Heated bed relay wiring confirmation
May 20, 2015 11:19AM
3D Experts,

I'd like to add a relay to my Prusa i3 heat bed. It's got a nasty time trying to get to temperature on anything past 95c or so.

Easy fix, according to forums everywhere, but before I begin - Can somebody with some electrical sense give my little attached PNG a once-over to make sure I'm on the right path in regards to wiring this thing up. (Not sure on the diode placement, but believe the goal of that thing is to protect the RAMPS board from any back fed electricity.

Thanks.

Side note: The relay I'm looking is 12v 30A DC, and the diode is a 12v one.
Attachments:
open | download - RelayWiring.png (430.2 KB)
Re: Heated bed relay wiring confirmation
May 20, 2015 11:24AM
You have the diode placement wrong. It needs to go in parallel with the relay, not in series. The end with the stripe must be connected to D8+, and the other end to D8-.

What sort of diode is it exactly? One with a rating of 12V would be very unusual.



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].
Re: Heated bed relay wiring confirmation
May 20, 2015 11:39AM
Thanks for jumping in here. I very much appreciate the assistance.

I'll get the exact specs of the diode when I can take a look at the packaging... Was informed by the electronics tech that it was rated enough for what I was trying to push through it. I most likely misspoke when saying it was just a 12v one.

Please forgive my ignorance, but you're referring to the following then? *Attached.
Attachments:
open | download - RelayWiring.png (419.9 KB)
Re: Heated bed relay wiring confirmation
May 20, 2015 12:13PM
Quote
usslindstrom
Please forgive my ignorance, but you're referring to the following then? *Attached.
Yes. It's serving as a flyback or supression diode. When the RAMPS board cuts off the heated bed, the inductive load caused by the relay coil can cause a voltage spike. The diode allows the spike to flow back around through the relay where it's dissipated rather than back into your electronics causing damage.
Re: Heated bed relay wiring confirmation
May 20, 2015 12:17PM
Perfect! - Thanks guys. I'll get on wiring everything as depicted.

Loving this community. smiling smiley
Re: Heated bed relay wiring confirmation
May 20, 2015 12:45PM
If terminals 30 and 85 on the relay are the coil, and terminals 86 and 87 are the normally-open contacts, then that diagram is correct. However, the Omron relays I found on their web site do not have those connections. Please link to the datasheet of the relay you intend to use, or at least provide its part number.



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].
Re: Heated bed relay wiring confirmation
May 20, 2015 01:51PM
I'll post pics of the actual electronics when I get home after work... Those pics posted were just a quick google image search for relays and diodes. Thanks.
Re: Heated bed relay wiring confirmation
May 20, 2015 03:44PM
Quote
dc42
If terminals 30 and 85 on the relay are the coil, and terminals 86 and 87 are the normally-open contacts, then that diagram is correct. However, the Omron relays I found on their web site do not have those connections. Please link to the datasheet of the relay you intend to use, or at least provide its part number.
This datasheet matches the appearance and has the same pin numbers, but the wiring diagram would not be correct. Pins 85 and 86 are for the coil. 87 the NO terminal, and 87a NC terminal, and 30 the common terminal on the other end of the contact.
Re: Heated bed relay wiring confirmation
May 20, 2015 08:43PM
Here are the parts I have. *attached.

If possible, can you guys let me know if I need to change the diagram? Thanks.

Edited 1 time(s). Last edit at 05/20/2015 08:44PM by usslindstrom.
Attachments:
open | download - tmp_7806-img20150520_19191028391630.jpg (41.4 KB)
Re: Heated bed relay wiring confirmation
May 20, 2015 10:00PM
You don't want a zener diode there - you want a basic rectifier, such as a 1N4002 . . . .

Zeners are for voltage regulation - you are snubbing a relay coil . . .

- Tim

Edited 1 time(s). Last edit at 05/20/2015 10:00PM by tadawson.
Re: Heated bed relay wiring confirmation
May 20, 2015 10:14PM
Wow. My head's about to implode.

I really have no idea on this stuff at all. Apologies. Even doing a quick search of those shows a ton of options

[www.google.com]

Edited 1 time(s). Last edit at 05/20/2015 10:15PM by usslindstrom.
Re: Heated bed relay wiring confirmation
May 21, 2015 12:24PM
Thanks for everyone's support on this thread. You guys are a great testimate to the community here!

*For the 1N4002 diode, it appears to have a few designations at the end (-T, -TB, -TP), are those significant, or just part #'s?
Re: Heated bed relay wiring confirmation
May 21, 2015 01:25PM
Quote
usslindstrom
*For the 1N4002 diode, it appears to have a few designations at the end (-T, -TB, -TP), are those significant, or just part #'s?
Normally what the designations at the end mean will be listed in the datasheet. -T stands for tape, -TB stands for Tape Box and -TP is for Tape Reel. If you're only buying 1 or 2 or 10 how they are packaged doesn't matter. If you're buying 10,000 for a production facility, you'd obviously want a format compatible with your machine.

Any 1N400* diode will be fine for what you're doing. The only difference in them is basically their voltage rating and the lowest is 50v. You want one that's rated for at least twice your expected voltage so unless you're going to operate at more than 24V, you're fine. Just look for a diode that's black with a white or silverish band.
Re: Heated bed relay wiring confirmation
May 21, 2015 05:06PM
Absolutely perfect explination. Thanks!
Re: Heated bed relay wiring confirmation
May 21, 2015 11:11PM
Jumping in here to ask

Would a SSR need the diode?

Thanks
Re: Heated bed relay wiring confirmation
May 22, 2015 01:14AM
No - no coil in an SSR, just an optical coupler, so the input signal will just see an LED.

- Tim
Re: Heated bed relay wiring confirmation
May 22, 2015 08:05AM
How much current are you actually switching? Are you powering the bed from the same 12V supply that is keeping the temperature from going above 95C? Are you expecting the relay to provide lower resistance than the on-board MOSFET?
Re: Heated bed relay wiring confirmation
May 23, 2015 02:08AM
Quote
tadawson
No - no coil in an SSR, just an optical coupler, so the input signal will just see an LED.

- Tim
Thank!
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