SSR Wiring with Heatbed and RAMPS

Howdy,

I am in the midst of sizing up my first heat bed and power supply but wanted to run a few things by the experts first.

I am planning on running a 250W @12v custom silicone heat bed on a cheap RAMPS 1.4 board as this is my first build and RAMPS has the most amount of literature online out there for newbies (seriously, its helped me tones so far). I know other boards are better/would handle my heat bed easier but you don’t go for high end first try when you know you might blow something up .

The heat bed would run around 20A of current which is much more than RAMPS 1.4 can handle so I plan on using a SSR, DC-DC rated for 40A at least , looking for suggestions on good quality brands/ones to stay away from if anyone knows of any. Also, ill probably throw on a heat sink and fan on it as these tend to create a lot of heat.

My main question is if anyone has or knows of a clear diagram or video showing how to wire up a SSR to a RAMPS board, silicone heat bed and an ATX power supply. My paranoia is telling me I will undoubtedly wire something wrong!

As a side question, for this amount of current would 8 AWG wire suffice? If so, is this wire too large for the RAMPS or SSR ports?

Finally, does anything in Marlin (or anything in general with the printer) need to be changed when using an SSR?.


Thanks,
Taylor

This one was recommended to me by mhackney

[www.auberins.com]

This one is known to work well. Be careful with any others because most of them use BJT transistors with a much higher on resistance 0.1 ohm (BJT) vs 0.006 ohm (FET).

I have my firmware set for bang-bang (on/off) control also, my understanding is that most SSRs don't like to be switched quickly so be careful if using PWM.

Thanks a bunch, this looks like the best SSR iv come across and its not tooo much more.

Still not sure how to wire this sucker up to an ATX and RAMPS, looking for that clear diagram/video if at all possible...

And is there a setting in Marlin that I have to switch to bang-bang from PWM?

Wiring is pretty simple. Just connect the RAMPS output to the two input terminals on the SSR making sure to keep the polarity right.

The output side is a low side switch

GND -> SSR -
SSR + -> Heat bed 1
Heat Bed 2 -> Power

I don't know how to setup the bang bang control in Marlin, maybe someone else can help there.

I've been using this Auberins SSR on 6 printers with no issues at all. I switched to it after I had an SSR literally catch on fire while I was printing. This one doesn't even get warm even after a long print session.

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[sublimelayers.blogspot.com]

A strategy for Successful (and Great) Prints [forum.seemecnc.com]
Strategies for Resolving Print Artifacts [forum.seemecnc.com]

[www.EclecticAngler.com]

Those are a great find. Much better than the cheap ones for what we need and not that much more expensive.

Quote
mhackney
I've been using this Auberins SSR on 6 printers with no issues at all. I switched to it after I had an SSR literally catch on fire while I was printing. This one doesn't even get warm even after a long print session.

Will order as soon as possible, thanks again.

I took a shot at what the wiring will be like from your support/other stuff online (check out attached pic), does this work? Will just do 8 gage just to be safe for 20A.

After researching more I believe that bang-bang is the way to go but still not sure how to switch this in Marlin at all

I switched to a 24v Mk 3 heat bed controlled via a SSR and connected to Ramps.
dc/dc SSR rated at 40 amps. Simple wiring 2 wires in and 2 wires out.
Huge advantage. Bed heats up to 110 deg C in less than 2 mins. No heat from Ramps any more.
Just bang bang (on/off) control. Switch to Repetier firmware for Arduino. It is easier to configure.

I would swap the bed and the SSR in the diagram. I put the SSR on the low side, not sure if it matters.

Quote
tKc
Will order as soon as possible, thanks again.

I took a shot at what the wiring will be like from your support/other stuff online (check out attached pic), does this work? Will just do 8 gage just to be safe for 20A.

After researching more I believe that bang-bang is the way to go but still not sure how to switch this in Marlin at all

Quote
dave3d
I switched to a 24v Mk 3 heat bed controlled via a SSR and connected to Ramps.
dc/dc SSR rated at 40 amps. Simple wiring 2 wires in and 2 wires out.
Huge advantage. Bed heats up to 110 deg C in less than 2 mins. No heat from Ramps any more.
Just bang bang (on/off) control. Switch to Repetier firmware for Arduino. It is easier to configure.

How? Thought that a standard RAMPS could only handle 12V.

Quote
WZ9V
I would swap the bed and the SSR in the diagram. I put the SSR on the low side, not sure if it matters.

Something like this then (I could still be way off ha ?)

Quote
tKc wrote:
Quote
dave3d
I switched to a 24v Mk 3 heat bed controlled via a SSR and connected to Ramps.
dc/dc SSR rated at 40 amps. Simple wiring 2 wires in and 2 wires out.
Huge advantage. Bed heats up to 110 deg C in less than 2 mins. No heat from Ramps any more.
Just bang bang (on/off) control. Switch to Repetier firmware for Arduino. It is easier to configure.


How? Thought that a standard RAMPS could only handle 12V.

The 12v heat bed output from the Ramps controls the SSR instead of the bed directly.
The SSR switches a separate 24V supply on to the new bed. Only downside is you need two psu's.
I reduced the 24v psu supply voltage so as not to exceed the current rating of the psu.
It is supplying about 17 amps.

I hooked up a 40mm fan to the control side of the ssr to keep the ssr cool. Works very well. Make sure you get a heatsink with the ssr!! Here is the link for the SSR. [www.mpja.com]



Edited 3 time(s). Last edit at 01/24/2016 01:22AM by elwood127.

My ssr runs cool, but I do have it bolted directly to one of the aluminium printer frame uprights.

My arduino also no longer needs a fan. All the steppers are cold to the touch.

Hi all,

I have connected 300x300mm heatbed with 40A DC-DC SSR, 600watt PSU, Marling, RAMPS 1.4.

Still I don't get the heatbed heated upto 55 deg C, it takes about 5 mins time to reach 50 deg C. Autotune also fails for 60deg C.

Is there any specific wire size to be used for this circuit?

Cheap DC-DC SSRs have a voltage drop of about 2V, so if you are using a 12V bed heater supply then your heater is probably getting about 10V and running at about 70% of its design power. You can check what voltage is reaching the bed heater using a multimeter.

For any bed larger than 200mm square it makes sense to use a 24V bed heater. A good electronics board can switch a 24V bed of up to about 350W directly. For larger beds, an AC mains voltage bed heater may make more sense.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It's OK to use PID control with an SSR, and it is better than bang-bang because it keeps the bed temperature regulated and that helps prevent print artifacts if your bed warps when heated. If you're worried about overheating the MOSFET, turn down the PID frequency. I was using an SSR to switch AC power into a transformer that was driving my printers 450W bed heater at 8 Hz and it worked fine. The only reason I turned it down was because the inductive current surge would cause the thing to blow circuit breakers in my house at higher frequencies. With DC power switching into a resistor (heater) you should be able to run it much faster, though there isn't much need to do so.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Saw you post digital dentist kind of watch yours lol we do allot of the same things. Anyhow how do you turn down the PID frequency. I have stuck with Bang Bang because of the PID cycling too much causing problems. I haven't messed with the PID loops (well beside in quadcopters) much so don't know which number to tweak in Marlin.