Relay switch addition to prevent heat bed cutting out

I'm having the same symptoms of the bead heat cutting out, particularly once the extruder heat is turned on. I'll give the relay a shot and report back.

For the record, my polyswitches are:
- F2: X16 CF1100
- F1: B R500 21335

 

Same problem here
My polyswitches are also:
- F2: X16 CF1100
- F1: B R500 21335

I've printed out some feet, to heighten the printer, and allow for a fan to be put underneath the board.
I will test this out later today, and post my results.

I need to fix this issue, as the consumers rely on a "plug & play" product.
So I will probably resolder some 14A polyswitches to the F2 for all the printers.

 

Thanks Jerry. I added this to the Robo 3D User's FAQ under section B.5.

 

I've tested with another 12V fan I had laying around, and I can confirm. Fan solution works.
Heatbed up to 100 C and printin' smooth ABS.

I've added feet to my printer, and the air is blowing down towards my desk and away.
I'm using a 80x80mm fan though, with some blue leds in it.
So now it looks like the printer is floating on some blue cool air

 

Give us a pic, that sound great.


Sent from my iPhone using Tapatalk

 

[Warning: I should have blogged but, wanted to share - Now! Wall-O-Words follow below.]

I have just built a printer and have had this same heated build platform (HBP) and RAMPS issue going. I read the data sheets for the RAMPS's stock 11A fuse (polyswitch) and STP55N60L Mosfet. These components are undersized for a HBP with a 1.2 Ohm measured resistance. The heating components are at their design/build limits. The RAMPS HBP Mosfet is rated 95 Watts Total Dissipation and this 1.2 Ohm HBP supplied with 12V is 120+ Watts consumption. This causes the Mosfet to get extremely HOT while the 11A Fuse is being pushed to over 10A and it too gets too hot to touch. I do not know what the HBP amp draw is while heating but, as you know, if touched, both electronic parts will burn a finger.

I've had some time to think here so take the following writing with out strife. I've read the offered solutions of: External Relay, External Fan Mosfet Circuit, upgraded Fuse (polyswitch) and installing the Fan. These solutions seem to me now as: brute force, prosthetic and/or partial fixes. Upon reading the datasheets and seeing that the Mosfet, in service, is over its specified 95 Watts and the 11A fuse (polyswitch) was at or momentarily over its stated limits with both devices being VERY hot under load - I went with the option to upgrade the two on board RAMPS components: The 11A fuse and the HBP Mosfet. My choice of a fix cost me ~$7.00 USD and two days to wait for the mail to arrive. I ordered a slightly higher current rated 15A fuse (polyswitch) and a higher wattage (300W) 55V 80A Mosfet.

After much thought - My thoughts on the Options were:

Option 1) A Mechanical Relay - Brute Force
Pros:
- It works!
- The solution removes Heat and Power from the RAMPS.
- It maintains the Software and some of the Firmware and RAMPS electronics to control the HBP.

Cons:
- It is old school on a NEW Toy.
- I'd have to buy one.
- It will not reliably use PID, PWM or other benefits of the microcontroller.
- It looks clugey and dangles somewhere.
- Defeats using New Technologies and some features. See: PID, PWM above.
- Too many more wires.
- Too many unknowns for me in the firmware to adjust for the Relay.
- Should use Bang-Bang only in the Firmware?
- Is NOT Cool to hang on a NEW 21st Century HIGH TECH 3D Printer.
- It works through an existing system to add another system.

Option 2) Fan Mosfet Circuit from Thingiverse - Prosthetic Device.
Pros:
- It works.
- I get to Make a proto-board circuit.
- Kinda cool
- Sets up a MOSFET to remotely control the HBP (techie.)
- New Tech - kind of.
- I have the components which would work.
- I got to think of and search for some alternate components which would work.
- Learn a little more electronics.
- It maintains the Software, Firmware and RAMPS electronics to control the HBP temperature.

Cons:
- The circuit does not look correct with the capacitor in parallel with the diode rather than in series. See: Snubber on Wikipedia. And the circuit does not contain one more needed resistor for a proper snubber. (?)
- My built board did not immediately work AND my FOURTH MORE PREFERRED Option came in the mail!
- More Wires.
- It works through an existing system to add another system.
- No LEDs.
- Had to find a mounting point.
- Hand made circuits on proto boards - look cheap.
- (Optional) Buy and wait to receive a pro circuit from the designer?

