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I have been printing for a while now with my Rostock Max, but have been having troubles with the hotend and heated bed not maintaining temperature very well. I am using a fan duct (http://www.thingiverse.com/thing:104483) and the hotend gets to temp eventually with it off, but when it is on it can't maintain anything above 195C.

Am I expecting too much from the heating capabilities of the printer? I would have thought that at least the hotend heating element, with two heating resistors would be powerful enough that it would be able to handle the cooling from the fan and still maintain temperature.

Attached is a picture of the temperature curve in Rep Host.

I suspect either the heating resistors are not making good contact with the hotend or the temperature probe is not making good contact. Most likely the resistors though, you really need the foil to be tight and make as much contact between the resistors and the hotend for optimal heat transfer.

So, even with the fan off it won't get above 195 I would start at the Rambo-check output there. If that's good check wiring /connections to hotend/heatbed, if that's good. Check both resistors, maybe only one is functioning? Could be PSU issues too? Tough to find these problems? I built my hot end with K&S aluminum tube as inserts instead of foil. I can consistently get 235. Good luck

With the fan off it can reach 225, just takes a while. I will try taking apart the hotend and using foil on the resistors. I just used the RTV silicon.

K

That may be your problem. It's like Lordbinky said "optimal heat transfer" the RTV is insulating the resistors. Good luck!

Took apart the hotend, and the resistors are both shot. Physical cracks in the sides, melted casing. Looks like they overheated pretty badly. Tested resistance, they are at 8ohm+. Anyone replaced these with heater cartridges? Is the RAMBo capable of driving twin heater cartridges (seen mostly 40W, 12V)?

Going to replace them with: http://www.ebay.com/itm/V1NF-Cartridge- ... 4acb090d04

12V/20W versions.

pyrophreek wrote:Took apart the hotend, and the resistors are both shot. Physical cracks in the sides, melted casing. Looks like they overheated pretty badly. Tested resistance, they are at 8ohm+. Anyone replaced these with heater cartridges? Is the RAMBo capable of driving twin heater cartridges (seen mostly 40W, 12V)?

Use only one cartridge, not two.

Honestly I'm fairly impressed with the RTV, I wonder what temps the resistors were getting to.

lordbinky wrote: Honestly I'm fairly impressed with the RTV, I wonder what temps the resistors were getting to.

Damn HOT! To bad the heat wasn't getting to the hotend.
Geneb's manual says to wrap them with aluminum foil, not RTV.
Oh well, we all make mistakes.

Way way back I wrote the manufacturer of the High temp RTV and they confirmed that it is not a heat transfer idea material. It can withstand alot of heat but not transfer it very efficiently. So getting the resistors in there with alu-foil is important. I am not at all a fan of using the resistor however as they can and do short easily and cause Rambo failures. The heater carts are much nice to use in many ways.

They have long leads moving any bulky plugs up and away from the hotend and removing the extra weight as well.

They are far less prone to short the hotend and feed high temps back through the thermistor (ruining or killing your Rambo thermistor ports, been there done this....twice)

They heat the hotend faster and last far longer.

You only need one, not two, however this is actually a partial "con" as well since the seeme hotend was designed to be heated from both sides evenly with the resistors. This is a very minor shortcoming however and easily compensated for with the benefits of the carts.

One thing to be careful of is the batch of very cheap and poorly made heater carts that have from time to time appeared on ebay. Check your resistance on the cart before attempting to use it. You do not really want high resistance values. Mine all are around 6-10 Ohm, you simply do not want to use the few that are 24-35 Ohm

If you find a bad one cut the wires off of it and stick it in the second hole just so the hotend looks balanced.

Eaglezsoar wrote:If you find a bad one cut the wires off of it and stick it in the second hole just so the hotend looks balanced.

HAHA funny guy!

So you don't think I should use two 20W heater cartridges instead of one 40W to get the even heating? As far as I can tell each of the resistors was supposed to be delivering ~20W, so replacing each with a 20W heat cartridge should be ideal.

pyrophreek wrote:So you don't think I should use two 20W heater cartridges instead of one 40W to get the even heating? As far as I can tell each of the resistors was supposed to be delivering ~20W, so replacing each with a 20W heat cartridge should be ideal.

Have you found 20 watt heater cartridges?

pyrophreek wrote:

pyrophreek wrote:Going to replace them with: http://www.ebay.com/itm/V1NF-Cartridge- ... 4acb090d04

12V/20W versions.

See, that is what is nice about this forum. Not only do people come here looking for help but in the
process even the old timers learn something. I had no idea that the cartridges were available in the
20 watt versions. Thanks for educating me.

Actually took me a while to find them myself. They are not as common. Figure two of these should work much better than the resistors currently in use. Maybe even something to suggest to SeemeCNC to replace in their future kits.

I actually talked to John about that last week. The reasoning is that if you have a thermal runaway (due primarily to a failed thermistor), the resistors will at worse melt your PEEK section before they finally fail. A heater cartridge can do fun things like turn your hot end into a puddle of aluminum or set the machine on fire. I use heater carts in some of my machines, but I never let those run overnight or unattended. At some point there will be a way to reliably detect the runaway, but it's not here yet.

g.