Rambo 1.1B 2 heated beds and 1 extruder?

doomstrike

Rambo 1.1B 2 heated beds and 1 extruder?
December 05, 2014 01:34AM

Registered: 10 years ago
Posts: 9

Hi guys,

I'm building a scaled up version of a Lautr3k. What I want to know is if the Rambo 1.1B board can be used to power 2 heated beds and 1 extruder instead of the default 2 extruders and 1 heated bed. I have close to no knowledge regarding electronics from an electrical engineering point of view and wondering if this is possible or if I'll just damage the Rambo board or blow it's fuse if I even try. Hoping to be able to build a print area that's around 600mm x 600mm smiling smiley

I realize i would have to go and make firmware changes for it and I'm not worried about that aspect as I am a programmer.

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cdru

Re: Rambo 1.1B 2 heated beds and 1 extruder?
December 05, 2014 08:51AM

Registered: 10 years ago
Posts: 869

Not without some hacks if you're running at 12V. The default board only has a single high-current (15amps) output for a heated bed. Hooking up two standard 10+amps heated beds to the single heated bed output, or trying to repurpose one of the extruder outputs for a heated bed will blow the fuse if you're running 12v. If you go up to 24v, then your current needs are halved so you could operate two heated beds off the same output. Alternatively, you could use relay (very cheap, but annoying noisy clicks), solid state relay (easiest and silent, but more expensive), or a fairly simple mosfet circuit (cheap, but some electrical and soldering skills needed) to act as a switch that's triggers the heated bed.

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enif

Re: Rambo 1.1B 2 heated beds and 1 extruder?
December 07, 2014 06:45AM

Registered: 9 years ago
Posts: 590

If you go with the cheap 40A mechanical automotive relay (as I do), you can change the BED_CHECK_INTERVAL from the default 5000 to 15000. This reduces the clicking sound mentioned by cdru to max. once every 15 seconds, so it's no longer an issue (at least for me). But the temperature of the heated bed will still be kept to within a few degrees from the target value. In Marlin the BED_CHECK_INTERVAL is in Configuration_adv.h, in Sprinter it's in Configuration.h.

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cdru

Re: Rambo 1.1B 2 heated beds and 1 extruder?
December 08, 2014 08:18AM

Registered: 10 years ago
Posts: 869

Quote
enif
If you go with the cheap 40A mechanical automotive relay (as I do), you can change the BED_CHECK_INTERVAL from the default 5000 to 15000. This reduces the clicking sound mentioned by cdru to max. once every 15 seconds, so it's no longer an issue (at least for me). But the temperature of the heated bed will still be kept to within a few degrees from the target value. In Marlin the BED_CHECK_INTERVAL is in Configuration_adv.h, in Sprinter it's in Configuration.h.

Maybe after a while you wouldn't notice it, but I still think every 15 seconds hearing a click would get annoying. I guess it would also depend on how loud it is over normal (and unavoidable) sounds the printer makes such as steppers and fans.

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doomstrike

Re: Rambo 1.1B 2 heated beds and 1 extruder?
December 13, 2014 03:45AM

Registered: 10 years ago
Posts: 9

I reached out to RepRapElectro and this was their reply:

Quote
RepRap Electro
From an electronic point, it is possible, the mosfets that are used for the heat-bed and for the heat-0, fan-0 and heat-1 connectors are the same, however they are using different power rails. The heated bed uses a separate power rail which is protected by a 15A fuse while the heaters use a different power rail protected by a 5A fuse.
The fuse for the heaters can be replaced with a similar fuse with higher current rating but it will be sharing the current with the hotends and fans.

The fuse is a Nano2 fuse and Littelfuse has one rated for 15A with part number 0448005.MR (http://www.littelfuse.com/products/fuses/surface-mount-fuses/nano-2-fuses/448/448015.aspx).

The RAMPS for example uses a fuse of 11A for the heat-bed and a 5A fuse for the heaters and motors, so I think 15A should be able to handle both the additional heat-bed and the hotends, you may want to check the current requirements of your heated beds.

An alternative solution could be to replace the 15A ATO fuse for the heat-bed and wire both heat-beds to the same connector on the RAMBo, the mosfet itself should be able to handle up to 60A.
You will however have issues if the heat beds don't reach the same temperature at the same time, as you won't be able to control both separately. The connectors themselves might also not be suited for such a high current, so I'd be worried that the connectors might melt.

In either case though, know that these are not tested configurations and while they should work, there are no guarantees that they will.

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