Home  |  Contents 
Microcontroller and PC projects
  Forum Index : Microcontroller and PC projects         Section
Subject Topic: Electronic heater plate.... Post ReplyPost New Topic
<< Prev Page of 4
Author
Message << Prev Topic | Next Topic >>
MicroBlocks
Guru
Guru
Avatar

Joined: 12 May 2012
Location: Thailand
Online Status: Online
Posts: 2062
Posted: 08 January 2018 at 5:32pm | IP Logged Quote MicroBlocks

You would need to know the resistance of the wire when it is cold.Then you can calculate how many amps will flow through it. With that you can calculate how much it will heat up.
The resistance will change with heat, maybe the mentioned resistance is when it is used at full power or it is when it is cold.
A test will make that clear.



__________________
Microblocks. Build with logic.


Back to Top View MicroBlocks's Profile Search for other posts by MicroBlocks
 
Warpspeed
Guru
Guru


Joined: 09 August 2007
Location: Australia
Online Status: Offline
Posts: 1361
Posted: 08 January 2018 at 5:39pm | IP Logged Quote Warpspeed

They use nichrome wire in electric radiators, and it runs brilliant red hot.
The change in resistance is not that much, less than 10%

Rising from maybe 20C to 40C its going to make bugger all difference in resistance.

__________________
Cheers, Tony.
Back to Top View Warpspeed's Profile Search for other posts by Warpspeed
 
Phil23
Guru
Guru


Joined: 27 March 2016
Location: Australia
Online Status: Offline
Posts: 1217
Posted: 08 January 2018 at 8:36pm | IP Logged Quote Phil23

Grogster wrote:
@ Palcal and others asking about eggs: Velociraptor. It'll be fine - they are all female so won't breed.....


See,

Dragons.....

Quote:
Velociraptor was a mid-sized dromaeosaurid, with adults measuring up to 2.07 m (6.8 ft) long......

Fossils of dromaeosaurids more primitive than Velociraptor are known to have had feathers covering their bodies and fully developed feathered wings.[11] The fact that the ancestors of Velociraptor were feathered and possibly capable of flight had long suggested to paleontologists that Velociraptor bore feathers as well, since even flightless birds today retain most of their feathers.






From Wiki....

Phil.
Back to Top View Phil23's Profile Search for other posts by Phil23
 
redrok
Senior Member
Senior Member
Avatar

Joined: 15 September 2014
Location: United States
Online Status: Offline
Posts: 165
Posted: 09 January 2018 at 1:19am | IP Logged Quote redrok

Hi Grogster;
Grogster wrote:
I am planning to use a Fairchild/ON RFD14N05 MOSFET, as I have several of these in stock. 14A S-D current, Vgs(TH) of 2v(so should work well driven directly from a MM 3v3 output), and Rds(ON) of 100 milli-ohms. You can get MOSFETS with better specs then this(specifically the Rds(ON)), but this is what I have, is small, yet can handle the current of the pad no problem. TO252AA SMD package.

P=I2R:
P=4-squared-R
P=4-squared x 0.1
P=1.6 Watts @ 4A load worst-case, so I think this can easily be dissipated within the copper pour with some heat vias to the bottom layer.

Hell, I probably have THAT wrong now!

MOSFET would be a LOW-SIDE switch, with the heating pad between 12v and Drain. Source to Ground. Gate to MM I/O pin.

Do I have that right?
I believe so.
Although it would be prudent to have a 100K gate pulldown and a 1K series to the uMITE pin to protect from charge injection due to the MOSFET Miller capacitance.
I like the RFD14N05. It is one of the standard parts in my junk box.
I measured the RDSon at 64mohm @ 3.3V.
The full on power dissipation would be only about 1 Watt.
This part will have to be insulated from the plate. However, at 1.6W or even 1W, the package would not need a heatsink at all.

Another part, TF2618L in a "Fullpack" insulated package and only 16mohm @ 3.3V.
The full on power dissipation would be only about 0.25 Watts.

And another, IRLI2203N in a "Fullpack" insulated package and only 8mohm @ 3.3V.
The full on power dissipation would be only about 0.125 Watts.

I've a listing of many parts on one of my web pages, see:
Parts with which I've Used, Tested, or have an Interest. Lots of data here.

