Biltong box - need to power a 100W bulb and a 12V fan

[frustin]

This whole project seems beset by a combination of insufficient knowledge, insufficient thought, insufficient research, and an apparent desire to overcomplicate and use inappropriate components. An LED driver for a fan?

A light bulb for heating?

What on earth is wrong with using a 230V 100W enclosure fan heater?

The light bulb (located at the bottom) for the box, which measures 900x500x400, is supposed to heat the internal area to roughly 60degsC. The moisture, from the drying meat, is sucked out of the top by the fan.

In that case an LED driver in the box will fail quickly. They are not designed to run in an ambient temperature of 60C.

I plan on running the electrics on the outside of the box. The fan will be mounted in the wall.

I have bought and mounted a MK Shockguard Batten Lampholder. The cable runs straight into the back of the box and is connected to the lampholder already.

My dilemma is really regarding powering the fan. However I've now bought a small junction box:
http://tinyurl.com/lguga5g

I just need the 230v to 12V converter now.

 

[frustin]

The light bulb (located at the bottom) for the box, which measures 900x500x400, is supposed to heat the internal area to roughly 60degsC. The moisture, from the drying meat, is sucked out of the top by the fan.

BAS is undoubtedly right in saying that the same could be achieved, 'more simply', just by using a 230V 100W enclosure fan heater - located near the bottom, with a vent at the top (as well as the 'input vent' at the bottom, for the heater) for it to 'push' the moist air out. However, where I seemingly differ from BAS is that I have no problem with 'improvisation', such as you propose, so long as it is done satisfactorily.

However, don't forget that, even with your proposed system, you'll need an input vent, probably somewhere near the bottom. If 'new air' can't be 'sucked in', the fan at the top will not be able to blow anything out.


Kind Regards, John

Thanks, yes I have some grated fan enclosures, which are mounted in the bottom of the box to allow air to come in.

I should also say that the bulb will not direct heat in one direction, as a fan heater would. My worry about using a fan heater directed up, would be that it'd cook the meat rather than dry it, which would not have the desired effect.

 

[stillp]

Try it without the fan. Hot air rises after all!

 

[stillp]

Whoops, posted before I'd finished typing!
If you really need the fan, why not a 230V fan?
http://www.maplin.co.uk/p/80mm-240v-main-axial-fan-yp46a

 

[frustin]

Try it without the fan. Hot air rises after all!

Indeed, but, despite having 80mm holes in the top walls of the box, the air flow might not be enough to draw the moisture out quickly enough. This would produce condensation and the meat potentially stewing/steaming/moisture dropping to the bottom of the box and causing a puddle.

The lamp is shielded by the way from any falling juices/food stuffs.

 

[frustin]

Whoops, posted before I'd finished typing!
If you really need the fan, why not a 230V fan?
http://www.maplin.co.uk/p/80mm-240v-main-axial-fan-yp46a[/QUOTE]

Definitely worth a consideration. There's no problems with using a fan of this size? Slightly concerned about how the power is distributed in the fan, are they prone to over heating that sort of thing. 12V fan seems a bit safer.

 

[JohnW2]

If you really need the fan, why not a 230V fan? http://www.maplin.co.uk/p/80mm-240v-main-axial-fan-yp46a[/QUOTE]Definitely worth a consideration. There's no problems with using a fan of this size? Slightly concerned about how the power is distributed in the fan, are they prone to over heating that sort of thing. 12V fan seems a bit safer.

The fan could be mounted outside of the box, pushing air in from the bottom (the air exiting through a vent at the top).

However, the main problem with using a fan which is 'too powerful' (in relation to the size of the heat source and box) is that it might simply blow out all of the heat, leaving the inside of your box at roughly ambient temperature! The fan size needs to be fairly critically matched to the size of the heat source (and size of the box).

Kind Regards, John

 

[stillp]

Many PCs (and servers) use mains voltage fans. They aren't known for being unreliable, and they certainly aren't unsafe.
The only advantage of a 12 V fan would be easier speed control, if you find that necessary, but if you needed to reduce the airflow then you could easily blank off some of the air inlet.

 

[JohnW2]

... but if you needed to reduce the airflow then you could easily blank off some of the air inlet.

That's true.

Kind Regards, John

 

[diyer56]

If you want something more substantial could you use an inline extractor fan?

 

[JohnW2]

If you want something more substantial could you use an inline extractor fan?

I would suspect that 'more substantial' is the last thing he wants/needs - as I've said, if he used a mains extractor fan the main issue would be restricting the airflow enough so as not to deafeat the heating.

Kind Regards, John

 

[frustin]

230V fan looks like the answer.

Thanks very much everyone for being so helpful, i'll post some pictures when it's finished.

 

[ban-all-sheds]

The light bulb (located at the bottom) for the box, which measures 900x500x400, is supposed to heat the internal area to roughly 60degsC.

What calculations have you done to show that a 100W light bulb will do that without needing a thermostat?

 

[frustin]

The light bulb (located at the bottom) for the box, which measures 900x500x400, is supposed to heat the internal area to roughly 60degsC.

What calculations have you done to show that a 100W light bulb will do that without needing a thermostat?

dry air is 1.00 kJ per kgC
the density of air at 30C is 1.2 kg/m^3
my box is 0.18m^3

0.18x1.2=0.216Kg of air
100joules (what the bulb is supposed to be producing)=1000 joules per kgC x change (delta) in temperature x 0.216Kg
delta temp = 0.1/0.216
delta temp = 0.46 degrees C in one second
temp @ 1 min = 27.78 degrees C in a 1minute

This obviously doesn't account for a lot of factors in things like wood insulation, gaps in the wood, how efficient the bulb is, but you can see that it's going to produce plenty of heat and i need to draw it out using the fan.

 

[JohnW2]

This obviously doesn't account for a lot of factors in things like wood insulation, gaps in the wood, how efficient the bulb is, but you can see that it's going to produce plenty of heat and i need to draw it out using the fan.

I guess that's what BAS was getting at when he wrote "...without needing a thermostat". As you suggest, you're probably going to be reliant on the fan (and probably adjustment of airflow through the fan) to get the temperature you want. Whether you'll be able to keep the temperature constant enough (and avoid the risk of it catching on fire!) without some explicit thermostat is another matter - if you want to carry on improvising, you could use an appropriate thermostat to control the lamp and/or fan.

You certainly would be advised to have something which would switch off the lamp before things became sufficiently hot to become a fire risk (whether due to ambient conditions, fan failure or whatever).

Kind Regards, John