I just disassembled my RAMPS 1.4 and took a look at the input connector. Apart from the RAMPS being a little dusty because of active cooling, the input connector was badly scorched. These chinese knock-off connectors are NOT designed to carry anything close to 10A (your typical MK2A heatbed current @12V), although the connector says “300V15A”. The bright-green output connectors on the other hand are German-brand 12A rated connectors and look totally fine. I’m definitely going to order more of them.
Use a SSR
@Javier_Prieto is right. Might as well use a solid state relay at that current level. Your heat up time will be significantly reduced and I believe it’s a safer option
And your input conectors need to handle less current
Even a true 15A rated connector won’t survive more than 10-12A in this usage case because it has to be de-rated for current in adjacent pins, and perhaps ambient temp/airflow depending on your setup.
@Griffin_Paquette @Javier_Prieto I know, I already have a 230V 600W silicone heater + AC SSR for my second printer (300*300mm). I just need to get it done, and as soon as it prints properly I am going to take this printer apart and use the parts for something else.
I have seen a case where someone bought a regular DC SSR off of ebay and still had bad luck with it. It literally went up in flames from the 10A that the MK2A “only” draws.
This post was just meant to be informative / a warning for everyone using a cheap chinese RAMPS. :)
Well standard puck SSRs do t get rid of heat well without a heat sink, so if run at or near full load without one it’d burn up. As well ssrs fail closed so if your heater is powerful enough to burn itself or other items when run at 100% permanently the ssr could cause a fire on the machine if it fails, which they do eventually.
Wow glad I’m running non heated bed build at the moment. And like 100 wats.
Heatbeds are a biiiig point for 24v PSUs. Half the current.
@Ryan_Carlyle Only when you have a small heated bed. Above 200*200mm or so it does not make sense anymore. Imagine my 600W heated bed: You’d need a 700W+ PSU, wires capable of carrying more than 25A and mosfets / SSRs that are able to switch insane currents.
You also have to see it from the efficiency side of things: Why convert mains (e.g. 230V) to 24V with big, expensive and ineffective PSUs, have big (=expensive) copper wires and overkill (=expensive and ineffective) “switching units”, all of which have heat losses that you need to radiate away.
I agree with you though that 24V is generally a good way to go when it comes to hotends and motors.
My opinion is that mains voltage wiring is too dangerous for most casual hobbyists/builders. I would argue that if you need a 600w bed, a heated bed is simply the wrong approach and you should enclose the printer and heat the chamber instead. But lots of people will disagree with me on that.
@Nathan_Walkner Agreed, although a UL-listed small space heater with a PTC heating element is safer, easier, faster, and cheaper…
@Nathan_Walkner Lessee… Built-in over-temp limit switch, heater element resistance increases as it gets hotter so it can’t go into thermal runaway, designed by somebody whose job is designing heaters, UL-listed… Yeah, that space heater sounds way more dangerous than an ebay heater mat powered by a counterfeit SSR, controlled by Marlin/RAMPS, and wired up by somebody with no electrical engineering or mains voltage experience. Sure.
You can be safe or dangerous either way. Depends on who’s doing the design and assembly.
@Folke_Schwinning At that power level you should consider a 48VDC power supply with a 15A SSR, Crydom makes them. Back it up with a snap-disc set to 150C for extra protection to kill the P/S if the PCB runs away. It’d be simpler than using AC with a zero-cross SSR or phase angle controller. DC power supplies are available at very high efficiencies these days, if I recall right Puls makes supplies that are 95% efficient, though they maybe beyond the cost of hobbyists.
@Ryan_Carlyle I have to agree about safety. Being an engineer in the field of designing equipment for semiconductor fabrication there are plenty of low probability dangers I see in hobbyist 3D printers. Some can be down-right scary if people aren’t careful. And a few ideas are just out there.
Though I blame industry to some extent. We’ve learned tremendous amounts over the years, made safety standards and design rules. Then we decided to not share what companies learn and to charge hundreds for copies of those safety standards. It’s completely contrary to the hobbyist maker mentality.
That said, yes my printer has multiple safety sensors and an EMO loop built in. Cost goes up but with how often things go wrong in odd and unexpected ways, it seems worth it.
@Nathan_Walkner Sorry, seen too many SSRs burn out and fail on, and seen too many hobbyists asking “how do I wire this” questions without a clue. Big-ass bed heaters are fine for competent people, but they have major issues for your typical hobbyist.
@Nathan_Walkner That’s the kind of attitude that leads to accidents. It’s not safe for most hobbyists with little or no training. No amount of bombast is going to change that. You’re giving poor advice to noobs.
For me using a relay is more of a hassle in this app. I like 24 volt polyimide or silicone heaters. I’ve used them up to 300 x 300 with no issues. The packaging and wiring for an ssr is not elegant and you need to build some protections around the bare terminals.
I do use ssr in both my small reflow (10 amps @ 120vac) oven using a Reflowduino and a larger (20 amps @ 240 vac) for my powder coat oven.
Even the knowledgeable can make mistakes, and low level (below 40V) DC is far more forgiving when they happen. Your heater can still burn up and electronics can fry, but at least it’s not likely to cause injury just from accidentally touching terminals or a loose wire hitting ungrounded metal. Safety standards are written with that in mind, mitigating risks and hazards based on the fact that even well made machines built and run by the knowledgeable can still have issues and cause hazards.
When using 600W of power (max) it’d be a decent idea to at least run it through a Meanwell SE-600-36 or SE-600-27 or SE-600-24, bigger number is better to keep amperage down. They’re about $60-80 (I know it’s a lot) and yes using DC means you have to use a DC switching SSR, which can cost more. These power supplies are 87-88% efficient, so not slouches. If extra load and power factors are a serious concern for any reason there are better efficiency power supplies.
If you can make things properly safe even when things go wrong feel free to use 6kW of RF voltage even. [Seriously don’t do that.] But it’s always wise to ask “is that really needed…” when someone is venturing into less common ideas that could increase risk. It’s hard to tell if the person knows enough to make it safe or is just tinkering and doesn’t realize possible dangers.
Of course on the flip side, yes trying to repurpose a device can be dangerous on its’ own. The same precautions should apply then too. I would think using a space heater to create a heated enclosure up to 100C would have to get the same eyebrow-raising “are you sure about that?” And we can only hope the answer is “yes, the manufacturer information shows it to be safe and precautions are being taken.”
That is one of many reasons why Chinese products are so cheap. Most products barely fulfil the basic requirements what they should do.
Put the space heater outside and duct the air in. That’s an easy one.