Isaac's Blog

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WMR968 Fan aspirated temperature sensor

I noticed my temp readings just didn't seem hot enough. I was able to validate this with my MESONET/CWOP data recently. I remembered some fan thingy a while back, AND i ran into the same fan thingy recently while trading some emails on wunderground. So heres the "fan thingy". After reading it, I realized this guy didn't really calculate any measurements. He just threw stuff together to make it work. So, like B.A.S.F.... lets not invent something, lets make it better!

12v for a 80mm fan is about 30-40CFM at around 160-200 milliamp (numbers based on which fan you actually buy). That's a bit much for this application. A 12v 800ma is a bit overkill for a 200ma fan. A full 12v runs about 2500-3000RPM. You could easily half all these numbers and get adequate airflow. Running a similar setup, I used an 80mm 12v fan, at 6v. Comparing the readings to nearby stations showed it to be doing the job perfectly.

My goal for aiming for 6v was to use a solar battery charger to run the fan 24/7. I ordered this Silicon Solar battery charger. Just add some leads from the batteries and I have a solar by day, battery by night.

Parts list:
~3ft 1in sch40 PVC (I chose schedule 40 over the other thin one, so there is less radiation)
1- 2->4 reducer
1- 2->1 reducer
1- 1in elbow
1- 1in elbow w/ 1 side NPT thread
1- 1in threaded male coupling
1- 1in T w/ 3/4" threaded center
1- 3/4" threaded plug
1- 12v 80mm fan (like the one from your old power supply)
1- THGR968, stripped from casing (mushroom sensor from WMR968)
1- 4AA solar battery charger
4- 4AA 2900mHA rechargeable batteries (anything over 1800 should work.... havnt tested this part yet)
~5ft old rj11 cable (2line/4copper cable). Any 2copper cable would work.
2- 3in "L" brackets
2- 1in overhead electrical conduit brackets
spray foam

I'll post pictures and more specific steps once I get the solar unit in and take picts. Thanks go to Garth Olson for giving me something to work off. (Btw garth, the third yellow wire is for getting the fan speed).

UPDATE: So the solar charger I got wasn't the one I ordered. Turns out the one I want is discontinued. Plus their "replacement" for the one I ordered only gets up to 4.73v in the bright light from the heat of a texas summer day. Lame. Once I get my RMA in and my money back, I'm going to try for this one: Flexible Solar Battery Charger (SolLite-4AAE). After googling/ebaying similar ones, this one ends up being lowest cost, AND is flexible for that nice hail we get in TX.

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