regarding heating of peltier elements - Page 1
Forum section: electronics / projects

author: msrinivasan1995
author_rank: Contributor
timestamp: July 18, 2017, 06:38:20 am
content: I want to heat a aluminium block using peltier element which temperature is switched from 70-90'c and vice versa for continuous cycle. Max current rating of peltier is 8A. I wanted to know how to control the current to the circuit so that the the peltier can be heated to the required temperature and change its current value to reduce the temperature. The current rating to the peltier must vary from 6-8 A regularly to increase or decrease the temperature. Which circuit can be used to complete my application. Suggestions are welcome.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 18, 2017, 07:09:32 am
content: If you just want to heat a chunk of aluminum why go to the cost of a peltier when a simple power resistor would do the job ?

author: sdouble
author_rank: Frequent Contributor
timestamp: July 18, 2017, 07:15:56 am
content: usually peltier elements are used to cool down stuff.

author: msrinivasan1995
author_rank: Contributor
timestamp: July 18, 2017, 07:28:38 am
content: Quote from: fourtytwo42 on July 18, 2017, 07:09:32 ami want the block to be heated uniformly.Quote from: sdouble on July 18, 2017, 07:15:56 amit can be used to heat also, by using the other side instead of the cold side.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 18, 2017, 07:32:02 am
content: Quote from: msrinivasan1995 on July 18, 2017, 07:28:38 amuse many resistors evenly spaced? cheap and low power consumption, but... since you are rich, who cares?...

author: msrinivasan1995
author_rank: Contributor
timestamp: July 18, 2017, 07:39:58 am
content: Quote from: Mechatrommer on July 18, 2017, 07:32:02 ammy block is 40*40*20, i dont think power resistor would do it. peltier coster around 20$, this is for biomedical device not for simple operation , accuracy is of high importance.

author: Someone
author_rank: Super Contributor
timestamp: July 18, 2017, 07:55:26 am
content: Quote from: msrinivasan1995 on July 18, 2017, 07:39:58 amThe controllers are off the shelf parts, for example RS 809-0991. As a suggestion buy a temperature controller with a PT100 sensor for temperature accuracy, the controllers are available in various output types and you can always add an additional solid state relay for DC applications.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 18, 2017, 09:19:24 am
content: Quote from: msrinivasan1995 on July 18, 2017, 07:39:58 amthey would. but...Quote from: msrinivasan1995 on July 18, 2017, 07:39:58 amas expected... below is half the price, with the right controller can make super many heating element of your size but...http://www.ebay.com.my/itm/NIC-1206-Resistor-1-Ohm-5-Reel-NRC12J1R0TRF-5000pcs-/161849051692?hash=item25aef48a2c:g:exkAAOSwAodWEvhvQuote from: msrinivasan1995 on July 18, 2017, 07:39:58 amyou dont get any accuracy from heating element, however expensive however cheap... what you need is closed loop feedback, here below easily available, but i'm not sure if its configurable PID parameters... ymmv...http://www.ebay.com.my/itm/220V-Digital-LCD-Temp-Temperature-Controller-Switch-Thermostat-w-Sensor-/142058801500?hash=item21135d495c:g:UnIAAOSwtnpXjaev

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: July 18, 2017, 09:56:16 am
content: We use TECs in cooling of camera sensors for Astronomy. Of course you can use them in reverse. In general if you want good accurate control there are basically 3 ways: PID; PWM; or Thermostat.PID basically using a controller to control current and voltage of the TEC. Complicated and expensive and gives best result.PWM...well TECs don't generally like PWM power but it can be used in low frequency. Basically with PWM you vary the duty cycle to heat/cool the device and this duty cycle changes as you near the required temperature..Thermostat. The device shown (LCD temperature controller) works as a thermostat. Basically on/off. They are cheap easy to use but do suffer from hysteresis. That said...I did control a camera cooler box to within +/-3ºC with one of these (DC version). Which is not bad. The I draw for this application was 12V@6~4A. The controller I used like this also had a Hysteresis setting so you can dial in this as well.What ever way you need to experiment with various voltages, currents to determine you needs. IMHO...go the Thermostat controller first. There are DV 12V/24V variants on fleabay for this. Just easier to use as mains can be unforgiving. If this is no goo then try PWM with maybe a PIC or Ardunio controlling it.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 18, 2017, 05:02:38 pm
content: Use something like this-http://www.minco.com/products/heatThere's no advantage using a TEC and reliability is likely to be lower than other methods. What would you have done with the moisture dripping off the cold side?

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 18, 2017, 06:01:21 pm
content: If your only goal is heating, then a Peltier makes no sense. Your original description mentioned switching back and forth between 70 and 90 C though, do you require active cooling to drop the temperature, or are you planning to let it passively cool? If you need active cooling, then a Peltier would make sense, if you can let it passively cool then we're back to a resistive heater.If you go with a Peltier you'd want to use an H bridge. Pelter or resistive you should probably just do low frequency PWM for control, I wouldn't bother with adjustable voltage/current.

author: mikerj
author_rank: Super Contributor
timestamp: July 18, 2017, 08:16:12 pm
content: Quote from: wasyoungonce on July 18, 2017, 09:56:16 amFWIW PID and PWM are different things.PID is a control scheme, PWM is a drive method. A PID controller can be used to adjust the duty cycle of a PWM drive to a heater or TEC, but PWM by itself is not a controller. PID does not have to be complicated or expensive, a controller can be implement with a few op-amps or a cheap microcontroller with on board ADC/DAC (or PWM) and a small amount of code.I'd also echo others suggestions of a heater for this application. They are much less fussy to drive and far more robust if reliability is a concern.

author: orolo
author_rank: Frequent Contributor
timestamp: July 18, 2017, 09:55:19 pm
content: You could try using nichrome wire as heating element. It is relatively cheap, and heating is uniform and controlable.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: July 19, 2017, 02:26:37 am
content: Quote from: mikerj ........FWIW PID and PWM are different things....[/quote