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Complete heated bed kit for Ultimaker

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Posted · Complete heated bed kit for Ultimaker

Can anyone with the ebay kit check the resistance of the bed (across pins 1 & 4 on the connector)? Mine is reading 1.7-1.8 ohms, I don't think it's possible to drive this from my 24V 10A supply as it will pull almost 14A. Indeed the voltage is dropping to about 16.5V under load and the supply got too hot to touch within 1 minute. I'm debating if I should contact the seller for a return or change to a 20A supply instead.

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Posted · Complete heated bed kit for Ultimaker

This one? http://www.ebay.com/itm/Heated-Bed-Kit-for-Ultimaker-Reprap-3d-Printers-MK2-PCB-Aluminium-plate-/161157442118?pt=LH_DefaultDomain_0&hash=item2585bb6a46

I believe they are shipping the third version.

I have the 2nd version with the thinner 2mm alum. It measures 1.9 (room temp) - 2.0+ (60C) ohms. There is enough drop in the wiring to measure 23v at the connector.

 

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Posted · Complete heated bed kit for Ultimaker

Yes, that's the one. It is 1.8 ohm per the spec so I guess it's not defective. But with a 24V supply this will draw 24/1.8 = 13.33A

When I drive this from a 24V 10A supply, the voltage measured across the power supply terminals drops to around 16.5V. So the heated bed is drawing around 16.5/1.8 = 9.2A and the power supply is current limited. It's not good to run a power supply like this.

To actually drive this safely at 24V it seems I will need a 15A minimum supply.

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Posted · Complete heated bed kit for Ultimaker

Try to adjust your PSU to 19 or 20V.

As far as I know, this is the recommended setting for this heated bed. Then, the current will ve around 10A and should be within the power dissipation specs of your PSU.

Frederic

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Posted · Complete heated bed kit for Ultimaker

Yeah, Jason should really update the PS requirements. I guess I got lucky as mine is a little higher in resistance and I went with a 280w PS. Only with the drop in the wires, I'm just barely within the PS spec.

An 18V - 20V is probably what should be used.

 

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Posted · Complete heated bed kit for Ultimaker

Also note that a PCB heater has a positive temperature coefficient. So the higher the temperature the higher the resistance. Now I don't know how these boards are specified but at room temperature or at 100 degrees can make about 20 to 30% difference in resistance. Meaning that your power supply must be able to deliver that extra squared!

So if the resistance drops 20% the amount of extra power needed is a factor 1.56.. So when the design needs 200W at 100 degrees than count on a power supply of about 300W for getting it started at room temperature. This is one of the disadvantages of PCB heaters. It is also the cause of many power supplies failing. The advantage is quicker heating up.

As anon4321 mentioned the voltage drop in the wires helps him so if you find that you are at the edge of what your power supply can do using thinner wires might help you out. It is counter intuitive that is true.

I also had power supply problems since I needed to increase the amount of power because 25 minutes waiting to reach 115 degrees was a bit long. Now I pump about 240W into the bed and this reduced it to about 15 minutes. (6mm aluminium takes its time but it remains flat). So I have a 400W 24V power supply and I also run my machine from that power supply using a dc dc convert to 19 volt. So I only have 1 power cord.

Getting the right amount of power in the bed with the right power supply is not a simple task.

.

 

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Posted · Complete heated bed kit for Ultimaker

Zoev89 it's quite easy to figure out the power supply requirements, the heated bed is just a resistor and so Ohm's law tells you everything you need. The lowest resistance point along the temperature curve will be the maximum power required, so divide your voltage by that and you have the amps needed. If the resistance drops as the temperature goes up then the power draw will go down, it's no problem.

Unfortunately I'm not able to adjust my power supply below 21V, so I'll have to source another one.

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Posted · Complete heated bed kit for Ultimaker

Hey Zoev, I thought about the temp coefficient which is why I measured twice, once at room temp and once at 60C. I didn't see much of a change.1.9 and just a little over 2 at 60C. At 100C you might see power drop.

Using this http://www.endmemo.com/physics/resistt.php

Resistivity, Temperature Coeffient: 0.0039

Original Resistivity: 1.9

Original Temperature: 24

Final Temperature: 60

Final Resistivity: 2.15992

At 100C:

Final Resistivity: 2.44872

 

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Posted · Complete heated bed kit for Ultimaker

Hi Anon,

Thanks for doing a actual measurement so we have some quantitative data. I can't measure it since I use aluminium clad resistors.

Well your numbers are quite right. Lets assume you use a 24V power supply then you get the following power profile

deg res power

24 1.9 303

60 2.15 268

100 2.45 235

So that is quite some variation and well within the 20-30% difference going from room temperature to 100 degrees. And as you see the power supply requirements are large.

I just realize the power consumption difference is not quadratic as I mentioned before it is linear.

 

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Posted · Complete heated bed kit for Ultimaker

I think the added resistance in the wiring is saving me at start up. I'm using a consumer type PS with overcurrent protection. It is 280 watts so on start up, without the added wiring resistance, I think the PS would shut down.

This is what I'm using : http://www.meanwell.com/search/GS280/default.htm

 

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Posted · Complete heated bed kit for Ultimaker

Hi Anon,

Well the spec of the power supply is saying 105 to 135% overload to rated output power (this gives you almost always 300W). So if you would overload it for a short time then it will probably not shut down immediately. And of cause the wiring and the on resistance of the mosfet if you use one also does something. But as you see that 280W is well spend...

 

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Posted · Complete heated bed kit for Ultimaker

Thanks, I meant to check on that and got distracted. That meanwell supply wasn't cheap (90USD) but worth the money!

 

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Posted · Complete heated bed kit for Ultimaker

If I may ask, why are you using any tape with a heated bed for PLA? I just print directly on to the glass at 220c/70c for the first layer and usually with a brim to control corner shrinkage. Seems to stick very well until the bed temp is allowed to drop for removal.

 

I am not for PLA, I do pretty much the same as you for PLA, however the use of the heated bed for me was for ABS and it's similar cousins... I learned about using the PET tape trick from using my Airwolf 3DHDs as I get better adhearance with the PET and Elmer's purple disappearing gluesticks. My Ultimaker 2 with ABS and just glass does not adhear as well with ABS.

 

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Posted · Complete heated bed kit for Ultimaker

HI

It already supports 3 point levelling, there are 6 extra holes on the 2 edges, there is one hole in between the UM's default screw holes on each edge, they can use for 3 point levelling.

 

Jason, my relay from like version 2 burnt up and I'd like to get a new one... I may also like to get a few more of your rev 3 heated bed kits with all the extras... I have already purchased some of Ultimaker's "official" heated bed kits but they are way way way more $$$ and I think you still have a huge market as far as offering another option that is pretty killer for extra printers that one can experiment with... please get back to me and I will order some right away, thanks.

 

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