D8 MOSFET December 22, 2015 12:26PM |
Registered: 11 years ago Posts: 1,277 |
Re: D8 MOSFET December 22, 2015 12:42PM |
Registered: 9 years ago Posts: 96 |
Re: D8 MOSFET December 22, 2015 04:09PM |
Registered: 11 years ago Posts: 1,277 |
It has a fuse but even a fuse wouldn't help this issue and it is an issue for everyone with a Ramps. If you look at the circuit schematic the mosfets close to ground and are floating open. So, when one blows (all electronic things have a chance of blowing even on a good day) they blow closed (most fets die with source to drain fused so in a closed position) which just acts like a direct connection to the power supply. Short of a real thermal protection (like they use on coffee pots, etc...) it will just keep getting hotter and hotter until something bad happens.Quote
DRobs86
That sucks. Why couldn't you fuse the ramps with an actual fuse of 25 or 30 amps. That way you would probably get a puff of smoke but not an inferno.
Re: D8 MOSFET December 22, 2015 08:51PM |
Registered: 9 years ago Posts: 96 |
Re: D8 MOSFET December 22, 2015 11:11PM |
Registered: 11 years ago Posts: 1,277 |
Nope, the fuses never tripped and the power stays on because the mosfet is shorted (dead).Quote
DRobs86
Its been a while since I looked at my RAMPS lately because hi do so much more milling than printingnthese days, but the RAMPS fuse is self resetting, correct? I am talking about an actual fuse from the power supply to the RAMPS so even if the MOSFETs were to fail closed the fuse would blow, leaving it unpowered.
For that matter, I'm not exactly sure why the fuse on the RAMPS isn't staying tripped in this condition.
I reiterate that I haven't looked at the RAMPS non a while though. If you have an idea for a safety improvement then you sure have my support.
Re: D8 MOSFET December 23, 2015 05:40AM |
Registered: 8 years ago Posts: 3,525 |
Re: D8 MOSFET December 23, 2015 07:48AM |
Registered: 11 years ago Posts: 1,277 |
I am the last post on that thread and I already purchased 5 IRLB3034 for less than 5 IRLB8743. Now this takes care of the heat (the original had been getting so hot it had stuck itself to the plastic D8 header) but it doesn't take care of the fact of the closed circuit. When I was removing the bad MOSFET last night I tore the pad off the bottom and the top of the middle pin which is the pin that is the on and off pin and is connected to the SMD led. Since that is the major pin I lay odds it was already weak due to the heat as I removed (just testing) D9's MOSFET and it came out cleanly. So, I need a new RAMPS (for safety concerns too) but I can't get a single ebay seller to answer me if the picture they are using is exactly what they are selling with the 35v capacitors. I use 24V so I have to have them or no dice.Quote
DjDemonD
There is a thread [forums.reprap.org] about safer mosfets that can be used which have a built in protection against this problem.
Also you might want to consider this fire safety device [forums.reprap.org]
Re: D8 MOSFET December 23, 2015 02:18PM |
Registered: 9 years ago Posts: 1,873 |
Re: D8 MOSFET December 23, 2015 06:23PM |
Registered: 11 years ago Posts: 1,277 |
Re: D8 MOSFET December 23, 2015 06:35PM |
Registered: 10 years ago Posts: 14,672 |
Re: D8 MOSFET December 23, 2015 06:52PM |
Registered: 11 years ago Posts: 1,277 |
Already have the mosfets on their way but no great loss if I don't use them but which board? There are a lot to choose from but I am not eager to spend for a smoothieboard (I see it is having some issues now too as of Nov, 2015 in special cases) and I did look around but I don't see many talking about anything other than RAMPS and Smoothieware.Quote
dc42
Overheating mosfets, lack.of sufficient 5V power, inadequately cooled stepper driver chips, no 24V capability, no software controllable stepper motor currents, no flow control on the USB interface - these are just some of the reasons why RAMPS sucks. Don't throw good money after bad, get yourself a decent modern 32-bit board instead.
Re: D8 MOSFET December 24, 2015 02:24AM |
Registered: 10 years ago Posts: 14,672 |
Quote
Dark Alchemist
Already have the mosfets on their way but no great loss if I don't use them but which board? There are a lot to choose from but I am not eager to spend for a smoothieboard (I see it is having some issues now too as of Nov, 2015 in special cases) and I did look around but I don't see many talking about anything other than RAMPS and Smoothieware.
