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Additional power supply for heatbed

Posted by KLucky_13 
Additional power supply for heatbed
May 18, 2014 08:50AM
Hello, I have a 3Drag/K8200 DIY 3D-printer and I am currently busy with installing a mosfet controller to fit a additional power supply since the original supply is not good enough to get enough heat to print ABS.

I think I'm almost there to fit everything together, I just want to ask a few questions before blowing anything up (I'm not that good with the electronic side of the 3D-printer so please help):

*First of all, I found 3 power supply's laying around and I'm wondering of any of these 3 is good enough to make this setup work:

First one is a power supply of a pc:
12v 32A = 380 watt
second and third one is a power supply of an old laptop:
20v 6A = 120 watt
19v 4A = 76 watt (which will be not enough a assume)

will any of these 3 perform good enough? I am planning on installing the MK3 alu heatbed from reprap.me later on, so keep that in mind that this might need more power?

*Second question is the wiring, I drew in paint what I understand of how this mosfet has to be wired (I can be completely wrong, but this is what I understand with my basic knowledge about these things):

A bit more info about this printboard: [labitat.dk]
I bought it from reprap.me

So on the control-board both left pins are positive and both right pins are negative, correct? Weird thing is, on the signal input is no + or - written (at least weird for me, probably this is logic for someone who understands :-))

*Final question:

There is a message on the back of the mosfet-printboard:

what does this normal or inverted means? I'm not that good with this kind of stuff (that's the reason i bought this printboard and did not assemble it myself). I assume I have to solder the "normal" jumper.

And by the way, if you look closely, the normal "jumper" looks like it is already connected to each other..

Thanks for your time ;-)
Re: Additional power supply for heatbed
May 18, 2014 11:37PM
From the Rev1 picture at [labitat.dk] it looks like are -/+ signs on the silkscreen side. It looks like the board switches the negative side, which is the more common configuration with MOSFETS so you should be reverse the reds and blacks, (positives and negatives) in your diagram. They also show the +/red side of the control connecting on the input side towards the power supply, so that red/black should be switched in your diagram as well.

The normal versus inverted would control whether you want this thing to power stuff when the board negative input is pulled low ('normal' operation for a low-side switch) or to power stuff when the negative input is floating high ('inverted' operation when compared to a low-side switch)
Re: Additional power supply for heatbed
May 19, 2014 02:17AM
To be honest, I did not look if the - or + was correct on the diagram, it's clearly indicated. I just wanted to know if the 3 components are connected to the right location :-)
Do you have any idea if this controller board is normal or inverted? Or how can I find out if you don't know?
Re: Additional power supply for heatbed
May 19, 2014 09:16AM
'Normal' electronics supplies a constant +12V (or +24V) on one of the heatbed terminals, and either lets the other terminal (-) float when no heat is called for or shorts the other terminal to ground to complete the circuit. To prove it to myself, I would put a 100 or 1000 ohm resistor across the electronics' heatbed ports and see if both sides read 12V when off and +12, 0 when on.

From your pic and the press releases i saw googling 3DRAG, it looks like your board is Sanguinololo-like, and it is likely 'normal'.

However, if when you apply power to the system but do not call for heat on the bed, the bed heats up, then your electronics may be inverted.
Re: Additional power supply for heatbed
May 19, 2014 03:44PM
when inspecting my board closely, resistor "R7" is missing from the board:

I know it's small to see, but it's missing...
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