small peltier based dehumidifier build

k2kaveh

Joined Jan 19, 2023
15
hello everyone! i've been trying to make a small dehumidifier with a tec-12706 and a bunch of fans and heatsinks i've salvaged from some old electronics

i live in north of iran in one of the cities beside the sea so we have a high amount of humidity here (higher than 75%all seasons,around 90% in summer)
i've been trying to come up with a small dehumidifier for a dry cabinet or something like that and i've been wondering if the condensation on the cold side has a direct relation with the size of the heatsink on the cold side?
i have tried multiple mixes with the fans and heatsinks
i've used H8 for maximum heat dissipation and h1 for the cold side and f3 as fan (marked all fans and heatsinks in the photo)
the combination above is the only one that condensates on the cold side
i have tried bigger sinks for the cold side. the cold sink gets cold but no luck on getting any condensation on them
condensation is the sign that the air is getting dried out, right? so what am i doing wrong here?

p.s: dehumidifiers are pretty expensive here,hence the whole thing with peltier going on

MrChips

Joined Oct 2, 2009
28,155
You don't need heat sink on the cold side.
It is important that the heat sink goes on the hot side.

Here is what you need to determine:

1) Ambient temperature
2) Relative humidity
3) Dewpoint temperature
4) Thermal mass

Let us assume that the ambient temperature is 30°C and the r.h. is 80%.
The dew-point temperature is 26°C.

Thus you need to get the cold side to below 25°C.
Let us assume that you can reach 20°C on the cold side and the hot side reaches 40°C. That is a temperature differential of 20°C. The TEC efficiency goes down as the temperature differential increases.

It is important that you keep the temperature of the hot side low for better efficiency. More importantly, the TEC will be destroyed if the temperature gets too high.

Now, on the cold side, the thermal mass is directly related to what it is that you are cooling.
If you put a large heat sink on the cold side, this represents a large thermal mass. You will not be able to reach your target temperature. You would have to install a TEC with higher power rating and increase the power output of the power supply to maintain the higher power requirements.

k2kaveh

Joined Jan 19, 2023
15
You don't need heat sink on the cold side.
It is important that the heat sink goes on the hot side.

Here is what you need to determine:

1) Ambient temperature
2) Relative humidity
3) Dewpoint temperature
4) Thermal mass

Let us assume that the ambient temperature is 30°C and the r.h. is 80%.
The dew-point temperature is 26°C.

Thus you need to get the cold side to below 25°C.
Let us assume that you can reach 20°C on the cold side and the hot side reaches 40°C. That is a temperature differential of 20°C. The TEC efficiency goes down as the temperature differential increases.

It is important that you keep the temperature of the hot side low for better efficiency. More importantly, the TEC will be destroyed if the temperature gets too high.

Now, on the cold side, the thermal mass is directly related to what it is that you are cooling.
If you put a large heat sink on the cold side, this represents a large thermal mass. You will not be able to reach your target temperature. You would have to install a TEC with higher power rating and increase the power output of the power supply to maintain the higher power requirements.

hey man! thanks for the tips
right now this is what i have tried and achieved:
i have used the biggest heatsink i have (h8) with a cpu fan on top of it to make sure that it doesnt get too hot since i did my research on what happens if you can't dissipate the heat correctly
the hot-sink gets cooled to the point that is warm to the touch
meanwhile the cold-sink gets cold enough (dont have sth to read it's temp with) to be counted as cold )
i've tried to contain the coldsink in a 9cm diameter x 11cm height plastic jar to see if i can catch condensations in it but it doesnt happen with other sinks except h1. and even though it happens the condensation doesnt get weight enough to be pulled down by the gravity force (at least that is what i have saw in typical small dehumidifiers)

i've been able to handle the hot side very well but i'm not sure if i'm getting any dried air out of the cold side

bassbindevil

Joined Jan 23, 2014
687
TECs are woefully inefficient as coolers. You'd be better off to find a discarded mini-fridge or water cooler.

k2kaveh

Joined Jan 19, 2023
15
TECs are woefully inefficient as coolers. You'd be better off to find a discarded mini-fridge or water cooler.
thanks for the advice but i have no plans to use it as a cooler, i want it to work as a dehumidifier in combination with the sinks.

bassbindevil

Joined Jan 23, 2014
687
Same thing, though. You need to chill something below the dew point, right?

k2kaveh

Joined Jan 19, 2023
15
Same thing, though. You need to chill something below the dew point, right?
this thing does chill below the dew point ( i guess?) but on the small sink (which condensates on)
i can tell that it reaches around 5 degrees on a bigger cold sink (room temp around 21) but doesnt condensate