Anyone added a fan to their DIY reflow oven? - Page 1
Forum section: electronics / projects

author: homeward
author_rank: Contributor
timestamp: April 09, 2018, 09:28:00 am
content: Hello,I have a fairly small (9litre) toaster oven that I've converted to a reflow oven, it generally works well but heat distribution is pretty uneven. The longer boards will be overdone in the middle and underdone (not reflowed) on the edges. I'd ideally like to stick a couple of fans in there to distribute the heat better but am unsure. All the fans I've looked at specify a max temperature of 70 dec/C, which is obviously far too low. Has anyone done this before that can advise please?Thanks.

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 09:48:07 am
content: Don't try to put motor in the oven. Get motor+fan from fan-equipped oven or just change oven to one with fanExample:https://www.buyspares.co.uk/cooker-oven/beko/main-oven-fan-motor/product.pl?pid=962574&path=462784:496321,110870:462790

author: ogden
author_rank: Super Contributor
timestamp: April 09, 2018, 11:13:51 am
content: Quote from: wilfred on April 09, 2018, 10:21:29 amHigh-volume industry uses convection ovens. In IR oven it is not possible to guarantee even heat for both black and reflective components. You can overcook black while reflective component does not get enough heat. That's why air/nitrogen convection is best bet. IR is good for rework purposes where you heat single IC at a time.https://www.7pcb.com/blog/how-the-modern-solder-reflow-oven-works.php

author: TechieTX
author_rank: Contributor
timestamp: April 09, 2018, 11:23:10 pm
content: On the convection toaster ovens I've looked at, the fan was entirely outside the cooking area in a separate enclosure, with the motor outside of THAT enclosure in essentially free room air. Steel shaft on the motor with a steel fan blade to handle the 230C max cooking temperatures or 245C lead-free reflow temp. A plastic Muffin fan won't last long at that temperature.I haven't seen any of the small toasters with a convection fan, and was considering buying a cheap convection oven to upgrade the small toaster I have, as the direct IR doesn't provide even heat distribution to the components on the board(s). A small volume is easier to heat to temperature, so it makes more sense for me to gut the fan out of a larger volume toaster and continue with the small volume unit that I know works.Mine doesn't have a profile controller... I have two thermocouples inside with meters outside, and I'm the reflow controller with my finger on a (normally-open) switch for the IR elements, and the other hand on the door. Yes it's low-tech, but it works.

author: ogden
author_rank: Super Contributor
timestamp: April 10, 2018, 12:52:53 am
content: Quote from: TechieTX on April 09, 2018, 11:23:10 pmYou can rest assured that virtually any cooker will be able to get up-to lead-free temperatures. They all are designed to heat-up & cook quite big chunks of stuff with thermal mass exceeding your PCB by many orders of magnitude. I think bigger cooker have better chances of even heat spread because you can place board further away from heater.

author: homeward
author_rank: Contributor
timestamp: April 10, 2018, 09:09:22 am
content: Quote from: ogden on April 10, 2018, 12:52:53 amAnd keep the board further from the edges of the oven.Am now thinking it'd be better/easier to get a bigger capacity oven with a fan built in. They almost all advertise 230 deg as the max temp, you reckon these will have no problems getting to 250 deg in the short time required?

author: ogden
author_rank: Super Contributor
timestamp: April 10, 2018, 11:25:31 am
content: Quote from: homeward on April 10, 2018, 09:09:22 amWhen you do not use original regulator - obviously higher temperatures are possible.QuoteDunno. Ovens differ. Those with fan usually have big enough heaters and supposedly good insulation as well. Trust me, nothing bad will happen with most of components of you prolong reflow cycle (preheat phase) for couple of minutes.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 10, 2018, 01:08:26 pm
content: I haven't added a fan to mine, but it is on the list of things to do. As stated previously, motor outside the oven, with heat resistant shaft to heat resistant fan.One reason this project hasn't been done is that I want to add the feature of using the fan to bring in outside air. I have had no problems achieving the desired heating profiles with my oven, but the cooling profiles have been a problem, requiring me to open the oven door to approximate the right rate. Getting this under automatic control would be good.

author: mjkuwp
author_rank: Unknown
timestamp: April 10, 2018, 05:10:42 pm
content: I realize you are in GB but here is an example of what you need - maybe you can have it shipped across the pond : )https://www.amazon.com/BLACK-DECKER-TO1675B-Convection-Countertop/dp/B0060VQFQ6/ref=sr_1_12?s=kitchen&ie=UTF8&qid=1523380049&sr=1-12&keywords=convection+toaster+ovenit's the same model I used and it works really well. I also put a copper plate under my PCB and use a thermocouple stuck to the copper plate as the temperature feedback. I only do surface-mount parts in there.I imagine the link will have a short lifespan so for reference this is a toaster oven with convection fan big enough for 2 slices of bread and advertised as 6 slice : |ALSO:Quote from: TechieTX on April 09, 2018, 11:23:10 pmI agree - I do have a fancy home-brew controller on mine but effectively it does what you describe and could easily be mimicked by a person with a little bit of experience. After I open the door I am a little 'box fan' into the oven to cool a little faster while holding my breath.PS - also I shortened the wires in the heater to raise the power level - tried to get it near the 20 Amp limit of my circuit but I think I ended up quite a bit shy of that. It's better to have the power be quite high so you can get from soak to flow pretty quickly.

author: phil from seattle
author_rank: Super Contributor
timestamp: April 10, 2018, 08:21:23 pm
content: One issue about convection ovens is that the fans blast a pretty high velocity airflow. I'd be worried about small components or even boards getting blown around. There should be a way of controlling the fan speed. I can't imagine you need that much flow to even out the temperature.

author: Emil
author_rank: Regular Contributor
timestamp: April 11, 2018, 11:35:32 am
content: I added a heat gun to my toaster reflow oven. Fan and heating element in one package. It works much better than the same oven with only IR heating.I got the cheapest one I could find, took out the parts inside and mounted it to the back of the oven. To mount it I drilled a hole in the back of the oven, the heat gun fits snugly inside and I secured it with a few tack welds and sealed it with copper tape.I'v been using the reflow oven at 1kW convective + 1kW IR, but I will try disconnecting the IR completely and use the heat gun at the the 2kW setting.

author: homeward
author_rank: Contributor
timestamp: April 13, 2018, 08:35:38 am
content: Quote from: mjkuwp on April 10, 2018, 05:10:42 pmYou know, I actually might just buy that model, thanks. The choices over here are pretty dire...at double the price. Am I right in thinking this model has quartz elements?Presumably the fan doesn't blow components off the board? Have you found the heat distribution to be even?Emil-Cunning!

author: mark03
author_rank: Frequent Contributor
timestamp: April 13, 2018, 02:33:59 pm
content: I did this with my reflow oven. It started life at a Ben & Jerry's franchise, with a wimpy fan and black "calrod" style heating element. In stock condition it would take longer than 10 minutes to reach reflow temperature, so I retrofitted a centrifugal fan and new motor, as well as 220V electric furnace heating coils. It works quite well:http://www.hau.nz/posts/reflow_oven.htmlAlthough I do like the heat-gun idea!Surface tension wins over airflow more than you might think. A more serious issue is vibration if the fan assembly is not sufficiently well balanced. This can make parts slide off before liquidus when surface tension kicks in.