relays to take the load off the main board?

I got my Reprap last month and I have already burned out the bed heater output on the main board. Would it be a good idea to use relays to take the load off the main board for the bed heater and the extruder? I have a Menze p1284 motherboard

If you search for SSR , you will find plenty of tips.
-Olaf

Edited 1 time(s). Last edit at 12/24/2015 03:48AM by o_lampe.

Cheap controller boards often have inadequately chosen mosfets. A good board has no problem driving a 12V 120W bed heater (e.g. a 200x200mm PCB heater), or a 24V 240W heater (e.g. for a 300mm x 300mm PCB heater). Above about 300W it is more practical to use an AC mains voltage heater and a zero-crossing SSR.

Do not try a DC-DC SSR. The cheap ones are no good because of their high voltage drop, and the ones that are any good cost about $100. There is a device from reprap.me called a power expander which costs less and may be OK (it is essentially a 5-terminal SSR), but I haven't tried it.

Edited 2 time(s). Last edit at 12/24/2015 03:56AM by dc42.

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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].

Quote
dc42
There is a device from reprap.me called a power expander which costs less and may be OK (it is essentially a 5-terminal SSR), but I haven't tried it.

I've used a couple of these - one one printer I can easily get a Mk3 heated bed to 110C at 12v, and on the other I can do the same at 24v. I can run the printers for hours and the MOSFET will be barely warm to the touch.

I also used high-current cable to connect from the power supply to the power expander, and from there to the heatbed (I use the silicone cable and connectors used by R/C modellers - not expensive). The combination of cable with a high current capacity (i.e. low resistance), high-current-capable connectors and a MOSFET in the controller with a very low resistance when conducting means that just about all of the power-supply's power gets to the heatbed. Any significant resistance anywhere along that line will knock the voltage right down at the currents we use. The device is switched using a pair of light wires from the terminals that were originally used to power the heatbed.

There's only one down-side to those power expanders - the device is supplied with a couple of screw connectors that you can solder to the board, and I'm not sure that they can take the current. I chose to solder my cables direct to the board, which is an option recommended by the supplier - there are big solder pads available, but you will need a decent-power soldering iron to make a good joint.