Hello,
I recently got one of these cheap in the hopes that I can heat up a small box of greenhouse.
However I can't find much info other than technical information on these on the web.
Could anyone give some pointers? This is specifically the one I got:
Are these technically resistors?
Can I safely connect these to a 12V powersource? What are some safety issues?
What are their limits?
I'm planning to use a simple relay board on Arduino and turn on 12V for a small amount of time until I can heat. Or do I need to work with PWM and PID?
I would hate to use a solid state relay for this purpose since as far as I know when SSR's fail they fail with the line ON... Meaning the heater will be quite dangerous. Correct?
So far I got this element in between 2 large heatsinks and I use a fan to dissipate heat. Not sure if this is the right way.
What easiest way would you recommend?
yes, they should be purely resistive. I would definitely consider putting a mechanical over temperature switch in series with it bolted to the heat assembly for example so that if the fan fails or whatever, it shuts off (put a 12v light across the switch so you know if it trips). When you say "small box of a greenhouse" - are you talking about the volume of a small greenhouse or a planting box in a greenhouse? If you are looking for the planting box heater, there are heaters you can bury in the soil as well as (just saw these on ebay) "behive heater" (10w heated mat you put under the hive). The heater you show is designed to run pretty hot at 12v (for melting the stuff for a 3D printer). I would consider using two of them in series, but it depends on how much heat you are going to need to heat your project.
Hi,
I was talking about a small greenhouse actually the size of a large ikea box. Thanks for your help, I googled behive heaters they seem great but non available near my home. While searching for that I also found that carbon Fiber tapes and films were also an option. But that is not available near my home. However I found reliable aquarium heaters really cheap I believe I will go with these...
Aquarium heaters are usually meant to be submerged in water as a heat sink. I think you may find you have problems with them in air since that will not conduct the heat away from the heater fast enough so it will tend to cycle fast and over heat the glass envelope they are in (at least those are the ones I am familiar with). I did notice that if you did a search on "12v heater" there were a number of ceramic finned heaters listed designed for use in a car etc. Don't forget in dealing with 12v (if you are considering a battery source) something like a 50 watt heater (which does not sound like much) is pulling a little more than 4 amps from your 12 volt source.
I found a super cheap second hand aquarium heater and actually submerged the aquarium heater in water in a deep container, and also filled this container with Zeolite, which apparently has heat holding capacity. There are two main issues though, one is that the aquarium heater works super slow by nature, and also it shuts off around 30 degrees which is not enough to give heat. The Aquarium heaters were 220v * 100watts so the current isnt high enough for the relays. The higher watt aquarium heats are pretty tall in size, and I dont think they would fit this greenhouse / propagation box I'm trying to build.
Another method I tried was to use a copper pipe and put the 40w hotend cartridge heater inside this pipe. It worked pretty good but still 2 issues: since the head of the cartridge didnt fit perfectly there was some space between the copper and the cardridge, I think this caused some overheating on the head. And it also heats up too much too fast without a way to control how much it heats up using the mechanical relay...
Usually, you use a thermistor next to the hot end and turn it off once the thermistor reads 240c or so.
If you find that the box gets too hot at 220 you can just lower the off temperature.
I think a mosfet might be better than a relay for this.