Option 3) Upgrade the Fuse (polyswitch) and add a Fan - Partial fix.
Pros:
- It works - For a while. Until something cooks.
- Places one better sized component for use - 12+A Fuse.
- Installs a Fan which is a good suggestion.
- Maintains the RAMPS configuration without more complexity.
- Not too many additional wires or items to stash - Fan.
- Looks professional.
- Get to read more Data Sheets, learn electronics and solder.
- Uses the Software, Firmware and general Hardware as designed.
- High Tech.

Cons:
- Another part to buy - Fuse.
- Desolder/Hack on the RAMPS board.
- Partial fix - the Mosfet is under sized for the HBP
- Fan - Means components are over driven and not properly sized for use.
- Unknown life expectancy of the undersized Mosfet.

Option 4) Upgrade two RAMPS Components w/Fan - Complete Fix.
Pros:
- Maintains the RAMPS configuration without more complexity.
- Get to think through and create my own solution.
- ~$7.00 USD to fix.
- Not too many additional wires or items to stash - Fan.
- Found in this Forum how Robo3D learned and shows how and where to attach the RAMPS fan to the two pin connector next to the X stepper driver and the 5A Fuse (polyswitch) - KUDOS!!!
- I get better at electronics and reading Datasheets.
- My own solution - It is a 'Sleeper' Upgrade - No one will know.
- Custom Higher power RAMPS 1.4 board - NOW!

Cons:
- Hacking/Soldering on a congested functioning electronics board (RAMPS).
- De-soldering multi-pin MOSFET and cleaning up old solder from holes. :-(
- Reading more Datasheets.
- A 'Sleeper' Upgrade - No one will know I succeeded unless I tell them.
- Ordering and waiting for the components. [ Was only two days from date of order.]
- I did not fully analyze the RAMPS board. The extra few Amps on the pcb traces could burn them up(?)!

Decision Process:
No - Option 1) Relay - It is proven to work with testimony but, Not Cool in a micro-controller world. And that is what these 3D printers are all about - Embedded electronics, Software control, Cool and New Tech on the simple. It doesn't use PID and will burn up.

No - Option 2) Thingiverse Fan Circuit Board - Since the components for Option 3) came just as I tried the Fan circuit and I had some build issue to troubleshoot I dropped fixing the Fan circuit to install upgraded components. Plus, I do not think the Thingiverse circuit design was quite accurate. It would work. Just not as intended or properly using all the components. I did not want to design a new circuit.

No - Option 3) It is only a partial fix. The Mosfet is designed to dissipate 95 Watts and this 1.2 Ohm HBP is 120 Watts.

YES - Option 4) Replace the RAMPS's STP55NF06L HBP MOSFET and the 11A Fuse (polyswitch) because it is the cleaner upgrade and the mail delivered. I installed the new components in about half an hour with goofing around. The board passed the Marlin Firmware gcode Auto Tune command to 100 degrees C (M303 E-1 S100) - easily. And without a Fan. I have now added the Fan because of paranoia for these components and the stepper drivers. But, if properly sized components and properly tuned/calibrated electronics the machine should not have too much heat. Example: My MakerBot Thing-O-Matic, of over two years, has no fan and no heat issues related to the electronics.

Possible Problem for some. It has already bitten me three times! I've seen that the heater wires must be fully seated within the screw terminals and have ample surface contact in the connectors. I use solder on my wire ends to keep them from fraying and have found that unless I pinch the soldered wire ends flat with pliers they do not make enough electrical contact for full current. This causes the components to either not work or not work properly. This is likely why my build of the Thingiverse circuit did not work for me on the first try - BUT - then, my Digi-Key mail came with the best option - new components for the RAMPS. ;-)

Here are the RAMPS HBP upgraded components I ordered:
Quanity Part Number Description Price
1 PTC RHEF1500CT-ND POLYSWITCH 15A $1.25
1 STP80NF55-08 MOSFET N-CH 55V 80A TO-220 $2.57

The Tests of the components worked! I can touch them most of the way through the calibration/heating cycle and where they would burn my finger before they now are noticeably warm to the touch. The Mosfet does get hot but, the fuse is warm. I used the gcode M303 Auto Tune command for the HBP. It works with Marlin firmware and runs three cycles on the HBP to the set temperature then shuts down. [gcode: M303 E-1 S100]
Test 1 - Run calibration without Fan. Ran Once and Easily Passed.
Test 2 - Run calibration with Fan. Ran Three Times and Easily Passed.

---- I am Happy... ----- :-D Thanks to everyone who has been posting in this discussion. I sure needed the support and information. Even if you didn't know I was lurking. ;-)

 

Ooops! I forgot. ----

We should add flyback diode/snubber components to relieve Inductance Spikes from frying our electronics? Yes? The RAMPS boards do not have this electronic protection circuitry. The Mosfets & fuses receive inductance spikes which come from the HBP (an inductance coil) when the power is turned off. This will happen in normal operations and with the use of PID/PWM. I did not add this yet to my fix. I do not know yet to design this properly.

