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Heated bed amps
Posted by carmojos
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Heated bed amps April 08, 2014 12:43AM |
Registered: 11 years ago Posts: 38 |
Hello reprap gurus,
I was investigating why my heated bed was not holding temp when I discovered that it was only pulling 4.37amps. Not sure what my problem is.
I pulled everything else off the ramps board just in case my PSU was underpowered and got the same results. I also replaced the 10a fuse.
Any ideas?
I was investigating why my heated bed was not holding temp when I discovered that it was only pulling 4.37amps. Not sure what my problem is.
I pulled everything else off the ramps board just in case my PSU was underpowered and got the same results. I also replaced the 10a fuse.
Any ideas?
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Re: Heated bed amps April 08, 2014 05:14AM |
Registered: 11 years ago Posts: 1,592 |
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Re: Heated bed amps April 08, 2014 09:14AM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 08, 2014 12:24PM |
Registered: 10 years ago Posts: 24 |
1.2 ohms appears to be a reasonable value for bed resistance.
I'm also assuming the reported bed temperature is a sane value. If it's not, the firmware will prevent heating.
Depending on your firmware settings, I believe there is a PID setting that limits the maximum current going to bed.
It's something along the lines of PID_MAX. You will want to increase this if it's less than 255.
If you have your bed configured for bit bang, then look for something like BITBANG_MAX and increase if less than 255.
I'm also assuming the reported bed temperature is a sane value. If it's not, the firmware will prevent heating.
Depending on your firmware settings, I believe there is a PID setting that limits the maximum current going to bed.
It's something along the lines of PID_MAX. You will want to increase this if it's less than 255.
If you have your bed configured for bit bang, then look for something like BITBANG_MAX and increase if less than 255.
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Re: Heated bed amps April 08, 2014 12:35PM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 08, 2014 11:54PM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 09, 2014 06:23AM |
Registered: 11 years ago Posts: 1,592 |
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Re: Heated bed amps April 09, 2014 03:12PM |
Registered: 12 years ago Posts: 258 |
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Re: Heated bed amps April 09, 2014 03:14PM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 09, 2014 08:17PM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 09, 2014 09:54PM |
Registered: 12 years ago Posts: 258 |
Ah... most people put 12V through their heated bed. With only 5V you'll get less than 1/2 the amps and less than 1/4 of the power out of a standard PCB board heater.
On the other hand, to get 120W out of a heater at 5V, you'd need 24A, and a resistance of 5V/24A=0.2 Ohms. I don't advise it, but if you want to get experimental, it might be possible to get 100W with what you have, but you should beef up your wiring and system to handle 24A, and then you might be able to turn the parallel double-loop trace of the typical PCB board heater into a parallel 10-loop circuit with some trace cutting and shorting.
Edited 2 time(s). Last edit at 04/09/2014 09:56PM by DaveX.
On the other hand, to get 120W out of a heater at 5V, you'd need 24A, and a resistance of 5V/24A=0.2 Ohms. I don't advise it, but if you want to get experimental, it might be possible to get 100W with what you have, but you should beef up your wiring and system to handle 24A, and then you might be able to turn the parallel double-loop trace of the typical PCB board heater into a parallel 10-loop circuit with some trace cutting and shorting.
Edited 2 time(s). Last edit at 04/09/2014 09:56PM by DaveX.
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Re: Heated bed amps April 09, 2014 10:07PM |
Registered: 11 years ago Posts: 38 |
I'll have to swap the pins around in the marlin firmware. I hooked up my RAMPS 1.3 as the wiring instructions said to and that puts the heated be on D8 which is only 5volts, but allows for 11Amps.
Any suggestions on how to wire it to 12volts other then changing the pin settings in Marlin and swapping it with the fan wiring?
Any suggestions on how to wire it to 12volts other then changing the pin settings in Marlin and swapping it with the fan wiring?
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Re: Heated bed amps April 09, 2014 11:01PM |
Registered: 12 years ago Posts: 258 |
I think RAMPS takes 12 V:
1.3: [reprap.org] [reprap.org]
or
1.4: [reprap.org] and [reprap.org]
Edited 1 time(s). Last edit at 04/09/2014 11:02PM by DaveX.
1.3: [reprap.org] [reprap.org]
or
1.4: [reprap.org] and [reprap.org]
Edited 1 time(s). Last edit at 04/09/2014 11:02PM by DaveX.
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Re: Heated bed amps April 09, 2014 11:36PM |
Registered: 11 years ago Posts: 38 |
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Re: Heated bed amps April 10, 2014 11:02AM |
Registered: 12 years ago Posts: 258 |
12 V through a 1.2 ohm heatbed would try to draw 10amps, dissipating 120Watts.
A 12V x 5A power supply is only capable of emitting 60W, which will be insufficient for a 120W heated bed. Your power supply is incapable of putting the full 120W or 10A through the heatbed.
When you hook the 5V x 16A power supply to the 1.2 ohm heated bed, it pulls the 4.37 amps for about 21W. The power supply won't fault because it is within its capacity, but it won't heat the bed up very much.
See [reprap.org] or [reprap.org] or [reprap.org] or
Edited 1 time(s). Last edit at 04/10/2014 11:07AM by DaveX.
A 12V x 5A power supply is only capable of emitting 60W, which will be insufficient for a 120W heated bed. Your power supply is incapable of putting the full 120W or 10A through the heatbed.
When you hook the 5V x 16A power supply to the 1.2 ohm heated bed, it pulls the 4.37 amps for about 21W. The power supply won't fault because it is within its capacity, but it won't heat the bed up very much.
See [reprap.org] or [reprap.org] or [reprap.org] or
Edited 1 time(s). Last edit at 04/10/2014 11:07AM by DaveX.
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Re: Heated bed amps April 10, 2014 11:54AM |
Registered: 11 years ago Posts: 1,320 |
your power supply didn't short - it overloaded. It is probably not rated for the 10 amps that the heated bed draws. What everyone else is saying is true. There is no 5 volt rail on ramps. There IS a 5 AMP rail and there is also an 11 AMP rail. Both are meant to take 12 volts. You'll never get your heat up to the required levels with 5 volts.
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Re: Heated bed amps April 10, 2014 03:14PM |
Registered: 11 years ago Posts: 187 |
Your PSU will never be able to provide enough power with those specs. Even if you max out the 5v rail, you're only going to get 80 watts out of it which still isn't enough and it would require modding the heatbed. Save yourself endless frustration and get another PSU. Hell, go to a computer repair store and they'll probably give you a broken one. The most common mode of failure with those is the 12v standby which you don't need for reprap anyway. I've been using my trusty "broken" Antec for over a year now and it's still going strong! 
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Re: Heated bed amps April 10, 2014 07:20PM |
Registered: 11 years ago Posts: 38 |
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