How to fix heating issues on Onyx heated bed

[msdevstep]

I fixed my Onxy heating issues using a 12 volt 30 amp mechanical relay connected to a 24 volt 14.6 amp PSU. I had originally tried with a solid state relay but it melted due to the heat. I would not recommend a solid state relay, because once it became too hot and melted, it did not cut the power to the heated bed, and had I not been around to catch it, a fire would have probably been the result. A mechanical relay works great, was only $5 at Frys, and produces no noticeable heat.

Using the repetier firmware there is a setting for delayed bang-bang control, so that it doesn't flip the relay until a certain amount of time has passed (5 second default). This prevents the relay from getting wore out, and a constant "clicking" once the temp reaches the set-point.

Here is a picture of my setup. I've included the solid state relay in the picture.

The attachment WP_20130602_003.jpg is no longer available

i have a 25 amp solid state cheap relay purchased off of ebay, it is still going strong. 36hrs or more in print time if I had to guess. it has not failed me.

you probably didnt' have the correct setup. you have to understand how to correctly choose and use it. I can't tell from the photos of what you used. there are considerations to take into account when selecting the proper electrical equipment. If yours got hot enough to melt it obviously wasn't cooled properly or not the correct amperage, incorrect relay type etc..

problem with bang bang is that it is less efficient at holding constant temperature. With mechanical relay you also introduce noise into your wiring so make sure you have proper shielding on your stepper motor wires.

stay safe..luckily that relay didn't catch fire..from your photos looks like you may have used an dc-ac relay. for this purpose you need a dc-dc solid state relay.
In your photos your using a 220d25--- 220 is ac voltage rating and 25 is current rating for the switch side of the solid state relay.

in my build log is an example of the correct relay dc to dc http://forum.seemecnc.com/viewtopic.php ... t=40#p7045 notice it says dc on both sides of the relay.

I don't believe I had it hooked up wrong, or chose the wrong relay. You are correct about not having proper cooling, as I now believe a heat sink is absolutely necessary if you do choose to go the route of a solid-state relay. However, the relay I'm using is a DC - DC relay, and it's specs are well beyond what my use case called for. I paid special attention to polarity when wiring it. It functioned properly before the melt down, holding the temperature perfectly at set-point. I do not feel that being able to use PID control for the heated bed is enough justification to introduce another component that produces this much heat. Additionally, the fact that this component does not have a fail-safe in the event it does overheat (e.g. not cutting power), there is no way I would recommend anyone else use one of these.

Close-up

[Eaglezsoar]

The SSR needs to be mounted on a heatsink made especially for this purpose.
What you have created should work also however the EMF generated by the coil
that is inside the relay could be problematic if it is induced into other wiring. Try
not to have any wires close to it like your motor wires, your endstop wires, ect.

I always use SSR but I also use the heatsinks. They do get hot if not properly heatsinked.

[cambo3d]

obviously have the correct type. thanks for the photo.

you have to understand without a heat sink the solid state relays maximum current draw for a 25amp relay is roughly 5-10amps maybe even less.

keep in mind chinese products are not always quality, could have just gotten a cheaply made relay, over rated.
In my opinion the better relays are the ones that are potted with encapsulation compound not this cheap plastic outer shell. such as this example: opto22 relays. http://www.opto22.com/documents/0859_So ... _sheet.pdf

The relay I use just barely gets warm, not enough to melt anything. I have left this thing printing for 14hrs straight on a single print job. I would be more concerned with noise from the mechanical relay. enough noise will effect your print quality.

as far as fail safe, none of these cheaper models will have that built in, but you as the builder need to add circuit protection as needed. (Ie, circuit breakers, fuses, thermal cut-off switches etc) i doubt that your 12v 30amp relay has a thermal sense feature either.

[Broose]

Here is the SSR I used: http://www.amazon.com/gp/product/B005X4 ... UTF8&psc=1
with this heatsink: http://www.amazon.com/gp/product/B005D6 ... UTF8&psc=1

It works fine with the 24V supply but it does get pretty hot. After the bed has been 100C for an hour, the heat sink is 70C (about 155F). I moved it to the other compartment behind the LCD display to keep the Rambo compartment cooler.

The Opto 22's may be worth the increased cost if, as Cambo3d said, they run more efficiently and don't need to dissipate as much heat.

[cambo3d]

Here is the SSR I used: http://www.amazon.com/gp/product/B005X4 ... UTF8&psc=1
with this heatsink: http://www.amazon.com/gp/product/B005D6 ... UTF8&psc=1

It works fine with the 24V supply but it does get pretty hot. After the bed has been 100C for an hour, the heat sink is 70C (about 155F). I moved it to the other compartment behind the LCD display to keep the Rambo compartment cooler.

The Opto 22's may be worth the increased cost if, as Cambo3d said, they run more efficiently and don't need to dissipate as much heat.

That's the same combo i'm currently using, but mine doesn't get that hot. just barely warm to the touch. do you have a drawing of how your wiring it? I have a fan in my compartment also. top left corner in the pic. It's a computer chipset motherboard fan that fits nicely in the corner and vents out between the hole cover supports. Also, I'm only running my bed at 85c so that could be the difference here. Maybe I'll take some measurements with my thermocouple at various bed temperatures and post results. I believe i can go to 125c before the software safety kicks in.

[Broose]

That's the same combo i'm currently using, but mine doesn't get that hot. just barely warm to the touch. do you have a drawing of how your wiring it?

Nice looking wiring job. I especially like the circuit breaker- is that a 20 amp?

I don't have a wiring diagram drawn, but here is a connection list

SSD Pin 1, plus output -> 24V supply V+ (fused)
SSD Pin 2, minus output ->Onyx plus side
SSD Pin 3, plus input -> Rambo Heat2 Bed plus
SSD pin 4, minus input -> Rambo Heat2 Bed minus
24V supply V- -> Onyx minus side

[cambo3d]

That's the same combo i'm currently using, but mine doesn't get that hot. just barely warm to the touch. do you have a drawing of how your wiring it?

Nice looking wiring job. I especially like the circuit breaker- is that a 20 amp?

I don't have a wiring diagram drawn, but here is a connection list

SSD Pin 1, plus output -> 24V supply V+ (fused)
SSD Pin 2, minus output ->Onyx plus side
SSD Pin 3, plus input -> Rambo Heat2 Bed plus
SSD pin 4, minus input -> Rambo Heat2 Bed minus
24V supply V- -> Onyx minus side

yep 20 amp, your wiring pretty much same as mine also.

[foshon]

Oooooooorrrrr just get a 24v kapton heater and run the power right through the Rambo.

[cambo3d]

Oooooooorrrrr just get a 24v kapton heater and run the power right through the Rambo.

yeah, i been hunting for one that fits so far only one ive seen is made by trinity labs they have a 240mm diameter kapton one there. unless i find a 9x9 square version

kapton would solve the warping of the onyx heatbed also.

[foshon]

Indeed it does.