I am in the middle of building an Ingentis printer, the only thing left to purchase is a heatbed.
I have spoken to the Chinese supplier recommended in the Ingentis BOM. They can make me a dual element heater like the fancy drawing attached to this post!
I realise that I would have to write some code in marlin for two heatbed thermsitors and drive the outer heatbed from a spare pin on my control board.
What power ratings would the separate elements need to be, I asked for the inner element to be 100w and the outer element to be 200w does this sound reasonable?
Can anyone see any problems with this idea?
Only problem I see (based on estimates):
Your 150x150 section is 1/4 of the total area, so the blue section is 3/4 of it.
I would imagine that, since the ratio of area between the two is 1:3, you would actually need around 3 times the power to the blue area compared to the green.
On TOP of that - the blue area is all on the perimeter, where ‘cool air’ can affect it, whereas the green area is inboard and will get some residual heat from the blue area also. I think the blue area should be MINIMUM 3 times the wattage of the green area, and possibly higher because this fact.
If you’re trying to stay around 300 watts total, perhaps green = 75, blue = 225 watts?
But this is speculation based only on maths, I do not know a lot about heated build plates, so do take this with a grain of salt! Just putting it out there, can anyone confirm this?
The outer section has 3x the area of the inner section, so it needs at least 3x the heating power. I would recommend 4x as a starting point, since the outer section experiences more heat loss.
However, your number for the inner section is a bit high. You normally want about .25-.3 W/cm^2, so a 150mm platform would normally need about 56.25-67.5W. The inner section will only border on hot areas, so it will loose less heat, while you want the maximum power for the outer section. I would try about 55W for the center section and 220W for the outer section. With the right ballance of heater powers a decent heat spreader, you shouldn’t need separate power inputs, though monitoring the temperature in multiple areas is not a bad idea. Of course, all but the center section is probably too much for the FETs on your controller board, so you should look into an SSR.
Of course, if you were thinking about trying to only heat the inner section for small prints, that all goes out the window, and the balance you posted is probably better (inner section needs more power to cope with conduction to the outer section), but I would highly recommend against that as the differential thermal expansion of the inner and outer sections will cause the platform to bow.
I wonder if 75W for the green is enough to be a good heater on its own. If it was used without the blue being turned on.
Just going to summon @Tim_Rastall as he hasn’t been invoked yet!
Are you using alirubber for the bed? I got my 350mm X 350mm X 400W bed from them. They can do zones, holes for mounting, sticky backed. Etc. Mine was only 25$ USD.
They make the beds for qu-bd.
If not I would give them a shot too.
Ali rubber are the guys mentioned in the BOM if memory serves.
Can some one post a easy to get in touch with alirubber?
@Mike_Ashcraft daisyhuang@alirubber.com.cn
But you will want to setup a aliexpress account to buy I think. Its like China’s eBay… Kinda.
I was planing to use the inner section for smaller prints. I was a bit worried about the outer section robbing heat from the inner one but the bed bowing hadn’t really crossed my mind.
What if the whole bed was heated before the print started and then turn off the outer section? Just trying to save some power seems a waste to heat the whole bed for smaller prints.
@Eclsnowman This is the company on ali-express I have spoken to http://www.aliexpress.com/store/709519 They quoted $25USD +10 for China Post.
You’ll likely end up with the platform edges slowly shrinking and causing the same bowing over the course of a print, assuming the object is tall enough for this to happen, and if it’s not, you could probably just as well turn the platform off once it finishes heating.
I’d make the center area at least 200200mm. Using empirical data as references, here’s what the bed will end up looking when only the center part is heating at an average of 75W (below 3mm of glass): https://www.dropbox.com/s/f0gg75r9rewmb57/squareSquare.PNG
The usable area, at least for ABS, is going to be about 100100mm for the suggested layout.
Thanks for all the great feed back, still undecided what to do. I may just try one but with a bigger inner section and if it doesn’t work I can just use both sections at the same time.
