]

But we're not talking about mains voltage, I should have said at 12v it would be 50amp hours.

That's just for one day. If a deep cycle 12v leisure battery was used you would need at least a 100ah battery (they shouldn't be discharged to less than 50%) - in fact you'd need 2, one to use and one to charge.

[Snadger]

Do as the Victorians did.............use a paraffin heater or hotbed!