Temperature stabilized bath for E6/C41
I have noticed a certain amount of interest in temperature stabilizing a water bath at 38C for use in the processing of color film. I did a very exhaustive search a while ago and found that many people were interested in modifying an aquarium heater for this purpose, with some limited success. I have come up with a different solution to the problem and would like to impart it to anyone who is interested.
My approach was inspired by a web site describing a homebrew sous vide cooking bath using cheap readily available parts: http://seattlefoodgeek.com/2010/02/d...-for-about-75/. I slightly modified the approach described in this article.
The heart of the unit is a digital PID temperature controller (model CD101) which is readily available on ebay - mine cost $28. The controller samples the temperature from a thermocouple or RTD (resistive temperature detector - basically a thermistor) and supplies an on/off signal to an internal or external relay which controls a heater. The signal is massaged to obtain the optimum correction to minimize the temperature error and improve the response to external temperature changes.
I use a plastic storage container for the bath whose volume is about 3 gallons. The developing tank and the mixed chemicals are placed in the bath - the latter in glass beakers in my setup. The sensor in my system is a platinum RTD (model PT100) in a sealed stainless steel tube - mine cost $6 on ebay. RTDs are preferred over thermocouples since the response is absolute, rather than the difference between two junctions in a thermocouple. The most expensive component was the 110 VAC heater, which is a 250 Watt titanium aquarium heater and cost $38. To keep the bath at a uniform temperature, I used an inexpensive aquarium pump, which works very well and cost $9 on the famous auction site.
With no tweaking, the unit immediately stabilized the bath temperature with an error of less than +/-0.1C (after a warm-up of about 1.5 hours). The controller unit I received used an internal relay, whose maximum current is 3 A (my heater needs about 2 A). This was adequate for my bath, though a 500 W heater would have been better (it would need the unit which powers an external relay). The relay clicks on and off: the on time is 10 seconds and the off time is about 5 seconds. A more powerful heater could equalize those times. (By the way, the ebay descriptions give little information on whether or not there is an internal relay - one should ask the vendor for this information). Using two identical BD oral digital fever thermometers, I verified that the maximum difference between the temperature at any two points in the bath is 0.1C.
One of the problems I had was that the temperature of the solutions in the beakers was 3F less than that in the bath. This was reduced to about 1.5F when I covered the beaker with aluminum foil. My (possibly crude) solution was to raise the bath temp. by about 1.5C (above 38C). I did some "dry runs" of the developing procedure using water and found that the temps were generally within the +/-0.3C for the first developer and certainly within the +/-1C for the color developer.
I have yet to try this on real film and will report my progress when I do. Feel free to ask questions or make suggestions.
try using stainless beakers instead of glass ones. better transfer of heat to the chemistry. You can get them through ebay as well . Make sure they're the type-316 s.s. tanks, not a more inferior quality.
could you post some pictures of your setup please? I'm re-reading through your description a 2nd time(because I'm interested in building a unit for myself to process color e-6/c-41 in), and I don't have a lot of $$$, or know-how on electronics/wiring....
Hi Dan. I did try the SS container approach, using my developing tank (an Arista SS tank) and found that stainless was better than glass but still had a temp drop of about 1.5F (if my memory serves me). I also found that SS beakers are fairly expensive (as much as 10x the price of pyrex). Since I had purchased a bunch of glass beakers, I wanted to find a solution which used them. (Being retired, I wanted to keep costs down).
It is currently after midnight - I'll post some photos tomorrow (and some more detailed descriptions). My approach is very similar to the sous vide article, though I put the controller into a separate plastic box (from Radio Shack) and included a power cord, fuse, switch and outlet for the heater to plug into.
Awesome Warren! I'm following this with high interest. Sounds much better than trying to find a Nova or Jobo! I notice the controller can handle a cold circuit too. In my area, this will be helpful in keeping b&w near 68 as well, once I figure out how to rig up the cold side. (Maybe use an automatic lawn sprinkler valve?)
One thing that would interest me is whether this has any impact on the final result. I have developed dozens of E6 film rolls in simple Jobo tanks, no external heating. I did make sure that the solutions had 38.0°C before I poured them. I am not aware of any development problems so far, but may not have looked careful enough or may just be happy with less than I could get.
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I just use normal daylight tanks on the counter.