This snubber circuit addition consists of a diode, a resistor and a capacitor - a snubber circuit. See Snubber on Wikipedia. --- Many machines do and do not use this circuitry. It is something that may only surface soon, later or not at all. [ We get away with a lot of errors because Modern Electronic Components are designed to take a lot of abuse.]

Oh, read the following to see from who/what/where I'd learned about this Inductance Spiking - http://reprap.org/wiki/Basics_about_switching_loads_with_MOSFETs

 

Hi.

I installed the fan and the problem continues. The bed has been three minutes at 90ºC and then stopped.

Any idea?

Thank you. Manolo.

 

@ Manolo ----- >>>>> You really need to read this thread!

A couple of posts above your request is my VERY LONG and Detailed story to the SIMPLE solution to THE Problem AND the why.

 

Hi Brian.

Thank you. But I think the solution must be given by the manufacturers. If they are are installing now the fan but the problem continues, they must find another solution. The printer is not expensive but neither cheap, and I don't want to install anything that ruins the board if it's not tested by them.

I'll wait some days for an answer.

 

Manolo,

If you are still having issues and want an answer from the Robo guys then you are better off contacting them directly through the Support link. They rarely respond on the forums and seem to prefer direct emails.

Brian's fix looks to be a well thought out solution. It's understandable that you prefer a fix from Robo. The solutions on the forums are for people willing to fix it themselves instead of waiting for the Robo Team and that's the help that is being offered here.

 

Hi Warlocke.

Thank you for your answer. I can buy those components, disconnect the old ones, and connect the new ones to the board. No problem (I have built this at home). But I don't have enough knowledge in electronics to know what I am changing with this new components.

 

Hi Jerry.

Sure. Here is the picture.

Thanks in advance.

 

Alert - My suggested choice of a Mosfet - stp80nf55-08 was not the best according to nophead. See another conversation (https://github.com/ErikZalm/Marlin/issues/688#issuecomment-34272834) with nophead regarding Mosfet's.

My suggested components are working better than stock on my RAMPS and pcb heater but, the Mosfet is NOT The BEST. I haven't searched out a replacement yet. I'm still digesting what nophead has explained and got other work to do. I apologize to you all for my lack of experience to give the best solution. But, I knew the area to fix. :-/ [P.S. The Mosfet I am using is cooler than the stock and combined with the upgraded 15A fuse the bed has had no problems getting to and maintaining the heated bed @ 110C for more than three hours. It is better than a fan alone.]

Best Regards, Brian.

 

My fix of changing the fuse and Mosfet works. But, according to another discussion the fix works more likely because of the fuse and not so much my selection of a stp80nf55-08 Mosfet. Because of it having a higher gate threshold it is not the bet selection for the 5V logic circuit. It does runner cooler than stock. The new Mosfet does have a lower RDSon from the stock but, the higher gate threshold is not spec'd right. Yet, my system is working quite well...

 

We are OK with my suggested MOSFET Fix ---- Sorry for monopolizing your list.

After more tutoring and more datasheet reading - The stp80nf55-08 MOSFET will work.
It is OK if you ordered the stp80nf55-08 MOSFET . The MOSFET is not fully driven or turned on in the RAMPS use but, this is going to work for our purpose. The MOSFET capability is up to 80A fully turned on with 10V. Or circuit is 5V on the MOSFET gate with a VGS gate threshold voltage of 2-4V. This means our MOSFET may not be fully opened/saturated/turned on. But, we are only passing 10-12A while it is partially turned on. We are OK. Mine does work.

I learned how to calculate MOSFET temperatures. The RAMPS stock MOSFET (stp55nf06l) is rated RDSon of 40 mΩ. If we run 10A through this then at worst it will have 4.0W to dissipate. [Watts = I^2*R] The device's RΘJA is 62.5°C/W and the device will raise 250°C above ambient - OUCH! No wonder I nearly burnt my finger. Now, the MOSFET I spec'd: stp80nf55-08 shows it to have an RDSon of 8 mΩ and at 10A it will dissipate 0.8W. With the same RΘJA of 62.5°C/W it will raise only 49.6°C. Much Cooler! And if you wish a better choice which will raise only 17°C above ambient then use IRLB3036GPBF. The caveat here is that this device is discontinued and in short supply. Why? I do not know. I'm not looking anymore.

Happy Printing!