UPDATE: Good news and irony!
As reported in my previous post that even after 5 days of power up the RH stayed at 80% so obviously something still is not working and I checked the resistance of the thermoelectric module or peltier unit's postive and negative terminal after unplugging from connector showed zero ohm which mean a dead short. Yesterday I ordered a suitable peltier unit from Element14 at Taiseng rd.
order no: 2466914 and paid $30.20 gst.Since stock is in uk it will arrive between 3 - 5 business days.
Later at night I removed the peltier unit from heatsink assembly, cleaned up the heatsink compound from both sides of the peltier unit and measured the resistance to confirm...it had a resistance of 1.5 ohm and 3.9 ohm depending on the polarity of the meter probes! What the...so to really test if peltier is functional or not I plug it back into the control circuit and power it up at the same time holding it between my fingers,the adjustment pot is at 12 o'clock position in the middle of the blue range (recommended).I also noticed not only the red power Led is lit but the green Led too faintly.(I also check the components
of the control circuit and they all test functional from what I can guess)
Sensing no heat at my fingers I cranked clockwise towards the red range and
wow it got hot fast to burn my fingers.Turn knob back to 12 o'clock and placed the hot side on heatsink and power on again but now my finger is pressing down on the cold side with hot side on heat sink and now I feel feel peltier is getting cold! That means peltier is working. Note that when you turn knob towards red range (clockwise) the green Led gradually brightens.
I reapplied heatsink compound to both sides of the peltier unit and placed the hot side on the big heatsink assembly and a small heatsink on the cold side facing the inside of the cabinet.Do not over tighten the screws with the round plastic clamps to heatsink, just enough that the heatsink does not move or slide easily with a push of the finger or else you night damage peltier or worse crack the ceramic body.
Then I reassemble whole unit back into drycab and power up.Within 30 minutes the RH dropped 1%. It's encouraging...this morning after 7.5 hours the reading is 62% down from the starting 80%. Woohoo.. it's working although it's still far from the recommended 45% - 55%.After about 45 min. it dropped another 1% to 61%. As I looked at the hygrometer reading just now it's still at 61% so the RH is not coming down in a linear manner vs time but calculating by 7.5 hrs. 80% - 62% is a difference of 18%.If you divide 18 by 7.5 you get 2.4%. so ASSUMING linearly it will take another 16 hours to get to target range but I don't think it's going to happen but longer at current 12 o'clock setting or cold temperature.It may mean that to get to target range Rh (relative humidity) I need to increase the coldness but still remaing in the blue range.
A little about how a peltier works in a drycab, A peltier is a semiconductor device made up of P and N junctions.Please google for more detailed discription. It has a hot and cold side. Technically it is a heatpump. Depending on the polarity of the power supply at it's positive and minus terminals which side get hot or cold.The cold side is used in the drycab to attract moisture to form on the small heatsink that becomes cold instead of hot.Condensation (water) forms on it and if alot drips into the "cup" and overflows into the sponge "outside" where there is an open slot so that
water can evaporate with the help of heat dissipated by the big heatsink or naturally.Mostly like thsi will not occur as mositure is little as can be seen in photo.
Generally if set in blue range not much heat is produced and this means not much electrical power is consumed but if you want RH to change faster you can also crank up more meaning get peltier colder but at the same time more heat is dissipated.Since I'm a miser..haha I will monitor tommorow if RH falls or not to target range and adjust accordingly.
Photo below to show proof that drycab is working. To be continued...
Note: I did not attach the peltier cover as I want to see and monitor the peltier.
My standalone hygrometer is for comparison, reading is not far off (63% vs 61%) I don't care about temperature but I think drycab meter can be adjusted but I'm going to leave it as is.
View attachment 13453