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How do I run an SSR on mains without killing myself?

Posted by MetalManDan 
How do I run an SSR on mains without killing myself?
October 29, 2017 11:43AM
So I want to build an XL printer with a big 400x400 heated bed and there for it appears I will need to harness AC power? While I am not physics or or math averse I'm no electron wrangler. I've never messed with anything more complicated that an arduino with R-circuits. I know I should ground my mains and SSR to the frame but other that I'm lost.
Re: How do I run an SSR on mains without killing myself?
October 29, 2017 12:38PM
Okay this is not a comprehensive guide so read around after reading this.

Get an SSR which can handle plenty more power than your bed. The cheap SSR 25DA units you see on eBay do work just fine.
If your bed is 500w then it will use 500/120=4.15amps if you are on 120v mains, and 2.08amps if you are on 240v. As you can see a 25amp SSR is plenty overspec'd - this is good as it won't get hot in use. Screw the SSR securely to something, ideally metal. The fixing points on the SSR make a good earthing point (see below).




Now connect the output from your 3D printer controller heated bed output to the DC side of the SSR pins 3 and 4 in the image. Polarity is important. So use diagrams from your printer board manufacturer to determine which is the + and - for your heated bed. Normally it doesn't matter as a DC bed heater can be wired either way.

Now for the (potentially) dangerous bit.

Always do all work with the mains completely disconnected (pull the plug to your printer fully out of the wall socket, don't rely on switches, which might only turn off the live and not the neutral, which will still give you a big electric shock if you touch it.

I have a RCD or (GFID) plug between my wall socket and my printer which has mains heated bed. These are excellent, they shut the power off if there is a short to anything, and they disconnect both live and neutral at the same time. USE ONE!

Best practice is to mount a kettle type socket on the side of your printer (or other similar mains voltage rated plug/socket like a cloverleaf).
From this run the live wire to the SSR AC side into pin 2.
the Neutral from your kettle socket then goes direct to the bed heater.

Now run the wire live from pin 1 on the SSR to the bed heater.

In this way the circuit is only made when the SSR connects, however the neutral is permanently connected to the bed heater, so don't stick a pin in it! And don't tinker with anything near the bed with the mains plugged in.

If your bed is stationary like in a delta, use whatever suitably rated wire you want, but secure cables properly. If your bed moves like on a corexy/cartesian, you need to use flexible mains wire of suitable rating, and route the wire so as it won't rub or catch on anything as the bed moves. Greater risk lies in using these on moving bed machines.

Now connect the kettle lead from printer to RCD/GFID plug and the wall socket.

You should use a thermal fuse, they can be bought very cheaply, they have a spring set in some sort of material which melts at a set temperature and the spring breaks the circuit. This is in case something in the control loop (thermistor, controller board, SSR) fails with the circuit closed/connected, causing the bed to heat up and continue heating. 150 degrees C type should be just right, mine has never failed in use and I've never had a thermal runaway to test it, they are single use so buy two in case you need it. It should be in line (so cut the live or neutral wire near the bed heater itself, leave yourself a little slack to play with) with the bed heater mains wires, firmly connected to the aluminium plate your bed heater is attached to (insulated if its a metal type as they can be live on the surface), and secure so it can't fall off. There is some really good advice here.

You need to drill a hole in the aluminium heat spreader of your bed and attach an earth wire, this goes back to the kettle socket earth pin. You also need to ensure that anything metal such as the frame is electrically connected to this earth. Test it by putting a multimeter on the earth pin of your kettle socket on the outside of the printer and then measuring resistance (or continuity) touch the other probe to all the various metal parts of the printer and ensure there is continuity. Aluminium oxide which is the layer on all aluminium exposed to the air is a poor conductor so scratch the surface a bit with your probe if you get no contact.

Follow this advice and you won't go far wrong. Do not skimp on the RCD, or the earthing.

I partially document my installation in this thread (with images).
[forums.reprap.org]

Some more info here:
[www.duet3d.com]

Basic schematic


Edited 10 time(s). Last edit at 10/29/2017 01:00PM by DjDemonD.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
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Re: How do I run an SSR on mains without killing myself?
October 29, 2017 01:39PM
Where are you getting your bed/heater from? I've been looking for one around 450 * 450 for a new build I'm working on.
Re: How do I run an SSR on mains without killing myself?
October 29, 2017 01:42PM
My recommendation (not paid to say this) is Keenovo via aliexpress. They are very good quality and can be made custom sized, custom voltage/wattage, and with whatever thermistor or PT100 you want to be embedded in them. The adhesive is proper stuff too.

