Monday, October 15, 2018

PROJECT: Heating-platform Mod

LINK TO PROJECT PACK

So my ReflowR has gone kaput. After contacting Lafras (the guy who designed & made the unit) it turns out the heating element is at fault as the element resistance is OC. Luckily he was a cool enough dude to send me a free replacement.

After doing a bit more digging I found that the ReflowR uses a mica core heating element which compared to a ceramic heating element (like the one in your 3D printer) has a few disadvantages:

  1. Mica cores are easier to damage, this is physically speaking
  2. Mica cores have a slower heat up rate
  3. Mica cores are not capable & suitable for high temperature operation, apparently you don't want to run the core >480°C as things start to break down

Picking the Heating-platform

After even more digging it turns out you can buy a fully assembled hot-plate, some of which use a cylindrical ceramic heating element:

I decided to go with the ZB2020JR as it:
  1. Uses a ceramic heating element
  2. Has a pretty good power per area. Others heaters offered a higher wattage but I had a feeling their numbers were skewed
  3. Has a proper PID controller (ZB102-6411)
  4. Has enough room for upgrades ;^)

Modding the Heating-platform

I wanted to control the unit via my PC so I also bought the PC410 which is a PID controller with an RS232 port.
NOTE: TTL and RS232 are not the same thing!!! Though their logic might be similar their signal levels are completely different, sparkfun has a good article on this.

I found out that the original PID controller (ZB102-6411) drove the ceramic heating elements directly with an internal Hongfa HF152F (16A 250VAC) relay. Since the relay inside the PC410 is only rated to 3A 250VAC I got the Opto 22 240D25-17 Solid State Relay, this thing is rated to 25A 240VAC so will have no trouble driving the heating elements (with appropriate cooling!!!).
UPDATE: If we use the magical P=VI formula it turns out the heating elements draw approx 3.5A, so the 25A SSR is a bit over kill. 

With all that said here are some pictures of the modding process:
  • The original wiring inside the unit was actually pretty good, all wires were crimped, marked and insulated properly:
  • Here is what the old (ZB102-6411) & new (PC410) PID temperature controllers look like:
  • Front hole expanded & PC410 loaded. The HOT POPO PLATE 9000 is starting to take shape:
  • And finally insides completed:
NOTE: If you want to control the hot-plate via RS232 or front panel (prog mode) you have to short pin 14 & 15 else the program will be halted as soon as it's started. See section 12.4 of PC410 manual (pg28).


Trying the Heating-platform

Turns out there are a bunch of programs out there that can talk with the PC410, most of which are clones of one another. The two programs I liked were:

BGA Mods Rework Software v1.1
This one is very minimalist but is also very easy to use. The only thing to be aware of is that the software expects to see the PC410 on COM1.

PSOFT Rework Station Controller v2.3.1
This program has way more features like: COM port configuration, heater duty cycle, alarm config... Also it is designed for rework stations that have a top & bottom heater, so was a bit overkill for what I was doing.


After going through PID self-tuning (section 9 of PC410 manual, pg21) I then did a bunch of tests to see just how different the surface temperature of a PCB and the hot-plate really are:

Turns out it's not that much (as you would hope) if the two are in direct contact, you only start running into large drops (~70°C) if there is a bit of an air gap between the PCB and the hot-plate, for example when using a non-uniform skillet.

Now the plan is to reflow a bunch of loaded PCB's and figure out the optimal technique/profile =^..^=

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