Custom size mk3 heatbed


#321

Then im down to the last 10 :slight_smile:


#322

Well I am kinda of ashamed because I got my heatbed from Marlark’s like almost a year ago I just installed today :smiley:
I got a couple of questions I didn’t see truly answered:

1 - The 320W/15V PSU is enough to replace the printers PSU AND power the heatbed?
2 - Whats the working temperature for the heatbed?


#323

Hey guys,

I’m having a strange fenomenon…

Assuming there was no error on my part assembling the heatbed ( followed every step from the “dummies” manual. ) what can cause the PSU switching itself off when powering the heatbed and extruder?

  1. My PSU is same has the one from manual ( 320-15 ) supposingly it should have enough “juice”.
    1.1 Since PSU is a 15V, is there any problem when supplying the PE?
    1.2 Should there be something in between PSU-PE to reduce voltage?

  2. Can the PE ( since I kinda overheated it with the soldering iron. I think ) be the cause? ( I ordered a new one just in case )

Regards
Jorge Oliveira


#324

There is a bunch on the subject but Danf explain it fairly good i think. SVDV have some experience on using the 320w 15V option so should maybe ask him.

[quote=“danf”]svdv,

The heat-bed has two power options; 12 and 24 V. The main benefits of using the 24 V option with an extra 24 V supply as opposed to 15 V:

  • Less than half the current, but slightly reduced heating time (24 V @ P=24^2/2.6 = 222 W vs 15 V @ P=15^2/.65 = 346 W)
  • You can safely use the power expander (20 A rated continuous), even with screw terminals mounted (likely rated ~10 A continuous)
  • You can use thinner wires, weaker connectors (max 9.2 A vs. max 23 A)[/quote]

#325

Then im down to 7 left.


#326

[quote=“Marlark”]There is a bunch on the subject but Danf explain it fairly good i think. SVDV have some experience on using the 320w 15V option so should maybe ask him.

[quote=“danf”]svdv,

The heat-bed has two power options; 12 and 24 V. The main benefits of using the 24 V option with an extra 24 V supply as opposed to 15 V:

  • Less than half the current, but slightly reduced heating time (24 V @ P=24^2/2.6 = 222 W vs 15 V @ P=15^2/.65 = 346 W)
  • You can safely use the power expander (20 A rated continuous), even with screw terminals mounted (likely rated ~10 A continuous)
  • You can use thinner wires, weaker connectors (max 9.2 A vs. max 23 A)[/quote][/quote]

Thanks for the quote, I knew it was around here somewhere…and I’m sorry for these dumb questions…

This means i need a 350W/15V PSU just for the heatbed? I’m asking this because as of now I’m getting power “disconnects” with both bed and extruder.
If I’m right I need not a 320W/15V PSU but a +400W/15V ( or extra one ). From what it is in the .pdf I thought one whould need only the 320W PSU.


#327

Hi Hyrokumata,

I quote myself:

[quote]I appreciate your (and everybody else) thinking along, but after a serious consideration I purchased a 24V PSU already.
I think Danf has made my problems perfectly clear. I did even understand it :slight_smile: The power expander can manage 20A. The 15V PSU with 12V heatbed connection rates 23,1A. So it’s getting too hot. As a second best option Danf suggests to lower the Voltage, but to be honest, I am fed up with this and want a safe solution.
Also ordered a new PE, which has to manage only 9,2A now. I won’t use the screw terminals but solder everything and if needed, put a fan besides.
It is a pricey experience but I learned a lot.[/quote]

This is what I did and it never failed or burned since then! I switch the 24V for the heatbed seperately. So it’s off when not needed. Used the 320-15 PSU I already bought instead of the original Vertex PSU. So now that has a fan too. The two PSU’s are mounted side by side on the bottom so it’s quite crowded and windy there :slight_smile:

Sorry, I did not update the pdf instruction and only made the red warning. Danf was right and clear. And to be honest, Marlark at the very beginning suggested a seperate 24V PSU too.


#328

Just received the heatbed.

Did measurments and IMHO the statement that [quote]Resistance at 12 Volt setting is around 1,5 Ohm [/quote] is wrong leading to multiple issues (maybe this is already discussed somewhere above).