I bought a no-name one originally, and the adhesive was failing in the middle, this is dangerous as the heater wire in the middle gets hotter than the rest of the wire as such its resistance rises and it can burn out. The Keenovo ones are barely more expensive than their competitors.


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
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[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
VDX
Re: How do I run an SSR on mains without killing myself?
October 29, 2017 02:30PM
... insteadof using mains voltages - better find a transformer from mains to e.g. 24VAC or highest 48VAC - they are not so expensive and can give up to 40Amps AC without any electronics or heat generation winking smiley

Especially when moving the bed, this would be a sort of "life-assurance" -- think about the "lifetime" of moved/bended cables and breaking wires ...


Viktor
Re: How do I run an SSR on mains without killing myself?
October 29, 2017 02:34PM
Good advice for moving beds... Mains beds are more popular on delta's or corexy's where the gantry moves in Z rather than the bed for just this reason.


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
[www.facebook.com] we want to see your first layer photos... give us a like/share


[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 03:42AM
If you use mains power to a moving bed, there are some suggestions at [duet3d.com] for how to keep it safe.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 08:39AM
How would I controll the bed via the board if I use a transformer? Also wre you thinking of something like this or an enclosed unit?
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 09:24AM
You could use a transformer to step up voltage to your bed, from your existing DC power supply (but this would require a fairly hefty supply) and would need a control unit such as an external DC mosfet. Or get a second DC power supply and use it instead of the mains supply. Rather than an AC SSR use a DC external mosfet board. Used in exactly the same way it has a large mosfet instead of a triac to control a heavy DC load using a tiny DC PWM signal.

However you wouldn't necessarily need to take all the precautions you would with mains. Not at 24v but still you won't get the same performance from a large 24v DC heater as you will from a 240v heater, and it will need much bigger wiring, which is still a fire risk. 48v might do it, but that a risk for electric shocks too, maybe not as much as 240v.


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
[www.facebook.com] we want to see your first layer photos... give us a like/share


[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 10:24AM
Thingiverse have several enclosures for the SSR's you should look there for a solution.
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 10:58AM
I used to use a 24V transformer to power a 450 W bed heater for a 305 x 317 mm x 6.35 mm cast tooling plate bed. I used an SSR with built in zero crossing detector to switch power into the transformer. I wouldn't recommend it. The transformer was huge and very heavy, making it a real PITA to transport the printer. The wiring was pretty heavy gauge- I resorted to using multiple braided wires to carry the current because I didn't have any heavy-enough gauge wire around. The heater is at the lower end of power for that size bed- it takes about 7 minutes to get up to 105C for printing ABS, and barely gets hot enough for printing PC.

I eventually switched that printer to a 24V 750W MeanWell industrial supply. A MOSFET switches power to the heater. I wouldn't recommend that, either. The power supply is bigger than the old transformer but not nearly as heavy. It has a fan that runs all the time to keep it cool and it is just short of a vacuum cleaner noise level.

What I should have done was use a 24V, fanless supply for the controller and changed the heater to higher, line powered unit. I have a 750 W line powered heater on the 300x300x8 mm bed in UMMD and it gets up to ABS temp in 4.5 minutes. The SSR that switches it on and off doesn't even get warm. Wiring for line power is really not rocket-science. Insulate the wires, strain-relieve and secure them mechanically at both ends, use a fuse to protect against failed wiring, add a TCO to cut power to the heater if the SSR fails, and ground the printer's frame. I'll probably be upgrading that older printer this way in the near future.

The 24V supply can deliver 30A to a short. Your typical residential line power circuit is fused at 20 or 30A, so in terms of fire starting, the two are roughly equal, except that you're going to use a fuse on the heater circuit that is going to blow before the line fuse does. There is greater potential for serious electric shock with line powered heater wiring, but if you check and double check things before applying power, it really isn't any harder to wire it safely than it is to wire a 24V 19A circuit (the 450W heater).


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
VDX
Re: How do I run an SSR on mains without killing myself?
October 30, 2017 02:50PM
... I used AC SSR's (zero cross) to switch the mains voltage to the transformer input and wired the transformer output directly to the heaters.

Switching the SSR's with 3.3V or 5V is straight forward too ...


Viktor
Re: How do I run an SSR on mains without killing myself?
November 25, 2017 09:21AM
Zero cross relays is not suitable for transformers. It is worse then stupid switch.

Two types of "smart" switches exists:
1. turn on after zero cross immediately -- for resistive loads.
2. turn on after zero cross + 5 ms -- for inductive loads (transformers)

Stupid switch will turn on in random phase with random magnetizing current spike.
Second type switch - will turn on in 90 degrees phase without crrent spike.
First type switch - wil turn on in 0 degrees phase with maximum current spike. Always.

