Fridge salami Experiment

[Oddley]

Ah but that would take all the fun out of it.

[Paul Kribs]

If all this comes together as intended, can we expect a detailed masterclass on components needed and methods etc.

I have a Maplin just 5 mins down the road so would be able to get components there. It's nearly a fortnight since I gave them any of my money.

Regards, Paul Kribs

[markh]

Oddley, I will try to sort out some images once I work out how I can get parts of my webspace freely accessable, I have only just gone broadband and have not yet sorted it out - Only just worked out how to access it myself! Don't hold your breath...

Sorry, going a bit techie again...

The kit is still in the construction phase at the moment, but I am using on the cold side, two alloy plates (approx 55 by 85 mm) fixed to a piece of acrylic the same(ish) thickness as the peltiers, which fit in holes cut to suit

The Wet plate has a water container - I am 'recycling' one of my 'La Chinata' paprika containers depleted in my chorizo episode

I am intending to use copper braid stacked inside to hopefully give a good wicking effect - like the fabric on a wet bulb.

On the other side of the acrylic, separately bonded so thermal leakage is through the plastic, the Hot sides of the peltiers are pressed against a single Heatsink - initially another bit of alloy 105 by 130mm with a 'Cooler Master' CPU cooler attached.

If practical I will try to add some heatsinks to the cold sides to improve the thermal coupling, and since I have some silicon rubber heatsink material left over from a previous project, I wont have smear everything with thermal grease!

Biggest problem is I dont have a decent insulated box to attach it to - I was going to use a plastic storage box for the test, but now think I would be better off (surprisingly) with a corrugated cardboard box!

Still, it is a proof-of-principle experiment

Will get back once I have some results - one way or another. In the meantime http://www.sensirion.com/en/02_products/00_products.htm?cat=3
offers some interesting possibilities for closed loop control.

[Oddley]

markh, You can always upload your images to http://imageshack.us/index.php and link to them. It is always difficult to share someone else's vision.

When I was looking into peltier devices, I noticed that they required really quite hefty heatsinks. Have you done any calc's on the heatsinks required, as the ones you propose seem a little small to me.

I think a corrugated cardboard box a good idea, that should give a reasonable level of thermal insulation. If it were me, I might be tempted to line the box with expanded polystyrene, for a bit of extra insulation. But as you say it's only a proof of concept experiment.

I also looked into the idea of a humidity sensor. But firstly it was finding somewhere to buy one at a reasonable price. Secondly keeping the device accurate, as from what I read they tend to wander off. Their accuracy sometimes, leaving something to be desired. If you decide to use one, I would be very interested in the outcome.

I think the idea you have is a good one too experiment on. The only downside I can see is the same one that put me off using the peltier device, it seems difficult to get more than 20 degs below ambient temperature. If you can get around the problem then you have it cracked.

[Platypus]

I don't know about markh but I was looking at a peltier needing to dissipate something like 70W:

Heat pump,CP1.4-127-045L 68.8W
RS Stock no: 618-730
Part No.: CP1.4-127-045L
�41.11

So I needed a fairly large heatsink. The one I found (without paying silly money) was:

Heat sink,0.43deg C/W 250x200x25mm 25g
RS Stock no: 490-7309
Part No.: S586/B/250
�14.14

This would still give a 30deg temperature rise if no fan was used.

I was thinking of controlling things from my PC using simple sensors and solid state relays. The RH sensor would probably be similar to this one:

RH sensor
RS Stock no: 407-7622
Part No.: HIH3610-001
�18.61

Regards
Platypus

[Oddley]

Hi Platypus, When considering a peltier device. I actually bought a coolbox from Macro's for �30 with most of that stuff on. I have always thought that RS were a little expensive.

The PC interface is an idea to consider. I don't know how my old woman would take too, more wires around the walls though.

How was you thinking of humidifying the box?

The wet and dry bulb thing of markh is a good idea if it works. But that means more expense with another peltier device.

[Platypus]

I know what you mean about RS, but when I'm looking at their website at work the boss thinks I'm still working

I hadn't got to the point of deciding on a mumidification method, but I like your idea of a fogger.

I have got myself a USB interface kit from Vellman which means I would only need the one control cable. It is a K8055 and has:
5 Digital inputs
2 Analogue inputs
8 Digital outputs
2 Analogue outputs

What temperature can your coolbox go down to?
At �30 could be worth getting one just to rip it apart for the bits

[Oddley]

Haven't really tested it. It says on the box it will go 20 below ambient. Whether this is true I don't know. I think it draws about 5 A so would be about 60W.

[markh]

I agree, the heatsink is the big problem.

The PC Chip cooler manufacturers dont tend to give thermal data, but I did a bit of empirical testing with the one I was using and with an ambient of 20.5 and a 20W input to the peltier (which also had a heatsink of unknown thermal resistance - I would guess about 8-10 deg/w, also in ambient - I was using it to clamp it on) and no thermal grease etc.

I was seeing a heatsink temperature of 23.6 and a cool side temp hovering around freezing. That's about 0.16 deg/w - I think the fan and extensive finning makes a big difference and being made in such quantity they are relatively cheap. (Even cheaper since the one I am using was scavenged from a PC being chucked out at work )

An interesting observation was that despite the module being rated at 50W, the lowest cold side temperature was achieved between 15 - 20W.

The RS data sheet I mentioned self-heating increases faster than the heatpumping capability and 'optimum' currents less than maximum, so I would guess this is expected.

Incidentally the Peltiers I am using are the 40mm ones from http://www.greenweld.co.uk/acatalog/Shop_Peltier_76.html. They are somewhat cheaper than RS!

Maybe you should go Bluetooth for control

I was thinking more in terms of a PIC device with maybe an RS 232 link just to set the required parameters.

[Oddley]

The peltier devices from greenwald are good value.

It's funny a cheap RS232 inteface was published in Everyday Practical electronics this month.

A pic base USB interface will be published in next months edition.

[Platypus]

I'd not come across greenweld before, they look pretty good and pretty cheap!

I think an afternoon of "work related" browsing is called for

Oooooh Bluetooth, now your talking

[Platypus]

Oddley,

Do you get the real version of EPE or the online one?

I have been toying with the idea of getting the online one but I'm not sure if it would be quite the same

[Oddley]

I get the online one, you are right it's not the same. I've got cupboards full of the magazine and am loath to get rid of them. The idea is to cut down on storage. Also you can crack the encryption easily and get the printed circuit legend for a light box etc. Not strictly legal but there ya go.

[aris]

What's being tried here is what is already done for wine coolers. They need a high hunidity to keep the corks from drying out. Perhaps we can take a chapter out of their book and learn something. Wine coolers are somewhat expensive.

http://www.wineware.co.uk/transtherm-1-temp-1.htm

[Oddley]

I have found the thread below, on another forum that might give people who have no electronics knowledge, a chance to dry salami in the fridge.

Apparently, if you enclose the salami in 1-2 brown paper bags at a temp of 55-60oF this controls the rate of moisture loss.

http://www.theingredientstore.com/foodp ... ?read=1407