I need some help.

(Daniel Marshall) #1

I need some help.

I got an external power supply to drive a new heated bed on a robo 3d r1.

I made the assumption that I could drive a relay from the existing heated bed wiring, meaning that the wires that used to drive the old heater have been replaced with wires driving a relay, then the relay controls power to the new heater.

Unfortunately, it’s not working. I’ve gotten out the multimeter and found that the wires don’t seem to be getting power regardless of whether the heater should be on or not. MatterControl says the bed is heating, but no voltage is passing through the relay.

I’ve checked the wires, watched what videos I could find, but I can’t figure out why this isn’t working.

Can anybody help?

edit - I should add, I have the relay hooked up to D8.

(Sebastian Schmidt) #2

Are you really sure you existing heatbed is driven only on or off ?
Mostly their driven with pwm. So can adjust the temps

(Daniel Marshall) #3

Not at all sure, honestly. I was told here earlier that to drive the new heatbed that I’d need a second power supply and a relay to turn it on or off. I assumed the wiring.

Is there another way to wire this?

(John-Paul Hopman) #4

Have you seen the Thomas video on using a Solid State Relay to control a heated bed?

Are you still supplying power to D8 via the second power input on the RAMPS board? I doubt it will need the 10+ Amps, so you could probably just jump power from the first input for the hotend and motors, but I believe it is necessary as D8 is on a separate rail / mosfet.

(Daniel Marshall) #5

If its the one I’m thinking, he’s doing AC, my power supply is DC. I could get a DC to DC SSR, but my initial confusion remains. I’m not getting any signal from D8.

(Jeff DeMaagd) #6

Have you flashed a new firmware configuration? Or is the stock one supposed to know to output to D8?

(Daniel Marshall) #7

I haven’t done anything to the firmware yet. Since D8 is the output for the stock heater, I didn’t think I would need to. I figured that the software would detect low temp and turn on the ‘heater’ (which is now actually a relay turning on the heater running off the second power supply).

(Hakan Evirgen) #8

on Marlin firmware you need to change the heating to bang-bang, compile and flash. If not, it will not work with any relays.

I assume you are using Ramps 1.4? In that case you need anyway to connect power source to all four power connections.

Anyway I had a broken Ramps which was heating the bed sometimes but stopped doing this. Maybe you have also a faulty device?

(Daniel Marshall) #9


(Ishaan Gov) #10

@Daniel_Marshall , Bang-Bang is basically a control system in which the heater is on if the temperature is under, or off if the temperature is over. It’s common in setups where you aren’t able to switch your load quickly (i.e. mechanical relay); the other option is to use a slower time base for the PWM in Marlin; I think that is also in the configuration.h

(Hakan Evirgen) #11

if you do not know yet, first google for your firmware and how to compile it yourself. There are plenty of resources describing in detail (usually you need the Arduino IDE and downloading the sources of your firmware).

Then you need edit configuration.h file and set parameters right. Search for bang-bang and you should find right part (normally the file is well commented explaining everyhing).

After you set the heat bed configuration to bang-bang you can compile and upload it to your printer via USB. That should be it.

(Daniel Marshall) #12

Issue is fixed, thanks for all the help. Turns out what I had would work, but a completely different issue with the extruder was preventing the bed from heating. Turns out, if the arduino thinks the extruder is 700C, it won’t turn on the bed.

I knew about it, but didn’t realize it was related and hadn’t gotten around to it. I had replaced the extruder thermistor but it was shorting out on the block.