Originally Posted by Ultrasonic2 (muffy)
You've somehow made a connection between Qc watts moved and Watts used by the TEC to Move it, that simply isn't there.
Ok....and no I wont run away though I am getting a bit short....
All TEC's of the 127 couple use pretty much the same performance graphs whatever the Qcmax at the same temperature. It helps to use a low amp chart for a low to mid amp and a high chart for mid to high amp.
At the same temperature the graphs for other commonly available TEC's are also similar NOT THE SAME but similar enough to get ballpark figures most commonly available TEC's are 127 or 199.
Indeed to get ballpark figures one could take the charts of an average commonly available TEC. (and we all know there aren't too many of those...)
and either 1.) interpolate the figures you want to the axis or 2.) use percentages.
When using charts there is no point in basing everything on a delta 0Âº, I am in the process of arranging some sensors to investigate this further but after a discussion with a person who was knowledgeable on TEC's we agreed that all things being fair and average with reasonable watercooling one could hope for a delta of 15-20Âº I generally use 20Âº to err on the side of caution.
If you get a Heat Rejection chart at 50% Imax the total heat rejected is roughly twice Qc (with Qc being the pump at the operating point.) as the % of Imax goes up the internally created heat becomes more than the Qc and obviously as the % of Imax goes down the internally created heat becomes less than the Qc.
If you use a high Qcmax TEC (over 300w in my opinion...and there arent too many commonly available ones.) to get a Qc of 100w is roughly a third Imax so the from the charts as a ballpark figure the heat rejected is the region of 1.6-1.7 times Qc = 160w-170w (after all hardly anyone uses stock CPU coolers !!)
Now considering the OP's 225w 40mm TEC
A third of 225w is 75w then taking a worst case scenario i.e. air cooling isn't as good as water so I take a delta% of 30Âº so then go to the chart for the 40mm 225w TEC the OP planned to use 75w Qc with a delta 30Âº is about 13v so he doesn't want to run his TEC above 13v absolute max if he plans to use the air cooler stated in his first post, personally I would use water over 10-11v. I do realize 13v is about 50% Imax but assuming my deltas are about right at 50% Imax heat rejected = twice Qc which is 75w times 2 =150w
If you used aircooling with a low Qcmax TEC i.e. sub 100w you will probably be talking about the 12708 an 80w TEC if you used it at full power the heat rejected would be about 185w which would be pushing an air cooler
So once you digest all this a high Qcmax TEC with an operating point of a pump (Qc) of 100w is around about the max you can put on it and the biggest TEC you can run at high power (no-one runs them at full power.) is one with a Qcmax of 100w....so to keep it simple 100w is max pump you can use on an aircooled TEC.
It may not be acceptable for those in the world who dot there i's and cross their t's but as a working ballpark figure it would seem quite acceptable.
ON HINDSIGHT:- if demonkev666 is saying that 150w doesn't seem the correct rating for his cooler as it was used to overclock 4 core CPU's he is forgetting that as a cooler on a CPU there is only the heat of the CPU and once a TEC is added to the mix.....150w is getting on for or greater than half the Qcmax of the commonly available large TEC's which as it happens when looking at the charts with a delta of 20Âº is roughly half the Imax so the heat rejected at 50% Imax is twice Qc which makes 300w and I don't think any air coolers can cope with that. So while air coolers may be rated at higher than 150w there aren't any TEC's that can be undervolted to take advantage of it.Edited by zipdogso - 4/13/09 at 6:13pm