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Choosing SSR and fuses for AC heatbed

Posted by jjfawkes 
Choosing SSR and fuses for AC heatbed
January 02, 2019 08:49AM
Hi,
I am building a new printer with Silicone heating pad 220V, 750W, 300x300 mm.
[i.imgur.com]
I want to install it properly with all the safety precautions, because I don't want to kill myself or burn the house down.

Which solid state relay and fuses should I be using? Are there some detailed guides/wikis/tutorials on how to install all of it?
What types of wires/cables must be used?

Thanks!

Edited 2 time(s). Last edit at 01/02/2019 08:54AM by jjfawkes.
VDX
Re: Choosing SSR and fuses for AC heatbed
January 02, 2019 10:29AM
... think about using a transformator with 16V to 50V AC instead of direct line -- will reduce the possible hazards drastically!!


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Choosing SSR and fuses for AC heatbed
January 02, 2019 11:06AM
Viktor, wouldn't it beat the whole purpose of having AC heatbed? If I underpower it drastically then it would heat at a similar speed as PCB or other types of DC regulated beds.
Re: Choosing SSR and fuses for AC heatbed
January 02, 2019 12:08PM
SSR: any DC-AC SSR with sufficient output voltage and current rating and with 3-32VDC control input is suitable. Current draw will be around 3.4A, but if you choose an SSR with a much higher current rating then you won't need a heatsink. Fotek SSR-25DA is a popular choice, although unfortunately many Fotek SSRs sold on eBay are fakes, with the triac inside rated at a lower current than it should be. Crydom D2425 is a more expensive alternative.

Cables: the silicon heater will probably come with a length of silicone covered mains cable already attached. The type of mains cable you need between the printer and the wall plug will depend on your local regulations.

Safety precautions:
- You must use a 3-pin plug and 3-core mains cable, and connect the bed plate and other metalwork of the printer to mains ground.
- For added safety use a GFCI (or RCD in the UK) protector in the mains supply.
- If the bed will be moving then use highly flexible cable to connect the bed heater wires to a terminal block on the fixed part of the printer, and you MUST use strain relief at both ends.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
VDX
Re: Choosing SSR and fuses for AC heatbed
January 02, 2019 02:11PM
... ich you already have a mains-heatbed, then go with it ... otherwise search one with lower voltage (eg. 12V or 24V) and drive it with slightly higher AC instead -- e.g. the 12V DC heatbed with 16V to 18V AC ... this will give pretty fast heatup times, compared to nominal DC winking smiley

You can drive the DC beds with higher DC-voltages too, but the idea behind this "tweak" is to use cheap salvaged transformators instead of more costly high power PSU's ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Choosing SSR and fuses for AC heatbed
January 03, 2019 08:34AM
dc42 - thank you for the info, it is very useful !
Viktor - yes, I already have a 220V heating pad.
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