Heated bed wont maintain more then ~100C March 25, 2016 11:24PM |
Registered: 13 years ago Posts: 42 |
Re: Heated bed wont maintain more then ~100C March 26, 2016 12:06PM |
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Re: Heated bed wont maintain more then ~100C March 26, 2016 05:14PM |
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Re: Heated bed wont maintain more then ~100C March 26, 2016 06:16PM |
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Re: Heated bed wont maintain more then ~100C March 26, 2016 09:20PM |
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Re: Heated bed wont maintain more then ~100C March 26, 2016 10:05PM |
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the_digital_dentist
MrBaz, you're absolutely wrong regarding power and Ohm's law. Increasing the supply voltage will increase current and power, and therefore, heat.
The bed heater is a resistor. Ohm's law applies- current=voltage/resistance. Power=current^2 * resistance
TbirdMan, a dc-dc converter is a power supply. Semantics aside, you can increase power by increasing applied voltage via another power supply (or DC to DC converter), or get a heater with a lower resistance that will use more power and create more heat from the supply you have, assuming that supply can handle the load. Be sure that whatever switches power to the heater (MOSFET or SSR) can handle increased current and make sure the PCB can handle it too.
Re: Heated bed wont maintain more then ~100C March 26, 2016 10:10PM |
Registered: 10 years ago Posts: 154 |
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TbirdMan
Ok, specs. My PSU is a 550W ATX power supply, one 12V 45A rail run through 8 wires (two for each + and - lead) to the RAMPS , so more then enough. As the digital dentist pointed out you are misunderstanding Ohm's law, doubling voltage for the same resistance quadruples power (P=V^2/R) and only doubles current (I=V/R) meaning it is more efficient. the bed is using PID that I ran the autotune on, max set to 255 (100%). PID constants are not the issue, 90W for 314cm^2 is just a bit anemic. it can hold around 100C printing if the part cooling fan is not at 100%, but barely. My bed is running through the RAMPS 1.4 MOSFET, the wires that came on the heater are beefy (maybe 10ga or 12ga) and get slightly warm to the touch under 100% dty cycle, but not excessively. the wires I added to reach the controller are either 18ga or 16ga (it is about impossible to read sometimes) from a computer power supply, doubled up on each line, they stay cool to the touch.
I realize a dc-dc converter is another power supply, I guess what i meant to say is I already have an ac-dc PSU that can provide more then enough 12V current, I would like to avoid adding another ac-dc supply as that would be both more inefficient, and would make it more difficult to implement the PS_ON control pin in the future. If i run 15V the current on the 15V side will only be about 9.3A, however the power on the 12V side will be around 12A, a bit more then i want to draw through the RAMPS board (especially with the polyfuses). I could either beef up the RAMPS with blade fuses and bridge wires to increase current capacity, or I can run a MOSFET from the RAMPS output to control a separate 12V line coming direct from the PSU. I like the second option more as it means if I should ever have to repalce my RAMPS board it should be a drop in affair rather then having to mod the new board.
I guess my biggest question is does anyone know what kind of current these MK3 direct on plate heaters can take?
Re: Heated bed wont maintain more then ~100C March 27, 2016 12:40AM |
Registered: 13 years ago Posts: 42 |
Re: Heated bed wont maintain more then ~100C March 27, 2016 03:23PM |
Registered: 10 years ago Posts: 154 |
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TbirdMan
it will hit 110 if I have the bed covered, but if the part cooling fan is on at all it plummets. I know how PID controllers work, I have programmed a few myself. that much error should have the PWM running 100% dty cycle. I turned off PID and went straight bang-bang and it took over 10min to go from 100 to 110. It is not PID, 90W is just under-powered for this size bed. I think the simplest solution is to find a higher wattage bed and either run it at 24V (meaning another ac-dc power supply, yuck) or beef up my ramps board bed circuit and run it at 12V. I suppose if I am getting a new heater anyway I could also go the SSR/120Vac silicone heater route.
Re: Heated bed wont maintain more then ~100C March 27, 2016 05:26PM |
Registered: 13 years ago Posts: 42 |
Re: Heated bed wont maintain more then ~100C March 27, 2016 05:59PM |
Registered: 9 years ago Posts: 1,873 |
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TbirdMan
it is a small 40mm blower with a custom duct I find it helps when bridging ABS. however when a heater like this is at it's limit it won't take much to cool it by a couple deg. I have been having warping issues and as part of the attempted solution I was trying to print at 110 bed temp. 100 worked ok, but still cooled a bit and got some excessive corner lifting. The advice I found suggested that temp's as high as 120-130 would not be out of line but the consensus I found was 110 for best results. It is not that I absolutely have to have 110deg, but it would be nice to have the option.
Re: Heated bed wont maintain more then ~100C March 27, 2016 07:08PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 07:31PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 07:37PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 07:44PM |
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IMHO they just waste a lot of energy for very little heating.
Re: Heated bed wont maintain more then ~100C March 27, 2016 08:27PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 09:13PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 09:17PM |
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Re: Heated bed wont maintain more then ~100C March 27, 2016 11:05PM |
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Re: Heated bed wont maintain more then ~100C March 28, 2016 08:43AM |
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Re: Heated bed wont maintain more then ~100C March 28, 2016 12:42PM |
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Re: Heated bed wont maintain more then ~100C March 28, 2016 01:36PM |
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Re: Heated bed wont maintain more then ~100C March 28, 2016 07:53PM |
Registered: 10 years ago Posts: 154 |
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TbirdMan
my bed is a single unit, the heater is directly attached to the aluminum bed. I have a paper/bubble-wrap shipping bag wedged on the underside insulating the bottom. the top is just bare aluminum with masking tape. the bed is mounted to the chassis by three ~1cm brass standoffs, so I suppose it can lose a bit of heat there, but likely not much. You also have the benefit of the glass not conducting heat very fast, so what heat is lost to air will not be so quickly replaced at the surface to be lost again if that makes sense.
Re: Heated bed wont maintain more then ~100C March 28, 2016 09:05PM |
Registered: 13 years ago Posts: 42 |
Re: Heated bed wont maintain more then ~100C March 28, 2016 09:39PM |
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Re: Heated bed wont maintain more then ~100C March 28, 2016 09:51PM |
Registered: 13 years ago Posts: 42 |
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nebbian
The easiest and cheapest way to get around the problem is to bump up your power supply voltage to around 14 volts, and add an automotive 30 amp relay to do the switching instead of putting full current through the polyfuse. I've done this to two printers, and it works well.
Re: Heated bed wont maintain more then ~100C April 26, 2016 03:49PM |
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Re: Heated bed wont maintain more then ~100C April 27, 2016 05:41AM |
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Re: Heated bed wont maintain more then ~100C May 04, 2016 06:37PM |
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