Hi, Im new to this forum.Im planning to build a peltier cooler box where I wanted to use MOSFET IRLB8721 to control the current thru peltier once the set point is reached by using pid controller.Im using 2 peltiers ,so do I need to use 2 mosfet or 1 will be enough ? BelowI attached the schematic of the circuit.Sorry for bad my english .Tq
One IRLB8721 will work fine, but the schematic shows a different transistor.
You need a 150 Ohm (minimum) resistor between R1 and the gate to limit the Arduino output pin current to a safe value.
The battery won't last long and MUST NOT be discharged below about 8V, or it will be destroyed.
Thanks for the reply and regarding the battery, I'm actually quite aware of the battery supply ,but since my supervisor asked me to make it portable and light weight hence I found this is the only solution.Basically , to power up the arduino and fans,LCD im using separate battery supply ,my question is should ground both connections together or just leave it separately ?
If the arduino is controlling the FET then they must have a common ground.
How are you sensing and hence controlling temperature.
PID is designed to control BEFORE the set point is reached so that excursions beyond the set point are minimised. (They can never be entirely eliminated as you need an error to 'tell' the controller what effect to make)
As for the sensing I'm using LM35 sensor and it help to control the temperature according desired temp .Here I attached another part of the circuit
Just curious about how you are getting rid of the heat removed from the box and from the Peltier unit itself?
Paul
Hi Paul..Well as for the as for the heat dissipation , i used cooler fan where it is attached to the heat sink of the hot side.
Well, I think the biggest problem of my project is portability ,where I knew the battery will never last long but that is my requirement .So connecting it in series will help it sustain last longer a bit compared to parallel connections.If I connect the system in parallel, each TEC will draw about 3.5 amp where in series it will be 2 amps for both TECs.
Jackrau18:
Well, I think the biggest problem of my project is portability ,where I knew the battery will never last long but that is my requirement .So connecting it in series will help it sustain last longer a bit compared to parallel connections.If I connect the system in parallel, each TEC will draw about 3.5 amp where in series it will be 2 amps for both TECs.
The heat transfer is based on CURRENT. So reducing the current will greatly increase the cooling time and may make no cooling possible. The Peltier diode junctions create their own heat.
Paul
So, in that case i will just connect it in parallel and may try to get battery with bigger capacity
How big is the box that you are trying to cool and what is it insulated with?
Have you done any kind of thermal analysis on this project.
Peltier coolers are pretty woeful and inefficient at cooling things.
The capacity of box is about 15 Litres and insulated with styrofoam .Hmm , I have no idea about thermal analysis.
Well how much cooler do you want the inside of the box to be relative to the outside, as the cooling capacity of the peltiers is dependant on the temp differance and the efficiency of the insulation.
Whats going in the box to be cooled?
2-15 Celsius in the box ,where two small heatsink and two fans inside will help to circulate the cooler inside the box
I have no idea about thermal analysis.
Pretty easy to do for something like a styrofoam box. The basic equation is the same as Ohm's Law.
Heat flow in Watts through box walls = (Toutside - Tinside)*(area of box walls)/(R-value of styrofoam)
Mind the measurement units. R for inch-thick styrofoam is about 3.5 m2*K/W
The Peltier devices have to deliver that heat flow to maintain the temperature difference.
Can't help thinking some fans and a wet surface would be way better for battery operation. Unless you are
in a high humidity environment evaporative cooling is powerful and you can replace most of your battery
requirement with a water tank.
Okay thnx.But what about the circuit connection, incase if I want to connect two TECs in parallel , do I need two MOSFET IRLB8721 or one will do ?
do I need two MOSFET IRLB8721 or one will do
It is time for you to learn how to decide for yourself.
Consult the data sheet to discover that the maximum on resistance of the IRLB8721 with 4.5V gate-source voltage (RdsON) is 0.016 Ohms.
How much current will be passing through it?
How much power will the transistor dissipate as heat (I2R) ? Is that safe for the transistor?
How much voltage drop will the transistor produce at that current (IR), and how much will you tolerate?
