Rambo Dual Extrusion Hot ends heat slowly and at different rates

So, I recently upgraded my Prusa i3 to dual extrusion using two 24v E3D-V6 all metal hot ends. I'm using a RAMBo 1.1b version board to drive everything. Before upgrading to dual extrusion, I had my heater cartridge short out mid print. it was the 24v 25watt heater. Before shorting out, it would go from 20C to 260C in about 30 seconds. I've replaced it with the same heater cartridge and that's what the second hot end has. With dual extrusion enabled, the first hot end will go from 20C to 260C in 3 minutes, the second hot end however, would only get up to 235 in about 8 minutes and I shut it off after no further progress by 12 minutes.. I've tried PID tuning, which has had very little impact. I've also verified that the voltage coming from the board when the hot ends are heating is 24.5 volts. The thermistors are seated properly. If I swap the inputs for Heat0 and Heat1, the heat times are reversed, so it's clearly not the heater cartridge. I've also verified the the resistance from both heater cartridges, and they're both the same and what they should be. I've attached my Configuration.h and Configuration_adv.h files. If anyone can provide any help, it would be greatly appreciated, I've been banging my head on this for the past 3 straight days with no luck.

Thanks,

Zack

Edited 1 time(s). Last edit at 11/20/2015 08:07PM by zborschuk.

It could be a mosfet problem, check the temperature of the mosfet. If it's dissipating a lot of heat, then that's where all the power is going.

Just to make sure: With pid auto tuning, did you manually enter the values in firmware or gcode? Is the eeprom enabled? if so the firmware settings are ignored, that could explain you didn't see any change.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Mosfets aren't too warm, just 32C. In terms of the PID settings, I entered them into the firmware files then uploaded them. EEPROM looks to be enabled, but when I look at the LCD settings for PID values, they're the newly uploaded settings.

Maybe you can try updating the PID values using gcode as per the guide here:
PID auto tune

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

I'll give that a try when I can. One of the resetable fuses blew, and I won't have a replacement until Wednesday. Think while testing voltage I accidentally shorted the fuse.

Well, since I only blew the fuse to the extruder and fan mosfets, I decided to check the EEPROM values before and after a firmware update to see if they change, and they did, so I don't think it's an issue with EEPROM keeping/using old settings. Any other suggestions?

Edited 1 time(s). Last edit at 11/24/2015 09:47AM by zborschuk.

So the heater cartridges work well on extruder output #0? It must be the MOSFET then. Replacing it will be difficult since it is a SMD, and the MOSFET tab is soldered to a large via rich PCB heatsink, which will make it harder to de-solder. Not impossible but you risk damaging the board even further. Might as well buy a new one. There's no telling if there are other problems that might be waiting after the shorted heater cartridge.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Well, I wouldn't say it works 'well' on E0, just that it will get to temp on E0, albeit taking far too long to do so. I was worried it was a problem with the MOSFET, but hoping it wasn't. Thanks.

I use 40W heater cartridges. I received a 25W one by mistake and it took longer to heat, almost twice as long as one would expect Luckily they exchanged it for a 40W one. These are 12V, there must be 24V 40W cartridges out there as well.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

That's just it though, the first heater cartridge I had that shorted, was a 25watt, and that one heated just fine. And I'd actually had a 40w as I'd ordered that as a mistake, and that didn't make a difference in heat time either.

Heating up in 30 seconds is too fast, should be atound 2-3mins. It's probably why it failed. Do realize the resistor in the cartridge may reach temperatures much higher than the heaterblock, and ultimately the thermistor may read.

But it seems the resistance of the heater cartridges vary quite a bit, and may depend on quality of the resistor wire.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

So, it turns out it was the heater cartridge wattage that was the issue. Seems I needed 40 watt heaters. Granted, E1 still heats slightly slower than E0, but it's only off by about 15-20 seconds, so at this point it's just a curiousity instead of a problem. Thanks again!