Heated Bed Woes

[mage2]

Hi there everybody.
So here is my problem.

I purchased the M2 in may of 2013, I stared with PLA, the stringing drove me a little crazy. I moved onto ABS. ABS needs to have a heated bed. Somewhere in the 100-110c range.
My heated bed on my printer will not for any amount of fighting with it get a 100c. I have talked to Josh in the forums back when I first noticed this. We thought that it could be drafts, causing it as it was located in a office. I put a box over it, and while that did help some it was still not doing very well, tried a towel on top of the bed, again it helped some. Now its in my garage and im located in texas, so lets just say its not chilled or cooled in anyway. Its still getting to about 85-90 and not going any higher. No matter what setting i set it to, no matter how long i wait. Nada.
So now Im circling back to the problem, because while using ABS slurry helps and im about to go down the path of hair spray, purple stick glue , etc...
So my troubleshooting so far was to start poking around, i noticed that the red plug right under the bed is rather warm, there also was a kink where the tie strap was.

So I was looking for some other hints. Could it be a firmware thing? ( doubt it but where is crossing my fingers)

[Dale Reed]

mage2,

Do you have a multimeter or other similar tools? Might help diagnose if there is some resistance in the bed heater circuit at places OTHER than the bed.

1. Of course, check the 12V power brick (I think yours is still a 12V / 19V two-brick unit, yes?) and make sure at least 12 volts is getting to the connector at the back of the RAMBo. This will be on the two pins nearest the LEFT side of the printer, with common (negative) on the far left pin, and positive 12V on the pin next to it.

2. Check that the six-pin (or two-pin and four-pin in your case) power connectors are solidly inserted. If the connector works a bit loose, the resistance of the power connection goes up, which makes it HOT. Inspect the pins of the power cord connector from the 12V brick and BE SURE to inspect the pins on the RAMBo side. The pins should be shiny and the plastic should not be deformed.

3. The hot red connector worries me. This may be a sign that the wires on that connector have been flexed back and forth so much that some wire strands are breaking. ANYTHING other than the bed that gets hot when you are trying to head the be is a problem! (Now, some heat from the bed is conducted down the wires, but this is pretty small compared to how hot the connector will get if strands of the wire start breaking.) I replace this connector and some of the wire from it into the wiring harness with thick super-flex test lead wire and Anderson PowerPole 30A connectors. (These are available at hobby shops, ham radio stores, MIcroCenter -- in the robots and kits section -- and other brickenmortar places, as well as online places like http://www.powerwerx.com .) I'd open up the loom over the wires and inspect for blackened insulation and such and see how bad the connections really are. If you're good with a soldering iron, you can fix this. And then add a "splint" or other strain relief to keep the wires from flexing right at the red connector.

4. Might consider getting the 24V upgrade for your M2 from Makergear. Your M2 is about the same vintage as mine, so it should have the V1.1 RAMBo (with the blue automotive fuse), so the 24V upgrade is pretty easy. You get a new bed heater (with more coverage of the bottom of the aluminum plate) -- the heater is designed for 24V, so the current is a bit less, which is a good thing for the RAMBo power connector and the red bed connector. People have reported times getting to 110C on the bed around 15 minutes or so, IIRC. (I've printed PET+ and PLA, but not ABS yet, so I'm working from memory of others' posts on this "factoid"...)

5. While you're checking the connections in #3, make sure the thermistor connection is good, too.

6. Get an independent measurement of the bed temperature to make sure the thermistor is telling you the truth. Any kind of sensor that you can firmly attach temporarily to the bed (preferably on the etched aluminum plate, as that's what the thermistor is attached to) should tell you if you're close. (Cover the contact point with cardboard or some other insulator just to get as close a reading as possible.)

7. The RAMBo firmware uses PWM (pulse-width modulation) to send electricity to the heater. There is a firmware limit on the "% ON time" for the bed heat electricity. This limit is in a 0 to 255 range, with 0 meaning never ON (no heat, which makes no sense, of course ) and 255 meaning heat ON 110% of the time. If this limit is set to, say, 200, you would only be sending current through the heater 80% of the time MAX. I believe the default for this limit IS, in fact, 255. But it wouldn't hurt to try a firmware update where YOU have set this value (in Configuration.h or Configuration_Adv.h) to 255 when building and downloading the firmware to the RAMBo. This process isn't too tough, especially if you've done any Arduino programming before. If you haven't done microcontroller projects, there is a bit of a learning curve to this --- just so you know.

