Heatbed relay questions Hi again reprappers. I was wondering about using relays and such. at first I was turned off by the though, but now ive realized that I will most likely need one as my printbed is about 17x17. So to get to the point, so far what I have learned from electronics(mainly what you awesome people have taught me) is that if I want something bigger, I will most likely need to run a relay and different psu. ok how would I go about connecting stuff up? so far what I got is that I will be connecting the heatbed to the relay and seprate psu while I will connect the thermistor to the ramps. am I missing something here? what kind of psu do you guys recommend for a 16x16 heatbed using a relay? also, I plan on using aluminum sheet metal I found at my local hardware store as the bed. Would buying a 8x8 and placing it in the center work, as the aluminum would distribute the heat evenly across the plate? I would of course place the thermistor on the aluminum. of course this would then cause false reading and maybe the bed would heat higher than what the thermistor says probably causing a long wait time or worse, the bed to burn out or something. thanks for your input guys. https://reprap.org/forum/read.php?1,518487,518487#msg-518487 Tue, 21 Jul 2026 15:19:30 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,518487,524550#msg-524550 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,524550#msg-524550 davedavedave General Mon, 22 Jun 2015 02:18:52 -0400 https://reprap.org/forum/read.php?1,518487,524192#msg-524192 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,524192#msg-524192 But an external switching unit does ( mech. relais, SSR or paralleled MOSFETs )

You should get a heater for the bed first, then we can guide you through the installation. It varies, depending on the voltage the heater needs. ( 120/230Vac or 12/24Vdc ? )
If you order a tailormade silicone heater, you´d get a DC heater with as high voltage as possible. ( 48Vdc or even 60Vdc is considered to be non lethal )
-Olaf]]> o_lampe General Sun, 21 Jun 2015 03:41:51 -0400 https://reprap.org/forum/read.php?1,518487,524104#msg-524104 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,524104#msg-524104 davedavedave General Sat, 20 Jun 2015 17:26:30 -0400 https://reprap.org/forum/read.php?1,518487,520575#msg-520575 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,520575#msg-520575 davedavedave General Fri, 12 Jun 2015 02:41:20 -0400 https://reprap.org/forum/read.php?1,518487,518847#msg-518847 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518847#msg-518847
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itchytweed
Running my heat bed (14 volts, 32 amps) using just an IRF4905 mosfet and a small heatsink from a celeron processor in PID mode. Barely gets warm.

Yes, a suitable mosfet, or 2 or 3 in parallel, is much better for driving a high current DC heated bed than a DC SSR because the voltage drop is much less.]]> dc42 General Mon, 08 Jun 2015 04:12:20 -0400 https://reprap.org/forum/read.php?1,518487,518742#msg-518742 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518742#msg-518742 itchytweed General Sun, 07 Jun 2015 18:30:14 -0400 https://reprap.org/forum/read.php?1,518487,518697#msg-518697 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518697#msg-518697
Bang-bang control is one of the many small compromises that contribute to reduced overall print quality and reliability. It's an easy, usually low cost, one to fix.]]> the_digital_dentist General Sun, 07 Jun 2015 15:47:31 -0400 https://reprap.org/forum/read.php?1,518487,518650#msg-518650 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518650#msg-518650
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the_digital_dentist
Not sure about DC SSRs, but the SSR I use to switch the 5A or so AC into the transformer under PID control has no heatsink and doesn't get warm.

I use an AC SSR to switch a 230V 350W heat bed, and it doesn't need a heatsink either. Both AC and DC SSRs drop about 2V at maximum current. Your AC SSR passing 5A will drop 1 to 2V, so will dissipate between 5 to 10W. But a DC SSR switching a 20A low voltage heat bed will probably drop 2V and dissipate about 40W - hence it needs a big heatsink.

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1. Would it be necessary to control the heatbed via PID? I have mine in bang-bang mode and that would work too for the big SSD-controlled one?!

2. When a SSD relais gets hot, would it be possible to put it under the aluminum bed acting as heatsink? 110°C would be OK for the SSD?

1. No. Unless you get serious overshoot in bang-bang mode (which could be because the bed heater is overpowered, or the thermistor is not in good contact with the heat bed), bang-bang should be sufficient.

2. 110C would probably be too high a case temperature for the SSR, unless it was operating at about 1/3 its rated current or less.]]> dc42 General Sun, 07 Jun 2015 13:52:04 -0400 https://reprap.org/forum/read.php?1,518487,518603#msg-518603 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518603#msg-518603
2. When a SSD relais gets hot, would it be possible to put it under the aluminum bed acting as heatsink? 110°C would be OK for the SSD?

-Olaf]]> o_lampe General Sun, 07 Jun 2015 11:12:22 -0400 https://reprap.org/forum/read.php?1,518487,518572#msg-518572 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518572#msg-518572
I would NOT recommend trying to switch the AC input to a switching DC supply under PID control. It will probably cause a few blown circuit breakers until it ultimately kills the power supply, which probably won't take long at all.]]> the_digital_dentist General Sun, 07 Jun 2015 09:36:58 -0400 https://reprap.org/forum/read.php?1,518487,518557#msg-518557 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518557#msg-518557 dc42 General Sun, 07 Jun 2015 08:52:26 -0400 https://reprap.org/forum/read.php?1,518487,518548#msg-518548 Re: Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518548#msg-518548


Thin sheet will help, but if the bed is 17x17 and the heater is 8x8, no, it won't be good enough. How are you going to get it flat over 17x17?
]]> the_digital_dentist General Sun, 07 Jun 2015 08:26:56 -0400 https://reprap.org/forum/read.php?1,518487,518487#msg-518487 Heatbed relay questions https://reprap.org/forum/read.php?1,518487,518487#msg-518487
also, I plan on using aluminum sheet metal I found at my local hardware store as the bed. Would buying a 8x8 and placing it in the center work, as the aluminum would distribute the heat evenly across the plate? I would of course place the thermistor on the aluminum. of course this would then cause false reading and maybe the bed would heat higher than what the thermistor says probably causing a long wait time or worse, the bed to burn out or something. thanks for your input guys.]]> davedavedave General Sun, 07 Jun 2015 04:33:24 -0400