On Sun, 24 Jan 1999 15:41:47 GMT Mike Harrison writes: >Could this be due to them acting as a generator when off ? Would >shorting the pins during the 'off' cycle help? If you did that, the flow of current will reverse from normal, thus the pumping of heat will also reverse from normal. The cold side would warm up to an equilibrium faster than if the terminals were left open. There may be a few cases where this effect is desirable, but usually not. The cold side can of course be warmed up very quickly by driving current into the module in the reverse direction, causing it to pump heat to the cold side. The amount of heat pumped increases linearly with the current, but the amount of resistive heat generated increases with the square of the current. Thus the higher the current, the less efficient the device is. At some point, increasing the current causes a decrease in the net amount of heat removed from the cold side. The rated maximum current is just before this point. Simple applications like a picnic cooler just apply near the maximum rated current for maximum heat removal (but not maximum efficiency) all the time. There are two major ways to control the heat removal to less than maximum, either chop the current off and on between zero and maximum rated, or use a steady DC current. Realize that both methods become equal when maximum cooling is demanded. The difference only occurs at lower cooling levels. Using steady DC results in less power consumption and heat at the hot side than pulsed, so it should be used when these two factors are limited. Again, the difference between driver types is only apparent when less than maximum cooling is demanded. Overall efficiency in any case is greatly improved by keeping the hot side as cool as possible. This should be a major focus of design efforts. A switching supply is best to supply variable steady DC if the driver's power loss needs to be limited (e.g. heat from the driver contributes to the cooling problem, or input power is limited). If you are able to waste large amounts of heat and power in the driver, a linear regulator would do fine too. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]