You can even buy online an 8" x 10" silicone heating pad powered by 120 / 240 VAC, then use an external PID controller and solid state relay to drive the heater. BEWARE, this puts some dangerous voltages in the "field of play". My advice would be to avoid these unless you are VERY familiar with electrical safety; going with the MG M2 24 Volt upgrade is WAY preferable.

If you have a variable voltage regulated supply that can put out 15A at something slightly higher than 12V, you could try using that instead of the brick. I have a 20A variable supply ( from http://www.mfj.com/ ) that can do up to about 15-20 volts. (It's designed around 13.8V for mobile ham equipment, with a detent at that voltage.) Double-check polarity if you hook up something like that.) But work your way up slowly and be VERY careful to have connections clean and secure so they don't overheat, and monitor the current. Again, the more experience you have experimenting with electrical stuff, the better.

I hope something in the above helps you get your bed temperature where you want it.
Dale

[mage2]

Well given that its mothers day i dont know how much time ill have to tinker till monday. we will see.
Yea I have all those tools, Multimeters, o-scopes, etc.
The connectors are plugged in tightly.
Ill check the red plug it gets warm enough that i dont like to touch it, and i forge as a hobby so im not exactly "sensitive" to heat.
I am wondering if flexing or something is causing the wire to come apart and its causing more resistance thus the heat at that point, and the lack of heat on the bed.

I am cool with 110, could be worse 220 is more painful 50kv is interesting as well (car ignition coil plugged into the wall)
So do you have a link for the heating pad?
the 24V upgrade is out of my price range right at the moment.
I do look forward to fixing it though.

And thanks for the quick reply, its pretty much what i was thinking.
I worry about tinkering so much cause I dont want to break anything expensive.

[Dale Reed]

Omega and Watlow both make rectangular silicone rubber heater pads. Something like the Omega SRFG-810/5-P might work well. Full 8" x 10" size, up to 5 watts / sq.in., and has adhesive backing. Lists for $57 USD on their site. A google search will likely turn up other vendors as well, maybe at a better price. (I'm guessing Omega's site shows List price.)

Dale

[Mount PrintMore]

For what its worth, I have problems with mine as well. I have found that moving the bed around manually causes the temp to come up. I think there is a problem somewhere with the temp measurement on mine. During printing, the temp drops to zero then instantly jumps back to the setpoint temp. During warmup before a print, sometimes it seems to "hang" around 90C forever and if I push the bed in the z axis to an extreme it jumps up and carries on. I received my machine around May 2013 as well.

[jimc]

if you drop to zero then thats a bad connection somewhere at or on the wire going to the thermistor/sensor.

[sprior]

If the bed temp drops to zero which should be a bad thermistor or wire, then the firmware will disable bed heating altogether as a safety measure.

[mage2]

With help of josh,. i totally over thought the problem and did alot of work. when i went to check the restance of the wire. noticed the melted connector on the bed. Emailed for a new plug. after installing a new plug will test it.
for now im sans heated bed and will be rocking my purple PLA

[mage2]

So I have the new molex plug in with the wire clamp.
I plugged it in and wired it up. I am still getting a voltage drop across the plug block. its showing up as about a 2V (12.3 - 10.5) drop.
Its causing the block to over heat.


[quote][/quote]

[Dale Reed]

I would suggest Anderson PowerPole connetors. Crimp and then solder (yes, do both) 30A pins securely to the wires, then insert the pins into the plastic blocks until they click. You'll never have a problem with the connectors again. The nice thing about these connectors is that they have 15A, 30A and 45A pins that fit the same connector shells.

Do you have a Micro Center or any ham radio stores near you, as they would have them (in typical red-black pairs). If not, you can get from a number of online sources, including http://www.powerwerx.com/ , as well as Mouser, Amazon and eBay. Amazon has a neat "combo" offer for 12 pairs of red and black shells, with 8 15A pins, 8 30A pins, and 8 45A pins, with free shipping. See near the bottom of this page:
http://www.amazon.com/Power-Pole-Connec ... B000QUZD4W

Dale