Heated Bed aluminium 31x31 FLSun Cube draining power

Hello guys,

I am in the process to upgrade lot of parts on my 3D printer, like PSU, Drivers, mechanics etc

I have a huge problem that is causing me lot of trouble with the Heated bed.

I dunno when the exact moment happened but now the Printer is start draining power from the PSU when a Heated Bed is fully On.

I have a FLSun Cube bought from Amazon and used happily for about two months.
Now The internal driver circuitry with the Makerbase 1.0 (whch uses the HY3403 Mosfet SMD) doesn't seem to work properly (the Mosfet is still controllable and it has no short)

the On/Off command is ok but not the Power necessary to heat the Bed (310x310 Aluminium plate with printed traces on the bottom surface).

I've checked the resistance of the Bed with a multimeter [0.7 ohm] powerd at 12V.
With a simple P=V*I I calculated roughly 200W necessary.
the PSU is a classic LED Power supply IP67 fanless 300W and dedicated only for the monstre power needed by the Heated Bed.

I tried to drive externally the Heated Bed with another driver (external classic power mosfet optoisolated module) but it is not enough. it starts blowing the traces and smokes).
Using the onboard mosfet only it started melting tin and burning copper aroung the infaust heated bed Connector (why less than 2mm thin copper trace between drain Mosfet and the connector nobody knows...).

with this problem the PSU Power meter detect an absorbtion of 388W !!!!!!

I read some information on the Internet but it is not really clear for me. Shorted Bed? how do I know if the bed is shorted witha measured Resistance of roughly 0.7ohm ?

I don't think is a damage on the brancd new Mosfet driver or the Makerbase 1.0 board at the Mosfet area all the signals are still ok and the Oscilloscope sees the PWM signals of the Gate drive.

Any power hungry free solution please ?

... the Extruder is working fine. even if I use the onboard mosfet or an external mosfet driver ( a FLIR camera shows cold temp. for the mosfet driving the heating extruder block)
... the Heated Bed start the warm up procedure and I see the temp rising but not fast (and power hungry).

thx.
callisto.

Edited 2 time(s). Last edit at 10/06/2018 07:11PM by callisto.

I shorted the cables at the entry point of the Heated bed and then checked again the resistance value with my multimeter.
Same 0.7ohm.

It looks like a shorted Bed.

How it is possible to have it shorted?

I naven't touched anything on the bottom layer of the Bed. the tracks are printed with a black layer to cover the conductive path and there is no short between Aluminium and cables.

any Idea please?

C.

The bed is mounted on 4 pillars, if these are lose they can rub away the insulation and short a bed

remove the bed and check for any damage

Hi Dust,

this FLSun 310x310 bed I have has very wide tracks and the screw's holes are far from the copper tracks.

the multimeter doens't show electric short along the screws and the power cables. it is an open circuit for my multimeter.

at the entry point where the cables are soldered the copper tracks are very well designed to avoid any sort of problems.


I can also make a test to see if the Mosfet onboard is correctly closing (full saturation I mean) by using the Extruder hotend as Load resistor.


I never seen a hotbed with 0 ohm resistor or at least a so low value.

C.

To show yours how my bed is,

I rebuild a PCB layout roughly with measures and shape of my bed 310x310, screws are 35mm far from each side. and tracks are between 5 and 6 mm

Just the connectors area is in reality a bit larger with the copper.

the track Length is 4.3meter. with that length I don't expect a short and a visible low resistance through the cable and pcb.

I used this tool: [circuitcalculator.com]
and for 434cm length width 5.5mm and 35oz copper thickness with a temperature of 100degrees it results approximation of 0.5 Ohm.


C.

Edited 3 time(s). Last edit at 10/07/2018 07:29PM by callisto.

Assuming that your 35oz actually means 35um (which is 1oz/ft2) the circuitcalculator.com gives indeed about 0.5 Ohm at 100C. At 20C however the resistance is 0.39 Ohm, which at 12V comes to an wattage of 12V*12V/0.39Ohm = 369W - which i quite near the value 388W that you measured with your power meter.

yes enif,

i set 1oz thickness, and I agree with the 20degree start temp.

I measured with the ICE680R classII analog multimeter and correctly it points at the low resistance you mentioned, the chineese s**t multimeter for values less than 1 ohm is not good at all.

what I still don't understand now is why my old 360W (12V@30A) PSU was able to run everything on my 3D printer since last week and now there is no margin to run atleast the heated bed (with the risk of frying the internal/external mosfet with the risk also to boil the PSU

I resoldered with a thick track the old thin burned track on the board near the green heated bed connector but it is not enough, after seconds my thermal camera shows a big red area and If I keep the power on I cannot touch the mosfet Case so hot is.

I ordered a new MKS board just in case the things starts going wrong.

my investigation still continue.

C.

Edited 1 time(s). Last edit at 10/08/2018 04:56AM by callisto.

I changed again the external driver, now the new one is completely cold the the power connectors are absolutely well sized.

- I started heating the bed with a target temp of 60deg
- I see that with the 20deg starting temp the power meter ticks 420W (included 10W general loss).
- once 40 deg is reached then I see the power meter showing decreasing the power up to 395.

- at 60deg I see max 240W roughly (there is a fluctuation in power meter probably due to the PID PWM controller).

the mosfet heater bed I bought is that:
[www.amazon.co.uk]

It has finally a really big connectors capable to handle the massive current for my Bed.

the PSU for my bed is still separated from the rest of the PSU to drive boards and motors just to avoid a collapse of the power supplies.

Crossing the fingers I can now use the heated bed but I am still concerned why my printer had a PSU of 360W who powers the motors, logics, the extruder, and the monstre heated bed rated for more than 360W.



C.

Edited 1 time(s). Last edit at 10/08/2018 09:51AM by callisto.