How do I install a heat bed relay with an ATX power supply?

[TehStranger]

Hey guys,

I recently bought the 8x12 upgrade for my Makerfarm 8" i3v and installed it but I do not know how to set up the heat bed relay (This is the one I have: http://www.makerfarm.com/index.php/heat-bed-relay.html). I looked for instructions on the Makerfarm site but can't find any clear answers. I would also like to know if my Power supply would even work with the heat bed, it says a minimum of 30A on the 12vrail is required but mine has 25A, could I maybe get away with it?

Thanks.

[TopJimmyCooks]

connect the two black wires from the relay to your terminals on your ramps/rumba/etc that your heat bed used to be hooked up to + and - don't matter here. mount the relay board to the printer. Apply 12V + and - to the input terminals as marked on the relay board. use decent sized wire such as 10 ga speaker wire or lamp cord. connect your bed to the output terminals- lead polarity doesn't matter. on the Amp draw I would just test it out. If the power supply cuts out you're over the line.

[ex-egll]

Before addressing how to wire up the heater bed relay I would seriously consider upgrading the power supply. As you say the bed needs 30Amps. The extruder heater probably needs in the order of 3.5 Amps. On top of that you have 5 motors plus the controller board to supply, lets take a guess of 2.5Amps for that. We have a total of 36Amps, nearly 50% more than the P/S is rated for.

Now you might be lucky and get away with it, but one day Murphy will strike and all 5 motors, the heated bed and the nozzle will all turn on at the same time, that will probably be the time that the P/S throws its leads up in the air and says "I quit". If Murphy is having a real good day that will occur 15 hours into a 17 hour print job.

Even worse than the catastrophic failure will be little glitches that could occur when the heater bed comes on, it could just drop the voltage low enough to upset the controller board causing intermittent, and highly difficult to trace problems. These problems take the fun out of printing!

In conclusion, try for a larger power supply, or as an alternative you could use a second power supply, if the current (no pun intended) one is sufficient to bring the bead up to temp in a timely manner, to run everything except the bed as it will be isolated by the relay.

Good luck

[rhonal89]

What ex-egll said. Most problem people have is not enought power for their electronics.

Before addressing how to wire up the heater bed relay I would seriously consider upgrading the power supply. As you say the bed needs 30Amps. The extruder heater probably needs in the order of 3.5 Amps. On top of that you have 5 motors plus the controller board to supply, lets take a guess of 2.5Amps for that. We have a total of 36Amps, nearly 50% more than the P/S is rated for.

Now you might be lucky and get away with it, but one day Murphy will strike and all 5 motors, the heated bed and the nozzle will all turn on at the same time, that will probably be the time that the P/S throws its leads up in the air and says "I quit". If Murphy is having a real good day that will occur 15 hours into a 17 hour print job.

Even worse than the catastrophic failure will be little glitches that could occur when the heater bed comes on, it could just drop the voltage low enough to upset the controller board causing intermittent, and highly difficult to trace problems. These problems take the fun out of printing!

In conclusion, try for a larger power supply, or as an alternative you could use a second power supply, if the current (no pun intended) one is sufficient to bring the bead up to temp in a timely manner, to run everything except the bed as it will be isolated by the relay.

Good luck

[TehStranger]

Before addressing how to wire up the heater bed relay I would seriously consider upgrading the power supply. As you say the bed needs 30Amps. The extruder heater probably needs in the order of 3.5 Amps. On top of that you have 5 motors plus the controller board to supply, lets take a guess of 2.5Amps for that. We have a total of 36Amps, nearly 50% more than the P/S is rated for.

Now you might be lucky and get away with it, but one day Murphy will strike and all 5 motors, the heated bed and the nozzle will all turn on at the same time, that will probably be the time that the P/S throws its leads up in the air and says "I quit". If Murphy is having a real good day that will occur 15 hours into a 17 hour print job.

Even worse than the catastrophic failure will be little glitches that could occur when the heater bed comes on, it could just drop the voltage low enough to upset the controller board causing intermittent, and highly difficult to trace problems. These problems take the fun out of printing!

In conclusion, try for a larger power supply, or as an alternative you could use a second power supply, if the current (no pun intended) one is sufficient to bring the bead up to temp in a timely manner, to run everything except the bed as it will be isolated by the relay.

Good luck

What ex-egll said. Most problem people have is not enought power for their electronics.

My power supply has two 12v rails, both of which are 25A.

I assume the worst thing that could happen is the bed won't heat up properly.

[ex-egll]

My power supply has two 12v rails, both of which are 25A.

I assume the worst thing that could happen is the bed won't heat up properly.

Ah, that makes a difference, just use one rail, switched by the relay, and dedicate it to the bed heater, and the other rail can run the rest. As you say, the worst case scenario will probably be a slower bed warm up.

[TehStranger]

Ah, that makes a difference, just use one rail, switched by the relay, and dedicate it to the bed heater, and the other rail can run the rest. As you say, the worst case scenario will probably be a slower bed warm up.

Sweet. I'll set it up tomorrow and post a picture before I fire it up just so you guys can confirm if I did it correctly or not.

Cheers

[TehStranger]

Is this how its supposed to be? http://puu.sh/hepch/7313169561.jpg

[ex-egll]

Looks OK from the picture.

[TehStranger]

Ok well I wired it up and its working but I set the bed to 60c and it's reading 60c but my IR thermometer is reporting 70-75c. I have the thermistor dead in the middle of the bed and it's secured with kapton tape.