I am starting to work on Peltiers....I am kind of confused on how they work. So, we heat (or cool, depending on your perspective) by applying DC current. To get the opposite effect (to cool when heated), we apply negative DC current. Here is where I am confused... Most peltier controllers use PWM, so that is not DC current.Well PWM is still DC current it just has a variable duty cycle switching from on to off, where the average on time determines the average DC current to the load, a peltier in this case. Correct me if I am wrong, but PWM chips (like the one found on MegaMoto) output PWM.Again PWM is just a form of controlling a variable DC. The only thing to keep in mind is that if you need reverse current PWM control, like for reversible speed control on a motor, or switchable heat and cooling for a peltier, the pwm controller must have a H-bridge output stage, that allows the switching of the polarity of the PWM current. If your load does not require reversing capablities then one can simple drive a switching transistor with the pwm control signal.Are we relying on the avg current to dictate the temp of the cooler? In other words, the faster the PWM goes, the more avg current is going into the cooler and vice versa. So, effectively, we are turning the peltier off and on at some frequency to get the temp we want to achieve. Is that correct?No, the switching speed (frequency) of the PWM signal does not effect the % of load current supplied to the load, but rather the duty cycle of the pwm signal determines the average current flow to the load. The ratio to on time to off time determines the average current, so 50% on and 50% off will supply half current capacity to the load, 25% on and 75% off will supply quarter current capacity, this is true regardless of the actual frequency of the pwm signal.Lefty
I am starting to work on Peltiers....I am kind of confused on how they work. So, we heat (or cool, depending on your perspective) by applying DC current. To get the opposite effect (to cool when heated), we apply negative DC current.
Since retrolefty did a good job covering the PWM aspect of your post, I'll dive into the theory a bit. Peltier junctions are devices based around the thermoelectric effect, specifically the Peltier effect, which describes how heat can effect the flow of current between two different materials. Like the Piezoelectric effect, the Peltier form of the Thermoelectric effect is a reversible process. Therefore not only can the temperature differential of a junction effect the current flow, the current flow can cause a difference in temperature between the two sides of the junction. With certain pairings of materials (e.g. dissimilarly doped semiconductors) this effect is strong enough to either cause a signficant temperature differential (i.e. heat one side of the junction, while cooling the other) if an electric current passes through it, or generate a small current at a specific voltage if a large enough temperature differential exisits accross the junction.Does this help you understand this part a bit better?