Warming problem with JOBO CPE-2 Plus

What is your room temperature? If it is < 15C the heater may have trouble raising the temperature _and_ combating heat loss.

Try using hot water to fill the tank and see if the system can maintain 38C. It should stabilise and cycle on and off. Do not assume that the temperature control markings are accurate. The element is intended to cycle on and off so that the temperature approaches the setpoint gradually and does not over-shoot.

It is normal practice to have the sensors right next to the heating element in water baths. Since the CPE-2+ does not have a circulation pump the most accurate peak temperature is near the element.

 

Stir the water occasionally if there is no pump.

Stand the unit on a piece of styrofoam to keep from loosing heat to a sink or countertop. This has helped mine considerably.

 

My darkroom is usually at 20-22C and my CPE2 has no problems maintaining 38-40C. When running at a high temperature I set my CPE2 to 1C above the temperature I need as the developer will fall by about 2 degrees as it runs in the tank. Test yours first with water to see what temperature drop you get over the development time.

The machine maintains +/- 0.5C precision thanks to the wonders of the high specific heat capacity of water and its consequent thermal inertia...

If you turned it on with no water in the tank before you first used it, it is possible that you damaged the heating element - Jobo specifically say that doing so will damage the machine.

Don't rely on the temperature dial settings: use a calibrated thermometer. I use two: one in the water and one in the developer bottle. Swish the water around every now and again to keep the two temperatures the same.

Place the film in the tank and spin it for 5 minutes on the CPE2 before putting the first chemical in; that way you bring the tank and contents up to temperature before the chemicals go in. If you have the lift mechanism, things are quicker and timing more accurate but if you don't have the lift and have to lift the tank out of the water bath to fill it, do so as quickly as possible.

If the room temperature falls when you open a window, don't open a window...

Have fun! Bob.

 

Dont trust the temperature dial. You have to use a separate thermometer. ON mine the dial was normally 5-10ºC out.

 

I'd endorse what Bob F said. Unless you want to wait for a very long time then don't rely on the element heating water from say 15-16c to 38c. Use water at about 40c then the thermostat will allow it to fall to whatever it is set at. I find the thermostat accurate to within about half a degree but you should use a calibrated thermometer at each end of the tank. Once the right temp is reached, mine stays there to within about 0.2 degrees C. As the tank is rotating immediately above the water and has water in it at say 39c, then the drop in temp over 3 mins 15 secs for C41 is going to quite small. This is especially the case if the film has been spun dry in the tank for 5 mins while you do something else prior to loading with developer.

pentaxuser