I need to manually adjust the temperature of one hot and one cool 33W peilter module running from a 12VDC SLA battery.
Just doing it by feel, no calibration required. What is the simplest way to do this?
Has anyone tried a PWM speed controller such as this:
Any simpler ideas? Once adjusted no further tweaking required so could use fixed components.
Thank you,
Bob Randall
Hmm, You can't really adjust the temperature of a TEC. You adjust the electrical current.. which gives you a heat 'current'. The temperature of one side of the TEC depends what's on the other side... (Sorry you probablly know this.) So do you want to set the temperature or the TEC heat current? (Thermistor in a control loop makes easy temperature set point control.)
George H.
Hmm, You can't really adjust the temperature of a TEC. You adjust the electrical current.. which gives you a heat 'current'. The temperature of one side of the TEC depends what's on the other side... (Sorry you probablly know this.) So do you want to set the temperature or the TEC heat current? (Thermistor in a control loop makes easy temperature set point control.)
George H.
Maybe have a look at an adjustable electromechanical temp switch from RS or maybe farnell. They have a small temp sensing tube connected to a switch & temp setting control.
I wouldn't. Most TECs die very rapidly when you put them on a thermostat--there are dozens to hundreds of solder joints in series, and they can't handle the temperature cycling. Making a proportional control isn't that difficult--get a nice alumina RTD and attach it with a very very thin layer of epoxy or Krazy Glue.
The time constant isn't that long, so it isn't that hard to stabilize the loop. Make sure you put in an overtemp cutout, or your TEC will melt if the heat sink gets too warm. Ideally that would be a comparator running on the same RTD, and set a bit above ambient. That way the loop will always start up, but your TEC and payload will be safe.
If you really really want to use a thermostat, then run the TEC at some constant current and use the thermostat to control a heater on the cold plate.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
PWM isn't so good for Peltiers because it decreases the already miserable efficiency due to I^2*R losses. Less than 10-20% ripple is recommended. Maybe you could use a bench power supply or smething like that. IIRC, there are 'kits' minus power xfmr if you want something a bit more DIY-ish.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Setting the voltage on a TEC more or less sets the temperature difference. I would suggest a variable voltage power supply with current limiting as the way to go.
Use a buck-style converter (with inductor), but regulate on current. ...Jim Thompson
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I love to cook with wine. Sometimes I even put it in the food.
Just to amplify, a 50% PWM drive will drive (for example) 1A average and that sets the heat flow, but 2A peak. A filtered (buck-style) SMPS converter does 1A average, and 1A peak.
Cooling heatflow is the same in the two cases, but the ohmic heating losses
PWM: dissipation =3D 0.5 * 2**2 *R =3D 2*R SMPS: dissipation =3D (1)**2 *R =3D 1*R
Thus, unfiltered current to the device results in bad thermal efficiency due to the ohmic heating. The 'heat pump' thermal current term is the same in the two cases.
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