Originally Posted by Rudeofus
I keep the chemicals warm in a stew pot on a cheap adjustable hotplate from WalMart with the water at about 103-105F.
I keep a separate thermometer in the developer.
As long as I pour my C-41 developer into the tank at about 100-101F I seem to get very consistent results. For E-6 I start at about 101-102F.
There are so many other variables that I came to the conclusion that the only reason for me to try to "nail" a perfect 100F throughout the cycle was to try and match exactly what I might get back from a lab. That is actually somewhat of a crap shoot anyway so... I don't bother.
Mark Barendt, Beaverton, OR
"We do not see things the way they are. We see things the way we are." Anaïs Nin
Phoththerm makes a nice bath like this, a container with integrated heater and circulation pump, and thermostat. They are expensive new, but come up on ebay and elsewhere fairly often and are pretty reasonably priced.
I searched completed listings on ebay for "phototherm" and found nothing. The homemade stabilized bath cost about $100 in parts and took about 2-3 hours to make. The hardest part is cutting the holes in the Radio Shack plastic box for the PID controller and electrical outlet.
I made a few mistakes, due to the confusing (to me) data about the controller. I thought they included both an internal relay and a control signal for an external one. The units have either one or the other and one must specify the desired option to the vendor (this might change the price). The controller was initially a bit tricky to program - one *must* download a sheet giving additional options and play around with the settings a bit. They actually make some sort of sense after a bit of experimentation. Once the unit is set up, changing the target temp is very easy.
Yes, there is the option to control a cooler as well. I think this is done using a solid-state relay which (usually) controls a thermo-electric cooler (TEC). One might be able to control a solenoid valve as well. Again, I think one must order a unit with both a mechanical relay output and output for a solid-state relay to accomplish this. I am guessing about this, as the documentation is a little sparse.
My reason for going to all of this trouble is the sense I got during my research that temperature control is very important for E6 processing. This was further supported by the very small errors for the developer temperatures that appear in the Kodak documentation. I have no experience in developing color film and might be overdoing things a bit. I guess this approach is due to my background (a retired physicist).
Last edited by warrennn; 06-24-2010 at 12:08 PM. Click to view previous post history.
I'm going to try it, because it sounds like a fun project and I tend to be a bit picky about temps. I used to have a Jobo CPP-2, in fact I have owned two of them in the past. Unfortunately, due to moves and remodels they are no longer with me (sniff...). I really appreciated the accuracy of the Jobo for E6.
My wife complains that I cook the same way... everything has to be perfectly measured and timed.
I hope the other posters are correct that E6 and C41 is more tolerant than the instructions indicate. I've never ventured "outside the box" with those processes, at least as far as I could tell with the Jobo.
Here are some notes on the construction of the stabilized bath.
1. If you use the CD101 controller, the following files should be downloaded:
The first gives the additional settings and the second is a general CD101 manual.
2. If you use a Pt100 sensor, follow the directions in the first file to tell the controller about it. The Pt100 leads are usually color coded and should go to the following pins of the CD101:
red: pin 10
blue: pin 11
yellow: pin 12
3. The wiring is straightforward. The hot side of the power cord should go to a fuse (~3 A) immediately when it enters the box. The hot side of the cord is black, the neutral is white and the ground is green. After the fuse, the hot side should go to a switch and then to pin 4 of the CD101 (with an internal relay). Pin 5 goes to one side of the heater (or an outlet in the box). The neutral side of the power goes to the other heater connection (or outlet). Pins 1 and 2 should also go to the AC power, after the switch.
4. Be sure you order the correct version of the CD101 - there are many versions with different options. I believe one wants the 110 V ac input option and the internal relay (if a 250 W heater is sufficient). If you need more power, get the controller with the relay driver and purchase a 7-9 volt DC relay with sufficient current capacity (the Radio Shack #275-005 for $4.49 should work: it can switch 12 A). If you use my wiring with the wrong version, you can destroy the controller.
Here are some photos of the bath and a close-up of the controller in its box (I used a Radio Shack plastic box, 3"x5"x7"). The bath photo shows the heater (a long tube in the center of the bath), the pump (on the right side of the bath) and the sensor (sitting in the right side of the bath). The numbers on the controller are the set temperature (bottom) and actual temperature of the bath (they are different since the bath is heating up).