The resistance between 1-2 is 1.5 Ohms
The resistance between 1-3 is 1.5 Ohms
The resistance between 2-3 is 2.7 Ohms (and this is the configuration for 24V setup, circuit runs through 2-3)

However in 12VDC (15VDC) configuration those resistances work in parallel (1-2 is for “right” side of the bed, 1-3 is for the “left” side).
Thus the actual calculated reisistance is
1/Rt = 1/1.5 + 1/1.5
Rt = 0.75 Ohms

I did measure it in parallel (on 3 multimeters), it gave Rt = ~0.95 Ohms in reality (technically there is yet another resistance in serial, the trace from pin 1 going to the place where 2 and 3 branches divide off, which explains it), but I’ll assume 0.75 Ohms in calculations below.

Thus current @15VDC will be 15/0.75=20A
And power (PSU) needed is 400W (taking 300W calculated @ 75% factor).
Sure, the resistance will increase when everything heats up, but 15V 320W PSU suggested in the heatbed-for-dummies-v3.pdf is too low for heatbed alone!

This is bad as I trusted the specs in the original post.

I already bought 350W PSU based on “1.5 Ohm” resistance, given that it will need 200W for heatbed (meaning it can provide 150W calculated (15*15/1.5) @75%) and 100W for existing stuff + extra 50W) but it is too low for actual calculated 400W (300W calculated @ 75% factor).

One way would be running 350W PSU @ 15VDC through 2-3 (24 VDC circuit) as it will give 15/2.7 = 5.5A load, which would be safe for the PSU, but of course everything will heat up soooo much slower.

Other way would be taking the risk (and it seems many have here), because I have measured that dual head mode only on peaks exceed 50W, on normal operation it is ~50W. As resistance empirically for “12V circuit” is ~0.9 Ohms, it gives that heatbed will eat up 15*15/0.9=250W (and it can be considered as a pure resistive load which helps in this case, although way how traces are laid out introduces extra inductance, it is negligible) thus 350W PSU could “just manage it”, but in long term…

Thus beware and don’t buy 320W as suggested in heatbed-for-dummies-v3.pdf or 350W as I have, go beefier.


#329

[quote=“svdv”]Hi Hyrokumata,

I quote myself:

[quote]I appreciate your (and everybody else) thinking along, but after a serious consideration I purchased a 24V PSU already.
I think Danf has made my problems perfectly clear. I did even understand it :slight_smile: The power expander can manage 20A. The 15V PSU with 12V heatbed connection rates 23,1A. So it’s getting too hot. As a second best option Danf suggests to lower the Voltage, but to be honest, I am fed up with this and want a safe solution.
Also ordered a new PE, which has to manage only 9,2A now. I won’t use the screw terminals but solder everything and if needed, put a fan besides.
It is a pricey experience but I learned a lot.[/quote]

This is what I did and it never failed or burned since then! I switch the 24V for the heatbed seperately. So it’s off when not needed. Used the 320-15 PSU I already bought instead of the original Vertex PSU. So now that has a fan too. The two PSU’s are mounted side by side on the bottom so it’s quite crowded and windy there :slight_smile:

Sorry, I did not update the pdf instruction and only made the red warning. Danf was right and clear. And to be honest, Marlark at the very beginning suggested a seperate 24V PSU too.[/quote]

I think you are right about the windy:D
Think all holes and recabling is done…
Tomorrow will reinstall heatbed. And fingers crossed to not throw down any circuit on the house :smiley:


#330

Hi Marlark,

I really wanna be one of those Marlarks heated bed owners.
I have sent you 425.SEK and my contact data 25th April. Also a mail 5days ago but until now I have had no response from you.
Please, check your paypal/mail account and send me a notice.

Regards
fenderbassman


#331

Hi,

do you guys still get the not flat surface after installing the heatbed?
I still get around 0.1 - > 0.15 difference


#332

Hi Marlark,

Thanx.
I have received the heated bed today. Everything looks good so now I have to face the next exciting challenge. Order the other parts and start assembly.

P.S. Marlark has informed me that there is only three beds left so if you want one I recommend to make your choice now.

/fenderbassman


#333

Only 2 left know. Quick reply from Marlark for this much needed upgrade.
Thankyou.


#334

I bought one this monday so only 1 left.
Still waiting for it though. :slight_smile:
/TH


#335

Still waiting as well. Hopefully it will arrive this Week coming.


#336

Emailed Marlark a few days ago regarding the heated bed. No reply.


#337

Yah me too, hope nothings happened to him. :frowning:


#338

Well, its been nearly a month since I ordered and paid for heated bed. Have tried to contact Marlark with no reply. This is not looking promising.


#339

It will be a month for me on Wednesday…
It is odd. He has not been here since 8:th of may… His profile here together with his paypal e-mail adress makes him easily traceable so I wonder why this stunt.

If he could just get back whats the delay…


#340

Mine arrived today. So exciting. :slight_smile: