Heated Bed Relay

I've just had to replace my PSU after it died. In the past I've had melted PSU cables, melted connectors, fried sanguinolulu mosfet and various PSU switchoffs, which I'm presuming are due to excessive current drawn by the heated bed running through the sanguinolulu (and/or poor quality PSU).
I would therefore like to rewire my MK2 heated bed with a relay. I have the following circuit in mind, but am not electronic, so have some questions


1. I measure 1.5ohms (sl higher than the 1.2 sometimes quoted) when cold. So I'm calculating 8A when cold. I'm presuming this will be lower when hot, so current will fall slightly (a lot?).
2. I have an Corsair ATX 750W PSU rated for 62A on the 12V line (single rail only), so should easily manage power output. Unfortunately only 0.8A on the -12V line, so can't use this to inc voltage to 24V.

Questions:
1. Is my diagram reasonable, or should I use a 2nd small power supply to supply the sanguinolulu, rather than powering both with the same PSU. The following makerfarm diagram I found presumably uses 2 PSUs and other diagrams aren't even that clear: makerfarm relay circuit
2. I have some 240VAC 4A solid state relays. Can I wire them in parallel so the amperage doesn't burn them out, and if so do I need to use 2/3/4 or more to cope with variations in internal resistance (and thus variable amperage through individual relays)
Alternatively there are PID SSRs for £1.60 on ebay, but rated for 25A at 24-380V. Would they work using only 12V?
Would 12V automotive electromagnetic automotive relays cope with the rapid cycling when the duty cycle is decreased at stable temperature (or am I wrong about current being proportionally controlled by rapid switching?)...
3. I presume I need a pullup(?) resistor on the sangunolulu ground side?
4. I've read somewhere that I should wire a load on the PSU 5V line to stabilise voltage. Is this correct (or was it only true for older PSUs)? - On bed/heater switchon, I did get a drop in voltage on my old (cheap) PSU, but presumed this was due to poor quality PSU, but perhaps not.
5. Is there anything else I haven't thought of (and no I'm not going to wire it direct to mains).

Thanks
David

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Setup: Prusa/Ramps 1.4 running Marlin v1.1.9 firmware. Hosted by XenialPup64 7.5 (Linux) running Repetier-host v2.1.3. Slicing: Cura. Design: OpenSCAD 2018.09.05, Blender, Inkscape. Mesh Repair: Meshlab, Netfab Basic.

1. Yes that diagram is reasonable except for a couple of points. You don't need the 100 ohm resistor if the relay in rated for 12V on the coil or control input side. If it is a mechanical relay then you should also connect a flyback diode in parallel with the relay coil.

2. SSRs designed to switch AC cannot be used to switch DC. An automotive relay would work but as you suggest the high cycling rate would shorten it's life. Best solution would be a DC SSR rated for 10A or more, but that may be expensive. A less expensive solution would be a PNP transistor and a few resistors switching a N channel mosfet. Or you could switch the high side instead using a pullup resistor and a P channel mosfet, or 2 or 3 P channel mosfets in parallel.

3. There should be no need for a pullup resistor at that point if you use a relay or SSR.

4. Yes, ATX power supplies need a minimum load on the 5V rail to guarantee correct operation. Otherwise they may cut out or give less than 12V on the 12V rail. Better than an ATX PSU but trickier to wire is a 12V PSU of the sort sold on eBay for LED lighting and CCTV applications. A 300W one is more than adequate for a printer with 1 or 2 print heads.

I'm not at all sure that using a relay will avoid the problems you reported.

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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].

Thanks, I'll get a DC SSR for simplicity (the time to construct a MOSFET circuit would cost me more than the few pound difference in cost of parts)
(if you can wait for it to arrive from China around £4.50 - ebay SSR)

I'm expecting this will decrease risk of faults by having much lower amperage through the Sangino circuitry (which with heated bed is drawing around 4x it's rated amperage at the molex connectors), and by using a better quality PSU (12V output wires from my old one were warm to touch during operation, despite wiring every available (relatively thin) wire together)

Edited 1 time(s). Last edit at 10/21/2014 04:44PM by dgm3333.

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Setup: Prusa/Ramps 1.4 running Marlin v1.1.9 firmware. Hosted by XenialPup64 7.5 (Linux) running Repetier-host v2.1.3. Slicing: Cura. Design: OpenSCAD 2018.09.05, Blender, Inkscape. Mesh Repair: Meshlab, Netfab Basic.

before i switched to using a 220v heated bed run by a ssr , i was using a small 12v 10A dc contact relay to power my mk2 heated bed . It runs fine as long as you add a diode and capacitor in parallel to take care of the back emf.

Edited 1 time(s). Last edit at 10/21/2014 10:49PM by ekaggrat.

I just use an off-board IRLB8743 with its own power feed.


-Rob A.

@Rob,

I have created a seven switch 1.2 but unable to understand the connections to and fro from ramps/heatbed...

Can you explain me the connections?

Regards,
Prashant.

Quote
prashantdshinde
I have created a seven switch 1.2 but unable to understand the connections to and fro from ramps/heatbed...

That's a two-pin connector. One of them is GND/ground/0V, the other one (signal) goes to one of the free digital I/O pins. After that, the RAMPS-provided heated bed connector is still free and can be used for other purposes. You also have to adjust the pin in your firmware.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Hi Traumflug,

I am still confused...

Can you show me what is connected to what? in the ckt board..

What should be connected to below things:-

1. Connector1 - +12v... is this correct?

2. Connector2 - ?? where can I find free digital I/O pins???

3. Heater -- heatbed ??? You mentioned RAMPS-provided heated bed connector is still free and can be used for other purposes How? Then where to connect heater.

In the diagram but both pins of Heater connector shows 12v & 11v resp. Please clarify this as well...

sorry for more trouble... but I need the inputs...

Regards,
Prashant.

I have no RAMPS. How would I show you without even seeing what's on your table? And why would I try to, if I can be sure you won't even tell me wether your instructions worked, much less get a picture from you for uploading it to the wiki (or uploading it yourself)?

Quote
prashantdshinde
2. Connector2 - ?? where can I find free digital I/O pins???

The same way you do it on an Arduino without RAMPS. You can even look up [arduino.cc] .

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Hi Traumflug,

I have the setup the same as for Prusai3 3D Printer.

I just want to know the purpose of the "Connector2" as the PSU will be connected to Connector1 & Heatbed will be connected to 'Heater".

Will it be fine if I let the Connector2 empty without connecting anything to it?

I am from Mechanical Engg background & has very little knowledge about electronics thatswhy I asked you in detail.

Anyways, thanks for your valuable info.

Any other guy/member want to comment.....?

Regards,
Prashant.

Quote
prashantdshinde
Will it be fine if I let the Connector2 empty without connecting anything to it?

Of course not. I've described above already where and how to connect it.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

OK, in simple sentence.... What should I connect to signal pin of Connector 2?

And for what purpose?

The "Connector 2" I assume you mean the connector labeled "GND" and "Signal" in Traumflugs Picture. This is where the control signal that regulates the temperature of the heated bed must be connected. That is usually a PWM or a simple on off signal coming from the CPU.

In the usual Heated Bed setup the CPU (Atmel AVR) creates this signal. It is then send out of a GPIO Pin (Therefore the question for a free GPIO Pin) to a MOSFET on your electronics. The MOSFET then increases the Voltage of the signal from 5V to 12V.

As Traumflug asks for a GPIO Pin his board need the Signal in it's 5V form to work. So if you can figure out how to connect the 5V Signal from the CPU to the new board then you are ready to go. With configuration changes in the Firmware it is also possible to have such a signal on any other pin. So if your electronics has an unused Pin that you can use then that would also be an option.

I hope this helped make things clearer. There si also a lot of information available in the Wiki.

ok, so I should connect a +5v pin on RAMPS to the +5V signal pin on Seven switch... correct?

Can I use any +5v pin from Aux ports on RAMPS 1.4?

@prashantdshinde: Just my 2 bits:
The past 9 posts relate to a seven switch. A one second google search brought up the wiki page which shows not only the wiring diagram, but seems to cover in their entirety the first 8 posts.
Thus you could have just reviewed that.
Your question about pins in post 9 implies that you are expecting someone else to have done what you want to achieve, but the wiki still says
"If you've figured out how to connect your combination of electronics, firmware and signal pin, please insert your description as an example here. "
and as there are no entries it means you will quite possibly be the first.
This means you will still have to decide on your pin configuration (and there will be benefits/losses with various pins), figure out the firmware source code, rewrite it, then recompile and upload.

I would suggest it would be easier to ditch the seven switch and use a standard relay or SSR as per the first few posts which would run off 12v headed bed output.
From the level of your questions I'm guessing you're going to spent 10s of hours trying to figure this one out, and having done the same thing myself in the past (some years ago I wasted many hours rewriting an entire reprap firmware to match a board no-one else ever used because I wanted 'native' USB input) I would suggest your time was more valuably spent tackling an easier problem and having the reward of printing stuff (unless you want to learn how the code really works)...
David

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Setup: Prusa/Ramps 1.4 running Marlin v1.1.9 firmware. Hosted by XenialPup64 7.5 (Linux) running Repetier-host v2.1.3. Slicing: Cura. Design: OpenSCAD 2018.09.05, Blender, Inkscape. Mesh Repair: Meshlab, Netfab Basic.

Hi all,

I connected +5v from AUX4 to the signal pin on seven switch & was successful in heating the bed...

But when I connected the +12v from PSU I cannot control the ON/OFF of heatbed using the Pronterface....

If I connect the +12v of seven switch with the D8 of RAMPS, will I get more than 11AMPS out of it to heat the large heatbed without melting down the connectors??