Re: D8 MOSFET December 24, 2015 02:52AM |
Registered: 11 years ago Posts: 1,277 |
Those are some hefty price tagged controllers. I have seen some boards at 55-60 dollars that use the smoothieware and honestly I do not even know if this printer will work. It has been down since April and I am just replacing everything and starting over but its main issue was an unlevel bed. I wish I could use the aluminum spreader I bought but wasted money as it was too thin and thanks to that it shorted out my ramps (would have any controller board I imagine). I will probably end up getting the board mentioned on this thread as it is at least better than the RAMPS and not going to destroy my pocketbook in the process: [forums.reprap.org] I just need some more people to chime in and I am seriously trying to get away from Arduino based controllers as well.Quote
dc42
Quote
Dark Alchemist
Already have the mosfets on their way but no great loss if I don't use them but which board? There are a lot to choose from but I am not eager to spend for a smoothieboard (I see it is having some issues now too as of Nov, 2015 in special cases) and I did look around but I don't see many talking about anything other than RAMPS and Smoothieware.
Duet is becoming popular, you will find it talked about quite a lot in the Controllers forum. It is the only board that provides a good built-in web inteface including fast upload to the SD card. Two versions are available, the 0.8.5 from think3dprint3d and the 0.6 from RepRapPro and from Replikeo.
I prefer all-in-one boards like Duet, but if you want a 2-board solution with plug-in drivers, there is Arduino Due + RADDS, although again you get limited 5V power and you have to set the motor current using pots on the drivers.
Re: D8 MOSFET December 24, 2015 02:55AM |
Registered: 10 years ago Posts: 14,672 |
Re: D8 MOSFET December 24, 2015 04:37AM |
Registered: 11 years ago Posts: 1,277 |
Comparing the closed source/not closed source MBASE has X/Y/Z/E0/E1 for 56 delivered and the DUET 0.6 has only 1 less Extruder the leaning is towards the MBASE and I have read a lot of threads on it but little is said beyond the Smoothie people blasting it.Quote
dc42
You can get a Duet 0.6 from Replikeo for $50. The build quality isn't as good as the boards from T3P3 and RepRapPro, but Replikeo seems willing enough to replace faulty boards if you are unlucky enough to get one.
Re: D8 MOSFET December 24, 2015 07:02AM |
Registered: 10 years ago Posts: 14,672 |
Re: D8 MOSFET December 24, 2015 07:34AM |
Registered: 11 years ago Posts: 1,277 |
I see nothing was mentioned to answer my question so I guess until these boards start to fall in price I will do one of two things and that is go back to a RAMPS 1.4 or get that MBASE for 60. I will probably fall back to RAMPS for now since it is only 10 delivered and hopefully I can get the MOSFET unsoldered on it without tearing a pad but the Chinese barely use enough glue for the copper and the copper is thin too.Quote
dc42
You can use Pronterface with every 3D printer board I know of, including Duet and Smoothieboard - although once you have used the web interface on the Duet, you will never want to go back to using Pronterface because the web interface is so much better.
Don't forget that if you use dual extrusion on a RAMPS, you lose the controllable fan output, and if you drive both heaters at once you will probably overheat the 5A fuse. So I don't consider RAMPS to truly support dual extrusion.
Re: D8 MOSFET January 12, 2016 06:03PM |
Registered: 11 years ago Posts: 1,277 |
Re: D8 MOSFET January 12, 2016 06:48PM |
Registered: 9 years ago Posts: 1,873 |
Re: D8 MOSFET January 12, 2016 09:47PM |
Registered: 11 years ago Posts: 1,277 |
First thing I did but too late the mosfet is dead. From all of my specs and if my house was 25c ambient (15-17c in there right now) that MOSFET should hit around 33-35c which is less than my body temp.Quote
JamesK
By my reading of the datasheet I wouldn't expect it to get that hot so quickly. I'd check the gate voltage and make sure you're getting a decent 4.5V or better.
Re: D8 MOSFET January 12, 2016 09:54PM |
Registered: 9 years ago Posts: 1,873 |
Re: D8 MOSFET January 12, 2016 09:58PM |
Registered: 11 years ago Posts: 1,277 |
Re: D8 MOSFET January 12, 2016 10:03PM |
Registered: 9 years ago Posts: 1,873 |
Re: D8 MOSFET January 12, 2016 10:09PM |
Registered: 11 years ago Posts: 1,277 |
Already tested at the gate and was perfect. As far as a short goes I replaced the wire to the bed and I measured the resistance and it is 3.6 ohms. Now with a dead short due to the fet being destroyed I am unsure what to do next as that is two fets dead (the original crappy one and the better one).Quote
JamesK
I haven't tried, but my first guess is that the firmware won't care that the ramps isn't there, at least for a short duration. if you have the thermal runaway stuff turned on that will shut everything down after a while, but you should have plenty of time to measure the voltage. On the other hand, the lack of thermistors might cause the firmware to refuse to do anything. If I remember right, you can fake the thermistors out in the configuration.h, but I'm not sure it's worth the effort. I'd still reckon it's better just to measure the voltage at the mosfet with the ramps in place.
The other thing I think you need to check is the resistance seen across the bed connections from the ramps end. A short in the cable or at the heater connections would fit the description.