MK2A Heated Bed causes board to crash

[Veti]

e3d makes 300x300 beds
https://e3d-online.com/collections/printer-parts-electrical/products/high-temperature-heated-beds

but they are ac beds.

their variopower bed 24v is only available in 300x200
https://e3d-online.com/collections/printer-parts-electrical/products/varipower-bed

you could try and source a voron 2 buildplate with a Keenovo heat pad
https://store.digmach.com/collections/voron-parts/products/build-plate-for-voron-2-3d-printer?variant=31774400675885 (us store but sold out, you could ask on the voron discord for other suppliers)
the matching kenoovo heater is avaiable in 24v (though voron guide says go with ac version at nearly twice the power)
https://keenovo.store/collections/standard-keenovo-silicone-heaters/products/keenovo-square-silicone-heater-3d-printer-build-plate-heatbed-heating-pad?variant=8324020895799

but to be honest if you are going for a 300x300 bed, you are in the territory of ac beds.

[Phaedrux]

https://www.amazon.com/310x310mm-Aluminum-HeatBed-Thickness-Creality/dp/B07H8DXVQD/ref=sr_1_6?dchild=1&keywords=cr-10+heated+bed&qid=1607369292&sr=8-6

[JamesM]

You could get a nice cast aluminum bed and put a 24v silicone heater on it. 713maker.com has some nice stuff. This is a 300x300 bed https://713maker.com/ft-5/ft-5-heated-bed

[bdelia]

@Phaedrux said in MK2A Heated Bed causes board to crash:

Do you have a link to the item you've purchased?

Here is a link to what I purchased:
http://www.zyltech.com/zyltech-3mm-aluminum-heated-heat-bed-3-sizes-available/

If you look at the description I purchased the one labeled as 300 x 300 MK2A Heated Bed.
300 x 300mm MK2A Heated Bed

Outside dimension: 330x330 mm
Usable size: 300x300mm
Resistance: 1.05-1.3 ohm
Voltage: 12-24 V (recommend 24V for better performance)
Pre-wired with thermistor and power cable

[Phaedrux]

Thanks. That helps.

In that case your measurement of 1.4 ohms is closer to the 1.3 ohms they specify.

Still not clear how it's capable of 12 or 24 without different wiring, but at least Zyltech is a recognizable brand and not just some ebay seller or something.

[A Former User]

Still not clear how it's capable of 12 or 24 without different wiring, but at least Zyltech is a recognizable brand and not just some ebay seller or something.

From the specs it is effectively a powerful 24V bed, at 24V it is nominal 0.52W/cm^2 which is a little over the recommended 0.4 and at 12v it is at 0.13W/cm^2 which is borderline useless imho - so calling it dual voltage is BS.

At 24W and 1R05 to1R3 it's 550W to 450W and 23-18A, but OP is using a external mosfet so that should be fine, leaving voltage drop due to thin wiring or power supply over current protection kicking in (prematurely).

[Phaedrux]

@bearer said in MK2A Heated Bed causes board to crash:

so calling it dual voltage is BS.

Ok that makes more sense and explains why the reviews of the heater say using it at 12v is pointless because it can't reach even moderate temps.

[BoA]

@bearer Well... If You are on the lower R side, and close to 23A then bed alone is 550W + hotend 50W + motors + duet and over current protection might be triggered not so prematurely as You might think. Best would be to measure current from PSU, but not many multimeters can do it for range higher than 15-20A

[Veti]

@bdelia said in MK2A Heated Bed causes board to crash:

Mosfet

the duet will definatly not handle the current of that heated bed.
maybe the mosfet you have can not either.

Just to be on the save side, for 23-18A you need 10 AWG wire btw!

[A Former User]

@Veti said in MK2A Heated Bed causes board to crash:

the duet will definatly not handle the current of that heated bed.
maybe the mosfet you have can not either.

thtas a good point, but i don't think an under dimensioned mosfet would cause the board to reset

the peak current also probably won't last long due to the ptc characteristic of the copper traces, so I'd use silicone wirng for the flexibility and the increased temperature rating means you can probably get away 14 or even 16 gauge. (given op measured the resistance and putting himself in the lower power range, even the 18A rating of the Duet could work, but too close for comfort imho)

[dc42]

Your 24V PSU probably has a voltage adjustment potentiometer. If you turn it down to the minimum, which is probably about 20V, then the current should be just about within the rating of the Duet. The hot end power will drop too, however most hot end heaters are over powered anyway.

[bdelia]

@dc42 said in MK2A Heated Bed causes board to crash:

about within the rating of the Duet. The hot end po

Thanks for all of this discussion folks.

If I read the comments after I posted the link to the bed and specs, can I assume you all feel this board can be used safely at 24V?

I do run an external Mosfet and I will get 10 gauge wire to help with safety from the Mosfet to the bed.

I am in a email conversation with the seller and am trying to determine if I should ask to return this board and look for something else. I do not want to introduce AC power as I am not yet comfortable with that concept, it feels more nuanced from a safety lense.

Thanks
Brett

[bdelia]

I just got word from Zyltech that they updated the specs based on my experience...I guess I am also confused how the dual power works, most dual power beds I have seen you need to solder differently to change the input voltage.

http://www.zyltech.com/zyltech-3mm-aluminum-heated-heat-bed-3-sizes-available/

300 x 300mm MK2A Heated Bed

Outside dimension: 330x330 mm
Usable size: 300x300mm
Resistance: 1.05-1.3 ohm for 12V
Resistance: 1.5-2.2 ohm for 24V
Voltage: 12-24 V (recommend 24V for better performance)
Pre-wired with thermistor and power cable

[A Former User]

@bdelia said in MK2A Heated Bed causes board to crash:

Resistance: 1.05-1.3 ohm for 12V
Resistance: 1.5-2.2 ohm for 24V

lol, the resistance is the same regardless of voltage when there is just the two connections to the bed..

edit:

.I guess I am also confused how the dual power works,

it kinda doesn't work, but it boils down to omhs law, resistance stays the same*, voltage changes and that changes the power. power=voltage x voltage / resistance.

*) the resistance will change a little with temperature, but thats just being pedantic

[bdelia]

Is the consensus then that this bed is safe with how I have it set up?

I run a Mosfet between the Duet 2 Ethernet and the bed, I will be upgrading the 14 gauge wire to 10 gauge as recommended in a previous post.

[A Former User]

@bdelia said in MK2A Heated Bed causes board to crash:

safe

i'd add a thermal fuse before rubber stamping it as safe tbh

[Phaedrux]

Safe in that it won't immediately melt at least.

[bdelia]

@bearer I will definitely look into that, thanks

[Veti]

@bdelia said in MK2A Heated Bed causes board to crash:

Resistance: 1.05-1.3 ohm for 12V
Resistance: 1.5-2.2 ohm for 24V

just this statement tell you that the seller has no idea what he is talking about.