The resistance of the rubber heater will change with temperature, that's inevitable, however, the absolute operating temperature of the wire is not much higher than ambient so the change of resistance is minimal.

The first order approximation of resistance VS. temperature is:
25degC + 273degC = 298degK ambient
35degC + 273degC = 308degK the Bees
( 308degK - 298degK ) / 298degK * 3.2ohm = +0.11ohm resistance change
3.2ohm + 0.11ohm = 3.31ohm
That's not a significant change in resistance.

Have fun!
redrok
Back to Top View redrok's Profile Search for other posts by redrok Visit redrok's Homepage
 
Quazee137
Regular Member
Regular Member


Joined: 07 August 2016
Location: United States
Online Status: Offline
Posts: 78
Posted: 09 January 2018 at 2:19am | IP Logged Quote Quazee137

As my Granddaughter hates this. But back in the day "early 1960's"

My Dad and Grandfather had me help with this task.

We use a big ZIPPO heater and metal cigar tubes wrap the egg with
tissue then in the tube and into the ZIPPO bag.

We'd get about 20 each time.

The incubators for the chickens, ducks and pigons was gas powered.



Edited by Quazee137 on 09 January 2018 at 2:20am
Back to Top View Quazee137's Profile Search for other posts by Quazee137
 
Grogster
Guru
Guru
Avatar

Joined: 31 December 2012
Location: New Zealand
Online Status: Offline
Posts: 5293
Posted: 09 January 2018 at 9:15am | IP Logged Quote Grogster

@ Phil23: Trust you to actually research that comment. "Clever girl."

@ redrok: I usually just provide a small-ish zone of insulated copper pour on top and bottom layers for heatsinks for these kind of parts.





Thermal vias are filled with solder during assembly, but I doubt I would even need the bottom copper 'heatsink', but if you have room, why not allow for it. I will add a 100k pulldown to the gate, and a 1k series.

@ Quazee137: Owwwww. Gas powered. Fried eggs.

__________________
Smoke makes things work. When the smoke gets out, it stops!
Back to Top View Grogster's Profile Search for other posts by Grogster Visit Grogster's Homepage
 
Quazee137
Regular Member
Regular Member


Joined: 07 August 2016
Location: United States
Online Status: Offline
Posts: 78
Posted: 14 January 2018 at 3:41am | IP Logged Quote Quazee137

Quote:
@ Quazee137: Owwwww. Gas powered. Fried eggs.


It was small boiler much like an old peculator coffee pot.

Hows the work going?


Edited by Quazee137 on 14 January 2018 at 4:00am
Back to Top View Quazee137's Profile Search for other posts by Quazee137
 
Grogster
Guru
Guru
Avatar

Joined: 31 December 2012
Location: New Zealand
Online Status: Offline
Posts: 5293
Posted: 14 January 2018 at 10:53am | IP Logged Quote Grogster

PCB's ordered, made, and on DHL to me now.(have arrived at Auckland Airport according to tracking)
Waiting on heating pad to arrive. I got two.
I will assemble the PCB while I wait.
The PCB is designed as a backpack to a 2.8" SPI LCD with touch, so I can add some basic touch controls to the LCD screen. Old design used a red LED display, but the SPI LCD's can be setup however you want - including red 7-segment if I want it.
Pad has NTC, but I have elected to use a couple of 18B20 temperature sensors, as they are much more accurate then a passive NTC would be. I have allowed for connection of the NTC to an ADC pin on the MM2 chip, just in case I elect to use it.
I will post back to this thread as I progress with the project.
Thank you for your interest.

__________________
Smoke makes things work. When the smoke gets out, it stops!
Back to Top View Grogster's Profile Search for other posts by Grogster Visit Grogster's Homepage
 


If you wish to post a reply to this topic you must first login
If you are not already registered you must first register

  Search the forums using Google.
<< Prev Page of 4
In the news...
 
Post ReplyPost New Topic
Printable version Printable version
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot delete your posts in this forum
You cannot edit your posts in this forum
You cannot create polls in this forum
You cannot vote in polls in this forum

Powered by Web Wiz Forums version 7.8
Copyright ©2001-2004 Web Wiz Guide

This page was generated in 0.1094 seconds.
Privacy Policy     Process times : 0.02, 0, 0, 0.09