I bough a "B-Grade" Sanyo Denki 120mm fan to find it was a 4-wire model offering rpm reading and thermall comprl. However the spec for the Thermistor is: and I am getting a little overwhelmed looking in farnell for an equivalent.
That's a bit of an odd value to find, you could try parallelling three 20k thermistors. Rapid do cheap (25p) ones with the same Beta. Or stick a 10k pot on it for a manual speed controller
From the spec I don't see a "-" so is that a PTC model or is the convention different? EDIT:This thermistormight be possible but Beta is 3300 vs 3950 required. I'm trying to think how this shunts the behaviour of the damm thing. EDIT: now reading http://www.betatherm.com/thermistortheory/betavalueb.htm
Oops. But I've actually picked out two 1k and one 4.7k which closer beta which gives me about the rigth resistance over 20-50C http://uk.farnell.com/jsp/catalog/viewproductdetails.jsp?prodId=679343 http://uk.farnell.com/jsp/catalog/viewproductdetails.jsp?prodId=679331 Should be ok, I guess. I found the formulae for thermistor resistance at a temperature and it was pretty close if done in series.
Ok now I'm getting into this........ The Fan spec say it will vary from 1300rpm to 2600rpm over 27.5C to 25C with that thermistor and flow above and below. according to the forumla: R2= R1/EXP(B*(1/T1+1/T2)) For this thermistor I have R(27.5C) = 6091R and R(35C) = 4424R So If I pick a new temp range of say 25 to 40 I should be able to solve for the B and R required.............................
....some time later...... Ok I remembered this project and propose to get onto it. My only (and critical question is: Does the thermistor go between 12V and the thermistor line in or 0V and therm?
Forgot the links! http://sanyodb.colle.co.jp/product_db_e/coolingfan/option/op.html http://sanyodb.colle.co.jp/product_db_e/coolingfan/dcfan/dc_fan_detail.php?master_id=565
Bump - any ideas. Afaik Papst V models have the themistor connected to +ve line, but those are PTC rather than NTC. Still not sure and see potential for disaster.