Quote
dgm3333
and as there are no entries it means you will quite possibly be the first.

Having something like 200 of these SevenSwitches shipped, it's very unlikely he's the first. As said, people couldn't care less to make a photo of what they did. That's how the RepRap community works (does not work).

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Hi all,
If I replace the Mosfet on RAMPS with IRLB8743pbf, will it be able to drive large heatbed...??

This seems to be the best alternative....

Regards,
Prashant.

Quote
Traumflug

Quote
dgm3333
and as there are no entries it means you will quite possibly be the first.

Having something like 200 of these SevenSwitches shipped, it's very unlikely he's the first. As said, people couldn't care less to make a photo of what they did. That's how the RepRap community works (does not work).

True. Sadly.
And when people ask for help they are dismissed by know it alls that tells you to search and read instead of just answering the question... this is a comment directed at dgm3333 and his smart-arse "the past 9 posts could..."
Seriously.. dgm3333 you give him a lecture about him not figuring it out, when he in fact tries to dig out some answers...

Edit: same goes for stupid answers about how to connect pins: same way on arduino... well. Most people who use Ramsp for printing have no idea at all about how pins Works and certainly not about how they Work directly on Arduino.. arduino is just the board under Ramps for most people...

So why don't I answer it? Because I'm still befuddled about the Relay thing, so I'm not qualified.

Edited 1 time(s). Last edit at 11/21/2015 01:45PM by dintid.

@dintid: Not sure why you're necro posting with irrelevant abuse on a post a year out of date.
However I still stand by my statement that the original post by prashantdshinde which hijacked the thread appeared to be totally lazy as he/she appeared to have not bothered to do even basic google research which would have answered his question far more quickly than posting on the forum.
I also stand by my second statement that if people aren't going to use their initiative to research the topic (implying they aren't actually interested in learning in the first place) they should go for more widely used options.

However feel free to answer prashantdshinde's question if you feel the original wiki page is missing something which didn't entirely do do...

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Setup: Prusa/Ramps 1.4 running Marlin v1.1.9 firmware. Hosted by XenialPup64 7.5 (Linux) running Repetier-host v2.1.3. Slicing: Cura. Design: OpenSCAD 2018.09.05, Blender, Inkscape. Mesh Repair: Meshlab, Netfab Basic.

Quote
dgm3333
@dintid: Not sure why you're necro posting with irrelevant abuse on a post a year out of date.
However I still stand by my statement that the original post by prashantdshinde which hijacked the thread appeared to be totally lazy as he/she appeared to have not bothered to do even basic google research which would have answered his question far more quickly than posting on the forum.
I also stand by my second statement that if people aren't going to use their initiative to research the topic (implying they aren't actually interested in learning in the first place) they should go for more widely used options.

However feel free to answer prashantdshinde's question if you feel the original wiki page is missing something which didn't entirely do do...

You just don't understand, that the available material is simply just not aimed towards novices or in many cases intermediate users.

It's a total lack of comprehension from many "established" 3Dr that some people (the majotiry) are struggling. This is killing all initiatives from new users instead of enabling them.

I have spent countless hours on learning about 3D printers (check my signature links)... and I still do not understand things like the seven switch. I only recently figured out what those "pins" were I read about.. because nobody, not once, bothered to explain it.. it was just IMPLIED that everyone ofcourse knew it... well, guess what.. that's not how the World is.
And believe me, I've googled to hell and back.. I still do not get any usefull information from the seven switch wiki as it IMPLIES way more Electronics skill than I have. (I'm colorbling for one thing).
edit: I also do not have time to study it.. all spare time goes into 3D printers as it is...

I do not write wiki's as I do not want to spent my time writing to someone "who (think he) knows better".. instead I write to people who really want to learn and can't find the information no where else.

Simple fact that you contribute lack of understanding with no effort spent is extreme arrogance in my book... and Again,... total lack of understanding and comprehension of how much people struggle...

Like my Complete newbie step by step, 3D printer with all parts lists - [www.instructables.com] try reading some of the comments.. and just the sheer number of reads, likes and comments and you will see what I mean... hopefully.

edit: some spelling (I'm Danish)

Edited 2 time(s). Last edit at 11/22/2015 04:35PM by dintid.

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My Instructables - both total newbie instructables and some for intermediate users.
My Designs on Thingiverse
YouTube channel containing a few 3D printing videos - they are videos for my Instructables, and mostly not standalone.
Ultius / Tantillus Thingiverse Group

i think the wiki is comprehensive and has a lot of information and the information is good enough for novices. If a person like me with no background in electronics is able to get 3 printers up and running from a bunch of parts ( not kits ) including a delta ( even the pcb is built by me ) then i don't see that it is incomplete. If you are looking for a kindergarten type instructions to put where every pin goes then yes it might be a little incomplete. regarding the seventh switch it has a very complete wiki and it is a part of the generation 7 electronics board.