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hot bed issues 24v

Posted by foshon 
hot bed issues 24v
February 17, 2013 09:54AM
I recently purchased and installed the Trinty Labs y-axis upgrade (Awesome!!). I hooked up the convertor for the heated bed and turned it on. It runs for a bit and then the ramps stops send power. I can connect the bed to the ramps directly but I only get up to around 45 degrees C. I don't think it's possible to screw up the connection to the board, 4 ports 2 in and 2 out. The heated bed is one of the kapton units they sell on the web site. I show 2.5 Ohms between the legs of the heater. Any ideas?

Edit: changed title to better fit description

Edited 1 time(s). Last edit at 02/17/2013 11:00AM by foshon.
Re: 12-24vdc convertor
February 17, 2013 10:59AM
Have you got a 12V 30A power supply? The kapton heater draws a lot of juice. 2.5R at 24V = 230W.
Re: 12-24vdc convertor
February 17, 2013 11:24AM
It's a PC power supply rated for 28A. I have a 24v 10A Lambda unit I could just use to power the bed directly but then I would not have control of the temp. Why is the ramps dropping just the bed port? The hot end keeps chugging right along.
Re: 12-24vdc convertor
February 17, 2013 02:05PM
You'll need to feed 24V to the RAMPS hotbed input, because the polyfuse limits current to about 11A. You could also connect 24V PSU to the hotbed input and have the temperature controlled by the RAMPS.
Re: 12-24vdc convertor
February 17, 2013 04:34PM
Got to tinkering, turns out the red hot bed PCB fits perfectly between the leveling set screws on the G10 sheet. I taped it to the bottom of the aluminum plate. It'll get up to 83 degrees, I'm going to insulate the bottom and see if I can get it up to ABS temps. Thanx for the help.
Re: hot bed issues 24v
February 17, 2013 06:02PM
Why not hook the 24v unit up to RAMPS for only the bed? This is why RAMPS has two power inputs, one is for "everything but the bed" and the other is for the bed only. Then you have control of the temperature by RAMPS and using 24v.

Perhaps a better solution, and if your board supports it, you can also run everything on 24v (though 10A might be a bit underpowered - I have 18A). Before doing this, so as not to blow anything check the following 3 things:
1. D1 is not installed. Remove your X stepper driver and check for the presence of diode D1 there. If it is there, it will need to be removed (unless you are using the Taurduino arduino clone, which can handle higher voltages)
2. Ensure your capacitors are rated for at least 24v. Mine were rated for 16, and I found out the hard way what happens when you overvolt a capacitor (it pops and lets out a lot of smoke, FYI)
3. Tune your hot end's PID_MAX down to 64 so as not to run too much through your hot end.

I use a budaschnozzle on 24v and everything on my system is fine. I have the bed upgrade and agree it's great!.
Re: hot bed issues 24v
February 17, 2013 08:50PM
How do you handle not having the usb port to run the Aurduino? Mines an SD card controlled lcd panel unit. Thanks for the advice, any ideas on where to get a reasonable 18A 24v supply?

NM found a 18.8A 24vdc PS at Jameco, OTW!!

Thanks again

Edited 1 time(s). Last edit at 02/17/2013 09:57PM by foshon.
Re: hot bed issues 24v
February 18, 2013 08:54AM
What do you mean "not having the USB port run the arduino?"

My setup is a bit more complicated. I have two power supplies, a 5v for a raspberry pi, and a 24v for everything else, which is split into 12v and 24v.

220vac comes in from the wall outlet and is divided into two parts, once to the 5v cellphone charger which is always on, and once to a relay which switches the 24v ps on/off (based on M80/M81).

5v "always on" goes into a raspberry pi, which then powers the arduino, LCD display and SD card (which I no longer use, thanks to the RasPi). Arduino provides a web interface with repetierserve where I can upload gcode to and print from any browser.

24 volts "switched" then gets divided again, once to a downconverter to 12v for LED strips, fans, and once to the RAMPS voltage in. This way when I switch the 24v on, the lights-fans come on at the same time. The 24->12v converter was a cheap one from ebay (around $1.50 or so), and cannot handle enough watts for my hotend, hence the hotend running at 24v.
Re: hot bed issues 24v
February 19, 2013 01:15AM
Just a note that if you're using 24V into the RAMPS Heated Bed input, be aware that the 11A Polyfuse is only rated for 16 Volts, and could lead to all sorts of general weirdness.

Personal recommendation: Desolder the 11A Polyfuse and replace it with a piece of wire, then put a proper fuse in-line to the input of the RAMPS, on the +ve line from your PSU.
Re: hot bed issues 24v
February 19, 2013 07:30PM
Noted all the 24v changes. Thanks a ton!
Re: hot bed issues 24v
March 05, 2013 02:46PM
I have hooked up the 24V PS and the kapton heater is rocking! Stable temps, big bed, I'm in geek heaven. My board (from ReprapDiscount the guys on Ebay) had 35V caps. I did have to remove the D1 diode, but other than that and the PID_MAX change it could not have been easier.

Cefiar: Thanks, what would you recommend using as an in-line fuse. Is an automotive blade fuse adapter acceptable?
Re: hot bed issues 24v
March 05, 2013 07:47PM
Yes, an Auto blade fuse should be quite acceptable.

If you're using a Kapton heater designed for 24V, then you will probably find it draws less than 10A, so a 10A fuse for just the heatbed will be fine. If you're using a heatbed designed for 12V, then you really need a higher powered fuse (20A or better) due to the lower bed resistance.

On my 24V setup, I use a 15A fuse for everything (hot ends, heated bed, etc), and I have a Kapton heater (the Mendel Max one) for my bed.
Re: hot bed issues 24v
March 06, 2013 07:28AM
One fuse on the main,the 11A connection right?
Re: hot bed issues 24v
March 07, 2013 05:01PM
If you still have the RF500 fuse on the board, then yes, one in the 11A connection only, on the +V side.

If you've replaced both with a wire link, you should probably put either:
One larger fuse on both (only if you're feeding everything the same voltage).
1 x 5A fuse on the 5A input, and 1 x 10-20A(*) fuse on the 11A connection.

Note: Fuses should only be put in the +V side of any connection. This avoids issues with things that have common ground (eg: a metal chassis) accidentally bypassing the fuse.

* - The size of this fuse should be greater than your maximum current. So if you draw ~8.5A on your heated bed (~200W Kapton heater from Trinity Labs @ 24V = 8.33A minimum), then you should probably use a 10A fuse. For a standard Mk2 PCB 11A bed at 12V, you'd want a 15A fuse. If you're very close to the next common value of the fuse, go one step up (eg: ~120W Kapton heater from Trinity Laps @ 12V = 10A minimum, so you should use a 15A fuse).
Re: hot bed issues 24v
March 07, 2013 10:16PM
Thank you very much!
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