Unresolved KEENOVO Silicone Heater Upgrade - R1+

The Robo can really only support about 140w bed directly powered from the RAMPS.
(11amp is the limit from the RAMPS at 12v ... do the math -- 132watts)

You may have to replace the RAMPS board at this point if the bed heater MOSFET is damaged.

 

All RAMPS boards have the same specifications as far as current.
You will need to drive that via a relay if you do not want to overload the RAMPS.

The Robo power supply is not going to be able to support that extra wattage either I suspect.
You may need to boost to a higher wattage supply as well. The Robo supply is 12v 30a (360w) so base your calculations off of that.
IIRC the last time I looked at this (long time ago) the free overhead for the stock power supply was less than 100w, but that is just what I think I remember Someone else might have better numbers (there are some older threads on here that go into that sort of stuff). With LEDs and the like that have been added since the early R1 days I imagine there is less free wattage than before...

 

Not a chance. There are precious few videos of any upgrades.

I can assure you that you will not get 700w out of the stock power supply for longer than an instant
If you attach a heater that really pulls that much you will get something to smoke (a fuse or the power supply).

Most people who did the type of modification you are describing used a SSR to turn the power on and off via the RAMPS output and a stand-alone 12v power supply to power the heater.

 

If the 12v supply you have has enough wattage to power the heater then you are good.
As for the mod... all you really need to do is to take the 12vdc output from the RAMPS that goes to the bed heater now and use it to power the coil of a 12vdc SSR. Then the contacts of that relay will turn the external 12v supply on/off to the bed (it needs to interrupt one side of the 12v line from the external supply to the bed).

This thread describes most of it: http://community.robo3d.com/index.p...nstalling-ssr-pid-control-instructions.17512/

Only difference is that the thread may still be using the internal supply, but switching that to an external is easy enough. Just use an external power supply through the relay contacts.

 

Those are fine and as fast (or slow) as the bed heaters heat the glass and the temperatures involved ... borosilicate glass is not a requirement. Plate glass is fine (and far less expensive).

Just plan on using that PSU just for the bed heater... not for the Robo and you should be OK.

 

Nobody else is using a 700w heater. That will heat quick enough that you might have those sorts of issues. Plate would be better than a mirror...

 

When I upgraded my bed heater in the R1 I went with a 300W. I did not place the heater directly under glass, but rather had a 1/4" aluminum plate cut to match the dimensions of the original bed then placed a single sheet of float glass (what is used for picture frames and single pane glazing) on top so that I wasn't building directly on the aluminum bed.

You might want to consider modifying the Robo firmware to use PID control of the bed temperature rather than the default Bang-bang method of heating the bed. I don't really know if that would help but I think the severe increase in temperature is what caused your glass bed to shatter.

 

Sometimes small details get lost in the multitude of words written in a thread.

Even at 300W if you just used thin float glass I can see where it would still shatter. The reason that glass only beds are usually borosilicate glass is that it is more stable thermally than float glass. Issues with borosilicate is that it chips rather easily with too much bed adhesion (as when using PETG). My suggestion is only use the float glass as a build plate or use much thicker glass than you can get at your local home improvement store. Using Aluminum plate as a bed would be your solution if thicker
glass is not a viable option.

Even the best silicone heaters do not heat evenly, they have embedded elements arranged in some sort of linear manner that heats outward, so some sort of heat spreader will help to avoid hot spots. It is those hot spots that cause the glass to heat in irregular patterns. Glass is an insulator and the hot spots resulting from the heater elements in direct contact with the glass will cause thermal expansion to happen at different rates. That is likely what caused the shattering.

When I did my heater upgrade I used a piece of aluminum plate cut to size, I purchased from Midwest Steel and Aluminum which turned out to be cheaper than buying from Amazon as well as most other online metal dealers and I could get it in the exact size I needed

 

See my additional added paragraph, it has to do with hot spots. That is why you need some kind of heat spreader. You will still have hot spots even though you may be using borosilicate glass, it is just that it is more thermally stable so reacts differently under even localized heating.

 

Well, you do not need 1/4" aluminum I can attest to that.
probably 1/8" or 3/32" would be fine.
A baking pan is probably good enough

 

I am pretty sure I went 3/16" from Midwest Steel then some cheap glass at Lowes cut to size and four spring clips from a bag of them I got at the Dollar Store