It is not significant for 500VA transformer and 25A SSR itself, but may cause EMI problems with Arduino or other electronics.
Re: How do I run an SSR on mains without killing myself?
November 25, 2017 03:03PM
How do you vacuum your home, or use a power tool? My god they are powered by mains power and have flexible cords. They should be outlawed!
Re: How do I run an SSR on mains without killing myself?
November 26, 2017 02:00AM
Quote
cwaa
How do you vacuum your home, or use a power tool? My god they are powered by mains power and have flexible cords. They should be outlawed!

Haha you make a good point. Although my Dad did get a shock off a lawnmower once which had a break in the insulation!


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
[www.facebook.com] we want to see your first layer photos... give us a like/share


[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
Re: How do I run an SSR on mains without killing myself?
November 26, 2017 04:58AM
That's why you use an electrical fuse and secure both ends of the bed heater power cable mechanically. Things can and do go wrong. If you anticipate them you can prepare appropriate safety measures.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: How do I run an SSR on mains without killing myself?
November 26, 2017 06:08AM
And use the RCD/GFID its really not a part to economise on.


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
[www.facebook.com] we want to see your first layer photos... give us a like/share


[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 06:28AM
Thanks for the excellent explanation!

Would the 150 degrees version of the following thermal fuse attached to the bottom of the aluminium plate be a smart solution? Does it need some kind of heatsink paste between the bed and the fuse?

[www.aliexpress.com]
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 06:33AM
Do I need the RCD/GFID if the 220v main circuit already has a earth leakage circuit breaker?
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 06:41AM
If you mean the earthleakage device on your home/office electrical distribution board then yes I would add another layer of protection. Most rcd plugs are around 10mA leakage current mains systems, in the UK in any case, are 30mA.

There are other benefits I use mine as an emergency stop button (using the test feature) so having it next to the printer is convenient and if there is a fault then you may not trip the whole house breaker just the printer.

As for thermal fuses, the more secure and thermally connected to the bed the better but even if this is suboptimal a runaway bed will heat the fuse to 150 deg C long before a fire breaks out or anything except some ABS parts nearby melt.


[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe.
[www.facebook.com] we want to see your first layer photos... give us a like/share


[www.thingiverse.com] DemonDeltaMicro - Micro Delta Printer & Things I've made/remixed.
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 06:49AM
Quote
wouterheer
Do I need the RCD/GFID if the 220v main circuit already has a earth leakage circuit breaker?

There are two types of ELCB: the old voltage operated ones, and the more modern differential current operated ones which are now called RCDs in the UK and GFIDs or GFCBs elsewhere.

If your mains supply has an old voltage-operated ELCB (which has the earth wire passing through it), then that won't protect you. Also it will be positively ancient and you should get an electrician to advise you on replacing it by an RCD and maybe get your electricity supply earthing changed from TT something else.

If your mains supply already has an RCD, then it probably trips at 100mA. For better safety, use a 30mA RCD/GFID with your printer.

Disclaimer: I am not a qualified electrician.

Edited 2 time(s). Last edit at 12/07/2017 06:50AM by dc42.

Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 06:50AM
RCD "residual current device" is a " earth leakage circuit" ( I think your from the Netherlands because we call it "aard lek schalelaar")

To be sure that it is 100% save to touch the printer, you should make sure, that all metal parts that can get in to contact with the 220V wire ( by wear/breakages of the isolation ),
are wired to earth ( I don't know if this is the correct word).
Then the RCD will already switch off before you touch it.

What is a GFID can't seem to find the correct definition, only something with God in it

Edited 1 time(s). Last edit at 12/07/2017 06:51AM by amigob.

P3steel DXL, with Due/RADDS/Raps128 dual Wade's extruder
Re: How do I run an SSR on mains without killing myself?
December 07, 2017 09:24AM
I reckon GFID = Ground Fault Interrupter Device ... there seem to be quite a few names for these things!
Re: How do I run an SSR on mains without killing myself?
December 08, 2017 05:10AM
No need to add anything.

Besides, it may be too late. The OP last post is from 30 Oct ! smiling smiley

May be he installed some crappy chinese differential breaker ?


"You failed to maintain your weapon, son" (Harry Brown )
Re: How do I run an SSR on mains without killing myself?
December 08, 2017 07:13AM
In the Netherlands we have the RCD also in older homes, but it doesn't have to be that all groups are going through it.
Having the metal parts connected to the Earth is extra protection if the RCD is not for the group the 3D printer is on,
and I had ones a fault RCD that tripped only with way higher currents, then it should.


P3steel DXL, with Due/RADDS/Raps128 dual Wade's extruder
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