DIY Precision Dehydrator

[Kevin Liu]

Alright folks, I could use some help on this project. I've perused through the existing Food Dehydrators topic and found some useful nuggets, but nothing approaching the scope of what I'm interested in.

I would like to build a simple dehydrator that is able to control both temperature and end humidity (the two most important variables in dehydrating) precisely.

For temperature control, I would like to use a hairdryer or similar heating element hooked up to a PID controller, with an appropriate thermocouple to measure temperature.

For humidity control, I doubt it would be feasible to set up some sort of steaming element, so I'm thinking something along the lines of "given an end temp of 60C, add 50 mL of water to a dish and once it's down to 40 mL, you should be at a relative humidity of 80%..."

Ideally, I'd like a cheap, simple system that could make strawberry fruit leather one day and powdered strawberries the next. Does that make sense?

Some specific questions:

- What thermocouple would be best for this situation?

- Would it be useful to somehow measure both the wet bulb and dry bulb temperatures?

- Will a hair dryer work or would a different heat source be better?

Thanks very much in advance!

[dcarch]

Hair dryer is not a reliable long lasting heating device. An inexpensive convection oven would work better. The PID controller can take over the convection oven's thermostat if you set the thermostat at the highest.

Why world you need to control humidity? You always want the air the driest.

To dry air at lower temperature, you need to have a refrigeration cycle to dry the air and then reheat the air to accelerate the dehydration.

dcarch

[andiesenji]

This seems just a bit like reinventing the wheel. I don't really see the point. Reliable dehydrators that are affordable have been available for decades.

A "simple" dehydrator can be just a vented box with dividers to hold wire trays and a small room heater with a thermostat. Something like a "barn" heater would work for a large volume box.

On the farm we used a couple of brooder heaters in a shed when we had to dry fruit in rainy weather.

A hair dryer is not intended to be run for lengthy periods. Neither is a heat gun.

The fans in dehydrators turn at lower rpms than in regular room heaters and are designed to run for days without overheating.