How do I run an SSR on mains without killing myself?
Posted by MetalManDan
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Re: How do I run an SSR on mains without killing myself? October 29, 2017 03:38PM |
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 04:00PM by DjDemonD.
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
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 04:00PM by DjDemonD.
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
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Re: How do I run an SSR on mains without killing myself? October 29, 2017 05:30PM |
... 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 
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
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
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
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
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Re: How do I run an SSR on mains without killing myself? December 08, 2017 08:10AM |
No need to add anything.
Besides, it may be too late. The OP last post is from 30 Oct !
May be he installed some crappy chinese differential breaker ?
"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Besides, it may be too late. The OP last post is from 30 Oct !
May be he installed some crappy chinese differential breaker ?
"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
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