I use the cheap ones with no controllers all the time in my greenhouse and have never had any problem with them. I set plant trays with ridged bottoms right on top of the mats, put my little pots in the trays, and put a cover on them at night, take the cover off during the day. Been using them for years and haven't killed anything. And I do germinate cacao seeds that way.
Carolyn
thank u, its begginning to sound like not all of them do problems ,but prolly just some deffective ones. I havent had the time to try Seanny's sand idea, but bought trays yesterday and will need to do it. Yeah i am extra coutious about this since i will have to place this in my house, i could place it in my gh but its colder in there and will be more difficult to heat the seeds.
However i am not in such a hurry becouse the seeds are in a tiny greenhouse, a nylon over a radiator and then another layer of nylon over the seed tray with air space between them that is warmed by the radiator heat. They have been there for 3 - 4 days now and they are sprouting up slowly , the temp stays around 20- 24 .
I a day or tho the heating sistem will be turned off and i will have to use the mat then ...
You should monitor the temperature of the germination media, not only the mat temperature.
If the mat has no controls except on/off, can you put it on a plug in timer.
Some of those have day and night or dials to set multiple times.
well timing is not a problem since i am at home most of the time, its just the max temp that wories me, i tested it for an hour and right on the mat the temp was around 40 C , with room temp around 20. I know that the soil temp will not be as hot, especially when i leave some space between the mat and the tray, so in this case i may need all the heat that the mat can provide. I found by my test of it that anything in contact with the heat mat prevents it from exchanging the heat, thus creating hot spots.
I have the tendency of complicating things, but i got several ideas form the tread and will post what i ended up doing as a setup with the mat in a day or two.