BED TEMP?

[Blade-Breaker]

Hi I have been printing successfully with my printer for a couple weeks now. When printing ABS I set the bed temp to 100 dec C. Getting the bed up to temp is very slow but it would always get there until recently. The other day during a print I noticed the temp dropped to around 93 and would not go back up to 100. I thought that a blowing air over the RAMBO board may help things. Here is the weird thing I found. If the bed is warming up and gets to 85-90 it will not get (or read) any hotter unless I turn the fan away from the board. Once the air is directed away from the board the temp spikes up quickly. If the fan is redirected toward the board again the indicated temp drops instantly. I have found that if the fan is set up to pull air away from the board but not blow on it directly I can get to 100 but it is painfully slow. Here is a summary of what I have tried so far with no changes. Hopefully someone can help because I am stumped. Also I am using the power supply that came with the kit. The voltage reads 11.6V under load.

1. Wires from board to bed changed from 12 ga to 10 ga 1050 strand wire. Had to neck it down to fit into the board connectors. Yes I know way overkill but wanted to rule out everything.
2. The power input molex connector feeding the board I thought may be a choke so I soldered some 10 ga wire onto the back side of the board where the pins stick through slightly and used a Deans connector. I have 6 wires each coming from the power supply to the Deans connector.
3. Tried a second power supply to supply power to the heated bed connector I added. This power supply holds 12.05 volts under the full load of the bed. This may be a slight improvement but still very slow.
4. (EDIT) I also did re-tune the PID loop for the bed.

I just noticed this. If I direct the fan at the area where the thermistators connect to the board the temp will drop instantly. If it is directed at other parts of the board the temp does not change. When the fan is removed the temp goes back up slowly to where it was before the fan was used. Is that normal?

The only way I can get to 100 is to have a fan pulling air away from the board in just the right spot and it is very tricky to get it set up right.


Any advice would be greatly appreciated.
Ryan

[Eaglezsoar]

There is a hole in the base directly beneath the Onyx heat bed.
When you put a fan inside to cool the Rambo board some of the air goes up and cools the heat bed thermistor.
You need to cover the hole that I described with some tape so the air cannot go up there.
You should not have to take anything apart, you can see the hole I am talking about, it is exactly in the center
of the base. Here is another discussion of this: http://forum.seemecnc.com/viewtopic.php?f=54&t=2576

[Blade-Breaker]

There is a hole in the base directly beneath the Onyx heat bed.
When you put a fan inside to cool the Rambo board some of the air goes up and cools the heat bed thermistor.
You need to cover the hole that I described with some tape so the air cannot go up there.
You should not have to take anything apart, you can see the hole I am talking about, it is exactly in the center
of the base. Here is another discussion of this: http://forum.seemecnc.com/viewtopic.php?f=54&t=2576

100% correct. I slipped a piece of cardboard in there and adjusted the bed PID max value to 255 and it works great!! Glad I didnt blow it up before I posted my question. My 24V power supply was next. I wonder why I was having problems before I put the fan in there? O well it was probably a draft going through that hole??

Thanks again!!!

[Eaglezsoar]

There is a hole in the base directly beneath the Onyx heat bed.
When you put a fan inside to cool the Rambo board some of the air goes up and cools the heat bed thermistor.
You need to cover the hole that I described with some tape so the air cannot go up there.
You should not have to take anything apart, you can see the hole I am talking about, it is exactly in the center
of the base. Here is another discussion of this: http://forum.seemecnc.com/viewtopic.php?f=54&t=2576

100% correct. I slipped a piece of cardboard in there and adjusted the bed PID max value to 255 and it works great!! Glad I didnt blow it up before I posted my question. My 24V power supply was next. I wonder why I was having problems before I put the fan in there? O well it was probably a draft going through that hole??

Thanks again!!!

You're welcome. If you decide to go the 24V route, I would recommend that you use a DC-DC SSR because the Rambo was not designed to have 17+ amps going through its traces.
Just take the output of the Rambo into the input of the SSR and the 24V would go through the output of the SSR. For a little money for the SSR you will save the grief of burning up
the Rambo.

[Blade-Breaker]

There is a hole in the base directly beneath the Onyx heat bed.
When you put a fan inside to cool the Rambo board some of the air goes up and cools the heat bed thermistor.
You need to cover the hole that I described with some tape so the air cannot go up there.
You should not have to take anything apart, you can see the hole I am talking about, it is exactly in the center
of the base. Here is another discussion of this: http://forum.seemecnc.com/viewtopic.php?f=54&t=2576

100% correct. I slipped a piece of cardboard in there and adjusted the bed PID max value to 255 and it works great!! Glad I didnt blow it up before I posted my question. My 24V power supply was next. I wonder why I was having problems before I put the fan in there? O well it was probably a draft going through that hole??

Thanks again!!!

You're welcome. If you decide to go the 24V route, I would recommend that you use a DC-DC SSR because the Rambo was not designed to have 17+ amps going through its traces.
Just take the output of the Rambo into the input of the SSR and the 24V would go through the output of the SSR. For a little money for the SSR you will save the grief of burning up
the Rambo.

Great info thanks!

[cope413]

Nice SSR's for sale here...

And it helps support the Smoothie board which is a great project. http://shop.uberclock.com/collections/all

[Blade-Breaker]

Nice SSR's for sale here...

And it helps support the Smoothie board which is a great project. http://shop.uberclock.com/collections/all

Thanks If I go with the SSR I will get it there.

Been looking at a adjustable voltage power supply and may just run the entire system from 14-17 volts. One can never have to many power supplies and I have many different chargers and things for RC planes and such. http://www.progressiverc.com/junsi-s120 ... upply.html

[Blade-Breaker]

Nice SSR's for sale here...

And it helps support the Smoothie board which is a great project. http://shop.uberclock.com/collections/all

Thanks If I go with the SSR I will get it there.

Been looking at a adjustable voltage power supply and may just run the entire system from 14-17 volts. One can never have to many power supplies and I have many different chargers and things for RC planes and such. http://www.progressiverc.com/junsi-s120 ... upply.html

I have this adjustable power supply connected now. Running at 14.5v the bed heats up much faster. Does the higher voltage have any affect on the life of the components? Thinking that I will turn down the volts once it's up to temp.

[Eaglezsoar]

I have this adjustable power supply connected now. Running at 14.5v the bed heats up much faster. Does the higher voltage have any affect on the life of the components? Thinking that I will turn down the volts once it's up to temp.[/quote]

The higher voltages should not have any negative effect on any of the parts. Many people run the Rambo from a 24 volt supply. I do not feel that it would be good to run the heat bed from the Rambo directly at 24 volts because the current
requirements would be over 17 amps and after looking at the connectors on the Rambo I would not trust them or the traces on the board to pass that much current. I personally use a DC-DC SSR between the Rambo and the heat bed at 24 volts.