Topic: Cheap and effective temperature control for developing C41 and black & white

[Kayos]

As promised in my intro post, I have written an article on how to achieve accurate temperature control very cheaply.

Disclaimer

This article involves mains electricity and water, if you are not 100% confident do NOT attempt this
I am based in the UK so please bare this in mind if you are considering this and are based elsewhere as things may be different

The problem:

We all want and need accurate temperature control for our developing, however its not that easy using hot and cold water while watching the thermometer and the stopwatch. My first attempt was to use an aquarium heater, however I soon found that it was inacurate and took far too long to react to changes in temperature.

The solution:

I decided to use a digital temperature controller, designed for process control it simply and effectively monitors the temperature and switches on the heating element when needed.

The exact one I have is this http://www.ebay.co.uk/itm/290971685906?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649  under £10



A few years ago these would have been very expensive but not now

I also have a small (50w) heater, in my final setup this will be replaced with two 200w heaters, so I can heat the water up faster
The heaters are just set at the maximum they will go to, printed as 37 dec C I have maintained a tank at 38 deg C for C41 no problem, but I have been using 25 deg C in the small setup

Below is a picture of a demonstration setup, I do not develop at the kitchen sink but the light is way better than my darkroom



I have it connected to a double socket so I can use two heaters for bigger tanks, the controller can switch 10A so even 400w of heaters are fine as it can switch 2.4kw in theory

As I said, this is a demo setup, currently the temp probe is hanging off my thermometer, I'm going to get a different sensor I can attach about a third of the way up the tank, as this give the best representation of the temperature

I intend to get a deep back box for the double socket and mount the controller in that, then extend the probe wires so the socket can be further from the tank. I will also screw it to the worktop in my new darkroom, making it a more permanent install.

I haven't included details of the wiring as its very simple, but if anyone wants them I will go into more detail

I hope this may be of use to someone

[ManuelL]

Interesting setup.

I only did C41 once and just used an aquarium heater. I used a bigger tub (I think it is a baby bathtub. It has more water, which keeps the temperature more stable and allows me to keep all the chemicals in the tub at the same temperature. It also has a very attractive colour  ). I developed at 25 degrees celsius. I would expect that temperature variations at the lower temperature are not so critical as the whole reaction is slower - but that's just my thought.

I agree that it would take too long to heat up the water just with the aquarium heater, so I kept adding hot water until I had the right start temperature. I also let hot water from the tub run over the chemical bottles to bring them to the right temperature more quickly.

[Kayos]

A bigger tub is easier to maintain the temp as theres more room for convection

I usually start  slightly over temp and put the bottles in, this tends to equalise everything, then leave the heater on to maintain it.

The finished version will be ready soon, this is just the demo

[jojonas~]

good tips, mr. KO! I was not familiar with these digital temperature thingies -something to look up for sure!
Thanks for the article

[Indofunk]

I haven't included details of the wiring as its very simple, but if anyone wants them I will go into more detail

Yes please ... I can't figure out where you would plug what stuff into that digital temperature controller ... just a circuit diagram or flowchart would suffice. Thanks!

[Terry]

This is excellent; thanks!

[jharr]

I was lucky enough to work in a lab that would throw out equipment on occasion and one day I snagged an oscillating heated water bath. The oscillator basket squeaks, so I took it out and just put my bottles in the water, but it heats up fast and holds temp +/- 1deg F. It also has a handy drain hose. It is probably over-kill for the amount of C-41 I do, but it's what I have. The temp controller is a good idea. You could even buy a sealed rope heater (tube heater?) and  probably gain some efficiency. Love the DIYers!

[Kayos]

Small update, i have lost the booklet but i will knock up a wiring diagram once my pc is set up again.

I will answer a couple of PM's I've had in this post too

Ive had a few issues with temperature drift, there is a correction option in the settings and the amount seems to be linked to the ambient temp, so once its adjusted it stays stable.

I chose the NTC type over a thermocouple one for several reasons.

1. Cost, NTC type are much cheaper
2. Simplicity, thermocouple types are generally more complicated and have features i don't need or want, they also cant switch mains directly so also need a relay which makes the wiring more complicated
3. Sensor  options. I can use any 10k sensor/probe and it will work, with any (within reason) length of cable, thermocouple ones are fixed as any join creates another thermocouple joint that will affect the readings.

Im going to try a better probe, one i can mount through the water bath and alter the temp correction to match, if i have to recalibrate every time i will possibly try a thermocouple type in the future.

Im currently building Mk2, along with setting up a permanent dark room

I have just developed a roll of Kentmere 400 and its come out really good, next up is some more C41 at 38 deg, rather than 25 deg, see if the comments on the interwebz about the lower temps affecting colour are true (i don't thing they are)

[Kayos]

Another small update

Firstly the temp sensor has been replaced with a better one, I can mount it through the side of the water bath plus its faster acting and more accurate


_MG_8343 by Kayos Photos, on Flickr

Secondly is the wiring, Ive uploaded a shot of the connections


_MG_8346 by Kayos Photos, on Flickr

1. Switch
2. Switch
3. Live
4. Neutral
6. Sensor
7. Sensor

Im currently on around mark 1.5, Im going to be dumping the aquarium heaters for 2 reasons, firstly I was sent the wrong ones and 300w has too much latent heat for maintaining temp (but is great for heating 11 deg c water to 37.8 dec c in no time) and secondly the glass is starting to bother me

Ive ordered some industrial style tube heaters, basically stainless heating elements that can be used under water, I have also ordered the bits to put it in a nice case with switches for the heaters as my plan to mount it in a pattress box failed due to a lack of space, so I might as well get rid of all the plugs too.

It is working out well when I use it, I wanted to be able to set the temp, warm the bottles and concentrate on the developing as I currently don't have running water where im working and its absolutely great, I just want a more permanent type of install and I will be happy.

Its still cheap too, even allowing for bits Ive bought and decided against its still under £50 and I do love building things that are actually useful