Hi,
I just got my aluminum MK3 heatbed http://reprap.me/heatbed/alu-235.html. Installation went fine but I broke off my old NTC wile desoldering it (be careful!). Heating is MUCH faster than with the original heatbed and its flat as glass so you can print directly onto it. I wasn’t planning on adding an additional PSU like many people seem to do. As I was hoping, the lesser resistance of the MK3 bed made it heat faster. What I didn’t count with was the higher current draw from the PSU. Once I got the ABS to stick to my new bed the PSU shut down. Probably not broken, just some safety thing going on inside as I could replug the power cord and start it up again. Or do you have any other suggestions? The fact that the reading of extruder temp ntc dipped while the bed was heating suggests to me that the higher current draw of the bed makes a voltage drop across the NTC, making a lower temperature read.
My conclusion is I need a bigger PSU, or an additional PSU (which I’d like to avoid).
Now I have a spare 500W computer power supply, Cooler Master B500 http://eu.coolermaster.com/uk/product/Detail/powersupply/office-home-b-series/b500.html It outputs only 12V so both heaters will heat a bit (noticably?) slower but draw less current, although it can deliver up to 24A @ 12V. The rest of the K8200 will operate just fine with 12v if I get it right.
Before I go and blow up something, or myself. Do any of you have any suggestions on this? Is it possible even?
Is it better to try and find a 15V PSU which can supply more than 6,6A/100W?
I have also mounted MK3 heatbed and have linked it to 24V to use the original psu for now.
It works well and heats faster than the original. If I decide to start print ABS I will use another PSU as well to heat the MK3.
Since power (W) is dependent on voltage and current, and current in turn is voltage divided by resistance (which is constant); lowering voltage might give you lower roof temperature. If the resistant of the MK3 is low enough to generate a high enough current, and thus wattage, it might work, but keeping a higher voltage is safer.
If you want a 15 V supply with moar powa, I’d suggest the MeanWell SP320 series. I have a 24 V connected to my stock heat bed, but they come in 15 V versions as well. The latter one kicks out a maximum of 20 A, so it’ll be enough for your needs.
keep in mind that the controller board cannot safely supply high currents. Check the specs, otherwise you risk damaging the most expensive part of the printer. There’s plenty of information in the thread “Additional power supply for heatbed”.
[quote=“Stingh”]I have also mounted MK3 heatbed and have linked it to 24V to use the original psu for now.
It works well and heats faster than the original. If I decide to start print ABS I will use another PSU as well to heat the MK3.[/quote]
Stingh,
How high temperatures can you reach with this configuration? I got ABS to stick with 80 C and blue masking tape. So if you can reach 80C this way (even if it takes a while) I could settle with this config.
So after some further investigation i decided to order two 1.8R 50W resistors to add in parallel before the heatbed at 12V setting. With the 12V 500W supply, that should limit the current flow through the heatbed to 5A which feels like a “safe” level. The bed’s 12V-setting is ~1.5R with two parallelled 1.8R that is a total of ~2.4R = 5A, 60W. About the same effect you’d get by adding a separate 24V to the original heatbed.
I’ll let you know how it works out.
I’m afraid that calculation is only half the truth. The total power dissipation will be 60 W, yes, but matching the resistances of the board and the additional resistors, those 60 W will split up into about 37.5 W and 22.5 W, respectively. That’s the same (bed) heating power that you have with the original PCB heating bed on 15 V, not 24 V.
Hello k8200 users,
I’ve just completed my aditional powersupply mod for the K8200 but alltough I give the original heat bed enough juice (24V 6A) my heatbed wont reach more than 99 to 110 degree. So I want to change the heatbed with the MK3 mentioned above. Can I simply swap the original bed with the MK3 or is there some work to do on the aluminium frame of the k8200?
direct mounting of the Mk3 alu heatbed is not possible. The original PCB’s mounting holes are set in a square of 157-158 mm, while the Mk3 has 209-210 mm distance between the holes. There are additional holes in the alu frame below the PCB, but they’re spaced 202 mm apart, so they won’t help either.
On a positive note: due to the custom mounting you have the option to include a thicker thermal shield below the heatbed.
I am planning on making a new mounting plate with all the original holes but a little wider for the mk3 bed.
And i want to look into how i can make it a little more sturdy without adding to much weight.
It is not perfect but i think it will work.
I cant cut with waterjet or laser. I have to do this on a punch/nibble machine which causes stress in the material and the nibbles visible.
With a lot of work i managed to get it straight again.
Should the heatbed be mounted with the black side up or down.
I think down because of the cutout in the kork heatblocker, but most of the pictures i see it is with the black side up.
Hello 3D Maniacs ;),
I’ve got my MKIII also and what schould I say, it’s awesome. The bedleveling is now easy as can be.
Allthough I’ve an additional psu to pwer the heatbed it doesnt heat up faster then the original heatbed, some say it does but mine doesn’t.
I’m also unable to print directly on the aluminium, which is not a big deal, cause I prefere printing on a cheap mirror.
Otherwise I loove this bed and van reccomend it to everyone.
Here is a picture of my custom mounting:
What I’ve done: I also ordered the aditional prusa i3 mounting kit and drilled custom holes to be able to mount it directly on the K8200 alu-frame. The bedleveling is done by the four spring guided screws between the mounting kit and the heatbed. You’ll loose a little bit of your printhight!
It has less power but maybe something in that laptop psu is limiting the potential output of the psu so I thought that a more labstyle psu will give me full power all the time.
So my question is: will the psu from Reichelt will do the job better, or should I check my circuit fo any abnormality?
Reichelt also has a version with ca. 150 W, which I’d recommend to use for the heatbed. While 100 W is enough to run it on 24 V in theory, it would mean to constantly use the power supply at 80 to 100% load. A supply a little bit larger will provide better stability and much lower chance to have its thermal or overload protection circuits triggered.
